I'm revisiting the concept of dual-loop control with linear scales closed at the servo drive. I found that the Delta ASDA-A2-M drives have this functionality, and while twice the price of the B2 version, aren't outrageously priced considering the potential accuracy. However, I also read on the Haas website that they don't recommend linear scales for 3d surfacing. (
https://www.haascnc.com/productivity...ions/ls-2.html) That's the primary purpose of my machine. Any ideas on why that might be? Is it something to do more with how Haas is implementing linear scales that impairs smooth motion? Or something fundamental to linear scales? Seems like many high-end machines suitable for mold work use them.
I'm a little confused as I thought one of the main differences between the standard VF series and the VM mold series is that the VM's are thermally compensated through linear scales, but digging a little deeper I'm realizing I may have incorrectly assumed that, as linear scales don't seem to be standard on those. Maybe they use other methods of thermal compensation.
The C5 ground TBI ballscrews I have are rated at 18 um/300mm, which is fine for the tolerance I need as the molds will be roughly 300mm in the longest axis, and getting below 25 um in general would be a pretty lofty goal for me and this first DIY machine. Realistically I hope to get it around or under 50 um. But I'm concerned about thermal growth of the screws on relatively long 3d run times. Thoughts appreciated