Denford Software & Machines

Trouble with worm is how do you preload it to take out the backlash but with minimal friction?

One route could be to use a recirculating ball arrangement like the old steering mechanisms - effectively a ball screw where the "nut" is replaced with a worm wheel. I'm not sure if these can be bought, looks hard to make with the required precision in the home workshop.

The design in MEW for a 4th axis used quite a low reduction belt drive but the maker had to re-cut the large toothed pulley to get rid of backlash which doesn't bode well for that approach. To get good precision you are also dependent on microstepping which isn't very accurate. The harmonic gear looks like a nice solution to me.

I've been in touch with the guy in China who supplied Mike's drive - "Tiamofaye" - and he is quoting me for a drive supplied without chuck or stepper motor - I'll see what that price is like and also if several people ordered we could get a better price. Maybe he could supply just the harmonic gear? It would be nice to be able to use collets.

John.

You would have to design in some adjustment to get the gears meshing just nice on assembly and use high precision gears from HPC or similar.

I asked him about just the harmonic drive but he didnt reply. Dont forget to ask for the ratio you want, I went for 100:1

Mike

JohnHaine wrote:Trouble with worm is how do you preload it to take out the backlash but with minimal friction?

One route could be to use a recirculating ball arrangement like the old steering mechanisms - effectively a ball screw where the "nut" is replaced with a worm wheel. I'm not sure if these can be bought, looks hard to make with the required precision in the home workshop.

The design in MEW for a 4th axis used quite a low reduction belt drive but the maker had to re-cut the large toothed pulley to get rid of backlash which doesn't bode well for that approach. To get good precision you are also dependent on microstepping which isn't very accurate. The harmonic gear looks like a nice solution to me.

I've been in touch with the guy in China who supplied Mike's drive - "Tiamofaye" - and he is quoting me for a drive supplied without chuck or stepper motor - I'll see what that price is like and also if several people ordered we could get a better price. Maybe he could supply just the harmonic gear? It would be nice to be able to use collets.

John.

I may be interested in a group buy if it gets that far. I would be looking for one to use on a TRIAC.

I`m not sure there would be enough interest to get a decent discount. If you decide to go for the complete unit then you would have to do some trials to see exactly what it is capable of doing. A big-ish job on a machine like a TRIAC may be a bit too much for it. They are sold for cnc router use really.

Mike