[antsofthesky]

Hello, First timer here...

I've recently begun to develop a series of industrial machines with small footprints and high rigidity. One of our prototypes has begun to do interesting things when taking moderate clearing passes in annealed stainless steel -- something it previous chewed through without any issue for hundreds upon hundreds of hours. The cut is 9mm down, 0.6mm load with a 1/4 roughing endmill.

The cut is dragging down as it makes a pass, the Z axis slowly gives way and drops down by a mm or two, slipping downwards as it moves on the X and Y just fine. The cut sounds pretty awful and chatters a bit.

The spindle is a 1.5kw servo, each axis is a 425 oz/in stepper (7 amps). Servo has its own 220v line and everything else is running off a 15 amp 110v line and a 48v power supply. I'm at wits end trying to go through all the options so I've come here. Here's what I've thought thus far.

Physical considerations -- is the ballscrew just too small? (1605) Is it vibrating loose? This seems unlikely or even possible... Gibbs are fine... The head of the mill hasn't changed weight since its begun doing this, and if it has, it's changed less than a pound or two. Its colder now but that's not something that should be this much of an issue, I'd imagine to cause this unless the frigid temperatures really do play this hard.

Electrical considerations -- is the motor too weak? It's a 425oz/in Stepper right now. I'm looking at going up to a 15000-1600oz/in Closed Loop in the immediately future. Is the Z motor losing power as the X and Y motors draw more? If that's so, I'll break out another power supply.

Any help is immediately appreciated, seriously, am trying to figure this out and under constant pressure -- thank you!

[awerby]

Could the tool be slipping in the collet? The helix on an endmill tends to put downward pressure on the tool as it engages with the material, and it can be dragged downward. Try putting a mark on the shank where it engages with the collet, and if this happens again, check the mark to see if it's any lower.

You could also check to see if the whole screw is getting loose in its bearing; which can also cause an apparent drift.

[antsofthesky]

Unfortunately, no. I've already put a marker on it, it's not moving.