[sploo]

Hi Sploo - How did the mod work out? Peter

Hi Peter.

Slowly getting there. There was an issue with the machining of one of the pulleys I bought so that had to do a round trip back to the supplier, then one of my servo drives packed up (doing a round trip back to the US).

I have now sourced the servo motor size I wanted, and I'm using a 50:1 worm gearbox with huge amounts of backlash (so 50:1 from the motor, and 3:1 from the gearbox to the 4th axis spindle = 150:1 total). Having tried a few "air cuts" there's a lot of "slapping" due to the gearbox backlash, and that seems to be upsetting the servo drive. However, torque under load seems pretty good.

I have a used 100:1 harmonic drive on the way, which (unless trash) should get rid of the backlash issue, and I'll make another judgement regarding the servo drive then.

I'm using a 60mm idler on the outside of the belt to get more tooth engagement on the small pulley, and with moderate belt tension it all seems pretty good. The current shonky prototype looks like this (but it will get better!):

Attachment 428278

[sploo]

Fwiw..
Even with HTD-8 profiles, about 3x and HTD-5, and 30 mm wide belts,
the results are not good for 4th axis apps.

Positioning, yes.
Angular holding, no.
With 10.000 count ac industrial 220V servos, 1:3 belts, 10 Nm cont, 30 Nm peak, 90 Nm at spindle.

With the absence of data to tell me what the forces would be from pushing an Nmm diameter bit with a Dmm depth of cut through wood at Xmm/s it's difficult to know what level of torque would be sufficient for my application. I've seen a few comments indicating that 27Nm is good for a rotary axis, but that lacked data on what was being cut.

My motor is rated to 0.27Nm, and at 300:1 reduction (100:1 gearbox, plus 3:1 pulley), should in theory result in ~81Nm of torque at the spindle.