Squaring my Incra miter guage - a different way

[Johnny Barr]

I've always used the 5 cut method for sleds but the use of feeler gauges isn't suitable for miter gauges until I stumbled across this video .... https://www.youtube.com/watch?v=sL3K_fPLHc4 and all its associated comments and opinions

I tried it and found this method quick, accurate and simple. Assuming your square is accurate this works brilliantly. So much so that I'll use this method for all future sleds and gauges. After this adjustment I thought I'd double check it using the 5 cut method and the final error was negligible.

Do people use this method?

[Mike Gresham]

I've been using Brian's method for years to square my panel sled fence.

[lowell holmes]

This shows how dumb I am. I squared mine with a square against the teeth on my blade. It is a carbide tooth blade.

OBTW, my cuts are square.

[Eric Keller]

if you have carefully squared the blade to the miter slot, using a square on the blade will be pretty close. Ok, so close enough for a hack like me.

[Johnny Barr]

if you have carefully squared the blade to the miter slot

I think that's why Brian's method is so good. It's squaring your fence against the miter slots not the blade so you don't have to rely on the blade being 100% parallel to the slots and I know very few are. It makes perfect sense to me to align against the slots as that's the way the sled is moving. I've always followed the "less than 5 thou" rule. If my fences and balde/slot parallelism is less than 5 thou then in the real world that's good enough. I've read people saying that parallelism needs to be zero or at the very worst less than 3 thou and yet wood expands and blades can deflect by more than that.

This squaring method gets me to a range of less than 5 thou in a few minutes unlike the 5 cut method and as I said above I don't think the 5 cut method is suitable for an Incra miter gauge

BTW I found another of his videos comparing the 5 cut method to his method. The comments and arguments make very interesting reading particularly his justifications. https://www.youtube.com/watch?v=UC_iF5pZxmI

[Osvaldo Cristo]

Thanks for share... simple and direct to the point. Perhaps it could be a good idea to repeat the test at the opposite direction just to be sure your square is "square"...

[Frederick Skelly]

Thanks Johnny! Alternate techniques are always welcome - never know when something will be handy.
Fred

[Johnny Barr]

Thanks for share... simple and direct to the point. Perhaps it could be a good idea to repeat the test at the opposite direction just to be sure your square is "square"...

That's a very interesting idea, Osvaldo I''ll try that and report back but I'm certain I'm square. As I mentioned above I verified squareness by not only the 5 cut method but the "flip one piece over after a cut" method and checking for daylight using a precision square. I'll bury the 5 cut method but in a shallow grave just in case.

EDIT .... Got the same result going in the opposite direction. Would have been surprised otherwise

[keith micinski]

This will absolutely work but it is counting on multiple things being perfectly square with each other instead of just one. I also have found that how you push a piece of wood through a cut and how you use push something for a measurable test isn't always the same and even when everything is perfectly square you don't always get a square cut. Plus the claim it's cheaper and easier has to be wrong because it's impossible to own a table saw and not own scrap for free and it's the exact same process of making test cuts, except now, I have to set up a second measuring device I may or may not have to run my test cuts.

[Johnny Barr]

This will absolutely work but it is counting on multiple things being perfectly square with each other instead of just one. .

There is only one. Fence and miter slot. If they are bang on square then you'll get square cuts regardless of blade parallelism. Yes I'm assuming, however, you are using a good quality square to check this with a smooth edge. That's the only assumption here. Well you could get pedantic and mention dial indicator quality and straight parallel slots of equal width but if your saw doesn't have the basics then the 5 cut method won't work either. I have now tested all my sleds and gauges this way and verified by methods mentioned above. I have clamped the square so there is no movement and pushed and pulled the sled/miter gauge at differing speeds and when the dial indicator has little or no movement I know the fence is perfectly square to the slots and its the slots that dictate the movement.

I'll do test cuts after that but really there's no need. I am convinced after using this method many times that the 5 cut method is not the only definitive method for fence squareness.

[Alan Schaffter]

That method ensures the miter gauge is perpendicular to the miter slot, the most important alignment. It also will yield a square cut even if the blade isn't parallel to the miter slot. However, a non-parallel blade (skewed blade) will result in a slightly wider kerf than normal- it is considerably much less extreme, but it is the same principle as cutting a cove on a tablesaw- the greater the skew the wider the cove. Also, if the stock is not clamped or held securely, a skewed blade can cause the stock to move sideways.

[Johnny Barr]

That method ensures the miter gauge is perpendicular to the miter slot, the most important alignment.

Also, if the stock is not clamped or held securely, a skewed blade can cause the stock to move sideways.

Yes Alan it is the most important, that's why I advocate you shouldn't use the blade as a reference. Good point about the clamping which you should probably do even if you do have a properly aligned blade. Its a bit hard to do however with an incra miter gauge unless you have some sort of hold down which my sleds have.

One thing the 5 cut method has over the way I'm promoting is that final adjustment with a feeler gauge. Its easier with the use of clamps and pivot points than trying to move a fence 5/10 thou by hand but once that dial indicator has little or no movement you know that you are there.

[Art Mann]

The blade would have to be aligned exactly with the miter slot in order to make an accurate adjustment with a square. A blade doesn't have to be adjusted that close in order to rip or crosscut accurately and many saws are not. Some people purposely misalign the blade slightly to insure the back of the blade doesn't create saw marks on the edge of the work piece. I just don't want to count on a previous adjustment that I have made still being dead on. The approach in the method here does not depend on any previous adjustments having been made exactly.


This shows how dumb I am. I squared mine with a square against the teeth on my blade. It is a carbide tooth blade.

OBTW, my cuts are square.

[Dan Russell]

The method in the video you posted is an exceptional alternative to the cutting methods but like Brian said, make sure your square is legitimately accurate. Don't forget to make sure your blade and fence are also square to the miter slots. I use a table saw dial indicator from Woodpeckers to ensure those are aligned parallel to the miter slot as well. Once I have everything aligned to within 0.002" or so, I'll make a rip cut using the fence and then a crosscut with the miter gauge and verify everything is blissful. If there's a gap, do it again and again until you get it right on. Sometimes if you are adjusting your saw blade, just tightening the screws that hold it in place can shift your blade out of alignment considerably. Same is true with your fence and the miter gauge so keep the screws as snug as possible yet allow very minimal adjustments when finalizing everything. Then hold it tight and tighten your screws gently and make sure there isn't any accidental movement while doing so.

[Matt Day]

That’s a great method, thanks for posting (and bringing back an old thread). I hate the 5 cut method!

[Lee Schierer]

I didn't see this thread the first time around and I have a small problem with a few of the comments regarding the blade not being parallel to the miter slot still giving perfectly square cuts. While that might be true for the angle of the cut being perpendicular to the direction of travel of the miter gauge, the cut is no longer vertical if you measure up from the table surface. While a few thousandth of and inch out of parallel might not be very noticeable the saw blade is a circle so as get out of exactly parallel with the miter slot you will begin to get a curved cut of the cut surface perpendicular to the saw table top.

You can see what I mean by getting down to table surface level with your eye looking straight down the blade so you only see the thickness of the blade. Now move to the left or right and you will start to see an ellipse instead of a flat blade.

[Nick Decker]

That’s a great method, thanks for posting (and bringing back an old thread). I hate the 5 cut method!

I'd like to echo that, Johnny. I vaguely remember someone posting that link a while back, but it really didn't sink in then. The five-cut is a PITA. Laying a square along the blade and fence is fine for measuring a certain point in space, but it doesn't measure the path traveled along the miter slot.

[Grant Wilkinson]

I started to think that I was dense. I didn't understand how a cut could be square if the blade is not square to the miter slot. However, now that I've read the comments on Dan's video, I see that I was not missing anything after all. He says, "No matter what method you use to square your miter gauge, your blade should always be parallel to the miter track. Everything should be aligned to the miter track." That's the way I always understood things.

I would appreciate if those here who have said that the blade does not need to be parallel to the slot could explain how you can end up with a square cut. I'm not trying to be argumentative. I'm simply trying to learn how, if the miter gauge is square to the miter slot, but the blade is skewed to the slot/gauge, you can still get a square cut.

[Ted Derryberry]

Felder forgot the miter slot when they built my saw.

[Glen Gunderson]

I started to think that I was dense. I didn't understand how a cut could be square if the blade is not square to the miter slot. However, now that I've read the comments on Dan's video, I see that I was not missing anything after all. He says, "No matter what method you use to square your miter gauge, your blade should always be parallel to the miter track. Everything should be aligned to the miter track." That's the way I always understood things.

I would appreciate if those here who have said that the blade does not need to be parallel to the slot could explain how you can end up with a square cut. I'm not trying to be argumentative. I'm simply trying to learn how, if the miter gauge is square to the miter slot, but the blade is skewed to the slot/gauge, you can still get a square cut.

The final cut occurs at a single point on the blade's travel. So the part of the blade nearest the miter slot is going to produce that cut on the entire width of the piece you're crosscutting. So as long as the miter gauge's fence is perpendicular to its path, you'll get a 90º cut. In fact, sliding table saws are often deliberately set to toe away from the blade at the back, but they still produce perfectly square cuts because the crosscut fence is set exactly 90º to the path of the table.

Now if it's way off, you're going to have problems because the kerf will run into the body of the blade which will want to pull the wood one way or the other, but for small inconsistencies it doesn't matter. The miter gauge being 90º to the slot what's important.

[Nick Decker]

Grant, I'll try: Visualize your saw from above. There's a straight line, running from front to back. That's the miter slot, which guides your stock from front to back in a straight line past the blade. OK, there's another straight line which is your saw blade. Ideally, it's parallel to the other line, which will cause to wood to pass by it with the least resistance. But, if that line that is your blade is skewed out of parallel, since it's a saw blade it's gonna cut everything that passes by. It'll cut a little wider swathe, but if the wood is secure it'll still cut a straight line.

So, the job of the fence on your miter gauge (or sled) is to hold your stock perpendicular to the line that the miter gauge follows. Blade gonna do what blade gonna do, regardless.

[Grant Wilkinson]

Nick and Glen: I appreciate your efforts to explain this to me, but I'm still not there.

Here is how I am thinking and you can point out where I am wrong. Let's say that everything on the saw is perfect. The gauge fence is perpendicular to the slot. The blade is parallel to the slot and, therefore, perpendicular to the gauge fence. Therefore, any cut must be perpendicular (90°) to the edge of the board against the fence. I think we can all agree on that. (I hope. :-) )

OK, now we change the fence setting from 90° to 89°. All else stays the same. The slot is still perp to the blade, but now the the fence is not perp to the slot. Nor is it perp to the saw blade. So, we get a cut that is no longer 90° to the edge of the board against the fence. It is 89°. I assume that I'm OK so far, as this is how we cut miters on a table saw, by changing the angle of the miter fence with reference to the blade/miter slot.

OK, now lets change the fence back to 90°. Nothing else changes and all is well.

Finally, we change the angle of the blade to the slot. Depending on whether the trunnions are table mounted or cabinet mounted, we loosen something and bump the table until the slot is no longer parallel to the blade. It is, in fact 1° out. Now, the miter fence is still perp to the slot, but it is no longer perp to the blade. it is out by 1°

If I understand what you both are saying, the cut will still be perp to the edge of the board against the fence.

This is where I am lost. In both of my examples, the fence of the gauge has been changed by 1° with reference to the saw blade. In my first example, it was changed by adjusting the miter fence by one degree. In the second example, it was done by moving the miter slot by that same one degree. (We just did this by changing the relationship between the slot and the blade.)

If you agree that, changing the miter gauge to 89° will result in a non-square cut, how does changing the miter slot by that same one degree not result in the same non-square cut?

[Nick Decker]

The miter slot never changes. Re-read your last sentence.

The only things that change are the position of the BLADE, relative to the miter slot, or the fence, relative to the miter slot.

If the blade is skewed off of parallel (with the slot) then it will basically "plow" through the board rather than slicing cleanly through it. The resulting cut will still create a straight line, just a wider straight line.

[Grant Wilkinson]

But, Nick, the slot does change - relative to the blade. We can say it any way we want. The blade angle changes relative to the slot, or the slot angle changes relative to the blade. The result is the same. The slot and the blade are not parallel. That seems to jibe with your second sentence.

The issue to me is not the angle of the slot to the blade. It is the angle of the board we are cutting to the blade. If the fence is 90° to the blade, the cut will be 90° to the edge of the board that is against that fence. If we change the angle of the fence to the blade by loosening the miter gauge and changing the fence from 90° to the blade to 89° to the blade, we get a cut that is no longer 90° to the edge of the board that is against the fence.

If we change the angle of the fence to the blade by changing the angle of the miter slot to the blade, we have, in effect, changed the angle of the fence to the blade, since the angle of the fence to the blade is dictated by the angle of the slot to the blade. (I know this is starting to get convoluted.) So, why is the cut not 89°?

Maybe if I use a sliding miter saw as an example, it will help explain what I am trying to say. Using a sliding miter saw, we hold the board against a fixed fence and angle the blade to the wood. If the blade is set to 90°, we get a cut that is 90° to the edge of the wood that is against the fence. If we change the angle of the blade to the fence by 1°, we get a cut that is 89° to that edge. We can get the same result by putting a 1° wedge against the fence and putting the board against the wedge. With the blade at 90° to the fence, the cut will be 89° because we have skewed the board using a wedge.

So, I keep coming back to not understanding why, if the blade of a table saw is skewed from 90° to the board, it can still make a 90° cut.

[Nick Decker]

Your miter saw example might be instructive, although it doesn't apply. With the miter saw, the saw blade is traveling, not fixed in place like a table saw, but the miter saw blade is still traveling (hopefully) in a straight line. Try imagining that the miter saw blade is traveling in a srraight line, but that the blade is slightly out of skew with that straight line. What happens? A straight cut is made but the blade plows a wider swathe through the board.

(I once had a miter saw whose blade didn't travel in a straight line, so I got rid of it.)

[Glen Gunderson]

But, Nick, the slot does change - relative to the blade. We can say it any way we want. The blade angle changes relative to the slot, or the slot angle changes relative to the blade. The result is the same. The slot and the blade are not parallel. That seems to jibe with your second sentence.

The issue to me is not the angle of the slot to the blade. It is the angle of the board we are cutting to the blade. If the fence is 90° to the blade, the cut will be 90° to the edge of the board that is against that fence. If we change the angle of the fence to the blade by loosening the miter gauge and changing the fence from 90° to the blade to 89° to the blade, we get a cut that is no longer 90° to the edge of the board that is against the fence.

If we change the angle of the fence to the blade by changing the angle of the miter slot to the blade, we have, in effect, changed the angle of the fence to the blade, since the angle of the fence to the blade is dictated by the angle of the slot to the blade. (I know this is starting to get convoluted.) So, why is the cut not 89°?

Maybe if I use a sliding miter saw as an example, it will help explain what I am trying to say. Using a sliding miter saw, we hold the board against a fixed fence and angle the blade to the wood. If the blade is set to 90°, we get a cut that is 90° to the edge of the wood that is against the fence. If we change the angle of the blade to the fence by 1°, we get a cut that is 89° to that edge. We can get the same result by putting a 1° wedge against the fence and putting the board against the wedge. With the blade at 90° to the fence, the cut will be 89° because we have skewed the board using a wedge.

So, I keep coming back to not understanding why, if the blade of a table saw is skewed from 90° to the board, it can still make a 90° cut.

For your sliding miter saw example, the same applies. What's important is the travel of the slide mechanism, not the angle of the blade. If the blade was slightly misaligned with the slider the angle of cut would still be dictated by the slider's relationship to the fence, not the blade's angle.

Let's use an extreme example for a table saw. Imagine your blade is skewed 45º to your miter slot while your miter gauge is set at 90º. Now imagine you're cutting 1/32nd off the end of a board by using your miter gauge normally. What do you think would happen? It certainly wouldn't be a 45º cut. Essentially you'd end up with a poor cut, there'd be a cove on the end of the piece because of the blade's skew, but ultimately the end of the board would be a 90º cut because it's the miter gauge's fence's relation to the path of travel that dictates the angle of the cut.

[Grant Wilkinson]

I want to thank both of you again. I'm really not trying to be stubborn here. It just comes across that way.

I'm sitting here with pieces of paper representing saw blades, miter slots, miter gauges and chunks of wood. At some point, the light bulb will come on and I'll get it. The damn thing is that I do quite a bit of flat work. It simply has never occurred to me that having the saw blade anything but parallel to the miter slot is no big deal, at least when it comes to the accuracy of the angle of the cut.

Interestingly, the author of the video that started all this discussion is mistaken. He says that his method of dialing in a miter gauge depends on the miter slot and the blade being parallel.

Take care, and thanks for the discussion.

[johnny means]

Wait, explain why you wouldn't just square the miter gauge to the square?

[Chris Parks]

Felder forgot the miter slot when they built my saw.

I use this method to square the cross cut fences on my slider because it is so quick and accurate. Woodpeckers are offering a new one time tool that is ideal for the job, a phenolic 18" square. The thickness of it will make it easy to use the DI which with thin bladed squares can be a bit painful.

[Lee Schierer]

You can't get a straight cut in the plane perpendicular to your table top if the blade is not parallel to the miter slot. The line of the cut along the table surface will be straight and you will get a wider cut and probably some teeth marks and burning. Since the blade is a rotating circle perpendicular to the table cut is not a straight line. Look at the two sketches below:
379283 This is what your wood sees in a cross cut with a blade aligned with the miter slot.

379284 This is what you piece of wood sees when the blade is not aligned with the miter slot. Note that the cut right at the table surface will be wider than the cut near the top of the blade.



379285 To take it to an extreme, would you cut wood on this saw?

[Glen Gunderson]

I want to thank both of you again. I'm really not trying to be stubborn here. It just comes across that way.

I'm sitting here with pieces of paper representing saw blades, miter slots, miter gauges and chunks of wood. At some point, the light bulb will come on and I'll get it. The damn thing is that I do quite a bit of flat work. It simply has never occurred to me that having the saw blade anything but parallel to the miter slot is no big deal, at least when it comes to the accuracy of the angle of the cut.

Interestingly, the author of the video that started all this discussion is mistaken. He says that his method of dialing in a miter gauge depends on the miter slot and the blade being parallel.

Take care, and thanks for the discussion.

I wouldn't say it's no big deal to be out of alignment (unless we're talking a couple of thousandths), just that that's not the reference point people need to use for crosscuts. As Lee points out, an out of alignment blade will lead to the top face of the piece of wood being longer than the bottom face after a cut, though that's generally a minor issue in most realistic scenarios. And the cut will still be 90º to the edge even with the misalignment

So good blade alignment is important, it's just that aligning your miter fence to your blade isn't the important part of getting a square cut. If your blade is out of alignment and you reference off that, all you're doing is taking one error and adding it to your miter gauge. Whereas if you reference your miter fence off the slot, you know that's correct regardless of what else is going on.

[Nick Decker]

I use this method to square the cross cut fences on my slider because it is so quick and accurate. Woodpeckers are offering a new one time tool that is ideal for the job, a phenolic 18" square. The thickness of it will make it easy to use the DI which with thin bladed squares can be a bit painful.

I don't have a slider, but I like the fat blades on the WP squares for this method:

https://www.woodpeck.com/1281.html

[Marv Pelkey]

Lee has hit on a point that I don't think others have considered. On a table where the blade is not perpendicular to the miter slot (let's say for sake of argument that the miter guide is 90% to the slot), the lower the blade, and the less of a full cut the blade makes, the more the top of the cut is narrower than the bottom of the cut (as in a cove cut where the travel of the wood is skewed from the blade). This results in the edge of the cut not being vertically straight and completely 90% to the table. It's actually less of an issue of parallelism between the edge of the cut and the blade or miter slot but more that the edge of the cut-off end of the wood being not flat vertically. Having said that, most cuts are made where the top of the blade is above the wood (for a through cut-off), so the "cove effect" is hardly noticeable.

I think all of the other comments are treating the saw blade more like a bandsaw blade and not like a round object.

Just my 2 cents.

[Glen Gunderson]

I think the important thing to remember is that referencing the miter gauge off a misaligned blade does nothing to correct the problem of misalignment and it just introduces another unrelated problem. To use an extreme example, if your blade is 1º off of your miter slot and you set your miter gauge to 89º in an effort to align it with the blade you're not going to get a 90º cut; you'll end up with an 89º cut AND a cove cut on the end.

Given that, they should be treated as separate issues. So when aligning a miter gauge, the slot should be the reference point.

[Lee Schierer]

So when aligning a miter gauge, the slot should be the reference point.

The miter slot should be the reference point for miter gauge squareness and alignment of the blade and fence. You can't adjust the slot location on many saws. There are some saws that have the saw trunions mounted to the cabinet and not the table that you move the table to align to the saw blade. Then everything else gets aligned to the miter slot.

[Glen Gunderson]

The miter slot should be the reference point for miter gauge squareness and alignment of the blade and fence. You can't adjust the slot location on many saws. There are some saws that have the saw trunions mounted to the cabinet and not the table that you move the table to align to the saw blade. Then everything else gets aligned to the miter slot.

Very true. I should've said that when aligning a miter gauge, the slot (and not the blade) should be the reference point. Everything should be referenced off the miter slot.

[Charles Lent]

My blade and fence were aligned to the miter slot in my Unisaw as perfectly as I could get them using a dial indicator. I use my MiterSet gauge to set the miter gauge to 90 degrees, or any other angle that I may want, in 1/2 degree increments. The five cut test for 90 degrees comes out perfect after doing this.

Charley

[Johnny Barr]

I use my MiterSet gauge to set the miter gauge to 90 degrees,


I didn't want to get into a discussion of the miterset as that's been done to death and I started this thread to show a brilliant alternative to the 5 cut method but the miterset isn't recommended for the Incras and Kregs. Here is a quote from their website
"MiterSet is meant to be used with a standard miter gauge. It does not work with some of the large precision gauges from Incra and Kreg."

The reason is basically due to the expansion rings or screws that come with the Incras and Kregs which don't provide a consistent snug fit in the miterset slot. I originally bought a miterset to align my Incra gauge easily but I ended up selling it due to inconsistencies. Even that disclaimer, which was added to their website after I bought it, confirmed those inconsistencies. Brian's dial indicator method has provided the simplicity I was looking for. Also following the fruitful discussions above about blade/slot/fence alignment, check out this video which clearly shows why the slot has to be the reference point
https://www.youtube.com/watch?v=NrTeFQ0iQ5k&t=8s