[mactec54]

Well this conversation has spiraled down a rabbit hole more times than I could count while reading through the 7 pages

Quinn, you are correct about the DMM drive limitation, I faced the same issue when setting up my servo spindle although I didn't run into a need for ultra fine positioning like you do. Totally agree with your concerns.Unfortunately, your only solution would be to select a drive/servo with a high encoder resolution AND a higher input frequency. I am using Allen Bradley Ultra 3000 drives with AB bulletin MPL motors. Something like 2 million counts per rev with a 4MHz input frequency.

You are also correct about belt stretch. I would be willing to bet that your machining on a part held still by the belt and servo would have pretty poor rigidity even with the wide belt. The problem is that DMM servos (and most servos) don't respond well to high frequency loads like would be encountered during machining (tuning issues) and a belt will never be perfectly rigid. If you were to tension the belt high enough to get acceptable stiffness, you would likely run into problems with side loading of the shafts and issues at higher speeds. You might want to consider a disc brake for clamping the workpiece when indexing.

Last comment on the belt (found through painful experience) is at higher speeds, timing belts suck air into the teeth of the pulley and make a loud pop when exiting. When this happens a few hundred times a second, the belt noise can get pretty crazy. I talked with engineers at SDP-SI and their recommendations were to use a belt with smaller teeth (I changed from a L series to a GT3 series pulley), select a curvilinear tooth profile (GT2, GT3, etc), select a fabric faced belt, and if wider belt widths are required for stiffness or load, use multiple thinner belts in tandem (allowing air to escape between the belts). This coupled with a low belt tension took my spindle from a painful 86dBA to a comfortable 68dBA. This was at 5000rpm.

At the end of the day, tuning the servo to hold acceptable stiffness will most likely contribute 90% of the issue you have with deflection under load compared to the belt.

Don't claim to be an expert on anything here, but my comments come from knowledge gained as an engineer at a major industrial automation company doing servo motor applications (and tuning ).

Lets try to keep everything civil here, it is better for everyone who would want to learn from this conversation in the future.

Fortunately the OP won't have to do much with servo tuning as Dmm have auto tuning and adaptive control, there are only 3 parameters to change so a very simple servo drive to setup

I agree with that the his biggest problem will be making everything rigid enough especially the mechanics for the belt tensioning

Guys you all need to rethink this and what he is doing, Quinn stated he is only going to be machining up to 1" diameter 25mm material, all the tech information is available from Gates, Education on Belt sizing, the belt he has selected a plus 100 Hp belt that will be driven by a 1.8KW motor or 2.4Hp, you can figure this out for yourselves

Yes there is always some stretch and deflection but is all controllable if you design it correctly, correctly tensioned will be the first step all these belts have a cord modulus that you have to work with, and if you know what you are doing you can eliminate most of any stretch problems, the belt drive I posted a photo of has a 1micron resolution