Scallops Aplenty

[KMWren]

we're trying to dial in our powermax 85. We have fine cut consumables and we are getting some unwanted scalloping. everything is tight on the machine and we have double and triple checked for gear slop, we have none. We cut 8 parts out today and the results are below (left most part on is book settings and the parts fall in order beyond that). What are we missing? how do we get rid of the scallops?

[weldguy]

Are you only seeing this on arcs or do straight lines also look like that?

If you turn off the THC does that problem go away?

What table are you using?

[KMWren]

seeing it a little bit on straight lines, not as bad. the more i've played with it, the better the straights have gotten. The THC is off on all the above cuts.

I'm using a wright CNC 4x8

see below for straights. that has gone down a little but is still noticible.

[weldguy]

You could be traveling too slow however I see no dross so that's likely not the case. I suspect your cnc machine is stepper driven and just not refined enough for smoother motion. Have you contacted Wright?

[KMWren]

yes i have, he's been very good, just busy. i sent him my file and i've gone through some trouble shooting stuff with him.

can you explain stepper driven what i may need to do to refine more?

[acourtjester]

There are switches on the drivers for each axis (2 drivers if slaved axis either X or Y depending on how you look at the table).
These switch are for operational current for each motor, and pulses per revolution of the motor shaft. Depending on the drive gearing and the pulses from the driver they are used to calculate the distance the axis moves. These should have be setup by Wright from the start unless something changed. Now a different problem could be the drawing you are using, there could be to many nodes used to make the shapes. A simple circle g-code should only have 4 lines of code for the actual circle cut ( more line for other things). You also could have a bad stepper, if you cut a square and only 2 sides have wavy edges that driver or stepper may be bad.

code.JPG (54 KiB) Viewed 1026 times

code.JPG (54 KiB) Viewed 1026 times

[KMWren]

i've made sure there are not too many nodes, i re-drew everything that was excessive in nodes (poly lines and such). i tried to cut this out today to see what you're speaking about and this is what happened.

[SeanP]

I was starting to get that on my machine a while back, a new pinion gear on the gantry near enough got rid of mine, could well be the rack/pinion either wear on not a smooth mesh, a spray of chain oil won't do any harm.

[acourtjester]

Ok since you show 4 images I assume that you cut a square and that is the 4 sides with scallops, I'm no expert but I think you have a mechanical movement problem (Vibrations). One other thing which I do not believe would cause a problem but though I would mention it. On your drawing what is the width of the paths, I try to keep the path below 0.004" to keep the detail crisp. Again this is very far out.

[WyoGreen]

I've seen something like that before. It was caused by the torch moving rapidly up and down. And that was caused by a software setting. Now if I could just remember what and where the setting was.....

It seems like it had something to do with the amount of variance the torch voltage could have before the DTHC would react. Perhaps someone else can remember more. If this is your problem, you should be able to see or feel the torch doing it.

At any rate, resting your finger lightly on the torch while cutting may give you a clue as to what is going on.

Steve

[acourtjester]

Wyo
The setting your are talking about is the sensitivity to the arc voltage. He said the THC was off

[Johnstone]

Did you ever resolve this issue? It would be helpful to others like me if you would post how you fixed this problem. I'm having the same issues. Thanks