Burning Cuts

[Chuck Wick]

I have a Dewalt DW717 sliding miter saw, its a couple years old and lightly used in the home workshop. Ever since I can remember it's burnt wood while cutting, straight and bevel cuts leaves a burn mark. 2x4's, oak, walnut, etc. When the blade slows to a stop I can hear it brushing against the wood with each rotation which leads me to believe the arbor (?) might be bent. The burn is always at the left hand side rear of the blade (see picture).

It did it with the original blade which I just changed out for a Forrest chopmaster 2 days ago and I still have the same issue.

Any suggestions on diagnosing and repairing this?


360097

[Matt Day]

First thing to check of course is alignment. Is it a true 90* everywhere? Is there excessive flex anywhere? Also check for runout of the arbor with a dual gauge.

[Jerrimy Snook]

Here are some thoughts/possibilities in no particular order... It burns all materials, does it burn both sides of the cut or just the left? Is there visible or measurable wobble to the blade? Does the burning happen if the slide is pulled all the way out then plunged and then pushed toward the fence. Is the blade shut off and allowed to slow down while in the cut? Has the blade to fence alignment and blade to table alignment been checked?

[Steve Demuth]

First thing I'd check is that the plane of the blade is parallel to the slides (the arbor is at right angles, in other words). Second thing would be runout on the arbor, but given the localized burning, I'd bet that it's the former.

[Wayne Lomman]

If you leave the blade in the cut to slow down and stop, it will burn. If your workpiece is firmly restrained, there is no danger in lifting the blade while it is running. Your saw alignment is likely to be fine. Cheers

[Chuck Wick]

Thank you everyone for your responses.

I don't have a dial indicator for checking runout though I've checked the blade/fence/table alignment with various squares and it seems to be ok. I have not checked if the blade is parallel to the slides and not quite sure how to go about doing so, if anyone has suggestions or a link to a description I'd like to check that out.

I do let the blade come to a stop while in the cutting position, perhaps this is a habit I should break.

[Bryan Lisowski]

If the alignment is fine, your blade may be dull.

[Brian Tymchak]

Have you tried clamping the left side down and then makng the cut? I found that I sometimes was unconsciously putting pressure toward the blade while holding the piece to the fence. I was getting occasional burns. I still don't clamp very often but now that I'm aware of the issue, I have better results.

[Chuck Wick]

If the alignment is fine, your blade may be dull.

Brand new blade.


Have you tried clamping the left side down and then making the cut?

I have, it happens clamped or not.

I'll have to do some more testing, it doesn't happen every single cut, but most of the time it does. It seems more likely to burn when sliding the arm as opposed to vertical chop cuts. Also because the burn appears where the blade comes to a rest that leads me to believe if I stop letting it come to a rest against the wood it won't burn, like Wayne suggested.

[John K Jordan]

I don't have a dial indicator for checking runout though I've checked the blade/fence/table alignment with various squares...

I dial indicator is incredibly handy in the shop - some are surprisingly inexpensive and precise enough for woodworking, for example:
https://www.amazon.com/Magnetic-Base-Adjustment-Indicator-0-0005/dp/B01JU18A0Q


JKJ

[Wayne Lomman]

Chuck, my suggestion is based on what happens for me when I do an awkward cut that I suspect will cause worse damage somewhere and I shut down the saw before withdrawing it. Your picture is exactly that. Tasmanian Oak is the worst as it burns if you look at it sideways. It happens on one side because if like me you are right handed and you and everyone else right handed fractionally pulls the saw to the left when using it. Cheers

[Alan Lightstone]

I don't get any burning with my Kapex and I always keep the blade down until it stops. FWIW. I don't think that process guarantees burning. Quite the contrary in my experience.

[Wayne Lomman]

Nothing is guaranteed except death and taxes. That aside, it is a general rule that you don't stop the cutter while it is in contact with the timber. This holds for any machine whether saw, 6 head moulder, planer, machining centre, router or whatever. If you stop the feed rate and keep the cutter in contact with the timber while the cutter is rotating you build up localised heat and you may get burning. Cheers

[Art Mann]

Try keeping the blade rotating full speed until you have retracted it from the kerf.

[Alan Lightstone]

Nothing is guaranteed except death and taxes. That aside, it is a general rule that you don't stop the cutter while it is in contact with the timber. This holds for any machine whether saw, 6 head moulder, planer, machining centre, router or whatever. If you stop the feed rate and keep the cutter in contact with the timber while the cutter is rotating you build up localised heat and you may get burning. Cheers

I was taught to keep it in contact to reduce tearout, which has been my experience.

[Wayne Lomman]

Tear out is not caused by a rotating blade. It will be some other reason. Proper industrial saws switch on and run all day without tear out. Vibration, run out, imprecise slides, incorrect blade geometry, blunt blades etc cause tear out. Cheers

[Lee Schierer]

I would recommend getting a dial indicator and mounting it securely to the table and then checking for side to side play of the entire carriage. Burning is generally caused by an alignment issue.

[Mike Kees]

I have set up and played with a couple of different sliders. To me it seems that your problem could be as simple as getting your fence aligned for a true 90 degree cut. My first slider was a delta sidekick and I would have to go thru it and adjust everything about every 2 years. I would get those burning cuts when it was out of square or my blade was dull. The dial indicator advice from everyone else is good ,just be sure your fence is dead nuts square first. Good luck,Mike.

[Chris True]

An out of square fence has nothing to do with burning, it just makes an out of square cut. Now if the blade is heeling, that will make a difference. Heeling is when the blade is not exactly parallel with the line of travel. Not sure how you fix that on a slider, it is adjustable on a RAS.

[Chuck Wick]

Right, the fence is out of square any time a miter cut is made. That alone shouldn't cause burns, no? I would think only blade misalignment with the slides, play in the arm assembly, or a bent blade/arbor would cause burning.

So far lifting the blade before letting go of the trigger seems to be a work around.

[Chris True]

Just be carefull with small and thin offcuts. They tend to fall back against the blade and if you lift with it still running the teeth can grab those thin offcuts and throw em pretty energetically.