[nlancaster]

nice

[kmagyoyo]

I'm having an issue when the Y and X axis are run in tandem, as in a diagonal line or circle, I get a wavy cut. This is intermittent. Oddly the wave is synchronized between the upper and lower passes.

I have observed that on 600 IPM rapids, the X axis motion does not appear to be steady velocity.

In the photo below, these 9" dia 1/2" thick PVC discs were cut one after the other using identical tooling and programming. Only the upper disc has waves on sections of the arc where X and Y are both at top speed. Tool is a 1/4" Amana O-flute running two .250" DOC passes, climb cut with .007" chip load at 300 IPM. Chamfer was cut first.



To recap the machine specs:
Centroid Acorn controller
Clearpath NEMA 34 SDSK servos running 800 steps/rev
Timing belt reduction to ball screw

[skrubol]

Does the period of the waves roughly match one turn of a lead screw? I'd guess one of your screws is slightly bent causing it to be harder to turn for part of the rotation, and the servo can't quite keep up in that half of the rotation, but on the easier half, it catches up. How much following error are the drives configured to allow?

[Shawn_M]

Your Acorn needs to have a bare minimum setting for "steps per revolution" of 1600. For your Acorn/Clearpath combo I'd set them both to 3200. I have mine both set to 3200. Change the motors steps per rev in the MSP software and then set Acorn to match. Your chatter is a combination or hold down, climb cutting and speeds and feeds.

Shawn

[kmagyoyo]

Still unsure what caused the wavy cut. Chalking it up to a workholding issue. Steps per inch were increased to 6400 on both controller and drives, will decrease to 3200 if I see a need.

Which leads me to my latest modifications: improving the workholding.

I've already added a pad for mounting a milling vise. Gave up about 11" in the X axis but for small parts it has been great.

Sorry about the sideways pics. Tried rotating but no luck.



Next up: swapping the pod-and-rail system for a good old fashioned vacuum table with spoilboard. The vacuum pods were great for any rigid sheet goods but just didn't have the versatility for most of the parts I wanted to make.

Heavy duty aluminum sliding door track that was leftover at work used to space the plenum board off the frame.



Found a 1" phenolic board (also leftovers at work...I love my job!) and routed 0.250" grooves for vacuum distribution. 0.375" dia EPDM cord will seal off sections of the table. Planning to reuse the existing 1 HP rotary vane pump. Table has 3 zones in case the vacuum can't hold the entire 30 x 49" table. Maybe a bigger or second pump later. 3/4" MDF spoilboard will go on top.