Trunnion non-linearity

The latest Fine Woodworking on news stands now has a review of table saws (cabinet and hybrid) where the author tested miter slot/blade parallelism at 90 and 45-degrees. I was surprised to see many of the saws showing a difference of .01" and more between these readings.

That is enough that an owner would want to adjust the trunnion. I have only seen trunnion adjustments mentioned when it comes to contractor saws, so this kinda surprised me.

Furthermore, I thought hybrid/cabinet saws were immune to this problem due to their design (assuming they were manufactured correctly).

I'm not going to post all the results, as I think that would be unfair to FWW magazine. However, the Craftsman hybrid (as an example) showed a .01" difference.

Anyone ever test their saw for this difference, or is everyone assuming it is a non-issue because of what they've read?

A given cabinet saw may have been manufactured to some production-line tolerance, but an owner might want to tweak it so that it is better than the production-line tolerance. I tweaked mine.

Here's a thread...http://www.sawmillcreek.org/showthread.php?t=15546

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Originally Posted by Phil Thien

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Furthermore, I thought hybrid/cabinet saws were immune to this problem due to their design (assuming they were manufactured correctly).
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Not at all!

I would expect to see this more frequently with a cabinet saw since the trunnions are attached to the cabinet instead of directly to the top. This type of misalignment is almost guaranteed to happen if the top isn't properly shimmed when it is installed on the cabinet.

A comparative difference in parallelism between blade and miter slot at the 0 and 45 degree tilt settings is the result of the blade tilt axis not being parallel to the table top. The correction is simple in concept but can be somewhat tedius in practice. Shims at the proper location between the cabinet and the table will correct the misalignment. Shim the front of the table higher to move the front of the blade in the direction of the blade tilt. Shim the back higher to move the rear of the blade in the direction of tilt.

I used to think manufacturer's gave the tools headed to the test articles a little more TLC than the production models. This obviously isn't so or we wouldn't see things like we do in the reviews. My 22124 needed quite a bit of lateral adjustment of the table right out of the box but the 90* and 45* were identical at .001" once dialed in at 90* (oh lucky me). :)

As Tom points out, cabinet mounted trunnions are great if all is well with the cabinet. I set my cabinet dead flat before I began the rest of the assembly and setup process (thanks to warnings and advice from fellow Creekers). Failure to do this sets you up for a cumulative error (although small) that is hard to defeat.

All brands have something slip by now and again. Many machines will arrive less than perfect just due to their weight and the handling of those who do the delivering. Then there are the folks who have to semi-dismantle their tools to get them into the shop in which case "out of the box" specs are "out the window". On the upside, if your blade is out .01 at 45*, the saw marks or smoke ought to point it out to you right away :eek:.

These variations explain to some degree why a recent test rated one tool as a 10 (for example) and the same tool painted a different color, as a 5 (for example) on the same feature :confused:. I'm sure we've all had the experience of some mag rating something we hate as "Editor's Choice" or "Best of the Pack". We stare at the article, head shaking . . .

Geez, if any joint I made was .01" in tolerance I think it would be time to jump up and dance (with the machines OFF). We're talking wood here which expands and contracts much more than that. I'm old school and if my phat phinger nail don't find it, it's good to go.

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Originally Posted by glenn bradley

...My 22124 needed quite a bit of lateral adjustment of the table right out of the box but the 90* and 45* were identical at .001" once dialed in at 90* (oh lucky me). :)

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The numbers for my 22124 are exactly the same as Glenn's, after adjustment and to the best of my ability to measure. I actually thought the numbers they published were pretty good. The problem with publishing measurements for a comparison is that they're only representative of that particular machine, and not necessarily all the tools of the same model number. True of any tool that requires adjustment. Not to mention how difficult it is to measure accurately to those minute levels.

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Originally Posted by Jeff Raymond

Geez, if any joint I made was .01" in tolerance I think it would be time to jump up and dance (with the machines OFF). We're talking wood here which expands and contracts much more than that. I'm old school and if my phat phinger nail don't find it, it's good to go.

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My saw suffers from just this problem and I haven't been able to shim it out, or fix it any other way.

.01" may not seem alot, but if the blade is heeled away from the fence during bevel rips, one side of the cut will suffer from burn marks. Also these "mitered" pieces will not close up completely when you try to assemble them. Imagine a six sided box with every edge being 45 degrees. If they're all not spot on, it will never assemble correctly.

And not all "wood" expands that much...an expensive veneer laminated to an mdf core won't change much at all in dimension.

This is easily adjustable on the SawStop. I used an Industrial 14" dewalt RAS as a 90 degree cuttoff station and the heel adjustment was critical on that saw too. I'd like to see how the older american made Unisaws and PM66 compare to the Taiwanese and Chinese tools in this respect.

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Originally Posted by Joe Jensen

I'd like to see how the older american made Unisaws and PM66 compare to the Taiwanese and Chinese tools in this respect.

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My 1970 Unisaw is < .001" at 45 and 90 degrees.

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Originally Posted by Cary Falk

My 1970 Unisaw is within .001" at 45 and 90 degrees.

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I don't know about this measurement when I had my old Unisaw, and then a PM66. Both never burned at either 90 or 45. I have a friend with a well known Import saw ( I won't name it to avoid flaming) that has this issue (burning). He's tried several times to shim the top with limited success. I think it's partly due to a machining issue..joe