Author Topic: Burn Marks  (Read 3114 times)

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Offline bevans

  • Posts: 95
Burn Marks
« on: August 25, 2017, 10:11 AM »
I cut up some 1/4 by 8" x10" maple pieces yesterday and when I finished the cuts I noticed that on every piece there is about 4" of burn marks on the first part of the off cut side of the cuts. The board did have a slight bow. Upon inspection of the blade I do not see any pitch build up but I did cut a lot of vinyl flooring last week with the saw. What baffles me a little is that it is only at the start of the cut. When I turned the board over so that the convex part of the bow was facing up and I cut the board (only the first cut) there are no burn marks. Is the issue my saw out of alignment or maybe pitch build up I did not notice or maybe the physics of the cutting action....or something else?
« Last Edit: August 25, 2017, 04:32 PM by bevans »

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Offline Gregor

  • Posts: 1204
Re: Burn Marks
« Reply #1 on: August 25, 2017, 04:45 PM »
I take it you use a TS on a rail?

Rail used to clamp the workpiece to the table? Offcut side without additional clamping?

The workpiece would get flattened by the rail when clamping - then while cutting the free part of the offcut in the making then flexes back into being bowed and that pushes the kerf on the offcut a bit up and inward - where it gets an additional, unwanted, meeting with the side of the blade.

Offline bevans

  • Posts: 95
Re: Burn Marks
« Reply #2 on: September 01, 2017, 09:46 AM »
Thanks for responding Gregor. I should have been more thorough with my set up and technique but your esponse may still be correct. I am using a Kapex and am holding down a 20" section of the blank with my left hand flattening the board and sliding the blade using my right hand. The fact that only first 1/2 section of the board is burned.

Offline Gregor

  • Posts: 1204
Re: Burn Marks
« Reply #3 on: September 01, 2017, 04:03 PM »
With the convex side up you can hold the board down (or better, when using the Kapex, use the clamp) onto the table and both front and back sides will be supported by the table.

With the concave side up (as you did the cuts) you can't do that easily (as you would have to push both the front and back sides down) and reliably the board will tend to roll on the table. With the first 1/2 of the offcut most likely in the air (not supported by the table) it can easily vibrate or move, which could well be the reason for the burns.

I found it better with the Kapex to always have the concave side down on the table (as the workpiece can't roll in that configuration) and use the clamp. In case I have to cut wider bowed material (wider than the side tables of the Kapex are deep) I switch to using the MFT with the rail since then both sides the board will be supported - while on the capex the side toward you wouldn't be (as of being in the air) and the board would only sit on the back of the table/extension and near the cut on the zero-clearance insert,  making it hard to make sure that the workpiece is flat on the table (so it can't vibrate excessively around the blade).

Offline QuailRider43

  • Posts: 83
Re: Burn Marks
« Reply #4 on: September 01, 2017, 11:39 PM »
When I had problems with burning wood last year (here), it turned out to be a dull blade.  It may be a wood position / curvature issue, but a dull blade may be part of the equation.

Offline ear3

  • Posts: 3623
Re: Burn Marks
« Reply #5 on: September 12, 2017, 07:44 PM »
I would prophylactically clean the blade anyway  just in case for pitch.
 I have found in the past that there can be buildup right on the side of the carbide teeth that was not all that visible to the eye.
My suspicion though is that in your case it probably has to do with the workpiece warping slightly as tension is released by the cut.
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Offline glass1

  • Posts: 486
Re: Burn Marks
« Reply #6 on: September 12, 2017, 09:37 PM »
Check if blade is parellel to slides.  Clamp 12" board to tables. Do a chop cut in fully retracted position, with motor still on lift head up pull all the way forward and push head down and mate the cuts. If the kerf cuts do not line up blade is not parellel to slide bars causing burning and binding as out of parellel blade is dragged through the cut.