table saw tuning......

[Karl Card]

Curious as to what number is considered very good in a table saw setup. My blade is just about dead on as far as the blade to the miter slot but miter slot to fence is about .003 off. I mean that the end of the fence on the back side of table saw is .003 away from blade than the front part of the fence. I have only set up this saw once and had another person helping me or well pretty much doing it but that has been many years ago. I dont mean to be ignorant but I dont have a problem asking questions when I am not sure.

[Derek Cohen]

Karl, if you ripped a 4 foot length of plywood or MDF, with one side flat and straight, what is the difference in the widths at the ends? And what difference are you comfortable with?

Regards from Perth

Derek

[George Makra]

Its customary to have the back side (post cut)be a few thousand wider to allow the wood to expand from the cutting process.

[Karl Card]

well I did what Derek had explained and for a 4 foot piece of plywood it was perfect as a tape measure goes. I am pleased. 6.5 inches on each end. Not dealing with very small tolerances on a daily basis tends to make me not be able to put .003 in perspective. I did use an A-Line-it deluxe kit to help with this.

[Derek Cohen]

Its customary to have the back side (post cut)be a few thousand wider to allow the wood to expand from the cutting process.

George, I imagine that the ideal/best design for a rip fence could see it running parallel to the mitre slot (and blade), but only extending to the middle of the blade, itself?

I have not compared the quality of a rip cut with short- and long fences. Has anyone here?

Regards from Perth

Derek

[Jacob Reverb]

That .003" is thinner than a sheet of ordinary copier paper. Sounds dead nuts on to me.

IMHO, some people make far too much of stuff like this. We're woodworking, not machining, and this ain't NASA.

I generally allow about 1/32" of clearance (that's over 10X your .003") at the back of the blade, as George said, to give clearance if the kerf releases stresses and/or the wood moves after the cut, to help prevent burning/kickback. YMMV.

[David Kumm]

Rip a piece but stop as soon as you clear the front teeth and shut off the saw. Look at the cut on both sides of the board or mdf. If you can see the back teeth on the fence side and a slight ridge on the front end, you know the back teeth are cutting and the fence is set too far out of square towards the blade. If the ridge occurs on the offcut, the fence is set too far out. If you can't see or feel any difference between where the front teeth cut compared to the back teeth on either cut you are good. I also measure the kerf vs the width of the teeth. to determine runout. The kerf should only be a few thou wider with a 10" blade, assuming the blade is good. Dave

[George Makra]

Forest blades use to have a real nice write up on setting up your saw. You can call them and ask if they could email it to you.

It covers everything and IRRC it about 4 pages long.

[Nick Decker]

At .003, I'd leave it alone. I think you'll find that just switching blades can change that number at least a thou or two, maybe more.

[Jacob Reverb]

At .003, I'd leave it alone. I think you'll find that just switching blades can change that number at least a thou or two, maybe more.

Plus, saw blades are tensioned, which means you can't even measure them to the .003" level of precision – or not in any way that matters – unless they're running.

Which ain't recommended. :cool:

[Chris Fournier]

If you're using a tape measure then you're not really in the spirit of the post.

[Mark Hennebury]

" Dead On" "Dead Nuts" " Very Good" "Tape measure" " It's Only Woodwork"
To some 0.003" is a lot, to others it's nothing,
it depends who you are, what you do, and what you care about.
What is considered good is in the eye of the beholder.
You are asking questions that you have to answer yourself.

[Steve Demuth]

I'm curious - you say .003" difference from the blade. So, is the .003" over the length of the exposed blade, or over the length of the fence?

[Andrew Seemann]

0.003 over the 27 inches of a Unisaw top is plenty square. Actually some folks would say too square; there is a school of thought that a fence should angle very slightly away from the blade to prevent the back of the teeth from catching the wood, maybe a 1/64 or so away from the blade over the length of the fence.

Here is the thing about the 0.003; I am going to say that you can't even measure squareness that closely on a saw. First, to measure that accurately, you need better training, better tools, and most importantly, a better reference on the saw. Many machining operations are not done to within 0.001 over 12 inches; the main reason is that they do not need to be.

There is a chance your miter slots are not within 0.003 of parallel to each other. The miter slot itself may not be 0.003 within straight of itself. It is highly unlikely your fence is within 0.003 of flat to itself. The front bar of the fence is probably not within 0.003 of itself over its length. I'm not sure of the runout spec for a Unisaw arbor, but I wouldn't be surprised if it was a couple thousands.

Despite those tolerances, table saws work just fine for woodworking. Actually, I have used plenty of metalworking machines more out of tolerance than 0.003 over 27 inches, and they worked just fine for most metalworking as well. In one shop I worked at in college, we had a lot of WWII lathes and mills owned by the Navy on long term loan to the University. After 50 years of use, not everything was as good as when new. Whenever we complained about one, the bossman would say. "If it was good enough for MacArthur, its good enough for you!"

[Jacob Reverb]

" Dead On" "Dead Nuts" " Very Good" "Tape measure" " It's Only Woodwork"
To some 0.003" is a lot, to others it's nothing,
it depends who you are, what you do, and what you care about.
What is considered good is in the eye of the beholder.
You are asking questions that you have to answer yourself.

It also takes some pretty sophisticated setups to even measure .003" accurately. For example, if the rod in your dial indicator isn't perfectlly perpendicular to your fence/blade/whatever, you're gonna get another .006" or so of error.

Then there's the issue of the straightness of the materials used to construct your fence. On my Powermatic's Accufence for example, the factory BB panels that cover the rectangular tubing of the fence vary by probably five times that – .015" – in and out, like a sine wave, all along the length of the fence, due to the clamping pressure of the t-nuts used to fasten the BB to the tubing. But even if you stripped off the BB panels, unless you scrape and polish the steel tubing of the fence, a speck of rust is gonna quickly throw in another .010" or so.

If you add to that the fact that your wood is going to move maybe five or ten times that .003" every time you so much as breathe on it, you quickly realize that three mils has as much meaning in this discussion as three Angstroms.

I'd be interested to see the woodwork done by those who think half the thickness of a human hair is "a lot." :p This kind of thing gets silly after a while.

[Brian Holcombe]

A very basic setup can measure .003”. Take the angle out of the indicator by eye.

Breathing on wood doesn’t change it .003”.

Wood moves in a relative fashion in many cases, your mortise and tenon fit does not change even as the parts move throughout the seasons.

[Mark Hennebury]

It also takes some pretty sophisticated setups to even measure .003" accurately. For example, if the rod in your dial indicator isn't perfectlly perpendicular to your fence/blade/whatever, you're gonna get another .006" or so of error.

Then there's the issue of the straightness of the materials used to construct your fence. On my Powermatic's Accufence for example, the factory BB panels that cover the rectangular tubing of the fence vary by probably five times that – .015" – in and out, like a sine wave, all along the length of the fence, due to the clamping pressure of the t-nuts used to fasten the BB to the tubing. But even if you stripped off the BB panels, unless you scrape and polish the steel tubing of the fence, a speck of rust is gonna quickly throw in another .010" or so.

If you add to that the fact that your wood is going to move maybe five or ten times that .003" every time you so much as breathe on it, you quickly realize that three mils has as much meaning in this discussion as three Angstroms.

I'd be interested to see the woodwork done by those who think half the thickness of a human hair is "a lot." :p This kind of thing gets silly after a while.

406486406487406488406489406490406491406492406493

[Mark Hennebury]

The last Photo is 30 years after the joint was put together.
406494406495406496406497406498406499406501

[Mark Hennebury]

these business card holders are made from one piece, tolerances are pretty tight.


406502406503406504

The ones below are even tighter tolerances.
0.003" out on these card holders and they are trash, tops either wont fit or will fall off.
Joints wont line up, they just wont work.

406505406506406507

I guess that you have never set up a supersurfacer; 13.250" long blade and back-knife on the small ones, Taking shavings down to 0.001"
To some people 0.003" is a lot.

406508406509

[Jacob Reverb]

I wonder how much glue fits into a gap of 15 ten-thousandths ... assuming you can get it assembled, even dry, without a sledgehammer. ;)

[Mark Hennebury]

Jacob, In some instances, for some setups 0.003" is a lot, other situations its not.
Depends what you are doing.
When you are doing very complicated items with multiple parts and setups, it may be necessary to keep high tolerances to avoid accumulated problems down the road.
Having your machines setup the best you can doesn't hurt anything.

Each to his own of course, but don't dismiss others for working to whatever standards they see fit.

The whole point of working to high precision is you don't need a sledgehammer.

[Brian Holcombe]

Mark, those table bases are exceptional, really nice work.

Jacob,

Tolerance, or error, in machine setup depends on the machine and the operation. I like to minimize it to as near to nothing as possible because it allows me to find confidence in my machines.

People often associate looser tolerances with a faster pace of work, but the opposite is often true. Maintaining tight tolerances throughout a project can greatly reduce the amount of time spent making joints look tight or marking out by hand, etc. I did a set of frames recently that used to take me days to do, and completed the cutout in a few hours because I have much tighter cutting tolerances now to the point where I don't need to trim to fit.

[Mark Hennebury]

Thanks Brian, I had an awesome time doing them and hope to get back to doing some more of that stuff soon, its been way too long.
The is no downside to running tight tolerances and having a good system to reference, check and verify each step; its just good project management, what makes stuff fit, without any problems or worry.

[John K Jordan]

Forest blades use to have a real nice write up on setting up your saw. You can call them and ask if they could email it to you.


There is also an article by Tom Burroughs in American Woodworker, Feb '95, on "Supertune Your Tablesaw". Excellent article and great diagrams. On the following page is a review by Ellis Walentine on a couple of tools that could help. Hmmm, also 4 pages...

JKJ

[Bill Carey]

If you're using a tape measure then you're not really in the spirit of the post.

Made me laugh out loud. Thanks. Needed that.

[Jacob Reverb]

There is also an article by Tom Burroughs in American Woodworker, Feb '95, on "Supertune Your Tablesaw". Excellent article and great diagrams. On the following page is a review by Ellis Walentine on a couple of tools that could help. Hmmm, also 4 pages...

FWIW, if you have a contractor-style saw, the PALS gizmo makes what is ordinarily a nightmare – making the trunnion and miter slots parallel – much faster and easier.
After seeing how it works, I considered making something to accomplish the same thing, but for $20 it wasn't worth the time and trouble.

https://www.in-lineindustries.com/products/contractor-saw-pals/

[Brian Holcombe]

Pretty sure you're off by a decimal point on the above, everything you say makes perfect sense at one decimal point further (IE it's difficult to measure .0003", a spec of rust might be .001") I've seen BB ply panels that varied by a few thousandths but not by 15 thousandths.

Most dial indicators read thousandths (.001"). 'Test' indicators often read .0005" or .0001".

[Jacob Reverb]

Pretty sure you're off by a decimal point on the above, everything you say makes perfect sense at one decimal point further (IE it's difficult to measure .0003", a spec of rust might be .001") I've seen BB ply panels that varied by a few thousandths but not by 15 thousandths.

Most dial indicators read thousandths (.001"). 'Test' indicators often read .0005" or .0001".

Thanks, Brian, but I'm aware of the difference between a mil and a tenth. (I was going by memory when I said my Accufence varied by .015" ... since my memory dims year by year, I just checked, and it varies by about .007" trough-to-crest, so we're talking ± .003" or .004" )

For grins, I measured a rusty spot on my Freud blade, and it was raised by about .006" from the surrounding plate.

I suspect there are also large variances in the straightness of the miter slot. Then there's the runout in the arbor, which I suspect is .002" or more, yet within the specked tolerance.

Since my miter slot is 6-1/4" to the left of the blade, there's also a lot of rod between the dial indicator and the blade to "take the angle out of the indicator by eye," as you phrased it. But here's the thing: A small angle off from perpendicular makes for a large linear difference when we're talking about mils. If my trig is right, an error of just 2° off perpendicular there (88° or 92° instead of 90°) will cause an error of almost .004" in one's measurement of the distance between the miter slot and the blade/tooth.

It's easy to say, "Well, gee, just take the smallest measurement there," but it ain't that easy, at least on my Freud LU84 blade, because it makes a large difference (like ± .005") where, exactly, on the tooth the tip of the dial indicator's probe bears, since the tooth is shaped like a trunked "V" and the tip of the probe is shaped like a ball-point pen tip. So if you slide the dial indicator forward and aft in the miter slot and try to get the minimum measurement (assuming that this will indicate that the probe is square), you'll also move where on the tooth the tip of the probe bears, and since the tooth is wedge-shaped laterally, the linear distance registered by the dial indicator changes. Lots of moving parts, lots of things to think about, and not enough hands to hold a square, and the blade, and the dial indicator, and the probe, and the mirror, and the magnifying glass, and the leash on Schroedinger's cat.

All this and more makes it quite difficult (for me, at least) to measure to a .003" level of precision. Maybe you're better at it than me. I'm not a machinist. But I believe that even for a machinist (and I believe a machinist registered his views above), getting into the realm of .003" precision on many of these machines is a fantasy because it simply isn't in the wood, because the machines themselves simply aren't made to that level of precision. Quite simply, you're getting into such small numbers that the noise overpowers the signal. (And Mark's UberDooberSurfacer's ability to take shavings of half an Angstrom, while impressive, isn't really relevant to a discussion of .003" misalignment of a TS, or if it is, I've missed the relevance, though it wouldn't be the first time.)

For a fairly new woodworker seeking advice on table saw tuning, this can be overwhelming and disconcerting. "Golly, my table saw has a whopping 10 mils of slop. I'll never be able to do quality work on that." And so they go down the rabbit hole chasing mils that don't matter when they would be far better served by using what they've got, building their birdhouses and workbenches and bookcases, and learning along the way. And this, not the striving for accuracy, is what I oppose: The notion that one has to have a $10k machine to do good work, or even that a $10k machine will necesarily produce better work than the $100 Craftsman 113 from 1972. Or that .003" is "a lot" – except in the very rarest of cases, and never in ordinary cabinetmaking for mortal men.

You see the same thing in competitive shooting, where the guys with the $10k rifles sneer at the beginners with their $2k Savages, and try to discourage them, suggesting that there's no way they can be competitive unless they spend $X. It's baloney, and often enough, the beginners show them it's baloney.

Anyway, the indian is far more important than the arrow. And the way to improve the indian isn't by chasing mils, but by milling wood. (I also believe design is more important than execution – so long as the execution is clean – but that's another argument for another thread.)

Finally, as said before, TS blades are tensioned, so what you measure on the blade at rest isn't even necessarily what you have when the blade is running ... and measuring it while running isn't for the faint of heart.;) Better to measure what the blade does to the wood IMHO, since that's where the rubber meets the road, and all that matters is what comes out of the downstream end of the sausage factory, to mulch yet another metaphor.

YMMV. :D

[David Kumm]

Biesemeyer and clone fence plates were notoriously out of flat so you need to know that if measuring. Measuring the kerf tells you the run out but not the cause. Different blades yield different results but when I swap the same blade from saw to saw, I get the same results, but only after I've trued the flanges. At the end of the day, you get a pretty good feel when a machine is operating well. When you get into the Mark and Brian world, you find that you are only happy with really good machines that you can calibrate and that stay that way. Dave

[Brian Holcombe]

OK, These are my experiences and opinions:

Machine setup is not relative to wood movement, it is independent of it and so it can be looked at independently. IE wood may bow or cup after I joint it, but I wouldn't want my jointer to produce a bow or cup intentionally, I want it to make flat boards. It's up to my ability to chose wood properly at that point to get something that remains reasonably flat. Same goes for any other operation, I want the operation to produce a proper result irrespective of what the wood may do at some point down the road. Wood movement is something I need to plan around as a designer, I plan my joinery with respect to wood movement. I wouldn't work around looser tolerances than can be had because wood moves.

Tolerances can be tightened until the point at which they no longer have effect on the work that is noticeable. For fine furniture making my personal feeling is that it should be a few thousandths if the machine will allow for it (many of them will, even my Felder can hold that tolerance). My goal is to minimize time spent 'fitting', fitting by hand for a zero gap is extremely time consuming and I'd rather spend time up front prepping a machine to the best of my ability so that I can minimize fitting time. Fitting by hand offers no benefit to the end consumer if the same result can be had by machine quickly.

I worked for a very careful machinist, if you mentioned to him 'a few thousandths' that would raise a suspicious eyebrow. I suppose I like working with that ideal in mind and find comfort in minimizing machine errors so that my results improve. I'm far from perfect, I find myself combing over my own work looking for spots to improve each time I have the opportunity to do so.

My goal is to make a very good product and manage my time effectively. Tight tolerances help that for me.

Specifics:

Dial indicator. The distance from which you are measuring is not meaningful, a dial indicator is used to measure a relative distance. So, in respect to your saw blade you would be measuring low to high. The distance your indicator travels in that range is what will be effected by angle. I won't argue that angle has no effect, but your math is incorrect in that it's based on the assumption that the distance between the indicator's mounting point on the machine and the saw blade has an effect, it does not. It would be that angle measurement over the length of travel of the indicator. So if the indicator is traveling .003" at a perfect 90 degrees, it would theoretically travel .0045" if it were pointing at 45 degrees toward the same position (realistically the indicator probably wouldn't travel very nicely). So a few degrees is not going to have a meaningful effect in this case.

I agree with you that a setup is only as good as it's result, I like to work out the errors I can find up front, and then check my work with material to see if my work is accurate. If I missed the mark, the wood will tell me.

Assumptions:

- No where does Karl mention that he is a beginner. No reason that an advanced user can't wonder what tolerance range is good.

[Mark Hennebury]

Jacob,

My reply was to your comment about measurements of 0.003" being silly.

there is nothing wrong or silly about people trying to keep tight tolerances in the thou for certain situations, machines and joinery.

If "Good enough" was the battle-cry of the human race we would still be living in caves.

All that we have achieved as humans has been in the pursuit of better.

That's why we left the caves, to build a better world to live in.

In almost all aspects of life, better is celebrated; sports, medicine, science, engineering, dance etc.. only in woodworking do i see the the "good enough" philosophy celebrated and the ones that strive to do better ridiculed.
I find that quite sad; it is i guess why we have pallet wood furniture so popular.

In the eighties i taught woodworking to over 400 students in my shop, in evening classes. They didn't make birdhouses, they learnt to see wood, to understand its cell structure and properties, and they spent many, many hours tuning up a
$50. handplane turning into an UberDooberSurfacer, and at the end of the class they were taking their first shavings, 0.001-0.002" thick, they saw the incredible beauty of a fine planed surface, and a beautiful shaving. The students had such pride in their shavings, and would show each other and carefully fold them up to take home to show their family.
I only had them for a short time, i could have shown them how to build a shelf unit, and at the end they would know how to build that shelf unit.
I didn't teach them to make stuff, that they can learn on their own. I showed them the wonder of wood and cutting tools and working with them, i hoped to inspire to learn more. Once you are inspired and shown how to learn you can go far on your own. I feel that you do far better starting people of right. They should learn about the wonder of wood, about sharp, about cutting tool geometry and its relationship with wood structure, so that they understand what they are doing. they should understand about marking out and precision, referencing, these are the tools with which they can build anything.

Most of the machines that i have owned were old cheap machines that i tuned. Most of the machines that i currently own are from the fifties.
The table base joints were done on a cheap old beat up wadking AGS table saw with an MDF sled, i think that it probably cost me $500
Its not about having the best, its about trying to do the best. Working with what you have to make it as good as it can be.
Always pushing, onward and upward.
So if you saw fence is out 0.003" try to get it to 0.002"
Better. that's all, that's it.

406609

The best inspires us all to try to do better.

[Jacob Reverb]

...but your math is incorrect in that it's based on the assumption that the distance between the indicator's mounting point on the machine and the saw blade has an effect, it does not. It would be that angle measurement over the length of travel of the indicator. So if the indicator is traveling .003" at a perfect 90 degrees, it would theoretically travel .0045" if it were pointing at 45 degrees toward the same position (realistically the indicator probably wouldn't travel very nicely). So a few degrees is not going to have a meaningful effect in this case.

Actually, the distance between the reference point (miter slot) and what you're measuring to (the blade) DOES make a difference, and in this case, a 2° error from perpendicular on a measurement from the miter slot to the blade, when they are 6.25" apart, amounts to almost .004" in error – larger than the number we were arguing over being "a lot" – .003"

This is what I mean when I say that after a certain point, the whole exercise becomes silly, because the noise (measurement error stacked on top of machine tolerances) becomes larger than the signal (actual error in misalignment).

See below, where the length of side b is the distance from miter slot to blade (6.25") , and the length of side c is the distance you would measure if you were 2° off (angle A) from perpendicular. As you can see, instead of getting a distance of 6.25" (or zero on your dial indicator), you would get a distance of 6.2538" (or .0038" on your dial indicator), leading you to believe that your miter slot and blade were not parallel when in fact they were, and the error was that your dial indicator probe was at 88° instead of 90°:

https://i.ibb.co/ypCnYHj/screenshot-854.jpg

If you were to halve the distance between the miter slot and the blade, to 3-1/8" (side b), that same 2° off from perpendicular (angle A) would only cause about .002" of error (or .0019" to be more exact) in the distance measured along the hypotenuse (side c) between the miter slot and the tooth:

https://i.ibb.co/tstBpdP/screenshot-855.jpg

So yes, the distance between reference point (miter slot) and what you're measuring to (edge of tooth) DOES matter, because the larger that distance is, the greater your error will be in measuring that distance for a given error in angle (2° in this discussion). In competitive shooting, an aiming error of 1 minute of angle will only create an error of 1 inch off the bullseye at 100 yards, but at 1000 yards, that same 1 minute of angle aiming error will add up to 10 inches of error off the bullseye. In the same way, in land surveying, a (seemingly) tiny error of a few seconds of angle when turning a corner can add up into many, many feet of error when the length of your shot gets long. These examples aren't perfect, because we're talking about the opposite leg of the triangle getting longer over distance, but the hypotenuse (side c) also gets longer as leg length increases.

Calculator:

http://www.carbidedepot.com/formulas-trigright.asp

If my math is incorrect, please explain how. It's been over 40 years since I took trig in high school, so maybe I've gotten something cattywampus.

The bottom line is that there comes a point when you can't know – and simply cannot determine, or not without some pretty sophisticated instrumentation and techniques – whether the discrepancy is due to misalignment, or machine tolerances, or measurement errors, or (most likely) some combination of the three. And I would argue that at three mils, you have reached that point. And at that point, I would argue, it's time to put away the micrometers, dial indicators, and scanning tunnelling electron microscope, and just get on with the business of cutting wood with the confidence of knowing that the electron is in its proper shell, even if you can't pinpoint its precise position within that shell.

People who say "good enough isn't good enough" may not realize it, but they, too, are settling for "good enough." The question is, where?
.003" ?
.0003"
.00003" ?
We can add zeroes all day. Perfection is an ideal. But it isn't attainable. Which means this rabbit hole has no bottom.

Yes, errors stack. But they also sometimes cancel. And if they're small enough, you can stack them all day and still not end up with a RCH's worth of difference.

[Patrick Walsh]

My thoughts are much as mark.

Set people off with all the informantion they need to succeed to the highest level then let them choose.

Otherwise we are teaching a whole race to that good enough is good enough and soon enough the wheels are falling off the whole thing.

Actually look around the wheels are falling off this whole thing.

Politics, climate change yada yada we have all succumb to lazy and Everyman for himself mentality even those whom think they are not. Largely we take care of ourself first it's human nature. But just because it's human nature does not mean it's not a flawed.

Just like accepting half measures in one work.

A terrible terrible reality the human race has become..

[Brian Holcombe]

The distance is the difference between the peak and valley. Nothing to do with where the miter slot is.

Your measuring the difference over the distance not the distance itself.

[Jacob Reverb]

Okey doke.

Hey, I gotta go cut some wood. Have a good one, guys!

[Joe Calhoon]

Our swim coach put this quote on the board this morning

“Beware the lollipop of mediocrity. One lick and you will suck forever.”

Made me me laugh and think of this thread throughout the workout.

[Robert Hazelwood]

It's not that your trig isn't correct, it's just that crunching numbers correctly doesn't mean anything when you've set up the problem incorrectly.

The distance to the miter slot is irrelevant because we are taking a *relative* measurement- how much further away from the slot is it at one end versus the other. Your calculations just tell you the length of the hypotenuse of a triangle with a horizontal leg running from the edge of the slot to the fence, and the hypotenuse elevated at 2 deg above the horizontal. Which relates to nothing useful.

We start out by zeroing the indicator at a certain spot on the fence. Assume our indicator is misaligned slightly at 2 degrees above the horizontal. Now place a 0.003 feeler gauge between the indicator tip and the fence. Like this:

406648

How far does the tip move when you insert the feeler? The difference between that and 0.003 is your error due to misalignment. Zooming in on where the tip is resting on the feeler:

406650


The relevant triangle is the one shown here, where the acute angle is 2 degrees and the true measurement is the horizontal leg. We know the angle and the length of the horizontal leg (0.003, the thickness of the feeler gauge), so using cosine we can figure the length of the hypotenuse, which is the distance the plunger will have moved at a 2 degree misalignment. Hypotenuse = 0.003/cos(2). So the plunger moved 0.00300182. Error is therefore 0.00000182, or not quite 2 millionths of an inch. Wood moves at least that much if you sneeze on it, so I wouldn't concern myself with it.

Also, I think you can see that the distance to the miter slot does not effect the error due to angular misalignment. The error is a function of the angle and the magnitude of the measurement.

Think about it. If what you said was true, dial indicators would be practically useless, yet machinists (not to mention woodworkers) use them all the time, and almost always are eyeballing the alignment.

[Robert Hazelwood]

Also, apologies for nerding up the thread. If the OP is still reading, I think a bit of toe out on the fence is desirable and if not too drastic, should not throw your rip cuts out of of parallel. 0.003" seems about right, and I'm sure some people use more. What I would look out for is the fence being out of flat, and most of them are. Now, the fence may work acceptably without being perfectly flat, but it means that simply taking a measurement on either side of the blade may not tell you what you'd hope it would, because you could be measuring a bump in the fence on one end and a hollow on the other. You have to kind of imagine a line connecting all of the high spots on the fence, that represents the actual cutting path of a board. If you have a straightedge or an accurately milled stick close to the same length as the fence, you can place it against the fence to represent this line, and take your measurements from the straightedge. The side touching the fence and the side you're measuring to need to be straight and parallel, obviously.

[Chris Fournier]

Made me laugh out loud. Thanks. Needed that.
Cigar smokers always understand each other!

[Bill Space]

Brian said:

“So if the indicator is traveling .003" at a perfect 90 degrees, it would theoretically travel .0045" if it were pointing at 45 degrees toward the same position (realistically the indicator probably wouldn't travel very nicely). So a few degrees is not going to have a meaningful effect in this case.”

This is a key point. I had not thought about it, and assumed if the dial indicator were angled it would indicate less than the actual deviation being measured.

But the reality seems to be that if the dial indicator is not perfectly perpendicular to the movement being measured, the indicator will display more movement than is actually happening.

So if someone measures 0.003 movement, an his indicator is not set exactly perpendicular, the actual movement is less than what the indicator displays.

Thanks for for posting this Brian!

[Andrew Seemann]

Experiment to try. Measure the width of your miter slot several places, say 8, over its length, not just front and back, see if they are all the same to a half thousand. Mine (1986 Unisaw) varies by about 2 or 3 thou. One of my old saws varied by around 30 thousands due to wear; it had probably been in a production shop at some point.

Now measure the distance between your fence and the miter slot in 8 places. Write down the values. See if the the value is the same, if it reflects a steady taper, or if it varies. Now move the fence and measure again. Do this at say 1", 2" 3", 4", 5" and 12". Do you get the exact same relative differences at each spot or does it vary by a few thousands of and inch? Mine certainly does. Ideally you would also measure at 18", 24" 36" 48" etc. as well. Now measure in one spot, but vary the amount of pressure on the fence handle. Light, medium, and full. Does the distance to the miter slot vary? If you want, you can try moving the entire saw and seeing if the numbers stay the same.

Now measure the width of your rip fence in several places. Is it identical to a half thousand, or does it vary. My Biesemeyer varies by at least 15 thou.

The point is, unless you have checked your miter slot to be parallel to your blade to less than a half thou, and you have checked that your miter slot is straight within a half thou with a known straight edge certified more accurate to more than a half thou over the 27" Why a half thou? Because you need to extrapolate the 8" of exposed blade over 27" length of the miter slot. Being off by a half thou would introduce at least 1.5 thou of error into the number over the 27", half of the 3 thou that is being discussed. And then your fence needs to be checked against that same known straight edge and be within the same half thou. Unless you can do all this, you don't know that your fence is within .003" of square or not. You just know that the difference between where you measured the front of the fence to the miter slot is .003" different than the far edge. Making it .002" doesn't make it more square. It just makes that number .002" instead.

There is a limit how accurately you can set up a machine, a woodworking table saw for example. After you exceed that limit, you are just measuring variance from the manufacturing process, not improving accuracy.

Myself, I used a 6" Mitutoyu digital caliper to get the blade within a couple thou of the miter slot; tightening one corner bolt on the top will change the number a couple thou, so you finesse a bit to balance accuracy against top tightness. After having moved the saw around for a few months, it probably isn't that accurate anymore. I set the fence to be flush with the right side of the right miter slot in front and to be just visually wide of the miter slot at the back of the saw, maybe a 1/64" - 1/32" to make sure the back of the blade didn't bind the wood against the fence. Everything is plenty close enough to work wood, a material than can change more than 300 thou in width over 12" between summer and winter. And yes, I used to be a machinist as well.

[Steve Demuth]

Experiment to try. Measure the width of your miter slot several places, say 8, over its length, not just front and back, see if they are all the same to a half thousand. Mine (1986 Unisaw) varies by about 2 or 3 thou. One of my old saws varied by around 30 thousands due to wear; it had probably been in a production shop at some point.

Now measure the distance between your fence and the miter slot in 8 places. Write down the values. See if the the value is the same, if it reflects a steady taper, or if it varies. Now move the fence and measure again. Do this at say 1", 2" 3", 4", 5" and 12". Do you get the exact same relative differences at each spot or does it vary by a few thousands of and inch? Mine certainly does. Ideally you would also measure at 18", 24" 36" 48" etc. as well. Now measure in one spot, but vary the amount of pressure on the fence handle. Light, medium, and full. Does the distance to the miter slot vary? If you want, you can try moving the entire saw and seeing if the numbers stay the same.

Now measure the width of your rip fence in several places. Is it identical to a half thousand, or does it vary. My Biesemeyer varies by at least 15 thou.

The point is, unless you have checked your miter slot to be parallel to your blade to less than a half thou, and you have checked that your miter slot is straight within a half thou with a known straight edge certified more accurate to more than a half thou over the 27" Why a half thou? Because you need to extrapolate the 8" of exposed blade over 27" length of the miter slot. Being off by a half thou would introduce at least 1.5 thou of error into the number over the 27", half of the 3 thou that is being discussed. And then your fence needs to be checked against that same known straight edge and be within the same half thou. Unless you can do all this, you don't know that your fence is within .003" of square or not. You just know that the difference between where you measured the front of the fence to the miter slot is .003" different than the far edge. Making it .002" doesn't make it more square. It just makes that number .002" instead.

There is a limit how accurately you can set up a machine, a woodworking table saw for example. After you exceed that limit, you are just measuring variance from the manufacturing process, not improving accuracy.

Myself, I used a 6" Mitutoyu digital caliper to get the blade within a couple thou of the miter slot; tightening one corner bolt on the top will change the number a couple thou, so you finesse a bit to balance accuracy against top tightness. After having moved the saw around for a few months, it probably isn't that accurate anymore. I set the fence to be flush with the right side of the right miter slot in front and to be just visually wide of the miter slot at the back of the saw, maybe a 1/64" - 1/32" to make sure the back of the blade didn't bind the wood against the fence. Everything is plenty close enough to work wood, a material than can change more than 300 thou in width over 12" between summer and winter. And yes, I used to be a machinist as well.

All of this.

I took a machinist straight edge - flat to within about .0002" / foot - against the bearing surface of my fence. It's basically 2 full sine waves over its length, with a magnitude of about .005". Did the same to the fence rail. Easily could slip a .002" feeler gauge in the low spots. Given that the fence bears on the rail only at two set points about 6" across, and the fence waves .005" all by itself - well, like Andrew says, toe-out of .003" measured over 27" isn't telling you much about the mechanics of the rip fence Vvis-a-vis the blade.

[Mark Hennebury]

If you want to tune up your saw you can do most of it without measuring squat.
you can lap your fence on a tablesaw top or jointer or surface plate etc. that will give you a reasonable flat surface to work with.
To set the fence to the blade rip a scrap and observe the score marks on both pieces, adjust to suit your preference.Do you want score marks from the front of the saw , the back or both. suite yourself.
To set the blade perpendicular to table and miter fence, crosscut a 2x2x40" long squared straight piece of stock in half and stand it on the cut ends, then push them close together, any deviation will be magnified 20x
To check the mitre slot to blade,, simply crosscut a piece and observe the scoremarks. You can see if the marks are from the front or back of the blade or both .
If you want the most accuracy every time, then check it every time.
If to want repeat-ability then everything needs to be snug and tight.

I am not a machinist, But i do own plenty of Mitutoyo gear and a few large surface plates and camel-back straight edges, surface grinder, lathe, milling machine etc.
And i do have a problem with the good enough for woodworking comments, especially when followed by wood shrinks and expands comment, because that infers that it is pointless cut wood to precise dimensions.
Yes, wood does change dimension-ally with changes in environment, Metal also does change dimension-ally with changes in environment. Moisture for wood, temperature for metal.
That doesn't stop metal from being machined to tight tolerance, or wood, as long as they are machined and fitted in the same environment. Any changes in environment will affect either materials in a relative manner.

You can cut a mortise and tenon joint to within 0.001" tolerance if you wish. If you make them at 30% relative humidity and check them at 50% relative humidity , they would have changed size, but would maintain the same relative change in size, just like if you cut them in metal at one temperature and checked them at another. So you can cut precise wood joints, and they will stay precise, they may change in dimension, but they will stay just as precise.

If you want to do high precision work you can, you don't have to have loads of expensive equipment and an engineering degree; you have to understand wood first of all. You have to understand referencing and how to check and verify. And most of all how to observe and analyze.

The video clip shows the close tolerance fit of one of the credit card boxes that i used to make. this box is still a nice fit 20 years after it was made and it has been used daily. That is closer tolerance than a lot work i have had from machine shops.
So ease up on the " close enough for woodworking"


https://youtu.be/Jy2soP-nbZM

[Brian Holcombe]

Experiment to try. Measure the width of your miter slot several places, say 8, over its length, not just front and back, see if they are all the same to a half thousand. Mine (1986 Unisaw) varies by about 2 or 3 thou. One of my old saws varied by around 30 thousands due to wear; it had probably been in a production shop at some point.

Now measure the distance between your fence and the miter slot in 8 places. Write down the values. See if the the value is the same, if it reflects a steady taper, or if it varies. Now move the fence and measure again. Do this at say 1", 2" 3", 4", 5" and 12". Do you get the exact same relative differences at each spot or does it vary by a few thousands of and inch? Mine certainly does. Ideally you would also measure at 18", 24" 36" 48" etc. as well. Now measure in one spot, but vary the amount of pressure on the fence handle. Light, medium, and full. Does the distance to the miter slot vary? If you want, you can try moving the entire saw and seeing if the numbers stay the same.

Now measure the width of your rip fence in several places. Is it identical to a half thousand, or does it vary. My Biesemeyer varies by at least 15 thou.

The point is, unless you have checked your miter slot to be parallel to your blade to less than a half thou, and you have checked that your miter slot is straight within a half thou with a known straight edge certified more accurate to more than a half thou over the 27" Why a half thou? Because you need to extrapolate the 8" of exposed blade over 27" length of the miter slot. Being off by a half thou would introduce at least 1.5 thou of error into the number over the 27", half of the 3 thou that is being discussed. And then your fence needs to be checked against that same known straight edge and be within the same half thou. Unless you can do all this, you don't know that your fence is within .003" of square or not. You just know that the difference between where you measured the front of the fence to the miter slot is .003" different than the far edge. Making it .002" doesn't make it more square. It just makes that number .002" instead.

There is a limit how accurately you can set up a machine, a woodworking table saw for example. After you exceed that limit, you are just measuring variance from the manufacturing process, not improving accuracy.

Myself, I used a 6" Mitutoyu digital caliper to get the blade within a couple thou of the miter slot; tightening one corner bolt on the top will change the number a couple thou, so you finesse a bit to balance accuracy against top tightness. After having moved the saw around for a few months, it probably isn't that accurate anymore. I set the fence to be flush with the right side of the right miter slot in front and to be just visually wide of the miter slot at the back of the saw, maybe a 1/64" - 1/32" to make sure the back of the blade didn't bind the wood against the fence. Everything is plenty close enough to work wood, a material than can change more than 300 thou in width over 12" between summer and winter. And yes, I used to be a machinist as well.

You make some excellent points Andrew. Especially about the machining tolerances, I've found that with my Bridgeport there is a reasonable expectation for deviation in a finished result because at some level you're simply duplicating the bed's error in the result. Same goes here, but as mentioned we don't know much about the OP's situation, he may be tuning in a Uni-saw or he may be tuning in a Martin. He made no mention of it as far as I'm aware, so a broad range of replies are not unwarranted.

I mentioned in each post that I felt that one should be working to minimize error, I made no statements to generalize what the tolerance should be for everyone but I did mention what I aim for for tolerance. I'm not sure why that sends people off the rails, but I've been happy to provide the logic behind my interest in having tight tolerances.

I measured my miter slot (14mm), it measures .5535 .554 and .5535. My straightedge which is accurate to .001" over 36" revealed no gaps along the length of it.

My saw is a sliding table saw, so I set the inner most outrigger support to be parallel to the table top and parallel to the sliding table support (this is confusing to describe, but there is a main bar which the table itself slides on. These items are accurate being that the table is planed flat at the bar is straight.

I then applied the carriage and set it to be parallel to the tabletop.

Finally I attached a digital indicator to that via a stand and measured the distance differential between the saw blade front to back. It was .003" further away at the backside. Being that it's fixed in pins and the table is not adjustable in that way I decided to leave it that way and for the most part assume that it was set that way intentionally to avoid cutting on the backside of the blade.

I continue to debate getting a set of granite standards for my shop to check my checking equipment.

[Jacob Reverb]

Brian said:

“So if the indicator is traveling .003" at a perfect 90 degrees, it would theoretically travel .0045" if it were pointing at 45 degrees toward the same position (realistically the indicator probably wouldn't travel very nicely). So a few degrees is not going to have a meaningful effect in this case.”

This is a key point.

Actually, if the miter slot is 6.25" away from the blade (side b below), and if the dial indicator's pointer were pointing at the blade at 45° (along side c below - note that the triangle pictured does not change with the values you input, its sole purpose is to label angles and legs/hypotenuse) then the distance measured would be 8.838" or +2.588" difference from the datum at 6.25".

https://i.ibb.co/1ZTVnN4/screenshot-856.jpg

A far cry from 3 mils.

But you don't need a trig calculator to understand this and you don't need a scanning tunnelling electron microscope to measure it. You could clock the distance differential with the odometer in a dump truck.

Here's the measurement you would get if your probe was at 45° to the miter slot:


https://i.ibb.co/m9zyNKS/IMG-3028.jpg

Here's the measurement you would get if the dial indicator's probe was at 90° to the miter slot:


https://i.ibb.co/D1mT0Xv/IMG-3030.jpg

Yes, I understand that we are comparing the measurement at the front of the blade versus the measurement at the back of the blade.

But the item of contention that got this whole digression started was my assertion that a very small error in angle on the dial indicator (88° or 92° instead of 90°) would lead to a "large" error (specifically, almost .004") in the measurement of the distance from the miter slot to the blade, as detailed in my post above. I stand by that assertion.

Brian said you could eyeball that the dial indicator probe was square to the miter slot. I disagreed, since I don't think I can eyeball 90° to within 2 degrees. I stand by that assertion, as well.

[Brian Holcombe]

Brian said:

“So if the indicator is traveling .003" at a perfect 90 degrees, it would theoretically travel .0045" if it were pointing at 45 degrees toward the same position (realistically the indicator probably wouldn't travel very nicely). So a few degrees is not going to have a meaningful effect in this case.”

This is a key point. I had not thought about it, and assumed if the dial indicator were angled it would indicate less than the actual deviation being measured.

But the reality seems to be that if the dial indicator is not perfectly perpendicular to the movement being measured, the indicator will display more movement than is actually happening.

So if someone measures 0.003 movement, an his indicator is not set exactly perpendicular, the actual movement is less than what the indicator displays.

Thanks for for posting this Brian!

My pleasure!

[Robert Hazelwood]

But the item of contention that got this whole digression started was my assertion that a very small error in angle on the dial indicator (88° or 92° instead of 90°) would lead to a "large" error (specifically, almost .004") in the measurement of the distance from the miter slot to the blade, as detailed in my post above. I stand by that assertion.

Sigh. That is not how dial indicators work- the distance from the slot to the blade is not what you are measuring. Your numbers would be appropriate if you were measuring with a ruler, and held the ruler at an angle,... Please read my earlier post.

[Jacob Reverb]

Sigh. That is not how dial indicators work- the distance from the slot to the blade is not what you are measuring. Your numbers would be appropriate if you were measuring with a ruler, and held the ruler at an angle,... Please read my earlier post.

Sigh away. This is like pulling teeth.

Here, maybe this will help explain why, to get a valid measurement, the dial indicator's probe must be perpendicular (90°) in two planes:
- forward and aft horizontally, and
- up and down vertically
to get a decent measurement.

Even the slightest deviation away from perfectly perpendicular, in either the horizontal or vertical planes, even by just a couple of degrees, will throw the measurement off, and by more than the .003" that is supposedly "a lot" of misalignment.

In this video, the tip of the probe's point of contact with the tooth does not move appreciably. (I can can tell when its point of contact on the tooth moves, because it makes noise when it drags across the carbide, and it didn't when I did this.) The only thing that changes when I rock the blade back and forth (by maybe 3/16") is the angle of the indicator probe, away from 90° and then back through 90° and beyond, and then back, in two planes. Watch what the needle on the dial indicator does.


https://youtu.be/YfRLXFA7bIc

And as I and Andrew have said repeatedly, this is just one of several places where errors – or machine tolerances – of more than .003" can be introduced.

This is why I say that beyond a certain point, it is "silly" to pursue it further, because you're chasing your tail. You simply don't know, and can't know, without a lot more sophisticated instruments and procedures, where the discrepancy lies. It gets lost in the "noise." You might as well debate how many angels can dance on the head of a pin.

Furthermore, it's "good enough" (gasp) for woodworking because other sources of error – how well you hold the wood to the fence and down to the table, etc etc etc etc etc ad nauseum infinitum – will be orders of magnitude larger than any remaining misalignment.

And with that, I declare this horse officially beaten into dogmeat.

Have fun!

[Mark Hennebury]

Jacob, what you are demonstrating in the video is not errors of machine tolerance, it is the use of the wrong tool and a flaw in your method of measuring. It has no relation to the cut the accuracy of a cut on a piece of wood. Clamp a piece of wood to the mitre fence/ sliding table and cut it, and look at it, that will tell you a whole lot more relevant information.

[Michael Costa]

Whoa. I thought it said table saw "turning" and not tuning. I was curious to know who was so brave. Lol.

[Jacob Reverb]

Jacob, what you are demonstrating in the video is not errors of machine tolerance, it is the use of the wrong tool and a flaw in your method of measuring.

Exactly what I was attempting to show:

"And as I and Andrew have said repeatedly, this is just one of several places where errors – or machine tolerances – of more than .003" can be introduced."

I should also add that I agree with you: To align my TS, I don't use the much-vaunted dial indicator. I just clamp a rule to the miter fence and align the trunnion such that a particular tooth just drags against the end edge of the rule at the front of the table and at the back of the table. In my experience, using a dial indicator for this is a good way to start drinking and tearing your hair out in big wads. Does this method get me within .003" or .0003" or .0000000000000000000003"? I don't know, and care even less.

Finally, anyone who doubts my claim – that "After a certain point, the whole exercise becomes silly" – needs only to look at this thread.

[Brian Holcombe]

Jacob, if the probe is moving then the fixing point is not strong enough.

Also I’d probably use a shorter indicator and get it closer to the blade with a magnet stand (I have a good old mitutoyo which locks firmly.

[Robert Hazelwood]

This is why I say that beyond a certain point, it is "silly" to pursue it further, because you're chasing your tail. You simply don't know, and can't know, without a lot more sophisticated instruments and procedures, where the discrepancy lies. It gets lost in the "noise." You might as well debate how many angels can dance on the head of a pin.

Furthermore, it's "good enough" (gasp) for woodworking because other sources of error – how well you hold the wood to the fence and down to the table, etc etc etc etc etc ad nauseum infinitum – will be orders of magnitude larger than any remaining misalignment.



The video is kind of fuzzy, is the tip flexing or is the whole indicator rotating in its mount? Either way, that is a different source of error- movement or flexure of the measuring tool. Not from angular deviation of the inidicator while taking a proper reading, which is what you seemed to be arguing.

If you zero the indicator out against an object, then rotate the whole indicator two degrees in its mount, then the measurement will change based on a triangle that extends from the pivot point to the tip, which in your case might be 4 or 5 inches long. So you would see quite a lot of error and the reading would be garbage.

But if you lock your indicator down rigidly like you should, prior to zero-ing, and the indicator happens to be some small angle out of perpindicular, then the measurement error will be described by a triangle whose long side is the length of the discrepancy you are measuring (a few thousandths). So the error is extremely small.

I am trying to address the specific claim that you can't rely on dial indicators because you can't ensure they are 100% perpendicular to what you are measuring. This is not correct. Yes, it's critical that the indicator mount be rigid, and the accuracy of the reference surface (in this case the miter slot) limits the reliability of the measurement. But the indicator being a few degrees out of perpendicular is not a problem. Dial indicators are extremely useful, inexpensive, and can be used in myriad ways if you are clever. If your original claims were true, they would be entirely useless. And despite all of the potential sources of error, can you seriously claim that you can get a better setup on a tablesaw with a ruler than with an indicator and a good mount?

I am sympathetic to the general point that there are many sources of error, and that the smaller you try to measure the more significant they all become. I get that it annoys you that some people insist on 0.001 accuracy. For me, if I am doing a setup and it is not that much extra work to get it to, say, 0.002 according to my indicator instead of 0.010, then why would I not do that?

[Robert Hazelwood]

I just clamp a rule to the miter fence and align the trunnion such that a particular tooth just drags against the end edge of the rule at the front of the table and at the back of the table. In my experience, using a dial indicator for this is a good way to start drinking and tearing your hair out in big wads. Does this method get me within .003" or .0003" or .0000000000000000000003"? I don't know, and care even less.


That's not a bad method. If you are picky about how much drag you accept, then you can get it just as accurate as with an indicator. You can set jointer knives by seeing how far they move a ruler or stick when you rotate the cutterhead- also a good method, and very sensitive. But I prefer a dial indicator for the latter, not because of accuracy so much as that I can get real-time feedback as I raise and lower the knives, instead of having to tighten everything up before I can see what I've accomplished with an adjustment.

[Jacob Reverb]

Thanks, Robert.

Now I understand what you guys are saying – that the dial indicator should be mounted such that it can't get out of square or parallel with the table top – and I apologize for the confusion.

It's been years since I messed with that thing (I think it's called a "Superbar" jig or something like that, supposedly designed for TS alignment), and I now remember that the last time I used it, I realized that there was no way to use it accurately if it could get out of square or parallel to the table, and I remember cutting a block of wood to put under the probe to keep it parallel to the table, but I didn't figure out a really rock-solid way to keep the probe square to the miter slot, so it was an exercise in frustration more than anything, at least for me. Or maybe I wasn't using it right (not sure whether I re-read the instructions the last time I used it).

Anyway, guys, please excuse my boneheadedness on what you were trying to explain regarding the idea that "you can't get the dial indicator out of square." I see what you're saying now.

But I still contend that .003" of (apparent) misalignment between fence and blade (I think this was what the OP was talking about) is more than "good enough." Or at least it would be for me ... but I use fire axes for my "woodworking" as much as anything else. :D

Cheers-

Jacob

[Bill Space]

Jacob said:

Now I understand what you guys are saying – that the dial indicator should be mounted such that it can't get out of square or parallel with the table top – and I apologize for the confusion.


But...and thanks to Brian I came to understand this...if the dial indicator is not perfectly square, the measurement will actually be larger than the true measurement. So you when done your result will be BETTER than you think!

Before Brian's post (above) I thought an angular error in the dial indicator would fool me into thinking I was better than I was...but the angular error will actually fool me into believing what I am measuing is actually worse than it is.

[Jacob Reverb]

Jacob said:

Now I understand what you guys are saying – that the dial indicator should be mounted such that it can't get out of square or parallel with the table top – and I apologize for the confusion.


But...and thanks to Brian I came to understand this...if the dial indicator is not perfectly square, the measurement will actually be larger than the true measurement. So you when done your result will be BETTER than you think!

Well, if I'm not mistaken again :D the result could appear either better, or worse, than it is. It just depends on where you got the error.

As an example, assume that the trunnion was cocked clockwise, viewed overhead, in relation to the table, meaning that the true, accurately-measured distance between miter slot and blade was greater at the back of the blade than at the front of the blade.

If you measured accurately (perpendicular to miter slot and parallel to table) at the back of the blade, but got the indicator probe cocked at the front of the blade (either not perpendicular to the miter slot and/or not parallel to the table), this would make the misalignment appear less (and thus better) than it actually was.

But if you did the reverse – measured accurately at the front of the blade, but then got the indicator probe non-parallel to the table and/or non-square to the miter slot at the back of the blade – then the misalignment would appear to be greater (and thus worse) than it actually was.

As a third, though exceedingly unlikely, possibility, let's say you got the exact same degree of measurement error from having the indicator probe non-parallel or non-square, at both positions – front and back. In that case, since the (true, accurate) distance between miter slot and blade is greater at the back of the blade than at the front, your trunnion misalignment would appear (very slightly) worse than it is, because leg b of the right triangle (the true, accurate distance between miter slot and blade) is larger to begin with (by definition from the premise) at the back of the blade than the front, meaning that the hypotenuse of that right triangle (the erroneously-measured distance) would also be larger than it is.

Or that's my story, and I'm sticking to it (for now)... http://northlandphoto.com/campfire/images/smiles/lookaround.gif

[Jacob Reverb]

I feel like an idiot now because in cleaning up shop, I found the missing piece to use the dial indicator – a machined aluminum plate instead of the blade – and either I've never used the dial indicator with jig and the plate or I forgot about it, but I put in the plate today and measured with the SuperGage gizmo, and as best I could read it, arbor was maybe 1.5 mils out of parallel to the miter gage slot in 10". So I guess the clamp-rule-miter gage method works, too.

So maybe .003" isn't out of the question to measure. But it's getting down into the weeds...

Thanks for the patience, and please excuse my ignorance, in trying to explain it to me, fellas.

Not sure how my father aligned his saw, but I'm sure he never used a dial indicator though as an engineer he would have known how. He spent a day under his Craftsman contractor's saw loosening/tightening/checking the trunnion and by gosh and by gollying it, and eventually called it good and probably didn't touch it again. And he made custom furniture for years with some nicely machined joints (mostly done on TS) and it was good work. It'd be interesting to know how well aligned his saw was, but that was back in the '70s.

[Brian Holcombe]

No worries, it was nice if you to reply with your findings. That aluminum plate is a really good idea for this procedure, eliminates the possibility of the blade being the culprit.

One thing I did to dial in my chopsaw was to lightly hone my arbor flanges to ensure there were no high spots causing the blade to wobble.

[Patrick Walsh]

Oh forget it.