Harmonic drive - info needed

[erasma]

Hi all,

Wanting to make an electronic dividing head - already have the code and working prototype. I was wanting to use a harmonic drive but understand very little about them. I know how they work and cost a small fortune.

I want to mount a 160 - 200mm lathe chuck

Are there any other types of gear reduction units with 0 backlash? If all else fails I will just buy an 8" dividing head and put a stepper on it.

Thanks in advance

 

[Hood]

I have used planetary gearboxes to good effect with some of my CNC stuff. The turret on my lathe used one, the Y axis motors (master/slave) on my plasma use them. You can get them with quite large reductions and very little backlash. They however are not cheap but still probably cheaper than Harmonic drives.

 

[Hood]

These are the ones on my Plasma.

 

[erasma]

I have used planetary gearboxes to good effect with some of my CNC stuff. The turret on my lathe used one, the Y axis motors (master/slave) on my plasma use them. You can get them with quite large reductions and very little backlash. They however are not cheap but still probably cheaper than Harmonic drives.

Thanks Hood great idea I just want to add gear cutting to my mill don't want full 4th Axis it will cost more then what I paid for the machine. I have one of those cheap Chinese 4th axis I used with my CO2 Laser table I used to own. Used that for the testing of the code.

When I am done will do a build video

 

[Dr.Al]

Hi all,

Wanting to make an electronic dividing head - already have the code and working prototype. I was wanting to use a harmonic drive but understand very little about them. I know how they work and cost a small fortune.

I want to mount a 160 - 200mm lathe chuck

Are there any other types of gear reduction units with 0 backlash? If all else fails I will just buy an 8" dividing head and put a stepper on it.

Thanks in advance

Out of interest, why do you need 0 backlash for a dividing head? Dividing normally means rotate to a specific angle and then work on the work-piece (as opposed to a rotary table where you're often milling while the table is turning). If you're rotating to a specific angle, you can lock the dividing head after rotating (and your electronics can ensure that the head always stops after moving in a particular direction: if running in the other direction you overshoot and then come back).

To answer your actual question, I would imagine a harmonic drive would be very difficult to make due to the requirement for flexibility of middle gear. That's probably why they cost a lot. The simplest (that I know about) zero backlash gearbox would be a non-zero backlash gearbox with a relatively powerful spring to force the gear engagement to be at one end of the backlash range. Alternatively make/use a gearbox where the backlash can be adjusted and get it close enough to zero to suit the application.

 

[erasma]

Out of interest, why do you need 0 backlash for a dividing head? Dividing normally means rotate to a specific angle and then work on the work-piece (as opposed to a rotary table where you're often milling while the table is turning). If you're rotating to a specific angle, you can lock the dividing head after rotating (and your electronics can ensure that the head always stops after moving in a particular direction: if running in the other direction you overshoot and then come back).

To answer your actual question, I would imagine a harmonic drive would be very difficult to make due to the requirement for flexibility of middle gear. That's probably why they cost a lot. The simplest (that I know about) zero backlash gearbox would be a non-zero backlash gearbox with a relatively powerful spring to force the gear engagement to be at one end of the backlash range. Alternatively make/use a gearbox where the backlash can be adjusted and get it close enough to zero to suit the application.

To be honest it's about being lazy would like to rotate and hold the part with the motor and not have to lock the dividing head. And I want something that won't cost another kidney

 

[Hood]

It might be worth looking on eBay for a Nikken rotary table, they are always on there, usually for quite a bit, £5K or so but occasionally you get them popping up for a lot less, almost pulled the plug on one a while back that was just over £1K but then gave myself a slap as I don't do the kind of work that really needs one.