worm gears, 4th axis

[senor J.]

Hi everybody heres my worm gear question... I have read that a worm gear setup is prone to a certain amount of backlash. could this be corrected (good enough) In mach2 with the backlash compensation feature? <---main question. I'm interested in a continous fourth axis set up for carving wood ( indexing you say? bah, humbug ) and of course backlash would not be your friend with that (although I think a small amount of backlash could be Ok as long as the gear reduction was high enough say 50 to 1 or 100 to 1) what are everyones thoughts on this. would there be a better system for an "A" axis reduction. Im gonna make a 4th axis even if it comes to blows

[HuFlungDung]

Just take the trouble to mount your worm in an eccentric bearing housing. This lets you either disengage the worm completely from the gear whilst dialing in your workpiece, or, allows you to snug the worm as tightly into the gear as it can possibly fit. You might even run it a while with some lapping compound on the gear teeth to take off any high spots.

Software backlash compensation is not likely to be satisfactory: your milling cutter will cause the work to jitter even while the rotary axis has no motion command to execute. Backlash comp only works for motion reversals.

[senor J.]

please pardon my noobishness huflungdung but what exactly is an eccentric bearing housing unit/design
thanks in advance

[HuFlungDung]

You know what the CN tower looks like? Well, that looks nothing like an eccentric bearing housing.

Seriously though, you would understand that the worm shaft needs to be cradled in a bearing. Now, instead of just mounting that bearing solidly in a hole in the main gearbox, you mount it inside of another sleeve. However, the hole in this sleeve is bored off-center relative to the outside of the sleeve. This is where the eccentricity comes from. This is how you can create a variable gear mesh distance.

[imserv]

Originally Posted by HuFlungDung You might even run it a while with some lapping compound on the gear teeth to take off any high spots.

Don't do this with brass worms, as the lapping grit will become embedded in the brass and cause premature wear of the pinion.

Fred Smith - IMService
http://www.cadcamcadcam.com

[mocnc]

I too want to build a 4th axis, I can get a worm gear set up with a 40 to 1 ratio. I was wondering if anyone knew of a free 4th axis drawing? I want it to have one end with a chuck to hold a round stock, with the tail end to be kinda like a tail stock on a lathe.

[senor J.]

for my 4th axis I think Im just going to use the headstock off a jet mini lathe. hey mocnc where could I get one of those 40 to 1 wormgear boxes?

[mocnc]

Sorry senor J I didn't mean to imply that it was a wormgear box.....I am able to get a worm gear with a regular gear. I am looking for plans for a box that I can use the worm gear. I want to be able to turn pool cues, so thats why I need a 4 or 3 jaw head stock and a tail stock. Any ideas??

[turmite]

Hey guys I designed my 4th axis and had a friend with a machine shop build it. I did not use a worm gear nor any typed of gearhead reduction. BIG mistake. While this setup works fine for soft material, (I forgot to mention this is made specifically for wood) it is not good enough for harder type woods or other materials. I designed the gearbox and used a stepper motor with timing gears and belts for my reduction. I would not go this route again.

Mike

[cbcnc]

I've had an idea cooking for a while now of building a 4th axis using the arbor shaft from a spin indexer. The inexpensive spindexers I have in mind have a ready made 5c collet. 5c collets go up to about 1 1/8" or there are lathe chucks that have a 5c backplate.
It would need a couple of large pillow blocks or the equivelent and a worm gear fitted to it.
5-C Spin Index
I would do it but my life is a mess right now as I am moving to another state. I got to pack up the CNC machine for a while.
I will try to stay in touch with The CNCZone.

Chris

[senor J.]

what about a 6 or 7 inch rotary table converted to operate with a stepper? Anyone have any experience with those? I wonder what the backlash would be like?

[ger21]

Mike, what kind of problems are you having with your rotary axis? I was considering building one with a stepper and belt reduction drive myself, and would like to know the downside(s)? Thanks