gouges on direction change while surfacing

Good morning All:
I have two photos to show you; two very similar toolpaths on two separate machines.
They are scallop toolpaths; one gouges significantly whenever the machine changes direction, the other is barely perceptible.

The disturbing thing is that the old beater Haas (Minimill vintage 2001) makes the better part than the near new Haas UMC 750 SS vintage 2015.

Both surfaces are cut with a 3/16" ballcutter speeds, feeds and stepovers are roughly comparable (the better part is Ti6Al4V, the worse one is 316L SS) (350 SFM 0.001" chipload, 0.005" stepover approximately)

So why do you thing the new machine does so much worse than the beater??

I have a theory; I'd love to hear yours.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www,vancouverwireedm.com

Tossing one in for the heavy table can't change direction as fast so the tool is unspringing into the workpiece. Surprisingly enough I get better finishes than the poor one running my tools at 10k and 80 ipm (.002 fpt) regardless of tool size or material in most cases.

I believe haas has an accuracy setting in the parameters, maybe you need to tighten up on the UMC parameter.

Hazzert said:

I believe haas has an accuracy setting in the parameters, maybe you need to tighten up on the UMC parameter.

Click to expand...

I'm having a hard time picturing why there is a such an abrupt direction change in that area, but I'm almost thinking it could be the opposite cause.

If there is a surface boundry in the CAD model along this gouge, perhaps the older machine is fudging the transition a little bit via a lower path accuracy/tolerance.

Does seem weird though.

possibly tool flex, worst case " spindle flex " if the old machine has a sturdier lower rpm spindle it may make a difference, does it matter what feedrate you run it at?

many machines have loose fitting turcite slides. like a 4 legged chair with one leg short on direction change they rock twist a bit. i have often seen on a horizontal mill changing Y direction effects Z. often can see with indicator and often it is only .0002 to .0004

WILLEO6709 said:

possibly tool flex, worst case " spindle flex " if the old machine has a sturdier lower rpm spindle it may make a difference, does it matter what feedrate you run it at?

Click to expand...

His other machine is a minimill, I sure fricken hope it's not more sturdy than his UMC750.

Tool or spindle flexing? Hope not. How much tool pressure is there on a finish pass? Enough to flex and gouge that much? I wouldn't think so.


My guess is accuracy settings.

Another vote for accuracy settings.