[marbles]

Hi,

I increasingly use a 4th axis in rotaty carving jobs. For a series of foam carving jobs i've made a lightweight 1 metre long trunnion to hold 200mm thick foam blocks to carve at 45 and 90 degrees degrees. The problem is its not got enough torque to hold itself in place at different indexed degrees when milling material.

I bought 12nm stepper and HSC86 closed loop driver to run a 1:1 HTD belt and pulley. The stepper is standard 12nm 1.8 deg and the closed loop driver can go up to 110vdc and 70ac. Its currently ungeared (Gearing this would have been better granted but time and budget got in the way.) The trunnion bed is about 8kg set back 30cm from the axis rotation.

As a 12nm stepper it should surely be able to hold better than it should. Without the obvious advantage of gearing where should I look first to improve its holding?

Any thought or suggestions how to improve the mechanical, electrical or software setting most appreciated.

[ger21]

12Nm can only hold about 8 lbs 1 ft from the shaft. You have almost double the weight a little bit further away.
Gearing is probably the only option.

[marbles]

Hmm foot for thought. Yes gearing I know would help.

I should have mentioned that I'm currently using a 48v supply, which is not helping matters. I would have thought a 100v supply would do a better job or am I looking at the problem the wrong way?

Not having access to a harmonic drive or low backlash wormgear unit I suppose in terms of gearing I could increase the size of the Htd pulley on the stepper and decrease the pulley size on the shaft, that would assist I would have thought?

[CitizenOfDreams]

If the trunnion is indexed (as opposed to continuously turning), maybe a motor brake would help?

[marbles]

If the trunnion is indexed (as opposed to continuously turning), maybe a motor brake would help?

I have what I call a manual positioner already that has a couple of disks that I lock off with gclaps. Works great with a digital inclinometer to give me the exact angle. I do totally need to add a brake just not quite worked out how to add this electrically or in the code.

[marbles]

Looks like as Gerry said some sort of gearing is the order of the day. I'll start the hunt for a low arcmin right angle planetary unit.

As i'll need it for both index holding and continuous machining what would you suggest as a good gear ratio?