Extra Table Saw Alignment Procedure

[GrayBeard Phil]

This is kind of an OT thread. It may be long.

Elsewhere, there was a long thread about a table saw alignment for a very high end table saw. I had never heard of this specific measurement before, and it took me several hours of reading, and re-reading, of the discussion before I could follow the discussion.

Just curious if anyone at this small corner of the woodworking world has heard about this, or have comments on this alignment.

Here goes, and this is complex:

After adjusting the blade to be parallel to one of the miter gage slots, and taking a reading on a dial indicator of the remaining error, rotate the blade to the 45 degree position (try for 45.0 degrees as accurate as possible) mark a spot on the blade below the deepest tooth gullet to avoid any set tooth errors, and take a measurement from the dial indicator rotating the blade front and back just like the procedure for blade alignment. Be sure to measure at the same spot on the blade as close to where the blade rises above the saw's table top.

This test is done at 45.0 degrees because for most TS, this is as far as the saw will tilt to the side. There will be a larger error than with the blade in its normal upright position. This is because this extra error is caused by the front and back trunnion under the table not being exactly the same height from the upper side of the table. This makes the two trunnions of unequal distance from the plane of the table top.

(Of course, if the saw was tilted over to 80 degrees from straight up, this would be a more obvious measurement.)

Then shims are introduced between the trunnion, and the bolt holes under the saw which in effect lowers the front or back of the saw blade. This (adding shims) should correct for the front to back height error.

This alignment procedure should have no effect on cutting when the blade is in its normal upright position. However, when the blade is tilted (this is where it gets complicated) without this alignment / shim procedure the saw will not be rotating in a plane that gives the least kerf width. The blade will be rotating almost in a 'wobble' dado blade pattern in the kerf. Some were making claims of an extra 1/32 (0.031) inch wider kerf when the blade is tilted to 45 degrees compared to the zero degree tilt with no adjustment. Of course the ideal is to have the same error as when the blade is upright.

It took me about 30 to 40 minutes to grasp the above point.

Aside: to calculate the needed shim thickness, is very long and complex that involves cosine (45 degrees), distance between trunnions, and several other factors. From there on it is trial and error with adding or subtracting 0.0020 thick shims.

Has anyone here done this test?
If so, did it really make a difference?
Just how many use their table saw at a tilted angle for critical cuts?

Or is this just a psych test to find all the woodworkers with a touch of German genetic backgrounds?

Phil

[GrayBeard Phil]

Sorry, I forgot to add, if my write up isn't clear, I can try again to explain it, but it won't get any less complex, sorry to say.

Again, this was my first exposure to this un-usual procedure.

Phil

[William Young]

Phil.
That was interesting and took me several reads to try to grasp it.
Personally I think it is a waste of time for the average woodworker . I measure mine dead on with a dial guage as first outlined with the blade in the vertical position and have never had a problem when tilting to saw at any angle after that.
I suppose for an extreme perfectionist type of person that is critcal about it being a thou or two out , the procedure would be a good thing.
For me , I can not detect such a small difference by eye and if the pieces fit together after cutting "looking" like they are a perfect match to each other , then that is good enough for this old wood butcher. :D
I sure like my 2HP contractors saw and it faithfully cuts to a great degree of accuracy for me ever since I initially set it up with my dial guage with the blade in it's vertical position.
W.Y.

[JTTHECLOCKMAN]

Phil

I can honestly say I have heard about this ( well maybe if it is the same thing you are talking about )but have not paid enough attention as to the cure. This problem will show up more on a contractors saw than a cabinet saw. The reason is in the way the trunions are mounted. Here is a way to check if this problem will affect your saw. Align the blade to the miter slot as always, in the 90 degree position. Now use a machinist square ( I like to use a draftsman triangle) and align your miter guage to the blade. Now the guage is a perfect 90 degrees to the blade. Now tilt the blade to 45 degrees. Using the miter guage and the square or draftsman triangle see if the blade is still 90 degrees to the guage. Usually it is a few thousands out. Is this a crucial measurement??? It can be because if you leave the guage in the same setting you can get burning on your miters. What I do is reset the guage to the tilted blade. The less tilt the less difference obviosly. Now if this is the same thing as what you are talking about I understand it but if it is something else than no I do not. :confused:

[GrayBeard Phil]

FYI: Some more information.

I discovered the guy who seems to be pushing this extra measurement procedure is Ed Bennett.

Ed is selling an alignment jig at his web site.

Link to video demonstrating the alignment jig:
http://www.ts-aligner.com/videos.htm
video is 15 minutes long, this extra procedure about 1/2 way thru.

best if you have Win XP and a broadband Internet connection. Dial up would be painfully slow.

The following is copied from the other thread written by Ed:

So, for example, if your blade is tilted to 45 degrees, then the correction factor is going to be 0.7071 (cos(45)). ...[As you rotate the blade's tooth for the measurement from the front to the back] ..If you measure 0.012" misalignment, then the actual change is (0.012 * 0.7071)= 0.0085".

If it was measured over a distance of 8" [10" blade and two measurement points are not a line thru the center of the blade] then you have a change of 0.0011" per inch (0.0085 / 8). [Depending on how the measurement is taken, this could be only 7 inches]

Then, if your [trunnion] bolts are 20" apart [front to back], then you should start with (0.0011 * 20)= 0.022" worth of shims. This isn't going to be exact but it's a good place to start.

End of quote. notes within [ ] are my comments.

Phil

[GrayBeard Phil]

I guess I have to agree with both W.Y. and JT -- this is not a necessary measurement and alignment.

I now believe it may have more to do with selling an alignment tool for seldom needed accuracy than something for me to loose sleep over. {And yes, I have lost some sleep thinking about the need for doing this procedure. which is why I continued to search for information.}

Phil

[William Young]

I now believe it may have more to do with selling an alignment tool for seldom needed accuracy than something for me to loose sleep over.

Yes Phil, I think that pretty well sums it up for 99% of woodworkers. I wonder how many will actually fall for that and pay the big bucks for it.
It was an interesting video though. It loaded up in 5 seconds and started playing right away . Then when the first session was finished in 3.15 minutes it was interesting to see it automatically start into the next ones and then next etc.
W.Y.