Thursday, February 25, 2010


The Balls Return

Well, guess what? Supplies of suitable belt in New Zealand have completely failed to materialise. This comes as no great surprise to me, but must typify the situation in developing parts of the world. So, I am going to do a beaded belt (aka ball-chain or bath-chain) version of Mendel, using no fancy belts at all. The only problem is that the X & Y gears need to be very small to have enough resolution.

Well, the improved stepper drivers we're using have a slightly higher resolution than the old ones - not as high as the 16 micro-steps or more claimed by the chip specs, but useful. Also my printing skills have improved. This means that it may be possible to match a slightly larger chain with a slightly larger printed drive gear and better 0.1mm accuracy.

If that fails, it's time to break out the frickin' big "laser" ...

To the workshop!

Vik :v)

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My mendel will also use a ball chain due to lack of available belts.

I obtained 3.6mm ball chain for a couple of dollars per meter. I measured the pitch at 4.77mm, and the minimum "gear" diameter as about 15.2mm (10 ball circumference) but better off with 12 ball circumference.

The gears I think will just be a cylinder with 3.6mm holes drilled into the outside at regular intervals to a depth of 2mm or so. I plan to make my gear too big, then shave it down until the ball chain fits snugly.

Joining the ends of the chain for the Z axis will be interesting. I've considered using standard joiners, but they won't work with gears as small as we need. We may have to open up the end balls, put in a bit of wire then re-close them.
There is an easier way to join the ends. If you grind the two end balls in half perpendicular to the axis of the chain, you can solder the flats together. the end of the following page has an illustrated description of the process:

Vik :v)
I don't suppose you asked RS to order large quantities to sustain the NZ region as you are working with Tim anyways to have a local distributor of Mendel bits?

As for making ball chain, I used Vik's method, instead I used a Dremel to open the ball(s).
Hi Vik,
If you are not getting the microstep resolution that the chip claims, i.e. x16, it probably means the component values are not correct for the motor or the current is set too high, or too low.
My biggest issue with the ball chain (i put together a ponoko lasercut darwin) is that over time/use it stretches and the pitch changes. i've still use it on my z-axis, with modification, but i couldn't use it on my x and y. well i guess i could, but i would have to replace it often as it started to skip teeth.
So Vik are the stl files available?
@grogyan - the chain is a standard type stocked at Mitre 10.

For STL files you could probably use a derivation the Ponoko gear set ( I've not done one specifically for Mendel yet, but I intend to over the weekend.

Vik :v)
@hhhealthy, yes the chain does stretch initially. But once the little internal burrs are worn away it's quite stable. It's certainly stable over the period of time needed to print several large parts.

Vik :v)
I've not had a chance yet , but you should try

for pulleys
Yes, the thingiverse thing looks nice. Hope I get a chance on the weekend!

Vik :v)
So you haven't "harrassed" any of the distributors of belts to keep stock of the belts for a New Zealand based source of RepRaps?

I'll be watching in any case to see how you get on.
Tim from has been doing the legwork. I've been round before. Basically, T2 and T5 belt are special order from Germany. Nobody wants to carry the stock. If I have to go special order, I might as well cut my own gears and use what's available locally, right? Support Kiwi Made and all.

Vik :v)
#8 wire all the way :D

Its strange though, when I looked on the RS New Zealand site a couple months ago, they did have stock.

As I myself will eventually make a Mendel once my RepStrap is done (been fun working on it), and I have already ball chain that I got from Bunnings/Mitre 10, so I for one am eager to get a hold of the STL's for the ball chain drive sprockets.
RS May well have stock in Oz or the UK. But I really don't want to expect everyone to have an RS account and pay RS prices. I certainly don't want to pay RS prices!

Ball-chain on the other hand is obtainable from just about anywhere. Including the blinds in reception. Hmmm.....

Vik :v)
did anybody consider using bike chains? cheap standard and available everywhere.
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