what are the shims between the table saw top and cabinet?

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Forum topic by joey502 posted 08-03-2015 04:31 AM 799 views 0 times favorited 4 replies Add to Favorites Watch
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482 posts in 938 days

08-03-2015 04:31 AM

Topic tags/keywords: question tablesaw

I was cleaning the inside of my TS cabinet today and noticed the belt was not sitting on the motor pulley correctly. At this point I decided the correction would be done from above the saw not laying inside it. I have not done any serious cleaning or maintenance to the saw in too long so today was the day for that as well.

As I was lifting the center section of the table from the cabinet I noticed a few shims had fallen to the floor. I am not sure which of the 4 holes they came from or if it was a combination of holes. Can someone explain to me why the table was shimmed? I am sure it was to correct alignment but alignment to what?

4 replies so far

View unbob's profile


692 posts in 1323 days

#1 posted 08-03-2015 06:09 AM

That is a good question, I believe the answer is not well known. In the manual for the discontinued Grizzly G5959 12” table saw. The method of correcting blade alignment error when tilted at an angle compared to being at 90, is done by shimming the table for alignment with the blade tilted. Then adjust the alignment with the blade at 90.

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4028 posts in 1619 days

#2 posted 08-03-2015 06:20 AM

The trunnions and table top need to be co-planer. If they aren’t, then the blade will skew when tilting the blade, and will be most pronounced at 45. To fix it, you add shims to either the front or back to make them co-planer. On cabinet saws, you shim the table… on saws that have table mounted trunnions, you shim them instead. At least that’s what I’ve heard – I’ve never had a saw that needed them :)


-- Brad in FL - To be old and wise, you must first be young and stupid

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Fred Hargis

3842 posts in 1913 days

#3 posted 08-03-2015 12:17 PM

At least you realized they were shims, a lot of guys think those are just washers. I don’t know of a way to figure out where they go…they only time I’ve fooled with them I was careful to keep track of which corner they came from.

-- Our village hasn't lost it's idiot, he was elected to congress.

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2619 posts in 2529 days

#4 posted 08-04-2015 02:24 AM

OK, here is a simple primer on table alignment.

If you are lucky, the shims have dust or something on them to indicate where they came from. There should be one, possibly two stacks of shims. This is because a plane is determined by three points (like in Geometry class). The fact that machinery typically uses 4 points makes it a little different.

Lay a true straightedge on your table, and make sure it is flat in many directions, just like a board.

If your table top is flat (your requirements may differ; mine is within .004” in any direction- it is an old cast iron thing), then the shimming will be easy.

Place the top on and try to rock it. If it rocks, shim the corners that have clearance. Again, hopefully the shims fell off in some order of stuck-together.

If the shims managed to get de-stacked, you will have to play with them a little. That means that you may have to tighten the bolts and check flatness a few times until you figure out where the shims should be, and change them around. Alignment is an iterative process. I’ve aligned lathe beds to within a few thousandths over 18 feet in the past. One of those exercises required waiting until the right time of day to allow for thermal expansion. It took days to get that lathe within tolerance.

-- Random Orbital Nailer

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