90 deg vs bevel blade alignment on table saw - Woodworking Talk - Woodworkers Forum
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post #1 of 78 Old 05-24-2019, 10:49 AM Thread Starter
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90 deg vs bevel blade alignment on table saw

All I ever seen online about this has been using a the blade set at 90 deg when aligning the blade to the mitre slots. However, it doesn't follow that the blade remains parallel to the slots when tilted for bevel cuts. That alignment requires separate verification, which I'm sure has been addressed somewhere on WWT or elsewhere online, but I've never come across it, not that I've looked. And I've never verified it on my saws.

Actually, I've never thought about this until thinking about digital angle meters as recommended in the pdf written and posted by @DesertRatTom in the helpful-tips thread:

https://www.woodworkingtalk.com/f97/...1/#post2056129

As far as remedies, I'm thinking shims between trunions and the table saw top.

Anyone here gone this far down the rabbit hole of precision?

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post #2 of 78 Old 05-24-2019, 10:57 AM
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Absolutely, to me step two of aligning the blade is to set it to 45 and measure. Shims are the way to go to make necessary adjustments.
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post #3 of 78 Old 05-24-2019, 11:04 AM Thread Starter
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Quote:
Originally Posted by Elden Cozort View Post
set it to 45 and measure
That measurement seems problematic to me, direct or otherwise. What's your approach?
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post #4 of 78 Old 05-24-2019, 11:25 AM
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This Grizzly video explains how to use shims:


Wise men speak because they have something to say; fools because they have to say something -Plato

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post #5 of 78 Old 05-24-2019, 12:31 PM Thread Starter
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Originally Posted by FrankC View Post
This Grizzly video explains how to use shims:

https://youtu.be/bpg39Lbwpu0
-10
I exited the video when I saw how they are measuring alignment at 45. Their credibility is wanting. Whoever was involved and/or oversaw that video doesn't understand the issues in carrying out the verification.
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post #6 of 78 Old 05-24-2019, 12:45 PM
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Quote:
Originally Posted by unburled View Post
-10
I exited the video when I saw how they are measuring alignment at 45. Their credibility is wanting. Whoever was involved and/or oversaw that video doesn't understand the issues in carrying out the verification.
Hopefully the video helps others that have a similar problem, it did come from the company that designed the saw so I think it has a bit of credibility, sorry it was not up to your standard.
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post #7 of 78 Old 05-24-2019, 02:11 PM Thread Starter
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Quote:
Originally Posted by FrankC View Post
Hopefully the video helps others that have a similar problem ... sorry it was not up to your standard.
You must not understand the measurement issues either. Their measurement technique is simply wrong. Worse than waste of time, it's likely to make things worse than the factory alignment. It's so wrong that standards are not even at issue.
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... it did come from the company that designed the saw so I think it has a bit of credibility ...
Same company, or maybe outsourced, but definitely not produced/overseen by people who understand the issues of the measurement when beveled.
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post #8 of 78 Old 05-24-2019, 02:23 PM
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Ok, let's get into that ....

The trunnions that allow the blade to bevel/tilt have a "theoretical" center about which they rotate. Without that, and having no need to tilt the blade, a straight shaft arbor could be used. So, how do you determine that the trunnions are not rotating in tandem? They are both connected by the saw's arbor casting in the center, so it must be that one of the support ends is not equal distance from the miter slot. This requires some device to measure that difference, either using the blade (a marked tooth) or at some other location on the casting. Is your issue with the tri-square and feeler gauge used in the video for the measurement? If so, what do you reccommend using that would be more accurate or where else would you measure from? Seriously asking......
This?
https://www.in-lineindustries.com/education/manuals/table-saw-test-3/

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

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post #9 of 78 Old 05-24-2019, 03:06 PM
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Quote:
Originally Posted by unburled View Post
You must not understand the measurement issues either. Their measurement technique is simply wrong. Worse than waste of time, it's likely to make things worse than the factory alignment. It's so wrong that standards are not even at issue. Same company, or maybe outsourced, but definitely not produced/overseen by people who understand the issues of the measurement when beveled.
.
.
Care to explain this mysterious misunderstanding? Because there's nothing wrong with the measurement technique. Alignment at 45 is the same as alignment at 90, in that you need to measure how far the front and back are from the miter slot. If your issue is with the tools measured, where exactly is the issue with using a square as a fixed reference point and feeler gauges to measure the gap? F1 engines get built with similar techniques, its not like its lacking in accuracy.

So, again, if you have faults in the method, why not explain them instead of acting condescending?
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post #10 of 78 Old 05-25-2019, 12:20 PM
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There are many youtube videos of people using combination squares, feeler gauges, and/or calipers to measure from the miter slot to the blade. I just received a commercial from a company about a tool that sells for about 250 to measure this. My problem with all of these is after you get it all set up how can you be certain that miter slot, blade and fence are all parallel.

But, I confess, I am not sure exactly what you are questioning about the videos attempt to measure the 45 degree angle. I have always favored trunnions mounted to the top and theoretically if the "legs" of the trunnions are exactly the same length then there is no 45 degree issue.

I think your point is that the center of rotation of the arbor shaft is several inches below the table top and measuring on the table top or partial inches above the table top cannot accurately measure the impact of the shim.

A method is needed that accurately measures the actual impact of the shim.

I have an idea, but I need to make a jig to test it, but in the meantime--if you set the blade to 45 and rip a board and both ends measure the the same would that suffice to say that the saw cuts accurately at 45 (assuming of course that the fence is parallel).
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post #11 of 78 Old 05-25-2019, 12:48 PM
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Quote:
Originally Posted by Elden Cozort View Post
There are many youtube videos of people using combination squares, feeler gauges, and/or calipers to measure from the miter slot to the blade. I just received a commercial from a company about a tool that sells for about 250 to measure this. My problem with all of these is after you get it all set up how can you be certain that miter slot, blade and fence are all parallel.

But, I confess, I am not sure exactly what you are questioning about the videos attempt to measure the 45 degree angle. I have always favored trunnions mounted to the top and theoretically if the "legs" of the trunnions are exactly the same length then there is no 45 degree issue.

I think your point is that the center of rotation of the arbor shaft is several inches below the table top and measuring on the table top or partial inches above the table top cannot accurately measure the impact of the shim.

A method is needed that accurately measures the actual impact of the shim.

I have an idea, but I need to make a jig to test it, but in the meantime--if you set the blade to 45 and rip a board and both ends measure the the same would that suffice to say that the saw cuts accurately at 45 (assuming of course that the fence is parallel).
The effect of the shim and how to measure it is outlined in the video, can't be explained much better, please bear in mind that there are those that post here simply to cause trouble for their apparent amusement.

As for accuracy, that is in the hands of the person making the adjustment, not the tool used to do the measuring.
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post #12 of 78 Old 05-26-2019, 12:06 AM
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Guys, guys, guys. We're not trying to set up a milling machine in a metal working machine shop. This is woodworking. In most woodworking cases close enough is indeed close enough. Or if you can't see the difference it is close enough.
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post #13 of 78 Old 05-26-2019, 11:37 AM
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Mr. woodnthings is on the right track. The axis of rotation around which the saw blade is tilted must be parallel to the table surface or the blade will toe up (leading edge higher than trailing edge) or toe down (leading edge lower than trailing edge) as it is tilted. With a toed up saw the lower trailing edge of the saw binds the underside of the cut against the table. With a toed up saw, the higher trailing edge tears up the upper side of the cut.

With smaller diameter saw blades, especially if they have a bit of wobble so they cut freer, this may not be a problem. With larger diameter industrial saws, which run truer and are less forgiving, this will degrade the cut and increase the danger of kickback.

The solution is to shim the table front and back until the tilt trunnions axis of rotation is parallel to the table surface. The last step in truing the saw is to set the indicator vertically on the miter gauge, tilt the saw to 45 degrees, tram the saw, and shim the table front and back until it trams true. Sequence is important. This has to be done last.

The best description of this process I've seen is an article and video by Ellen Kaspern in Fine Woodworking. I've had experienced millwrights look at me blankly when I've tried to explain this. She does a better job.
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post #14 of 78 Old 05-26-2019, 04:47 PM
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Watch this video ......

This video is demonstrating the blade alignment on a SAW STOP which is unique. There is a pivot pin about which the TABLE can be moved, using one of the adjustment screws to move it to the right or left depending. This is an entirely different process than would be used on a contractor saw which has the trunnions secured to the underside of the TABLE.

https://www.finewoodworking.com/2018...setup-tablesaw

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

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post #15 of 78 Old 05-27-2019, 11:20 AM
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This may explain the same procedure in more detail, but the video from grizzly says the same thing.https://www.popularwoodworking.com/t...your-tablesaw/

I must admit, when I tuned my table saw, I don't remember having to shim anything...but it's been a few years and it is worth a re check now. I can see where it would effect miters.
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post #16 of 78 Old 05-28-2019, 11:11 AM
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Here is a little jig I made to check parallelism of the blade, slots, and fence after using measuring tools to do the actual setup. This is not to set the parallelism, just to check

I started with a piece of 3/4 inch hardwood about 10 inches long and ripped it to 1 1/4 inches. I then took a scrap of 1X8 about 16 inches long, set the blade to 30 degrees and using a tenon jig ripped both sides of the scrap to create a 60 degree angle on one side. I then cut a 45 degree on both edges leaving about 1 inch at the edge. I then use CA glue to connect the two pieces together trying to center the 1X8 on the 1X1 1/4. Lastly, I placed a flat head screw in the 1 inch area at the end of the board. I added some masking tape to the back of the 3/4 piece so it would fit very tightly in the miter slot. It should be tight enough that it doesn't slide easily.

Setting the blade to 90 degrees, I place the jig in the miter slot at the back of the blade and very gently scrape the blade against the wood making a small mark (flat top blades work best, make sure to unplug the saw). I then flip the jig over and move it to the front of the blade, rotate the blade so I am using the same tooth and scrape again. If the marks align perfectly then the blade is parallel to the miter slot.

Now setting the blade to 45 degrees, I place the jig in the miter slot (this time with the 60 degree edge of the board to the blade). Repeating the scraping as above, checks the 45 degree parallelism. The pointed edge of the board makes it very easy to see if the marks align

Finally, with the jig in the front of the miter slot, I move the fence very close to the head of the screw, tighten the fence, and using a feeler gauge measure the distance. Move the jig to the back of the miter slot and measure again. I prefer to have the back of the fence .001-.003 further away so I adjust accordingly.

After several uses, the multiple scrape marks obscure each other so I break the glue joint, cut off some of the 1X8 and re-glue.
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post #17 of 78 Old 05-28-2019, 11:59 AM
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Just to be clear .....

If I understand this jig, it's basically an adjustable feeler gauge, the screw in the end being adjusted to touch the blade's marked tooth?
The 45 degree cuts are "arbitrary and do nothing except allow for clearance around the screw? You are relying on the snug fit in the miter slot for "precision"?
Simple jig, but it should be as accurate as your eye can see and the feel of the screw touching the blade's tooth is humanly possible!


I assume you can adjust the screw in or out by sliding it past the blade to allow for screw driver clearance? Variations of threaded bolts, jam nuts and a T nut would allow for instant adjustments ...
https://www.grainger.com/product/1XG...!g!82128465477!



Or these:
https://www.homedepot.com/p/Everbilt...8798/204806598

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

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post #18 of 78 Old 05-28-2019, 12:28 PM Thread Starter
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Quote:
Originally Posted by Elden Cozort View Post
I then took a scrap of 1X8 about 16 inches long, set the blade to 30 degrees and using a tenon jig ripped both sides of the scrap to create a 60 degree angle on one side.
Has the 1x8's long edge on the right side in the photo received two rips using the tenoning jig, leaving a sharp edge in the middle that is 3/8" from the two faces? Thanks
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post #19 of 78 Old 05-28-2019, 01:10 PM
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I'm having trouble understanding this ....

Quote:
Originally Posted by Elden Cozort View Post
Here is a little jig I made to check parallelism of the blade, slots, and fence after using measuring tools to do the actual setup. This is not to set the parallelism, just to check

I started with a piece of 3/4 inch hardwood about 10 inches long and ripped it to 1 1/4 inches. I then took a scrap of 1X8 about 16 inches long, set the blade to 30 degrees and using a tenon jig ripped both sides of the scrap to create a 60 degree angle on one side. I then cut a 45 degree on both edges leaving about 1 inch at the edge. I then use CA glue to connect the two pieces together trying to center the 1X8 on the 1X1 1/4. Lastly, I placed a flat head screw in the 1 inch area at the end of the board. I added some masking tape to the back of the 3/4 piece so it would fit very tightly in the miter slot. It should be tight enough that it doesn't slide easily.

Setting the blade to 90 degrees, I place the jig in the miter slot at the back of the blade and very gently scrape the blade against the wood making a small mark (flat top blades work best, make sure to unplug the saw). I then flip the jig over and move it to the front of the blade, rotate the blade so I am using the same tooth and scrape again. If the marks align perfectly then the blade is parallel to the miter slot.

Now setting the blade to 45 degrees, I place the jig in the miter slot (this time with the 60 degree edge of the board to the blade). Repeating the scraping as above, checks the 45 degree parallelism. The pointed edge of the board makes it very easy to see if the marks align

Finally, with the jig in the front of the miter slot, I move the fence very close to the head of the screw, tighten the fence, and using a feeler gauge measure the distance. Move the jig to the back of the miter slot and measure again. I prefer to have the back of the fence .001-.003 further away so I adjust accordingly.

After several uses, the multiple scrape marks obscure each other so I break the glue joint, cut off some of the 1X8 and re-glue.

For the life on me, I don't understand using "scrape" marks on the blade when the screw is used on the fence to check parallelism. Same conditions exist... whether it's the plane of the blade or the plane of the fence.

When the blade is at 90 degrees to the table, theoretically the trunnions do not come into play, since there is no tilting going on.
When the blade is tilted is when the trunnions are needed. The trunnions create a theoretical axis of rotation a few inches below the table surface depending on their radius. This axis must be parallel to the miter slots in top view and parallel to the table in side view. The side view is what becomes critical when the blade is tilted. If the axis drops at the rear when the blade is tilted, the blade will bind or rub on a bevel cut. If one leg of the rear trunnion is higher or lower than the other it will affect the smooth operation of the tilting mechanism. The side view trunnion axis orientation won't affect the cut at 90 degrees, it just means the blade will be slightly higher or lower at the rear .... or front, no big deal.


Measuring this theoretical axis is the issue when the blade is tilted at 45 degrees, since there is no actual reference, only the plane of the blade. There are precision ground plates for setting up the trunnions for those who want more accuracy:


https://www.infinitytools.com/10-san...with-5-8-arbor



The Setup & Sanding Plate (item SSD-010) makes table saw, radial arm saw, and miter saw calibration faster and more accurate. Like our table saw blades, the disk is laser cut from premium cold-rolled steel plate, and is guaranteed to be within .002" flat. It will allow you to fine-tune your saw for perfectly effecient and clean cuts. It's ideal for checking a machine's arbor for square or setting your miter gauge to the precise angle.



The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 05-28-2019 at 01:45 PM.
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post #20 of 78 Old 05-28-2019, 01:50 PM Thread Starter
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Quote:
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For the life on me, I don't understand using "scrape" marks on the blade when the screw is used on the fence to check parallelism. Same conditions exist... the whether it's the plane of the blade or the plane of the fence.

It's two jigs built into one. Note the length of the 1x8. The fence's alignment relative to one of the mitre slots is checked using only the screw. The blade's alignment relative to one of the mitre slots is checked using only scrapes.



(As has been pointed out in other threads. Fence alignment to a mitre slot is indirect, compounding deviancy, which can be avoided by aligning the fence to the blade.)

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