Sunday, March 14, 2010


Tiny ball-chain gears

I have finally managed to print tiny little ball-chain gears that work with 3.3mm and 3.5mm diameter ball-chain and still fit on the NEMA17's 5mm output shaft. The trick is to print the gears in two pieces.

As you can see in the photograph, I print two 4mm thick sections of gear and put them on the shaft with an M5 washer sandwiched in between. Make sure the teeth are lined up on both gears. This gives a channel to guide the ball-chain down the centre of the gear, and grips the sides of the balls adequately. As the gears age, it will also stop the balls grinding their way too far through the PLA, though I must admit that my experience with ball-chain Z axis gears suggests this will not be a major issue.

The gears themselves are designed to be "spiky", but the vaguearities of the printing and rendering process lop the spikes off and leave enough by accident to produce a functioning gear! SCAD and STL files are here:

As the gears are stuck on the shaft of the NEMA17, and the original Mendel Y Motor Bracket is thicker than the length of the NEMA17 drive shaft, a new motor bracket is needed. Also, the ball chain cannot take tight corners well, so a 608 bearing is mounted on the frame cross-member to act as a pulley. The same arrangement is fitted to the other side of the frame making the Y Idler Bracket obsolete. There are knock-on effects on the bed design and X Carriage which I'm still working around.

Vik :v)

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Cool, Vik! :-D

You have done great work on ball chains but what happens if they change the spec of the ball chain in the future and make your work useless? The part can still be a ball chain and not work on your design. I appreciate that the cost of timing belt is too high in New Zealand. I just feel you are trying to solve the wrong problem.

I feel this is a commercial problem i.e. T2.5 belt is too expensive. Rather than a technical one.

Anyway I am trying to buy a bulk load of T2.5 from china. The deal hasn’t happened yet but if it does go through would you be interested in 5M of T2.5 as a donation for all your hard work on the reprap project?

I have put an advert in the reprap form my user name is Stephen George,39400

Just leave me a note if you are interested.


Stephen George

Thank you for your kind and generous offer. It is heart-warming to see such support. Please, do donate this belt to some enthusiastic potential reprap owners in my stead. I can afford belt - I can buy ESky Helicopter Belt from DealExtreme in bulk. The problem is that I cannot print gears for T2 or T2.5 belt. Sure, I can get them lasercut, but I'm actually trying to fix the problem for people worldwide. People who can't get drive belt or lasercut parts for love nor money, possibly people lacking either.

Don't worry about the ball chain size changing - there are a number of standard sizes, and enough demand to ensure security of supply. It is a simple matter to rescale the gears to fit different sizes of chain. Indeed, there is some flexibility in the design of these spaced gears that allows a variety of chain sizes to be used with the same gears!

Vik :v)
Vik: which belts from DX are compatible with mendel? Or are you printing custom parts for them?
You have to make your own gears for the DealExtreme belt. I used sku.15586 which will do X & Y with 3 packs. For Z I used 4.5mm ball chain.
VIk, what method have you used to make your Z axis into a loop. I've tried using the standard coupling, as well as using wire soldered onto the balls but couldn't work out the method. Is there a trick to it?
@letsburn00 Why yes, there is a trick :) File the balls on the ends half-way down, tin the flat surfaces, and solder them together. This works best with brass chain. The process and handy clamps are discussed here:
Thanks for that Vik, you've saved me a load of trouble and madness.
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