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lumberjack_jeff
Sun 21 March 2010, 10:48
I was cutting parts out of 1/2" cdx ply last week when I found that at each corner of somewhat complicated shapes (i.e. slow feed ipm) the friction caused small burning spots. (And no, the bit was not dull)

Ordinarily not a huge problem, except I was cutting the material in two passes, and when the dust collector passed over the smouldering spot (filled with unejected chips and dust) on the second pass... :eek:

No harm done, but it was pretty scary seeing those sparks go up the dc hose.

From now on, it's upcut for me.

sailfl
Sun 21 March 2010, 11:30
Jeff,

Would you share a little bit more information about the cut? Like what speed was the router and what feed rate you were going?

Thanks

lumberjack_jeff
Sun 21 March 2010, 14:38
20,000 rpm, 180ipm on the straightaways.

The points at which burning occurred were probably 10ipm - sections composed of short line segments and reverses of direction.

rayditutto
Sun 21 March 2010, 15:51
.25" or .5"?
1 or 2 flutes?
do you have a pic of the bit?

cheers,
robin

lumberjack_jeff
Sun 21 March 2010, 19:05
Basic two-flute .250 bit.

Freud, I think.

rayditutto
Mon 22 March 2010, 00:48
I'm perplexed and concerned - perplexed because i don't see a clear answer and concerned because, well, it's fire

this is pure speculation but, here goes . . .
on straight flute cutters as you've described, the cutting edges on the bottom appears (i've not actually measured it) to slope upwards to the centre ever so slightly - also, the blade does not go all the way to the centre which is problematic when plunging
perhaps it is possible when the bit is moving slow that the bevelled bottom edges pack sawdust at the centre of the bit where friction creates the smoke
sawdust might pack into the center of the bit even if the bottom edges were not bevelled


still baffled,
robin

lumberjack_jeff
Mon 22 March 2010, 10:18
CDX ply is the only material I've noted this in... but then again, I use straight bits rarely now.

I think you're right, every place it happened was a place where the tool came to a near-complete stop as it negotiated a turn.

ger21
Sat 27 March 2010, 12:07
I'm curious as to why it's slowing from 180ipm down to 10 ipm?

Also, 20,000 rpm is probably quite a bit higher than you need at 180 ipm. Try lowering the rpm's down to about 15,000.

But, the bottom line is you shouldn't be cutting wood at 10 ipm. You need to figure out how to avoid that. Can I see the code, or get more info on what's causing the slow speeds?

Do you have a very low accel setting?

lumberjack_jeff
Sat 27 March 2010, 14:20
Thanks Ger,
I am now testing SheetCam. The postprocessor is much better optimized for EMC.

It is exactly true that I have a problem here with the code. But the problem was made serious (as opposed to simply inconvenient) by straight bits.

My accel settings are pretty low, an artifact of trying to solve a missed steps problem.