Beaded chain drive gears

So I am in the process of building a repstrap using mostly stuff you can find at your local hardware store. I am also a college student, so anywhere I can save cash is a major plus. I have decided to try out a beaded chain in place of a $30 belt from rrrf (the 12 foot chain was $4). It looks like it will work great as you can pry open on of the individual balls to splice a chain into together, but I am having one major problem; gears. I can not for the life of me find any suitable item to use as a drive gear for my z axis studding posts. Can anyone throw out some ideas to easily make a gear that will grip these beaded chains?

For reference the chain consists of 1/8" balls seperated by a tiny connecting post. They are the same things used to open and close blinds, for a pull chain on some high hanging lights, and even in bath tubs to pull the stopper out.

Someone please save me as this is the major thing keeping my progress on hold! Thanks in advance!

I'd be tempted to find or cut a plastic circle, then heat up the chain in a flame and wrap it around the disc. With luck this should melt little holes around the edge. You could also set up a jig to drill tiny holes around the edge of said disc to achieve the same effect. Both are fiddly though. You could always try and salvage sprockets from discarded blinds if you knew somewhere that would let you dig through rubbish. If all elses fails, bike chain
is a cheap, easy solution (~£8 for sprockets and chain for z axis)e

... look at the atached photos here: [forums.reprap.org]

Maybe this could help ...

Viktor

I've been planning to use bike chain in place of drive belt for a good while now. It's stronger, easier to work with, easier to find sprockets for and has virtually no backlash if you have good tension. Probably a bit more expensive than beaded chain tho.

Annirak: trying not to hijack the thread, but feel free to pm me if you want some advice on bike chain - i've been using it for a while and have found some neat ways to tension things. Cost me £20 for sprockets and chain for three axis, not sure how that compares.

For beaded chain though, if you could find a cog with the right spacing, you could loop the chain round a few times to increase sprocket-chain friction.

Annirak and James - I've been thinking of bike chain too for my next RepRap; I had a lot of trouble sourcing, and then using the 2.5 mm toothed belt and chain for my existing Darwin. Bike chain is pretty much available anywhere.

The two main concerns I had was the X and Y resolution - I've got 200 step Kelling steppers, and even with half stepping, I don't want to go much below my current resolution of 8 steps/mm. I couldn't find bike sprockets much smaller than 11 tooth, which works out to 0.35 mm/step, or 2.8 steps/mm. I suppose half stepping a 400 step motor would be close enough - 5.6 steps/mm.

Also, there are some positional errors due to the size of the teeth at that range, but I don't know if it's a problem.

James, do you have any photos or details about your setup - especially the X and Y shaft to sprocket connections?

Wade

Photos are at [picasaweb.google.com]#

For the shaft to sprocket connections, for the Z axis I'm just tightening nuts each side, because the torque is really low. The white discs stop the chain falling off if the tension is too low, only a problem for the vertical axis. The X and y, I've drilled a hole in the rod and some holes in the sprocket, and just shoved a whole load of polymorph around the edges. I'm remaking the Y-axis (the one that has to move the X-axis) to include skate bearings, and have found if you weld a large metal washer to the rod, you can just bolt through to the sprocket, which looks like a much tougher solution. This really depends on whether you can weld. Another thing I tried successfully was carefully drilling a hole through the entire sprocket and the rod, putting a metal rod in as a pin, then patching up the holes each end with hdpe. By the way, I get about 4 steps/mm with 10 step sprockets, but I find its backlash and wobble in my reprap that's the limiting factor. I'd be suprised and impressed if you could make the axis so well that the extra resolution really helped. If anyone's going for bike chain, I'd really recommend the entry level shimano jockey wheels at £3 a pair, there's no movement between the sprocket and chain like there is on another one I have.

Ok, so I am bound and determined to get some kind of gear system for my z axis working this weekend. I tried out melting the beaded chain into a plastic disc and it worked fairly well although the chain slipped off the thin disc on one of my prototypes so I'm going to rig up a little jig to help with that. The plan is to attempt to make 4 gears using this method of heating up the beaded chain with a heat gun and then applying it to the plastic disc. If this fails I already talked to some bike repair shops and I'm gonna follow james' footsteps and go pick up 4 jockey wheels and a chain or two. If I can get the beaded chain working I could have all my pulleys and gears for under $10! I'll keep you guys updated with the progress!

Would you mind posting some pictures of the sprocketty things you made? Also, for the z axis I found it much, much easier to use 8 jockey wheels and 4 loops of chain (see my photos) because otherwise only a couple of teeth mesh properly, and getting the tensioning is a real pain. It's an added cost, but I wasted so much time with one loop. I assume this would also apply to ballchain, because you have the redundancy of needing two belts to slip before you get problems.

I posted some info on my project blog about what I tried as far as getting the beaded chain to work. Here's the link

[cpwebste.blogspot.com]

I ended up going with bike chain and derailleur gears inspired by James' project. It also helped that I got all the bike chain and gears for free

Edited 1 time(s). Last edit at 03/16/2009 05:13PM by cpwebste.

Why not just take a deep-grooved pulley, pack it with epoxy putty, and take an imprint of the chain?