For the Woodworker, What Constitutes Adequate Precision Measurement

[Richard Wagner]

I've been reading threads all over (this forum and others) and I sense what might be called an obsession for accuracy.

What is a reasonable objective for accuracy in a wood shop.

As a caveat, I would like to say that I believe a serious hobbiest and a profession wood worker are no different in terms of accuracy.

[Mark Norman]

I would say it largely depends on what you are making and what is the desired end result. For example if yer building a house 1/4" tollerance is acceptable but the same 1/4" on a face frame of a cabinet would never fly. For the most part I think a sixteenth of an inch is acceptable for most wood projects and a 32nd would be considered precision enough for all except a few rare occasions.

[Leo Graywacz]

In my shop I strive for +/- 0.005". I have all digital measurement devices so it makes it feasable. Before that I would go for 1/64" (0.016"). For corner to corner square measurements I try to keep it to 1/32" using a tape measure. Since I have gotten the digital stuff life has been grand.

[Kent E. Matthew]

For me it's plus or minus six inches. :D

[Roger Newby]

My day to day job as a tool & die maker is +/-.0005. Therefore, 1/32" is tight enough to have room to swing a cat.:D Precision is a matter of how fussy you are. Allowing for the movement of wood due to changes in humidity, 1/16" or maybe 1/32" is plenty close enough. Tighter than that becomes an obsession IMHO.

[Leo Graywacz]

Therefore, 1/32" is tight enough to have room to swing a cat.:D .

That's funny, my saying is 1/8" gap!?! You could drive a train through that.:rolleyes:

[Myk Rian]

When I built my tool chest I kept things at 1/64 or less. I try to keep things close to that. Pride in workmanship I suppose. I repaired precision tools for 20+ years so being right on is a habit.
I never could have done that with my old C-man TS.

[Mike Henderson]

As long as it looks good, I'm okay with it. Many times, I don't measure at all, or use something like a story stick.

Mike

[michael osadchuk]

I've been reading threads all over (this forum and others) and I sense what might be called an obsession for accuracy.

What is a reasonable objective for accuracy in a wood shop.

As a caveat, I would like to say that I believe a serious hobbiest and a profession wood worker are no different in terms of accuracy.


hmmm..... serious hobbiests can likely afford to spend the time to be more "obsessive" about measurements....

more seriously, my answer is it depends on the function.... in setting up woodworking machinery and tools(infeed and outfeed tables of a jointer, flatness of the sharpening stone for blade of one's smoothing handplane) I'd want "machinist" accuracy......

...in terms of finished pieces of constructed projects, the ease of assembly, its final appearance and its longevity (including dealing with wood movement) will also inform your own level of care about measurements

good luck

michael

[Steve Jenkins]

It really depends on what you are doing. If you are making a 96" long table and it ends up at 95-1/2 does it really matter? If you are making a mitered border around the top of the same table and one miter is open .010" that really does matter.

[Peter Quinn]

I'm in the "It matters if you can see it" camp. Do I need a table top to be flat within .005" tolerances? Not hardly. I'm more concerned there with grain, color, and other aesthetics. You can't see it, it affects nothing. Do i need machine made matched joints to be within .005"? Yes, I need room for glue and not much else, and that is achievable. If i build a wall of custom cabinets that spans 14' and I make each box 1/16" too wide, that is a problem. If I make a free standing desk that is 1/16" too wide, that is not a problem. I find more and more that all the gizmos and measuring devices can be avoided by batch cutting parts with simple stops and using gauge blocks or story poles to set distances and thicknesses. It is often the cumulative effect of small errors that adds up to a large problem. If you start with a story pole that defines your overall length for a project and work backwards to calculate parts sizes things seem to go better, and you maintain the only accurate number you really need. Measure twice? How about not at all.

I recently made a series of 9' mahogany windows with 24 lites, 3X8. If each bar was 1/64" over on length, that adds up to a big problem. The lead guy at work taught me a simple system using MDF gauge blocks and punch sticks that guarantees a perfect job, puts all the mortises in the right place, cancels any error in either axis. No rulers, not digital whizmos, just $5 worth of mdf and a finger tip as a feeler gauge and you get within .005" over 7' and 7 horizontal bars. Much cheaper than a set of 24" calipers too!

[Billy Chambless]

As long as it looks good, I'm okay with it. Many times, I don't measure at all, or use something like a story stick.

Mike

Same here. I have one of those inside/outside/depth vernier calipers, but I almost never actually read it -- just use it to check or transfer dimensions.

[Jason White]

For me, if it's close enough it's close enough.

Seriously.



I've been reading threads all over (this forum and others) and I sense what might be called an obsession for accuracy.

What is a reasonable objective for accuracy in a wood shop.

As a caveat, I would like to say that I believe a serious hobbiest and a profession wood worker are no different in terms of accuracy.

[Bruce Wrenn]

Measure it with a micrometer, mark it with a piece of chalk, and cut it with an axe - precision work. All thing are relative as other posters have stated. Mainly what are you doing? In framing a house, an eighth is close enough, but in making a face frame for cabinets between walls, a sixty fourth is too much.

[glenn bradley]

I run along the lines of Mike H and Steve J. I use setup blocks and story sticks more now than earlier in my efforts. I have re-made many a part to achieve a "proper fit" after i had cut it three times and it was still too short ;-)

I like my joinery tight (but leave room for the glue) and try to stick to things I am comfortable with if I am delivering on an expectation but, I try to challenge myself on every new piece so that new skills become comfortable.

My machines, I shoot for .001".
My projects get what looks right.

[Brian Ashton]

I've been reading threads all over (this forum and others) and I sense what might be called an obsession for accuracy.

What is a reasonable objective for accuracy in a wood shop.

As a caveat, I would like to say that I believe a serious hobbiest and a profession wood worker are no different in terms of accuracy.

I don't know if obsession is the correct term. The vast majority of people here and on any other forums are hobbiest. The end result is the primary objective but the adventure, discovery and or exploration (sort of what Derek C once said but he mostl likely won't remember... ;)) of the whole process is often just as important. Which means a person will often be perceived to take on extra pedantic steps in their approach to a project. As one gains more experience they tend to relax their processes to some degree and become much more adaptable and flexible.

[Larry Edgerton]

[QUOTE=Mark Norman;1160767]I would say it largely depends on what you are making and what is the desired end result. For example if yer building a house 1/4" tollerance is acceptable but the same 1/4" on a face frame of a cabinet would never fly. QUOTE]

Not on my homes! I hired a fellow a few years ago and yelled a measurement to him a few times and they were always a little off. I call measurements in 1/16 light or heavy, and I try to keep all framing within a 1/16. Anyway....

I called this fellow over and asked him why his stuff consistantly did not fit and he informed me that he did not do sixteenths, he cut to the closest eight.

I informed him that he was unemployed.

Close tollerances are not at all time consuming, it is just a habit one needs to get into, and the time spent at an early stage will come back to you at the finish, and you will have a better product.

To answer the OP's question, I myself always try for perfection. I never quit achieve it but I always strive for it.

[Frank Drew]

At least with respect to built-ins, if you're fitting something between walls you'd better allow for scribe-to-fit, because it's a guarantee that the walls won't be anything like +- 1/64", or .005", over their entire length.

But for joints such as mortise and tenon or dovetails or simple glue joints... I don't want to see any daylight between the pieces, because if one thing is true about joints it's that they don't get tighter fitting over time.

[James White]

[QUOTE=Mark Norman;1160767]I would say it largely depends on what you are making and what is the desired end result. For example if yer building a house 1/4" tollerance is acceptable but the same 1/4" on a face frame of a cabinet would never fly. QUOTE]

Not on my homes! I hired a fellow a few years ago and yelled a measurement to him a few times and they were always a little off. I call measurements in 1/16 light or heavy, and I try to keep all framing within a 1/16. Anyway....

I called this fellow over and asked him why his stuff consistantly did not fit and he informed me that he did not do sixteenths, he cut to the closest eight.

I informed him that he was unemployed.

Close tollerances are not at all time consuming, it is just a habit one needs to get into, and the time spent at an early stage will come back to you at the finish, and you will have a better product.

To answer the OP's question, I myself always try for perfection. I never quit achieve it but I always strive for it.

Larry,

I would let you build my house! Although I probably couldn't afford it.

But more seriously this is my attitude.

"To answer the OP's question, I myself always try for perfection. I never quit achieve it but I always strive for it."

I have worked as a trim carpenter and an aircraft sheet metal mechanic and have always received praise from my bosses for the quality of my workmanship. I very much attribute it to this attitude.

That being said you do need to know were to draw the line. This only comes with experience. Therefore you need to start with these habits and when you develop the skills you are then capable of knowing what is appropriate.

So in my shop machines need to be set up to perform to less than .005" and I need to be able to perform to less that 1/64". Or as many have already stated what is visible. A gap of .010" is visible.

James

[James White]

Not on my homes! I hired a fellow a few years ago and yelled a measurement to him a few times and they were always a little off. I call measurements in 1/16 light or heavy, and I try to keep all framing within a 1/16. Anyway....

I called this fellow over and asked him why his stuff consistantly did not fit and he informed me that he did not do sixteenths, he cut to the closest eight.

I informed him that he was unemployed.


This reminds me of a slouch we hired from a framing crew. He was my cut man when we were closing in an archway. Every stud he would hand me would fall out if you didn't hold it. So I asked him why and he said there was no such thing as 1/16" in framing. It was 1/4" light or heavy. Later on after we finished that. I noticed that tab on his tape measure was bent 1/4" from dropping it. When I asked him about this. His reply was it didn't make a sh##'s bit a difference. He lasted less than a week and I had nothing to do with it.

James

[Jeff Miller]

I hire a guy that works for NASA to do all my measuring since I joined these woodworking forums.

Before I just used a cheap ruler.


But ya know what ,I can't see any difference in the final product:confused::D;)




JEFF:)

[David Keller NC]

"What is a reasonable objective for accuracy in a wood shop."

Richard - there is an implication here (maybe), that is a common mistake that most us, including me, take years and years to "unlearn". That is that for a hobbiest or one-off professional shop, you are not looking to cut parts to precise measurements.

Such a thing is absolutely critical to a factory, of course, but trying to do this in your own wood shop will not only likely drive you crazy, but is not appropriate to the task at hand.

As just one example of why this is not a good thing, consider that wood doesn't come in precisely defined sizes. So, if you're working from a plan and the case sides of a dressing table are listed as 18.5" wide, and you've got a couple of nice boards that are 18.25" wide, what do you do? I've seen woodworkers that haven't realized that building "to spec" isn't desirable make up a panel of two 9.25" boards with mis-matched grain so they can hit the 18.5" width on the plans, when there was a very nice slightly less wide single board in their stack.

The point here is that the best way to work is to fit one piece to the rest of the pieces. If you're cutting two rails for a frame-and-panel door, for example, you cut and fit each tenon on each end of the rail to one of the 4 mortises on the stiles. Like many, I spent years trying to make absolutely consistent width mortises and tenons so that any of the 4 tenons could fit any of the 4 mortises. Not only is it extremely frustrating, it's not appropriate - the ability to adjust each tenon for a precise fit in just one of those 4 mortises makes the overall result considerably tighter and more aesthetically pleasing.

[Leo Graywacz]

The obsession with accuracy as you so put it is not my obsession. I have quality tools and measurement devices. 0.005" is easy to obtain. You just read the dial and there you are. It is really important when you are stacking parts, the imperfections add up quick.

[John Thompson]

Interesting observation you have made Richard. In 38 years I have never seen a professional or serious amateur that was obsessed with accuracy. The use of story sticks and fitting joints to fit will almost insure accurancy to 1/32" which is enough in most cases. And... if the professional or serious amateur makes a mistake that can be seen with the eye.. they still don't get there shorts in a wad as they know how to fix it. That is my observations and own theory with accuracy. :)

Have a good father's day...

Sarge..

[Mark Norman]

Not on my homes! I hired a fellow a few years ago and yelled a measurement to him a few times and they were always a little off. I call measurements in 1/16 light or heavy, and I try to keep all framing within a 1/16. Anyway....

I called this fellow over and asked him why his stuff consistantly did not fit and he informed me that he did not do sixteenths, he cut to the closest eight.

I informed him that he was unemployed.

Close tollerances are not at all time consuming, it is just a habit one needs to get into, and the time spent at an early stage will come back to you at the finish, and you will have a better product.

To answer the OP's question, I myself always try for perfection. I never quit achieve it but I always strive for it.


I didn't mean to imply sloppy was acceptable Larry, but the fact of the matter is when building a house, the raw materials will be less than perfect and if a stud has a twist or warp ya don't toss it in the scrap pile. If it's off by even a half inch, the sheet goods will still have the seams landing on the stud/joist/truss and that is perfectly acceptable in the construction industry.

[Rick Levine]

Another reason I like living in New Mexico. The style of furniture is rustic, just right for my abilities. I really like Bruce Wrenn's thinking:



Measure it with a micrometer, mark it with a piece of chalk, and cut it with an axe - precision work.

[Bill White]

I guess that it is like the fellers who reset equipment every time they install a new saw blade.
I live by the old tome,"measure twice, cut once".
How close can you cut a piece of wood that will change dimensions each time the weather changes?
Bill ;)

[Kyle Iwamoto]

I agree with it depending on what you are building. A 95 inch bench, 1/2" is good. House, 1 inch is pretty close. Picture frame, no light through gaps is my criteria.

[Bill Huber]

My question is what do you use to measure a 5 foot long board down to .005 inches. I use story sticks a lot and that helps me get it all right.

Now if we are just talking about the tool setup then that is a whole different story. I want it as close to perfect as I can get it.

[Dan Friedrichs]

Not on my homes! I hired a fellow a few years ago and yelled a measurement to him a few times and they were always a little off. I call measurements in 1/16 light or heavy, and I try to keep all framing within a 1/16. Anyway....


Related to Bill's question, how do you measure framing members to within 1/16"? When you're doing "light/heavy", you're actually going to be within 1/32". I doubt you'd have an easy time finding two tape measures that are within 1/16" of each other over their entire range, let alone within 1/32".

[Mark Norman]

Question being,, why would you need to get more accurate that 1/8" when framing? When in just a few hours it would likely shrink due to drying or swell from moisture depending on the climate. As far as I am aware studs are green for the most part and could easily shrink 1/4" over a 8 foot stick.

[Chip Lindley]

I agree with it depending on what you are building. A 95 inch bench, 1/2" is good. House, 1 inch is pretty close. Picture frame, no light through gaps is my criteria.

*shakin' head*...I suppose 2 out of 3 ain't Bad! 1/2" in 95" is totally unacceptable anywhere in the civilized world. So is 1" ANYWHERE in a house!! No light at the joints of your picture frame sounds good in theory...BUT...

Kyle, you will never build a picture frame for me either. IF I asked you to build a frame around a 24"x36" picture, I am afraid you will end up cutting part of my picture off to fit your frame? But I digress....

Back to the Real Topic:
Machinery setup measurements within a couple of .001"s of an inch are necessary for best accuracy. Splitting .001"s into ten-thousandths is a waste of a woodworkers time, unless a *press fit* is needed for bearings, etc.

Dealing with wood, Tape measures only readily measure 1/16"s. But, I can measure with a pencil or scribe to 1/64" by interpolating visually! (BTW, use the same tape measure for a whole project) There is MUCH interpolation, visualization, and even tactile comparison by touch to assure two pieces are the same. All depends on the individual's acute or lax personal standards of *good enough*!

I use the *light/no light* method of deciding if tongue & groove, mortise & tenon, rails & stiles are too loose or too tight! I set up my router table and shapers by *eye*! As long as a whole set of cabinet doors are machined alike, and Fit Together, there is no error.

Machinery is in .001"s. Jointery is Loose/Go/No Go. Squareness requires Parallel Sides of Equal Length and Exact 90 Degree Cuts. The Form in between can be Anything you want it to be!

[guy knight]

i had a builder complain about my work not being perfect so i told him to call me after he had all of the trim work in and if he found any problems with my work then i would not charge him for the job and 15 years later he still uses me and i have not done a job for free framing and general construction do not require you to be within a 1/16 most of the time but when you get to finish work a 1/32 makes a difference and my furniture i will not leave any gaps or leave anything that anyone can detect so accuracy is relavent to what you are doing at the moment

[Cary Falk]

If I can't hide it, then it is not accurate enough.:eek::D

[Rusty Elam]

I like to use the " Yeah Baby " scale. When I am doing M&Ts or dovetails and after I fit them Yeah Baby is in my head I know its good enough.
One of the best things I ever read on this forum was " quit when your done"
Rusty

[Chris Friesen]

As far as I am aware studs are green for the most part and could easily shrink 1/4" over a 8 foot stick.

You'd be wrong. Generally studs are dried to an EMC of 15-19%, and will generally drop down to 8-12% or so as they dry. In any case, wood shrinkage with the grain is almost negligible, to the point where most people just ignore it.

As to the initial topic, as others have said it depends what you're building. Generally it falls into the "as accurate as required" category. Miter joints must be airtight, but that might be tweaked with a block plane. Face frame joints must be flush (unless designed otherwise) but that can be done after assembly with a hand plane. Mortise and tenon joints must be tight but not too tight...this gets tweaked with a file or router plane.

[Chris Tsutsui]

For cabinetry and furniture I will strive for 1/32".

Though of course everyone wants better accuracy, though lets be realistic... If a piece was off by 1/32" then I would not start over but would get it to work with the rest of the pieces.

What's more difficult is planning for wood movement or dealing with dancing pieces.

[Jacob Reverb]

What is a reasonable objective for accuracy in a wood shop.

One quadrillionth of an inch.

There, I've said it.

[Matt Armstrong]

Generally I shoot for less than 0.15um.

[Cary Falk]

Generally I shoot for less than 0.15um.
150nm? That's so 2 years ago. I think we are at 45nm with todays technology.:D

[Richard Wagner]

This has been very interesting and informative reading. The sum total of all the comments definitely provides an answer to my question. I have been obsessive in my quest for precision. In the future, my equipment will be aligned to my present "obsessive set of standards"; that being - all setups accurate to .005" and .1 degrees.

All cuts will be made as close as I can get them without getting a new pair of glasses. This does not mean that I will no longer be demanding of myself but it does mean I will quit beating myself up for slight mishaps.

I made doll furniture for all of the girls on my Christmas list. Not one of them complained about the gaps in the glue joints. The boys didn't complain either about the slight wobble in the wheels of their toy cars/trucks. Two of them thought the wheels were fantastic and want to know if they can make some with me (I think their dad put them up to that).

Thank you all again for your very constructive and candid responses.

[Matt Meiser]

I try to set up all my tools to "perfect" according to the tools I have available to me for measurement. So a couple thousandths on a dial indicator, no light between an engineer's square and a fence, no light under a straightedge, etc.

My projects improved a lot once I started building in an order where I make a critical part and work in or out from there. So for example the desk I just made I made the front panel, then built everything else around that. It maybe ended up 1/32 off where I'd planned but since I didn't cut anything else until it was done, I just cut the top/bottom/back sides to fit the front. Then I built the base to fit the top.

[Leo Graywacz]

0.1 degree is too much in my book. .005" is what I strive for. If you do 45 degree miters that at .1 degree off the last joint will look horrible. I try for .02 degrees and it can only be measured (in my shop) by the results of the joint.

[John Coloccia]

re: how close is close enough
Reminds me of a conversation I had the other day helping someone pick out a sharpening system for his turning tools. "Well, I'm not a pro, so I really don't need to get it sharp like a pro". My response was, "There's no such thing as pro-sharp. You're either sharp or you're not." So in answer to how close is close enough, it either fits or it doesn't. There is no close enough. If it doesn't need to fit, then it doesn't need to fit. Construction framing doesn't need to fit. A lot of furniture work doesn't need to fit. Inlays need to fit. Most instrument work needs to fit. If you're doing studio furniture/clocks/boxes/etc, it needs to fit.

To that end, I keep my machines setup as accurately as I possibly can because .001" here and .001" there add up to significant mistakes that I then need to fix by hand. It's far easier to setup the machine once a year so I can move from machine to machine without any significant errors creeping in. To get .005" in a finished product, your machinery had better be significantly better than that, IMHO.

[Brian Kincaid]

It really depends on what you are doing. If you are making a 96" long table and it ends up at 95-1/2 does it really matter? If you are making a mitered border around the top of the same table and one miter is open .010" that really does matter.

Agree 100%
-Brian

[Tom Rick]

Interesting observation you have made Richard. In 38 years I have never seen a professional or serious amateur that was obsessed with accuracy. The use of story sticks and fitting joints to fit will almost insure accurancy to 1/32" which is enough in most cases. And... if the professional or serious amateur makes a mistake that can be seen with the eye.. they still don't get there shorts in a wad as they know how to fix it. That is my observations and own theory with accuracy. :)

Have a good father's day...

Sarge..

Exactly right- I believe most experienced workers don't give it too much thought.
If the work calls for no visible gap- just cut the piece to fit and carry on.

The obsessive part I believe is the domain of the novice.
The experienced man has enough technique to bring projects together without struggling over every cut.

I frame to a contact fit- loose framing leads to lifted tape and popped screws as the mess settles. I have swung a circular saw around enough that it is no issue to drop the saw to a board and split the line.
A standard call to a good cut man is to "leave" or "take" the line. Things are framed up tight but no one is giving it much thought.
A furniture builder working by himself does clean work as a matter of practice. Why would he place the cut anywhere other than where it needs to be?

An answer to your question might include some reference to the degree of precision tooling required by the wood worker.
I have always felt that the craftsman's greatest tools are his heart and mind.
Primitive tools can yield superlative results in the hands of the master:

175519

Stradivari's tools

[Chris Fournier]

This has actually been a useful thread about this topic - which is very rare.

I have found on these woodworking forums that there is a certain personality who will claim anything to establish their mastery of the craft. If the plans call out for "+/- 0.10" they'll tell you that they hit .0005" all the time, with a hand plane no less.

You typically don't get this kind of nonsense on the machinist's forums which is ironic because they often do work to these infintesimal tolerances. The truth is that machinists have been taught how to measure and they know how expensive it is to just buy equipment that can reliably read to "tenths". They'll also admit very quickly that owning fine measuring instruments doesn't necessarily mean that they are able to use them properly and repeatedly to the resolution that they're capable of.

I think that precision is something that a consciencous craftsman will continue to creep up on during the length of his/her career. Early on the payback is huge, later on you may literally be splitting hairs.

Precision is costly on a sliding scale: low = cheap, high = expensive. I think that we all intuitively apply this correlation when we are working on any given project.

A good craftsman can split the line with a circular saw while building a home, slot a guitar fretboard that produces a well intoned instrument or make a cane fly rod that follows a taper formula measured in .001" resolution. The same craftsman can perform all three of these tasks but it is unlikely that he would be foolish enough to apply his standard of precision from any one of the projects to another.

[John Coloccia]

A good craftsman can split the line with a circular saw while building a home, slot a guitar fretboard that produces a well intoned instrument or make a cane fly rod that follows a taper formula measured in .001" resolution. The same craftsman can perform all three of these tasks but it is unlikely that he would be foolish enough to apply his standard of precision from any one of the projects to another.

+1

I think the debate comes in mostly with precision squares and dial indicators when setting up machines. I strive to set all my machines to +/- .001". I know it won't stay like that for long, and it's also kind of silly when the fence on my table saw isn't even that good, but I do the best I can. That doesn't mean I fit all my woodworking to that. All it means is that as I move from machine to machine, I'm not introducing more errors as I go along. For example, if my jointer fence is out, and my table saw blade is tilted slightly, and then I bring the work over to my router table and it's out a little bit, by the time I'm done, a couple of "within woodworking standards" errors can creep in and I end up with a finished product that is noticeably cockeyed. Think about all the trouble people have just making a simple 45 degree miter for a frame or moulding. If the tool is setup once to be dead nuts square and the miter bar is 45 degrees, you end up with a tight joint. That's rarely the case and people are frustrated to no end making a seemingly simple cut. Maybe .010" is acceptable for the final product, but if you're out that much already at the tool, getting there in the final product is an exercise in frustration.

I've often said that I would gladly pay for a service to come in and setup all of my machines once a year so I didn't have to bother.

[Neil Brooks]

I tend to think .... if the outcome was good (you produced a fine looking piece, with tight joinery), then ... whatever you did, worked -- no matter how whacked your machinery might be :)

But I DO I think it's a useful conversation -- particularly when it comes to the Diminishing Returns of that last (whatever it is) thousandth of precision.

I think it's useful to understand how the Lowest Common Denominator (or weak link in the chain) influences the level of precision that's ever worth seeking -- in our case, movement of the wood, itself.

And I think it's useful to draw distinctions between "precision," "accuracy," and "consistency," in these discussions.


I've often said that I would gladly pay for a service to come in and setup all of my machines once a year so I didn't have to bother.

It's actually a rather zen thing, to me -- one that I rather enjoy. It's also kind of an annual ritual, but .... with (+/-) weekly checkups and tweaks !

[David Giles]

If I can't feel it and I can't see it, it's fine. Since I usually mess up during the first 30 minutes of a project, everything else is adjusted to fit what has already been cut.

[John Coloccia]

If I can't feel it and I can't see it, it's fine. Since I usually mess up during the first 30 minutes of a project, everything else is adjusted to fit what has already been cut.

ROFL. David for the win.

[Rod Sheridan]

When setting up machinery, I like it to be accurate to a few thousandths of an inch.

For example my digital height gauge on my planer is accurate to 0.02mm which is great.

When planing pieces I can set it at 20mm for example, and receive the same thickness I had on the original pieces, makes repeats easy.

For length cutting I have the crosscut fence length calibrated to 0.1mm which is just fine for repeat measurements.

When I design furniture I might want 2 table aprons 1,400mm long, which is what I set my crosscut stop to.

If they're 1,400.02mm or 1,399.98mm who cares, at least they're both the same.

That's the key, all the parts that have to be the same size, are the same size.

If my cabinet is 0.02mm too wide or too narrow it's no sweat, unless it's a built in.

I machine most parts without reference to the other parts, based upon drawings I've made, then dry assemble the cabinets, there may be something like a drawer bottom, that I'll check the dry drawer for size before cutting, as it's a cut to fit condition.

It may not be the right way to work, however it's how I was taught.

Regards, Rod.

[Matt Winterowd]

Richard, I know that you expressed amazement on a recent thread about precision squares, and I want to make an observation about requiring accuracy from your tools vs. requiring accuracy to some arbitrary measurement in a project. If I'm building a cabinet, I don't really care if a side is 18" or 18 1/8". I just care that the two opposing sides are equal, and that the joinery is tight. However, I do want my reference tools to be accurate, so that if I do need to try and achieve squareness, for example, I know that I can rely on the tool giving me an accurate reading. Just like people strive for tight tolerances setting up their machines, I am willing to pay a bit extra to guarantee that my tools are telling me the truth, and maybe even more importantly, that they are all in agreement with each other.

[Greg Portland]

As long as it looks good, I'm okay with it. Many times, I don't measure at all, or use something like a story stick.

Mike+1. I know I'm in trouble if I have to start pulling out measuring devices. Make your cuts to existing pieces and use a story stick to setup your project dimensions (esp. helpful for built-ins).

[Steve H Graham]

The folks on this forum recently let me know that for some jobs, no amount of perceptible error is acceptable. I was trying to glue six pieces of walnut together to make a solid guitar body, and they told me a 0.002" gap was no good. I've also learned that snipe which is too small to show up on a dial caliper will light up beautifully when you take sandpaper to it.

The more woodworking I do, the more I appreciate my milling machine. I'm trying to put some inlays (structural, not thin decorative stuff) into the front of my guitar body, and I've found that the mill gives faultless measurements, straight edges, and perfect roundovers with very little effort.

I'm amazed at how precise my table saw can be. If I weren't so lazy, I'm sure I could get precision of a thousandth or less by ginning up an adjustment rig with a dial indicator on it. And it edge-joints perfectly, with a simple jig someone here suggested.

Mark Duginske has a funny part in his woodworking machines video, in which he ridicules people who blow wads of cash on "precision" doodads that get you within 1/32". He holds up a bunch of Post-its (his shims) and notes that each one is about 1/8 of 1/32" thick. Personally, I like doodads, because they are useful to people like me who have no skills, but I think he demonstrates more wisdom than I do.

Machinists use rolling papers to do even better. If you put one between a cutter and a surface and bring the cutter just close enough to make the paper tear when you pull on it, you're within a thousandth.

[Keith Outten]

Any measurements made to a tolerance of less than 1/64th inch need to be made in a temperature controlled environment.
Your measuring instrument will not provide the same results from an inspection you make at 65 degrees when your shop warms up to 75 degrees later in the day. If you intend to work to very close tolerances you need to keep your workshop at a constant temperature, otherwise your wasting your time. I have CNC machined inlays at eleven pm that fit perfectly that did not fit the following morning when my shop temperature had dropped by ten degrees.

The American Society of Non Destructive Testing specifies that the unaided human eye cannot discern a scale measurement of less than 1/64th inch which is 0.015" (fifteen thousandth of an inch).

Note that 0.005" is the diameter of an average human hair.

Calibration labs generally keep a constant 68 degrees F for the purpose of calibrating precision instruments for good reason.

When you start working to very close tolerances you must then consider the thermal coefficient of expansion for the material you are using. Wood will expand and contract, however you cannot pin down a close tolerance engineering specification for thermal growth on a material that is not man made.

Lastly, adjusting some machine surfaces to a tolerance of 0.001" is mute when you consider that the bearings in the cutter heads or blades may very well be manufactured to a run-out tolerance of +- 0.008" which is very common.
.

[Van Huskey]

Any measurements made to a tolerance of less than 1/64th inch need to be made in a temperature controlled environment.
Your measuring instrument will not provide the same results from an inspection you make at 65 degrees when your shop warms up to 75 degrees later in the day. If you intend to work to very close tolerances you need to keep your workshop at a constant temperature, otherwise your wasting your time. I have CNC machined inlays at eleven pm that fit perfectly that did not fit the following morning when my shop temperature had dropped by ten degrees.

The American Society of Non Destructive Testing specifies that the unaided human eye cannot discern a scale measurement of less than 1/64th inch which is 0.015" (fifteen thousandth of an inch).

Note that 0.005" is the diameter of an average human hair.

Calibration labs generally keep a constant 68 degrees F for the purpose of calibrating precision instruments for good reason.

When you start working to very close tolerances you must then consider the thermal coefficient of expansion for the material you are using. Wood will expand and contract, however you cannot pin down a close tolerance engineering specification for thermal growth on a material that is not man made.

Lastly, adjusting some machine surfaces to a tolerance of 0.001" is mute when you consider that the bearings in the cutter heads or blades may very well be manufactured to a run-out tolerance of +- 0.008" which is very common.
.

What Keith said is accurate (to within .0000001) and wise. However, I often find myself setting machines and making measurements to the best of my tools and my ability. In the end I tend to only sweat machine setup but it just makes sense to me even with the other tolerances of the machine, in some directions the lack of perfection can just stack on top of each other.

[Leo Graywacz]

1/64" is closer to .017" and I routinely do measurements by eye around .007".

Wood movement is more about humidity than temperature.

[John Coloccia]

I can certainly see better than 1/64". 1/64" is the difference between slight gap and no gap. That's not to say I always work to those tolerances, which would be silly, but to say I can't tell the difference is silly as well. 1/64" is 15 thou, and anyone who's competent at machining can certainly see .015".

[paul cottingham]

For me, if it's close enough it's close enough.

Seriously.
+1 dude.
Seriously.

[Steven Hardy]

I try not to build anything that wont bend to fit.....I figure wood comes from trees...and trees bend???:)

seriously tho....has anyone ever else ever wished they could buy a metal tape measure
that was flat without any curl and without the loose clip on the end of it???

[Steve H Graham]

anyone who's competent at machining can certainly see .015".Absolutely. A 0.015" pass with an end mill is fairly big, and in wood, it will make a very obvious slot. I was machining walnut with an end mill the other day, and I found that 0.003" was about as much as I could risk, when sneaking up on a measurement incrementally.

On a metal lathe, an accidental 0.015" cut in an otherwise uniform cylinder would be a glaring error visible from six feet away, and it would justify junking or resurfacing the work. I don't turn wood, but I'm sure an error that big would ruin a pen or bowl. Sanding it out would deform the entire piece.

I was able to see a 0.003" gap when I was joining pieces of walnut, and my eyesight is no longer sharp. A playing card is about 0.004" thick, and if you put one on a flat table and run your finger into the edge, it's extremely obvious.

When I'm checking squareness, a gap of much less than 1/64" will jump out at me and will be big enough to send me back to the saw.

The post-machining movement and dimension changes in wood are frustrating sometimes. It seems like you have to glue it up before it moves. I assume this only matters to people like me, who make silly mistakes that have to be covered with very precisely cut pieces of wood! I doubt a person making a big dining table would care about 0.015", unless it was on a prominent surface.

When I was a physics TA, I had to teach people how to use measuring instruments, and we were told we should always shoot for the nearest half-increment and estimate. I think that would be possible on a 1/64" scale with decent eyesight or old eyes aided by readers.

[Leo Graywacz]

I did a job that I needed to glue up a bunch of little reeds together that were 3/8" thick. I clamped them up, about 70 of them and they were the perfect distance. Then I put glue in them. The thickness of the glue screwed the whole thing up. .002" glue line x 133 pcs equaled about 1/4" oversize.

[Richard Wagner]

You have all been very helpful and have caused me to reassess my approach to this whole thing. I'll double check all of my tools for accuracy first and then make certain that all of my machines are properly tuned. Then I will get a new pair of reading glasses.

Hmmm. Maybe I should get the glasses first.

[Terry Welty]

I struggle with the voices in my head... The Quality Control voice insists on 1/32" and hollers "You'll be sorry" if the other voice, The Half-A_ _ guy wins with his "Aw, it's close enough"... Usually, if they would just compromise and settle within 1/16" we would end up ok with the most of the projects we work on.

Roses are Red,
Violets are Blue.
I'm schizophrenic
and so am I.