Table saw experts:- why can't my table saw cut straight?

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Hwale

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#296234 31-May-2022 18:42

I have a weird problem with my table saw not cutting straight, but bear with me because it's not because anything is out of square. The blade isn't cutting straight with respect to the blade itself, as if the blade is somehow twisting.

I have a DeWalt DWE7491. When I use a mitre guage or sled to guide a workpiece into the blade, the blade somehow does not cut in a straight line, but changes the angle it's cutting as the workpiece moves across the blade. Kinda hard to explain but the result is a weird twisted face across the cut portion. You can see it in the pictures attached.

So imagine the blade is a perfect 90 degrees to the table. The mitre guage is also a perfect 90 degrees to the blade. The resulting cut should be a perfect 90 degrees, but somehow it's picking up an angle across the face which worsens from one end of the face to the other.

As I said, it's as if the blade itself is cutting a twist but with a spinning blade I can't imagine how this is even possible. It's consistent across different blades too.

I've accounted for every adjustable factor I can think of but nothing seems to resolve the problem.

Any ideas?

RunningMan

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#2921086 31-May-2022 19:18

Damaged teeth - blunt on one side perhaps? Could cause the blade to walk sideways.

Hwale

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#2921087 31-May-2022 19:19

Does it with a brand new blade.

CrazyM

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#2921088 31-May-2022 19:21

How sharp is your blade? If it’s getting dull, particularly on one side, it can cause your cut line to turn.

Especially if you have a thin kerf blade

RunningMan

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#2921089 31-May-2022 19:25

Wear in the blade mounting shaft bearings then?

Hwale

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#2921091 31-May-2022 19:28

Possibly. Would that cause the blade to deflect while cutting? Is this a common symptom of bad bearings?

CrazyM

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#2921093 31-May-2022 19:32

Arbor bearings being bad is fairly unlikely, you could probably feel if there was any play by rotating the blade by hand and giving it a wiggle. Or put a dial gauge on it and measure if you have any blade runout

Does having the blade depth extended higher make the cuts worse or better?

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djtOtago

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#2921107 31-May-2022 19:57

A warp in the table top causing the wood to twist relative to the blade as it moves past. This is normally only noticeable when doing long cuts in sheets.

mdf

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#2921109 31-May-2022 19:59

Based on what you've already tried, your blade might not be parallel to the mitre slot (which is easily fixable) or your arbor bent or twisted (which isn't).

Dial gauge is ideal for diagnosing these issues. You can do the mitre slot with calipers in a pinch though.

RollyShed

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#2921111 31-May-2022 20:03

Is the yellow plastic deflecting? I have an aluminium plate there. Our Shed has a solid piece of wood replacing what ever was there originally.

On a totally different thread but still the saw, how do you stop it? Both hands full guiding wood, now what?

As soon as I saw this I fitted one to my saw -
https://rollestonshed.wordpress.com/safety-switch-on-circular-saw/

You switch the saw off with your knee and no need to find where as the "target" is the width of the saw bench.

If H&S were serious about H&S, they wouldn't allow a saw out of a shop without one of these fitted.

Hwale

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#2921152 1-Jun-2022 00:10

Thanks for the ideas so far.

The table isn't warped, or at least this isn't the cause of the problem. It happens on both mitre slots on both sides of the blade, and on a flat table saw sled.

The blade is definitely parallel to the mitre slot. At the very least it's much closer to parallel than the cuts the blade is making in the wood.

The yellow part is metal and doesn't warp. I can reference the workpiece from any part of the table and get the same result.

What I can't figure out is even if the arbor is twisted or the bearings damaged, surely a spinning blade will still cut 90 degrees because the warped part has to pass through every part of the wood if it's fed slow enough. The result would just be a rough cut, not a smooth cut with a gradual twist... 🤷‍♂️

Bung

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#2921159 1-Jun-2022 02:47

Is the riving knife exactly in line with the blade? Have you tried crosscutting without it?

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eracode

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#2921162 1-Jun-2022 05:43

You say you have the problem even with a new blade. It sounds as if the blade might be flexing when it gets some pressure on it. Is the blade a cheap one, too thin and flexing as you push the timber through?

When you push the timber through, are you pushing from one side so that one vector of the push is against the side of the blade - rather than from behind the blade? I guess moving the timber with the mitre gauge should eliminate any sidewards pressure on the blade - but maybe not entirely depending on how you do it.

You haven’t mentioned how things go when using the fence. Best fences have have a rail-lock at each end. Fences with a lock at only one end can make it difficult to get a straight rip cut - giving a result similar to your issue.

PS: I found this which may help you:

https://www.woodworkforums.com/f11/dewalt-table-196635

Several reviews mention the mitre gauge being sloppy in its track - fairly major issue which could lead to your problem.

Sometimes I just sit and think. Other times I just sit.

Bung

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#2921166 1-Jun-2022 07:29

Hwale:
The table isn't warped, or at least this isn't the cause of the problem. It happens on both mitre slots on both sides of the blade, and on a flat table saw sled.

It's happening even when a crosscut sled is used. It is a thin blade, the specs don't give kerf but body is 1.75mm. I have a similar blade in a circ saw and it cuts pieces the size shown without a problem. I think the work is being twisted after it hits the knife. That's not needed on crosscut as much as during ripping so I'd drop it down or raise the blade and try a cut without pushing past the blade.

MikeAqua

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#2921227 1-Jun-2022 09:33

Issues I've had with mine (cheap black and decker unit): -

The insert around the blade wasn't level with the table surface, causing the piece to dip and tilt at certain points in the cut. Solution: I made a zero-clearance insert sanded down to be level with the saw table top, after painting. Sanded a very slight chamfer around the edges, so there is edge effect. Looking at your pictures your insert looks very similar to mine. A cross cut sled should negate this issue.

Fence moving at one end under pressure. Solution: Changed how hard I was pushing the workpiece against the fence and for long cuts or large workpieces I clamp the far end of the fence in place

Riving knife kept getting out of alignment with blade. When the work piece contacted the riving knife it would deflect a little Solution: Adjusted it and applied thread-locker (the kind that will release with force)

Edit: for got to say I also had a sloppy mitre gauge, because it only had one runner. That also caused issues, so I added another one

Mike

mclean

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#2921342 1-Jun-2022 11:28

Not an expert, but it kind of looks like the wood isn't stable in the mitre gauge towards the end of the cut.

Maybe check that the throat plate is correctly levelled. It should be flush or just slightly below the table at the front, and flush or slightly above the table at the back. But if it's happening when you use a sled (running across both slots) then adjusting the throat plate isn't going to make any difference.

Also, if youre doing mostly through-cuts, it's probably better to swap the riving knife out for the blade guard, although that won't help with the crooked cuts.