Hi guys, I'm fairly new to cutting G10, or cnc for that matter. But Lately I have been cutting some parts from 1/16" G10 which need to be accurate within .002". Everything was going great until I purchased a new set of bits, .0394 bit here:
PCB Router Bits - Diamond Cut - Midwest Circuit Technology
Spindle is running about 20K, and feed rate is 14IPM.
Right away I started having issues.. all of my parts were too big and the holes too small by .006". I measure the bit and it measured at .0375. Strange that a bit is labeled .0398 but the cutter is actually .0375, that's a big difference.
So I figure no problem, I regenerate my g-code for a .0375 tool. Surprise all parts still to big with cutouts too small. Grrr... so I back down to .036.. .035.. .034 .. .033... and finally I am somewhere around .033 to get the right sized cuts but it's not consistent. Yes, the tool is cutting on the correct side of the path (cut2d does this automatically, and I did it manually with another package as well).
I figured it must be backlash. I measured the backlash on my X axis to be .001, and on Y to be .005. So thats it! I tighten everything up, re-measure and then enter that value into EMC backlash compensation. Now I cannot measure any backlash, the compensation works great.
Now with backlash fixed, everything snug, I set the tool size back to .0375, and surprise, parts are just as far off as they were before.
At this point I am sure it's a software problem, so I generate the g-code with a different program, but nope, same problem.
Getting desperate, I figure maybe it's tool deflection. So I slow down the cut rate to 4IPM, no improvement. I run a finishing pass, no improvement. Still need to set the tool size to .033 to get correct sized cuts.
Then I pull out a tool of a different brand... it's labelled .05" and measures .045". I regenerate the same g-code for this tool at .045 (as I measured it) ... cut the part. Bam it's within .001" of what it should be.
Now I'm really confused. They both appear to be the same design, but from a different manufacturer.
How can a .0375 tool cut a slot .032" in diameter? I thought maybe it was just a dull tool so I went through the whole set of brand new cutters and they all behaved exactly the same. Going back to a different tool, no problems.
Am I using the wrong type of bit to cut G10? Is it just a crummy bit?