Burning Wood!

Discussion/questions about software used with your CNC Shark and programming issues

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SharkNewbieGirl
Posts: 7
Joined: Wed Sep 04, 2013 9:08 pm

Burning Wood!

Post by SharkNewbieGirl »

I am not sure if this is a programming problem or not. I've only been using my shark for a few months now. Today I encountered a new problem on something I've done many times. I was using a .25 endmill to profile my work and the wood started burning. I slowed the FRO down to 50%, tried increasing and decreasing the routing speed. Neither helped. I am cutting Pine .75thickness, the pass depth was set at .126 at 6 passes, it was set on "Climb", stepover .1 40%. I'm not sure why this occured. I have only had this happen once where the bit started to burn the wood, but I think I loaded the profiling instead of v groove at that time :( .

Danwood
Posts: 44
Joined: Sun Nov 17, 2013 9:46 am

Re: Burning Wood!

Post by Danwood »

Burning wood can be caused by number of things.
Slow feed rates. If the cutter dwells too long in one place it can over heat.
wood ignites at 450 Deg F.
A dull bit will run with increased friction and can cause it to burn.
Deep cuts with slow feeds can also cause a burn.
Slow router RPM's can cause over heating.
I have a commercial power head on my machine. I run 0.50 bits and smaller at 22000 rpm and 100 IPM.
I also prefer regular metal cutting carbide bits with a high helical grind. they do two things, they give a better finish and clear the chips better. they are also made from a better grade of carbide and are sharper than bits made for wood.
Inadequate chip carrying capacity can also cause the cutter to overheat. The chips are not cleared from the cut and rub against the side of the cut causing a heat build up.
I had fire in my Legacy machine when doing thru cuts on a hollow spiral lamp. I was using a 4 flute spiral end mill cutting 0.500 deep per pass.
I did two things. I changed to a 2 flute cutter, More chip carrying capacity and changed the depth of cut to 0.375.
A good source of bits is http://WWW.cuttingtoolsource.com
Danwood

milo30
Posts: 553
Joined: Mon Mar 12, 2012 9:21 pm

Re: Burning Wood!

Post by milo30 »

I hear people talk about their adjustment of the FRO. I wanted to point out that the FRO only adjusts from the speed that you have set in vcarve. I adjust my feedrate in the vectric program and then only use FRO when I see it is needed while running the program. I know that for a particular type of cut with a particular bit that I need to run at 50 ipm for instance so I set that in my file then if I find that I need to slow it, I will use the FRO. In order to help better, we would need to know the initial setting of the feedrate. Danwood gave good advise. Try to make a log for different types of toolpaths, tools and woods as each can have it's own adjustments to operate efficiently. Is it burning throughout the cut or just at the beginning?

This is a good reminder why you should always be nearby to keep an eye on your machine because they have been known to start a fire.

TDA
Posts: 44
Joined: Wed Apr 13, 2011 10:33 am

Re: Burning Wood!

Post by TDA »

Endmills rely on the chips being cut to remove heat from the tool. So the simple answer is lower your RPM, increase your feedrate, take a shallower pass, and/or use a cutter with less flutes. A dull bit will make this worse. You may still run into an issue with some code as when you change direction the machine will slow down.

A couple quick things I felt needed pointed out about high helix tools (not trying to pick a fight). While high helix tools do pull material out faster they can cause issues in some soft media. Usually only VERY soft material will have an issue though. Also, while some manufacturers may use a different grade of carbide for high helix tools this is far from always the case. Just as an example we use the same grade carbide for almost all our tooling regardless of tool type (Soft media, metal, specialty). How sharp a tool is will not be dependent on helix it's dependent on rake angle. And again rake angle of the flute is a decision made by manufacturers for all tool types. So it's unfair to say just because a tool is high helix it's going to be better. Or at least it's unfair to say that without a specific manufacturer listed.
John Torrez
Think & Tinker / PreciseBits

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