90 deg vs bevel blade alignment on table saw - Page 3 - Woodworking Talk - Woodworkers Forum
Old 05-29-2019, 08:59 AM Thread Starter
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Originally Posted by woodnthings View Post
Apparently you are the only person on the planet that "understands the measurement issues"
Apparently

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Originally Posted by woodnthings View Post
As I stated above the alignment is needed in two different planes, top view and side view.
As always, agreed.

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Originally Posted by woodnthings View Post
All measurements are from the miter slot

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Originally Posted by woodnthings View Post
Finally, woodgears gives the math to make the 45 degree adjustments.
Woodgears seems to touch all the bases, I have no qualms with his measurement technique. He's wasteful on the 90 by measuring so high. Also he does have the math wrong. He needs to divide (not multiply) the dial indicator reading by square root of 2.

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Originally Posted by woodnthings View Post
What's my point, you ask? I have proven my point.
I must not be getting your point, unless your point is that you and some people agree.
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Old 05-29-2019, 10:51 AM
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I just have to ask, if you know so much about the measuring technique, why are you asking us?

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Old 05-29-2019, 11:29 AM
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Originally Posted by unburled View Post
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.

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?
Although I have not gone as far as shimming the trunnion, this article explains the procedure. https://www.popularwoodworking.com/t...your-tablesaw/

It explains that unless the trunnions are aligned, when you tilt the blade...a skew occurs and the blade is no longer parallel to the miter slot. Shimming the trunnions corrects this.

This process was also discussed in the Grizzly video.

I think if shimming is necessary, it should be done in order to improve the quality of angle cuts for miter joints, or any cut less than 90 degrees.

Gary

Last edited by gmercer_48083; 05-29-2019 at 11:35 AM.
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Old 05-29-2019, 12:11 PM
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Originally Posted by unburled View Post
[...]
I must not be getting your point, unless your point is that you and some people agree.
This is one statement from @unburled that is accurate. With no disrespect intended, unburled has made several statements where I disagree. I take particular issue with the idea that alignment errors are additive. They are not.

If we boil the arguments to the fundamentals, here is a statement to which all should agree:

The fixed reference points on a table saw are the miter slots and the plane of the table itself.

Again, focusing on fundamentals, here are our objectives as I see them:

* The sides of the rip fence should be parallel to the miter slots and perpendicular to the table. This should remain true at any rip fence position and whether the rip fence is on the left or right side of the blade.

* The miter gauge should guide the wood to be cut in a line that is parallel to the miter slots. The face of the miter gauge should be perpendicular to the table.

* As the blade cuts, the blade tips should form a fixed line in the plane of the table that is parallel to the miter slots. This should remain true at any blade height or angle.

Where most of us seem to disagree with unburled is the alignment process itself. Related to that, we all recognize that no alignment is perfect, and we disagree on what to focus on for best results.

I agree with most of the others that the best approach is to align the rip fence with the miter slots and align the blade with the miter slots as separate steps. In theory, this will result in the blade and rip fence being aligned with each other. In practice, this should result in an "optimum" alignment, distributing the alignment errors between rip cuts and crosscuts.

unburled wants to align the rip fence with the miter slots, then align the blade with the rip fence. This approach optimizes the table saw for rip cuts, but may also have a deleterious effect on crosscuts, possibly affecting crosscut safety. The root of this issue is related to unburled's assumption that alignment errors are additive, which they are not.

Finally:

It doesn't really matter. If unburled does a decent job of aligning the rip fence with the miter slot and the blade with the rip fence, then the blade should be reasonably well aligned with the miter slots, and we can all get back to cutting wood again.
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Old 05-29-2019, 12:50 PM Thread Starter
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duplicate post

Last edited by unburled; 05-29-2019 at 02:40 PM.
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Old 05-29-2019, 12:56 PM Thread Starter
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Originally Posted by Tool Agnostic View Post
unburled wants to align the rip fence with the miter slots, then align the blade with the rip fence.
Without responding to the rest of your post, where on earth did I write that?

Here is what I wrote:

Quote:
Originally Posted by unburled View Post
What is important is that the wood moves parallel to the blade.

If your blade/mitre alignment is off by X, then you carryout a fence/mitre alignment, and it is off by Y, then your fence/blade alignment is off by X+Y.

On the other hand, if your blade/mitre alignment is off by X, then you carryout a fence/blade alignment, and it is off by Y, then your fence/blade alignment is off by Y.

Choice is X+Y or Y

Kerouac, J.
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Last edited by unburled; 05-29-2019 at 12:59 PM.
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Old 05-29-2019, 01:06 PM
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Nice summary, except it does matter....

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Originally Posted by Tool Agnostic View Post
This is one statement from @unburled that is accurate. With no disrespect intended, unburled has made several statements where I disagree. I take particular issue with the idea that alignment errors are additive. They are not.

If we boil the arguments to the fundamentals, here is a statement to which all should agree:

The fixed reference points on a table saw are the miter slots and the plane of the table itself.

Again, focusing on fundamentals, here are our objectives as I see them:

* The sides of the rip fence should be parallel to the miter slots and perpendicular to the table. This should remain true at any rip fence position and whether the rip fence is on the left or right side of the blade.

* The miter gauge should guide the wood to be cut in a line that is parallel to the miter slots. The face of the miter gauge should be perpendicular to the table.

* As the blade cuts, the blade tips should form a fixed line in the plane of the table that is parallel to the miter slots. This should remain true at any blade height or angle.

Where most of us seem to disagree with unburled is the alignment process itself. Related to that, we all recognize that no alignment is perfect, and we disagree on what to focus on for best results.

I agree with most of the others that the best approach is to align the rip fence with the miter slots and align the blade with the miter slots as separate steps. In theory, this will result in the blade and rip fence being aligned with each other. In practice, this should result in an "optimum" alignment, distributing the alignment errors between rip cuts and crosscuts.

unburled wants to align the rip fence with the miter slots, then align the blade with the rip fence. This approach optimizes the table saw for rip cuts, but may also have a deleterious effect on crosscuts, possibly affecting crosscut safety. The root of this issue is related to unburled's assumption that alignment errors are additive, which they are not.

Finally:
It doesn't really matter. If unburled does a decent job of aligning the rip fence with the miter slot and the blade with the rip fence, then the blade should be reasonably well aligned with the miter slots, and we can all get back to cutting wood again.

Kinda takin' a chance there .......

unburled can do what ever he chooses, align the fence to the blade or the blade to the fence, BUT in so doing he negates the use of the miter gauge for crosscuts, a primary function of the table saw.

Why? Because now the only way he can crosscut at 90 degrees to an edge is to use the fence, the miter gauge and therefore the slots have been taken out of the operation. Imagine trying to crosscut a 4" wide x 24" long piece using only the fence ... totally unsafe.

I have never seen a You Tube video or read an article that recommends aligning the blade to the fence in all my 50 years of woodworking. If all you ever need to do with your table saw is rip boards to width, then yes it can be done, but that's just not practical. The blade should not be skewed in relationship to the miter slots either at 90 degrees to the table or at any angle including 45 degrees. I often check my miter gauge for 90 degrees to the table by pulling it out towards me until I see a thin amount of daylight between the face and the front of the table. It takes only a second to do and is reassuring when the face has been previously changed for cutting miters. This does make the assumption that the miter slots and the front edge of the table are 90 degrees to each other.

The reason I have invested this many posts on this thread is to inform those without years of experience that a proper table saw set up will enhance your woodworking experience and anything less than that will not. Carry on, men .....

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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Old 05-29-2019, 02:15 PM Thread Starter
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Originally Posted by Tool Agnostic View Post
I take particular issue with the idea that alignment errors are additive. They are not.
Suppose the mitre/blade alignment is carried out and the error is X. Suppose after that, a fence/mitre alignment is carried out with error Y. Then the fence/blade error is X+Y.

On the other hand,

Suppose the mitre/blade alignment is carried out and the error is X. Suppose after that, a fence/blade alignment is carried out with error Y. Then the fence/blade error is Y, not X+Y.

It's easy to disprove me: offer a counter example. Just draw out an example when they are not additive.

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Originally Posted by Tool Agnostic View Post
If we boil the arguments to the fundamentals, here is a statement to which all should agree:

The fixed reference points on a table saw are the miter slots and the plane of the table itself.
Nope, there are no fixed reference points. The frame of reference is a choice. If you need one, you can make it whatever.

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Originally Posted by Tool Agnostic View Post
Again, focusing on fundamentals, here are our objectives as I see them:

* The sides of the rip fence should be parallel to the miter slots and perpendicular to the table. This should remain true at any rip fence position and whether the rip fence is on the left or right side of the blade.

* The miter gauge should guide the wood to be cut in a line that is parallel to the miter slots. The face of the miter gauge should be perpendicular to the table.

* As the blade cuts, the blade tips should form a fixed line in the plane of the table that is parallel to the miter slots. This should remain true at any blade height or angle.
Your three fundamentals are rooted in single fundamental: For less overall tearout, less burning, and lower risk of kickback, the wood ought to move parallel to the blade.

From that fundamental, we derive: the mitre guage and rip fence ought to be aligned so as to constrain wood's movement to that direction.

That being said, there are scenarios where it's desirable for the the wood to move at angle to the blade.

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Originally Posted by Tool Agnostic View Post
Where most of us seem to disagree with unburled is the alignment process itself.
Actually, the disagreement concerns not the entire mitre/bevel alignment process, just the various techniques for measuring techniques for that alignment.

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Originally Posted by Tool Agnostic View Post
Related to that, we all recognize that no alignment is perfect,
Agreed.

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Originally Posted by Tool Agnostic View Post
and we disagree on what to focus on for best results.
Actually, the disagreement concerns the various techniques for measuring techniques for the mitre/bevel alignment.

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Originally Posted by Tool Agnostic View Post
I agree with most of the others that the best approach is to align the rip fence
Off topic. Read the original post, then look who drifted the thread with fence alignment.

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Originally Posted by Tool Agnostic View Post
unburled wants to align the rip fence with the miter slots, then align the blade with the rip fence.
Not true. Quote me. Off topic.

Quote:
Originally Posted by Tool Agnostic View Post
The root of this issue is related to unburled's assumption that alignment errors are additive, which they are not.
If a mitre/blade alignment is carried out with error is X, and then a fence/mitre alignment is caried out with error Y, then the fence/blade error is X+Y. To think otherwise is simply wrong.

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Originally Posted by Tool Agnostic View Post
Finally:

It doesn't really matter. If unburled does a decent job of aligning the rip fence with the miter slot and the blade with the rip fence, then the blade should be reasonably well aligned with the miter slots, and we can all get back to cutting wood again.
That is a big 'if' ... because I've never done that. Off topic.
.
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Old 05-29-2019, 02:19 PM Thread Starter
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Originally Posted by woodnthings View Post
align the fence to the blade or the blade to the fence\
I asked myself, what on earth does he mean? Ahh, he must think (wrongly) that i carryout the fence/blade alignment by adjusting the trunions. Case solved !
.

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Old 05-29-2019, 02:31 PM Thread Starter
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Here is my first use of the word fence in this thread. Honestly, I had never distinguished between the phrases "aligning the fence to blade" versus "aligning the blade to the fence." I've only ever considered a fence/blade alignment as carried out by working on the fence. The idea of adjusting the trunions was, I guess, just too screwy.

Anyway, by chance I used the correct phrase! fence to blade!

Quote:
Originally Posted by unburled View Post
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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Old 05-29-2019, 02:39 PM Thread Starter
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Originally Posted by gmercer_48083 View Post

It explains that unless the trunnions are aligned, when you tilt the blade...a skew occurs and the blade is no longer parallel to the miter slot. Shimming the trunnions corrects this.

This process was also discussed in the Grizzly video.

I think if shimming is necessary, it should be done in order to improve the quality of angle cuts for miter joints, or any cut less than 90 degrees.
There are two distinct parts to mitre/bevel alignment. One is measuring and the other is shimming. Early on, when thinking about the digital angle meter, which was a day or two before posting this thread, I suspected shimming would correct the alignment for a given bevel, say 45deg.

The tricky part is the measurement. The poor techniques for the mitre/bevel measurement in some of the videos make those mitre/bevel alignments futile. Hence those techniques are simply wrong.

The measurement is not really tricky, at least not in any deep way. In fact I'd guess that 90% or more of WWT readers have encountered the issues in other contexts. Yet no one in this thread nor anyone at the links, have spelled out the issues that make the measurement tricky and how to address the issues.

At this point I've thought about it enough that I've answered my own question. But basically, for people content with truing up their fences by aligning them to the mitre slots and not the blade (which leads to X+Y error instead of just Y), especially those who don't understand it is an X+Y versus Y choice, I can't see anything I have to say on this matter being of any consequence.

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Old 05-29-2019, 02:43 PM
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Congratulations, you have achieved over 50 replies to this post, was that your intention?

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Old 05-29-2019, 03:37 PM Thread Starter
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Originally Posted by FrankC View Post
My original intention was as stated in my original post, seeking to hear stories from WWT of their experience going down the rabbit hole of precision offered by mitre/bevel alignment.

Someone answered the literal question with not much more than a 'yes', to which I asked for details of their measurement technique. Shortly afterwards you, witting or unwittingly, posted a link to a video with an idiotic measurement technique. After that, fence alignment crept in off topic. Eventually people, wittingly or unwittingly, started misquoting other people.

At this point, I'm curious as to why no one here or in the linked videos/articles ever mentioned the crucial issues in measuring the mitre/bevel alignment, nor, of course, how to address them. What makes this really odd is that most on WTT, I imagine, have encountered the same issues in other contexts.

Also at this point, I've thought about it enough to have settled on a way to address them in my shop. For people content with truing up their fences by aligning them to the mitre slots and not the blade (which leads to X+Y error instead of just Y), especially those who don't understand it is an X+Y versus Y choice, I can't see anything I have to say on this matter being of any consequence.
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Old 05-29-2019, 03:43 PM
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I can't see anything I have to say on this matter being of any consequence.

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

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Old 05-29-2019, 04:20 PM Thread Starter
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Thank you.

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Old 05-29-2019, 04:21 PM
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this was THE statement that threw us off

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Originally Posted by unburled View Post
.....

(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.)

This is what started the whole confounding discussion, and what I spent many posts disagreeing with. As was suggested, your reference standard must be stable and non-adjustable and non-movable, IE the miter slots.

It follows that IF both the blade and the fence are precisely aligned to the miter slot each will be parallel to the other. Any variation in precision adjusting in one or the other will not effect the remaining one because they are independently measured and adjusted so any errors are NOT cumulative as was mentioned. In fact, some folks insist on adjusting the fence away from the blade at it's rear as a safety factor, but I never have subscribed to that theory..

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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Old 05-29-2019, 04:54 PM Thread Starter
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Originally Posted by woodnthings View Post
your reference standard must be stable and non-adjustable and non-movable, IE the miter slots.
Can you explain that, because it makes no sense to me.
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Old 05-29-2019, 05:59 PM
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OK, I'll try ....

Let's say we are laying out the foundation lines for a house. For various reasons, we know where one corner is and drive in a steel rod at that point. That is our "reference" stake off which all other dimensions/measurement will be derived. The other 3 corners of the house, a rectangle, will be based off the rod using the 3,4 5, principle to keep things "squared". A tape running out 30 Ft, another at 40 ft and a third one as the hypotenuse at 50 ft connecting the ends will determine the position of the side of the house. We will not move the steel reference rod until we pour the footings.

For a table saw alignment, you need a fixed reference from which to base all your succeeding measurements and the miter slots are the only factory milled place to start from. The arbor and trunnions and fence are all moveable and adjustable in their locations. The miter slots don't move and can't move or change their position. The slot allows for a tramming of a dial indicator or other measuring device to follow the marked tooth on the blade and is the full length of the table to align the fence. I don't bother measuring my fence when my sense of touch tells me it's flush with the right edge of the slot, that's all I need.

I have aligned a few contractor type table saws over the years using just a tri-square in the miter slot. A cabinet saw would be so much easier to access the bolts than laying upside down under a contractor saw. In my case, I stood the saw on it's back end so I could access the top for measuring and the underneath for access to the bolts. That was much easier, and then I put the saw on it's legs afterward.

I just remembered I had a different approach to aligning the blade using an extension made from a steel scale:
https://www.woodworkingtalk.com/f27/...er-slot-11185/

There are good posts within the thread, especially by niki.

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; 05-29-2019 at 08:34 PM.
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Old 05-29-2019, 06:36 PM
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Hi

I think I understand what Unburled is asking and is trying to say. Lets see if I got this right, take the blade measurements as close to the table top as possible in order to get the most accurate measurements.

Also in order to get the proper measurements you will need a machined disk similar to the one in this picture. If the bearing and arbor are worn and the blade tolerance is off then you will not be able to get consistent measurements, even after locking every thing down.
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Old 05-30-2019, 03:42 PM Thread Starter
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@woodnthings - I have a new thread in mind for fence alignment. I'll wait to respond to your post there. For here, I'll try to keep to the OP topic of the relative alignment of mitre slots and the blade at 45 degrees.
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