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What is the best way to cope with a table saw that has an uneven table?

I noticed inconsistent cut depths with my table saw so did some test cuts on a piece of oak known to be straight and measured the depths. Cuts were like this:

enter image description here

I made the cuts in a random order to rule out the possibility of the blade height drifting. I also noticed no play in the blade position or angle with my hands.

Results were like this (leading and trailing edge depths measured about 0.25" from respective edge, note x axis is mirrored wrt above picture, "throat plate far edge" is where the edge of the wood crosses the far edge of the throat plate):

enter image description here

The blade has angled teeth, and I measured to the center of the cut. I made the full set of measurements 3 times and found my results only varied by at most 0.0005", so I believe the relative measurements to be accurate.

The first thing I discovered was that I did a poor initial job adjusting my throat plate height (as evidenced; it was too low), so I fixed that. However, I closely inspected the table with a square (a friend lent me a Starrett) and found that it is not completely flat. There are large, smooth, ever so slight bends and dips in it, and the bit to the right of the throat plate is a few hundredths of an inch higher than the left side. I am presuming this is the cause of my inconsistent cut depths. I also can feel with my fingers that the miter slide's rail is slightly higher than the table although I'm not sure how this affects things.

I noticed an identical trend with a piece of MDF and a piece of poplar as well (this is actually what prompted me to do this experiment) although I did not make a full measurement set on those.

What is the best way to cope with this (or are my expectations too high; the saw is a Ridgid R4513)? I have not yet built any sleds. It seems like a sled with a nice flat base will solve the issue for cross cuts. I did read this great answer, however, I am still unsure what to do for non-through rip cuts, where the material is longer and I want to use the fence.


† After reading grfrazee's answer, I contacted Ridgid and they claim a ±0.016" manufacturing tolerance; further inspection of the table appears to verify it is within their tolerance. So it seems my expectations may be too high for this particular saw.

  • While off of course...If you grab the blade with your hand and try to lift it out of table do you fell movement? Silly question really as it would be hard to detect that level of variance. Have you tried to remove the blade from its assembly and reassemble it? I would also try another piece of wood for further testing. Also what is your teeth style? If it is not FTB you might have inconsistent test results (if measuring inside the cut.). – Matt Nov 5 '15 at 18:33
  • @Matt Added info. No play in blade position. Cuts were made in random order just to make sure the height wasn't drifting. Did not try to reassemble blade. Noticed trend first on MDF and on poplar which is what prompted the experiment. Angled teeth, I made multiple measurement sets, to the peak at the center of the cut, and found they varied by 0.0005" so was satisfied with at least the relative accuracy of the cut depth measurements. – Jason C Nov 5 '15 at 19:22
  • Out of curiosity (and not saying your needs are out of line), what are you working on where you need that level of precision? It seems like you are literally splitting hairs, and I'm interested in what real-world problems this may cause. – JPhi1618 Nov 9 '15 at 18:54
  • @JPhi A depth jig for woodworking.stackexchange.com/questions/2680/…. I was seeing differences between calibration/test cut heights and jig cut heights that were visibly noticeable. (See one of my comments on the question for a pic of the jig) That's when I decided to run this test. I built a sled (woodworking.stackexchange.com/questions/2742/…) since, but have not rerun the tests on it (I will though eventually). – Jason C Nov 9 '15 at 19:45
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What is the best way to cope with this? Or are my expectations too high?

It's hard to tell from your picture, but your issue could be one of a couple of things.

It seems like your throat plate is sticking proud of the table saw surface by some amount. You can easily check this using a known straight edge. Shim/de-shim the throat plate as necessary to make it flush with the saw bed.

If that's not the issue, then I hate to say it, but it seems like you got a lemon of a table saw. Assuming you're setting everything up correctly (i.e., no user error producing poor results), a 0.040" variation over 12" in a table saw bed is pretty horrible. I think most higher-end table saw manufacturers cast the beds and then grind to a flatness of +/- 0.005" to +/- 0.010". I can't tell who made your saw, but if it's a lower-end model, this could be the culprit.

Having a look at this related Lumberjocks forum thread, you might be able to shim the table saw bed to get it closer to flat. How you do this will depend on the model, so I really can't give you any good guidance on how to do so.


On a different note, let's not forget that we're working wood here. Wood will experience seasonal movements in excess of your 0.040" discrepancy very easily. This might just be a case of "good enough."

  • The throat plate is actually inset a bit (or it was, now it's level), the lighting in that picture just makes it look like it's sticking out. There are set screws around the edge for adjustments. It's a Ridgid table saw, I don't know what their usual level of quality is but I can tell you it was purchased at a particular Home Depot that often seems to sell products that didn't pass manufacturer QC, particularly power tools. Still for the price I paid I'm not too unhappy. I'm going to see if I can shim it up a bit before I try making a new surface for it. – Jason C Nov 5 '15 at 19:32
  • (The measurement jump was mainly because either a) the table to the right of the throat plate is higher than the part on the left, causing the wood to hit the right edge and raise suddenly, or b) the miter slide rail is higher than the table, causing the wood to plunge slightly into the previously misadjusted throat plate, hitting the right edge, or c) both. In both cases it's a table issue of some sort. I could repeat this experiment with the other miter track, but at this point I'm not sure how much value it would add.) – Jason C Nov 5 '15 at 19:34
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    @JasonC, Ridgid is a second-tier tool manufacturer, as far as I'm concerned. Their stuff works, don't get me wrong, but the fit and finish aren't on par with some of the better toolmakers. – grfrazee Nov 5 '15 at 19:35
  • @JasonC, if your miter slide rail is sticking proud of the miter slot, you might have to do some material removal on it too. – grfrazee Nov 5 '15 at 19:35
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    @JasonC, that seems reasonable. Bear in mind that that's +/- 0.016", for a total of 0.032" possible difference between two places on the top. For comparison, 0.032" is about 1/32". Definitely workable for the usual woodworking chores and easy enough to account for in design if you have to make minor tweaks. – grfrazee Nov 6 '15 at 18:29

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