Thread: Discussion GMFC Foam cutting software
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Old Dec 22, 2012, 06:14 AM
Geoff_S is offline
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Originally Posted by danfield View Post
Dang tough to explain, the issue of cutting greater than 2:1 is or can be related to the MIn/max speed issue but not exactly as they're separate issues.
Thanks Dan. My understanding is slowly increasing...

I've managed to do some testing with various heat and cut speeds (after first discovering and then fixing my PWM hot wire controller which had been going berserk).

1. Firstly, I did straight cuts at a number of different cut speeds. For each speed I tweaked the heat setting until the foam block was just on the verge of sliding along the cutting table, as per the GMFC help file. I also checked and the surface of the cut foam had just a few very fine hairs, so I was happy that this was a sign of non-contact cutting by radiation. I've put the results into Excel and produced the following chart. Interesting that it is not a linear relationship.

2. Now even though the maximum speed that my cutter is physically capable of running at is 4 mm/sec, I settled on 3.3 mm/sec as my "maximum speed" for the foam management screen in GMFC, and also chose 1.5mm/s as my "Minimum speed". I did some kerf test measurements on a 2:1 tapered block and entered the corresponding values in the "Kerf for speed S" and "Kerf for speed S/2" boxes. The following is the resulting screen in GMFC.

3. Now, I also did a kerf measurement at my "minimum speed" of 1.5mm/s with heat at the ideal value of 30% (as deduced from step 1 above). It did NOT match the kerf for my maximum speed - it was greater (0.825mm vs 0.635mm at max speed).

So, do I:
a) decrease the heat at min speed BELOW the ideal value, and accept that this will give more wire drag than ideal
b) increase the heat at max speed ABOVE the ideal value, and accept that this will give more kerk than ideal
c) get a life, and stop worrying about 0.2mm differences in a piece of foam...
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