a dual drive solution

[WhiteTiger]

I've noticed a lot of posts in threads all over these forums voicing questions and concerns about synchronising two drive screws on a single machine axis. Thought I'd post this just to hear reactions.

There's a relatively simple mechanical way to synchronise screws. The pic below illustrates the basic idea.

Obviously the large circles are sprockets, the small ones are idlers which can be adjusted up and down.

By adjusting them you change the total belt/chain length between the drive and driven spocket on that side of the run, and loosen or tighten the position of the other one to keep belt/chain tension. This effectively moves the tooth position of the slave side of the setup. You only need a total adjustment of one tooth if you use common sense in assembly and setup.

An elegant application would be to mount your drive motor dead center at your table end and use two of these arrangements to drive both leadscrews. The advantage is you would eliminate any need for flex couplings. Just mount your drive sprockets on the motor shaft and support the loose end of it with a bearing. It would also cut down on belt/chain whip problems by keeping the free runs short.

If you want a zero/low backlash setup using allthread, use two screws (stacked) on each side of the table and install one of these arrangements on the opposite end from the drive motor. Adjust the sync of this extra arrangement to take up the backlash by opposing the two nuts against each other.

Could be used with belts or bicycle/motorcycle chain, makes no diff. Of course the idea wouldn't be worth spit in tight quarters, but for some of these big routers and plasma tables it would be a natural since the drives tend to ride outboard and there's plenty of room available.

It could be a bit pricey for some, might be a huge economy for others, depending on how much accuracy you design into your application and what sort of screws you use.



Tiger

[project5k]

thats a very interesting approach... i was thinking more along the lines of rotating the sprokets in increments on the secondary shafts, but that could get ugly and might end up being a slipping issue, your setup could very easily be done so that both idlers move on a single plate so that adjustment could be made very accurately with a screw mech... i think i like that a lot

[wcarrothers]

On my rack I'm splitting the 1/2" shaft so I could sync the 2 pinions. I thought about building an indexing plate or degree plate (like they use for timing cams or something) but will start with an extra large shaft coupler. If it slips once I get it synced up the shaft might find itself welded to the coupler But anyway..

Looks like a good idea although I'm not a big fan of the dual shaft method..

b.

[project5k]

i understand... its just that much more mechanics that have to be first built, and then maintained...