Problem with speeds, feeds, and motor tuning

[joshv]

I am new at the CNC rounter and I am having a few problems that I could use some help with.

I have a 4 x 8 Gorilla CNC router with a 2.25 Hp Bosch router running Mach3. I am cutting 3/4 Melamine with a Freud 3/8 compression bit. What kind of speeds and feeds and depth of cut can I use as a starting point for this machine setup and tool?

One problem I am having is that if a tell the machine to cut 4) 24" x 24" parts some of the parts will come out at 24" x 24" and others ones at 24 1/16" x 24"
and others ones at 24 1/32" x 24 all in the same run. If this a problem with the machine? Could I be pressing the machine to hard and it is moving out of place. Or is this some I can fix in the motor tuning?

[jsheerin]

How fast are you cutting now?

Any details on motors would also help - motor type, gearing, drive system type, etc.

In general, start slow and with low accelerations and work your way up in speed and acceleration until you start seeing errors.

Another possibility is that something is misadjusted or loose. Have you verified that the machine travels accurately and repeatably with minimal backlash with no cutting load?

[ger21]

You'll probably want to cut as fast as the Bosch will let you. Ideally, you'd want more power to cut 3/4" in a single pass. Having said that, A guess would be to start at 100ipm?? Maybe 12,000-15,000 rpm?

Re reading your post, you mentioned depth of cut. A compression spiral is made to cut full depth in a single pass.

As for the size issue, you'll need to do a little testing. If you cut the same part over and over in the same place on the machine, are they all the same? If the parts are consistent when machined in the same area, but vary depending on where on the machine you're cutting them, then it's possibly errors in your drive mechanism. Is this screw drive or rack and pinion?