Scalloping problem

[Pacific Aerospace Limited]

Hi, we are having problems with some .020" ali sheet metal parts we cut on our router.

 

The parts are quite long and narrow and the narrow edge ends up with scalloping along it instead of a nice straight edge.

 

The pink dotted line is where the problem occurs, and at the other end which is similar. But nowhere else on the part.

 

Im not sure if it is a mechanical problem - cutter flex etc or a prob with the dxf. We use 6mm carbide single flute, neutral (no helix) cutters.

 

 

I have tried what was suggested in this thead

 

http://www.emastercam.com/cgi-bin/ultimate...t=036802#000000

 

i.e. turn off infinite look ahead and the arc filter, no change.

 

Any ideas what could be causing this?

 

Is there a way to upload the MCX file to this forum?

 

Any ideas or help appreciated!

 

Nick

[Leigh @ Kodiak]

My email is in my profile. You can email it if you like, and I will take a look.

[Superman]

Is the part being held down securely ?

 

I assume you use vacuum or tape for hold-down,

 

I would guess that the material is actually lifting or moving--

It may pay to alter the actal order of doing the contours

---RH & LH end contours 1st

then do

---top and bottom contours

 

This would allow maxumum hold-down grip while doing the ends, and the job's length will assist with hold-down when machining the long edges

[John Summers]

It's possible that the router is hitting some resonant frequency. Try dropping the feedrate on the scalloped line.

[Pacific Aerospace Limited]

The part is held on a vacuum bed, it doesnt seem to be lifting or moving.

 

We tried running it at 50% feed and 50% spindle, this time the scallops are still there but much smaller - by eye they look around half as far apart and half as 'high'!

 

What could this mean!?

[crazy^millman]

That would suggest a machining problem and not a code problem. Have you tried running it 1000 spm and 10 imp and seen if that makes a difference? Have you tired leaving a .002 tab to the bottom for additional holding power?

[Pacific Aerospace Limited]

I've tried running a few combinations, the spindle speed doesnt seem to have any affect, the more I reduce the feed the better it comes out. By the time I got down to 20ipm the scallops are gone - would that suggest a problem with the machine?

[crazy^millman]

To me it would suggest some gain adjustment has to be done at that end of the machine. The servos are not keeping up and over shooting as you speed up. Like any machine if the servos are fighting themselves then the faster you go the worse the problem gets.

[chip]

quote:

---

To me it would suggest some gain adjustment has to be done at that end of the machine. The servos are not keeping up and over shooting as you speed up. Like any machine if the servos are fighting themselves then the faster you go the worse the problem gets.

---

Are you running a Fadal?

[Pacific Aerospace Limited]

Thanks for the replies.

 

We run a Haas GR512.

 

Just looking at the machine visually the part doesn't seem to move or vibrate. I'll try screwing the part down and see if that makes any difference.

 

Colin, how would you go about changing the cutting order? We have tried using the change at point funtion (to slow the feed right down at the ends) but cant seem to get it to work properly.

 

Thanks again

Nick

[John Summers]

If the scallops got smaller at slower feed, it sure looks like you've hit some machine resonance. Servo tuning might fix it. Until then, maybe setting the part up at a different angle might get you out of the resonance zone.

Spindle speed probably doesn't affect anything.

[Pacific Aerospace Limited]

I've just tried screwing the part down and no change.

 

However i tried cutting it at opposite ends of the machine and the end closest to the control comes out better, not 100% but noticibly better.

 

Colin, yeah we have had problems with long narrow parts. For now we use the laser to cut them.

[Pacific Aerospace Limited]

A technician recently adjusted one of the X axis motor 'filters' to stop it making an annoying noise when not moving on that axis. Could that have anything to do with it?