How flat should a cabinet saw top be?

[Todd Worstell]

I have looked around on here, but mostly seem to be the flatness of the main top with the wings. I would like to know how flat the main tabletop should be by itself with no wings even attached yet. Like on a good quality cabinet saw. I don't see any specs from manufacturers either. Maybe there isn't any hard spec but I would think the community would have a pretty good idea about what one should be satisfied with and what would be unacceptable.

[Mike Cutler]

Todd
I don’t know that you will find a qualitative value without contacting each manufacturer separately.
On cheaper contractor and hybrid type saws, there may be less attention to quality that a person should expect, but on bigger, more expensive saws, I would expect the main casting to be statistically flat within a few thousandth’s.

[roger wiegand]

Probably depends on where the out of flat spots are and whether they are high or low. High spots on cast iron are pretty easy to remove, so that's probably not generally a problem. An old saw I had long ago had dips in the top that were on the order of an eighth or 3/16". As long as the piece being cut mostly bridged the dips it worked just fine. I used it for a few years without having any noticeable problems. I've never done anything to measure the flatness of my PM66 saw table-- I'm pretty sure the wings are off, as they were a bear to get flush when I first assembled it, but I've never had any problem that night cause me to go back and check. That's been 30some years now.

[Jim Becker]

The answer is generally "pretty darn flat"...and one area to pay more attention to is around the blade insert as that's a prime location that there "could" be distortion. Most saws are not going to be a problem. There might be "that one" floating around, however.

[John Kananis]

What Jim said and to add, if your extension wings are not flat, it will be absolutely no big deal until you use a sled. The operation can still be completed but you'll find that you'll have to square the blade to the sled when you install it. And then back again to the saw table when you remove the sled. If both wings are equally high or if they're both low, this isn't an issue. It's very obvious when right or left is higher than the opposing side though.

[Patrick Varley]

I thought I recall that SawStop's spec is 0.01 inch.

That being said, I'd be more concerned about whether it's causing issues with performance as opposed to a set number. And that is perhaps more closely related, as Jim said, to where it's "not flat".

[Cameron Wood]

My well used '40s Unisaw is within about .005 except the very leading and trailing edges which dip a little more- probably from wear.

[Lee Schierer]

What Jim said and to add, if your extension wings are not flat, it will be absolutely no big deal until you use a sled. The operation can still be completed but you'll find that you'll have to square the blade to the sled when you install it. And then back again to the saw table when you remove the sled. If both wings are equally high or if they're both low, this isn't an issue. It's very obvious when right or left is higher than the opposing side though.

When I purchased extension wings for my table saw, they came with instructions on how to level the wings with the saw table. It took a hour or two, but my wings are level with my saw table. You need to place shims above or below the bolts that attach the wind to the table to make it level when the bolts are tightened. I used aluminum pop can material to make my shims because I could cut it with a pair of scissors. After more than 35 years my wings are still flat with my table. I have several sleds and don't have to adjust anything other than blade height to use or remove a sled.

[glenn bradley]

The times I have called for specs I have been told .004" between any points on the surface of the main table. This was an Orion spec (read zip code saws and early Steel City). I tend to use this as my general rule. Of course the main test of flatness is how the tool "works". Make a few critical test cuts. If the results are OK, you're OK. This is coming from a .001" kinda guy.

[Richard Coers]

My well used '40s Unisaw is within about .005 except the very leading and trailing edges which dip a little more- probably from wear.
I can't even imagine how many thousands of miles of lumber it would take to wear away even just a few thousandths of cast iron. Why wouldn't the center of the table wear as much as the leading and trailing edge since the same amount of lumber slid over the center too?

[Warren Lake]

have wear on the leading edge and outfeed edge of my SCM jointer. People that dont use extension tables can put more wear there. My shaper has wear around the cutter area from having a power feed on it. SCM stuff had raised lines on the jointer infeed and outfeed and the shaper has machine markets. You can see the wear before measure. on the SCM saw there is dip around the blade area, dont think it had a feeder on it likely more sag and movement. DOnt remember how much on the saw plus ive flattened some amount sanding it flatter with more to do. Jointer tables were very accurate other than the wear areas. Old school quality. Never measured the cabinet saws will do that sometime.

[Maurice Mcmurry]

How does one check for that amount of flatness?

Dan Gelbart shows how to check with math and some granite blocks. It is beyond the scope of my math skills as well as my measuring tools. He gives the equation and example starting 23:10 minutes in in this video. Temple Grandin please help!


https://youtu.be/cwdoUjynpEk

[Warren Lake]

72" precision ground straight edge and feeler gauges

[Cameron Wood]

I can't even imagine how many thousands of miles of lumber it would take to wear away even just a few thousandths of cast iron. Why wouldn't the center of the table wear as much as the leading and trailing edge since the same amount of lumber slid over the center too?

I don't know about thousands, but no doubt miles, including lots of heavy construction lumber, painted, salvaged, etc., etc.. A 16' 2X10 might weigh 20 lbs. Plus the saw was 40 years old when I got it.

I'm guessing it would only take ten or fifteen minutes with a file to get a similar result.

[Michael Burnside]

Pretty flat. If it makes good cuts and beautiful furniture, it’s good enough.

[Ben Grefe]

I thought I recall that SawStop's spec is 0.01 inch.

That being said, I'd be more concerned about whether it's causing issues with performance as opposed to a set number. And that is perhaps more closely related, as Jim said, to where it's "not flat".

I distinctly remember this spec when I setup my SawStop many years ago too, but I looked through the current manuals online and it doesn't seem to say anything. I had to shim my wings with hvac tape in the joint to get them dead flat.

[Myk Rian]

How flat? All depends on how OCD you are.

[jim gossage]

Just checked my Saw Stop. The main table is generally within 0.002" but near the rear of the table it dips a bit to 0.006" relative to the front. I had an old dewalt table saw that cut pretty good except when I was making some tissue boxes, about 6" square on the sides. They were completely off. Pertinent to what Jim said, it turned out that the table dipped at the throat by about 0.015-0.02" as I recall, and this error really affected the smaller pieces because they weren't held up by the flatter parts of the table. I just built a sled that I clamped the pieces to and all was fine.

[roger wiegand]

I'm curious about what Bad Thing happens when a table saw top isn't perfectly flat? Having used saws with distinctly non-flat tops, like the one I described earlier, saws with stamped steel tops that were no where near flat (indeed, incorporated ribbing patterns with ~1/8" depressions to stiffen them), and even a homemade one with a plywood top that probably sagged a half inch at the edges, all of which could produce acceptable results, I'm not sure why it's important to have a top that's dead flat to within a few thousandths over several feet.

For sure, I often use mine as a reference surface when I'm trying to get something really flat and wouldn't intentionally buy a saw now that didn't have a pretty flat top, just on general principles, but I'm unconvinced how big a deal it is compared, say, to having a flat jointer top.

[Maurice Mcmurry]

Someone posted a neat old document a while back that listed acceptable industry standards for various machines. It seemed very sensible to me. My saw is fairly flat on the left side of the blade and within 16 inches to the right. When I acquired the saw it had a very distinct ridge where the kerf line exited. I worked on flattening the 3 main casting's with wet or dry sandpaper. My homemade wing on the right has not been flattened. I do not think it needs to be. I appreciate having a good flat saw top most when making batches of small parts that need to fit well.

[Jim Becker]

I'm curious about what Bad Thing happens when a table saw top isn't perfectly flat?

I think that it's a variable risk based on the size of the workpiece and the type of cut being made. Large things are likely not going to be affected all that much. Small things, as someone already alluded to, could be affected more relative to quality of cut including the cut not being perpendicular to the face of the material...it might be a small amount, but could be magnified for some kinds of joinery and noticeable.

[johnny means]

In 20 some years as a professional in the field, I've never run into a situation where table flatness was an issue. Table flatness seems like the polished chrome exhaust of the woodworking hobby.

[Bill Dufour]

Far more likely the blade insert is not flat to the table. A little sawdust under the leveling screws will raise it high enough a board will not advance past the front of the insert. When I cross cut I apply downforce over the table not the insert or I use a sled to average it out.
Bill D

[Keegan Shields]

Yeah but that polished chrome gives you an extra 5hp easy. :)

[Maurice Mcmurry]

After 15 years the out feed area of my saw is back to looking like it did when I got. Performance does not seem to be affected in any way. I should not have checked, now I am going to be thinking about lapping the top again.

492539

[jim gossage]

I agree that it does not matter for most woodworking. I've only noticed the problem once, when I was ripping a 45 miter on 6" pieces. The table dipped about 0.015-0.02" to the right side of the blade in the vicinity of the throat. As the piece got to the blade it tilted into the dip which threw off the miter angle. Multiply that by 4 pieces and its hard to close up your box, especially if you like tight miters. I could fairly be accused of having a bit of a machinist mentality when it comes to woodworking. Dewalt actually came out and replaced the top.

[Todd Worstell]

Thanks for all the thoughts on this issue. I just got a new table saw and I put a straight edge on it and checked various areas, sides, angles, etc. Some were pretty flat but a couple I could see light under the edge and rock the straight edge slightly. If I could find my stupid feeler gauges, I could post some numbers. Might have to go out and get some new ones.Anyway, I am only checking the main table. No wings installed and throat plate remove. Just seeing light, it is awfully hard to estimate the gap. Rocking the straight edge a little too. The light I saw was on the right side of the blade, past the miter slot, and dropping down slightly. So, at least its away from the throat. When I get my miter gauges I will have more info.Now, as far as how much is too much, I realize there are some factors like where, how much, size wood, using a sled, etc. But I just got a Rigid jobsite saw for my dad and trying to get the blade at 90 was impossible. My accurate square hit the top of the blade first from both the left and right side of the blade. There was a noticeable gap at the bottom on both sides. Returned it and got a Bosch. Blade hits 90 from both sides right on the money. It does have some small gaps under straight edge, but further away from throat. I suspect it is always preferable to have the flattest area around the blade and my new table saw appears to be that way, but even so, a big enough gap even far away from the blade could cause issues. Will be posting numbers/areas when I get them.

[Steve Rozmiarek]

In 20 some years as a professional in the field, I've never run into a situation where table flatness was an issue. Table flatness seems like the polished chrome exhaust of the woodworking hobby.

Yes!!! It's similar to lapping the soles of handplanes before you ever even see if they work as is.

[Cameron Wood]

Yes!!! It's similar to lapping the soles of handplanes before you ever even see if they work as is.



IKR- even sharpening plane irons is a waste of time.

[Steve Demuth]

I'm curious about what Bad Thing happens when a table saw top isn't perfectly flat? Having used saws with distinctly non-flat tops, like the one I described earlier, saws with stamped steel tops that were no where near flat (indeed, incorporated ribbing patterns with ~1/8" depressions to stiffen them), and even a homemade one with a plywood top that probably sagged a half inch at the edges, all of which could produce acceptable results, I'm not sure why it's important to have a top that's dead flat to within a few thousandths over several feet.

For sure, I often use mine as a reference surface when I'm trying to get something really flat and wouldn't intentionally buy a saw now that didn't have a pretty flat top, just on general principles, but I'm unconvinced how big a deal it is compared, say, to having a flat jointer top.

I would agree, particularly with respect to low spot that aren't overly large. If you're cutting wood with characteristic dimensions in the plane of the table that are many inches, it's not going to "see" dips in the table that are a couple of inches across. If you're cutting wood that's only a couple of inches in each dimension on a table saw (unless it's clamped to a sled or other floating surface), the flatness of the table is the least of your problems.

To some extent I feel the same way about jointers. A serious bow or warp that spanned the length or breadth of a jointer top is obviously not acceptable, but a .01" low spot that's an inch or or two in breadth and 10" away from the cutters? I don't see how that is in any way going to affect operation, accuracy or safety of a jointer. In fact, on my 6" jointer, the fence is easily 1/16" out of flat, and is bowed at least that much from end to end. But the fence is everywhere very square to the tables measured over a 3" height from the tables. It squares to within a thousandth or two on edges up to 3" wide on any stock with a flat face notwithstanding.

[Todd Worstell]

Got some filler gages. Staring on the left side going front to back, looks great, can't even get any gages under it. Move to left miter slot area 3 thou, left side of throat 5 thou, right side of throat 7 thou, right miter slot 9 thou, right edge almost 12 thou. All at about where the arbor is. Looks like a big dish with almost nothing on the left side to about 12 on the right side. No wings or throat plate installed yet.