RepRap: Blog

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)

Labels: beaded belt, frickin' big laser, Mendel, reprap

I've bought some "ball chain" or "beaded belt" from the local Mitre 10 hardware store for NZ$6.95 per metre. The balls on it are 4.60mm in diameter and have 1.80mm exposed length bars between them. I have plastic beaded belt of the same dimensions, so this is likely to be some kind of standard. Investigations continue, do clue us in.

I've designed a pulley (shown left) that can be fabricated on a RepRap - and made one. After a mechanical test, Adrian ran 4 off on the Strat. Note: Make one with a rim that lifts off in the future so I can fit the damn belt without resorting to violence.



Here is the video below showing them in operation. Note that the orange pulley under the bed in the lower left corner of the frame is rotating and that the old drive belt is not fitted. The red temporary join is a cable tie and is obviously not going to go smoothly around the corners. The chain is made from chromed brass, by the way.


To join the ends of the loop, I filed down the two terminating balls on the chain into approximate halves (measured with a badly-calibrated Mk I eyechrometer) while holding them in medical clamps. Then I held the clamps in a couple of angled vices so that the halves fitted together properly, finally soldering them together with a 30W soldering iron and highly toxic lead solder (yum). Better ideas welcomed! The joined chain is robust enough to turn the whole Z axis assembly with some enthusiasm. When I build the next RepRap the gears will go in the usual place.

Labels: ball chain, beaded belt, drive, gear, reprap

Here's an idea or 3 I've been kicking around to improve the Darwin design. Maybe they'll have to wait for Mendel but here goes:

1. Y Belt gear to outside

Move the Y belt gear furthest from the Y motor to the other side of the
Y axis bearing. This probably means mounting the Y belt clamps on the X
axis square jig, but avoids filing that long flat - the gear now just
slips on the end.

2. Z motor on top

Move the Z motor to the diametrically opposite corner and take it
outside the build area. We gain another 60mm of build height - or save
700mm of steel rod & studding. Forrest suggests we also use the shaft coming out the front, not the back.

3. Beaded belt for belt drive.

The right toothed belt is hard to source and expensive. We might be able to use the
sort of stuff used for window blinds and securing vicious attack biros in the bank's foyer. Some testing will be needed, as will new methods of splicing the stuff. Here's an industrial supplier: http://www.raymortool.com/Gen_Info.html

Right, enough brainstorm. Back to testing the new extruder temperature code.

Vik :v)

Labels: beaded belt, improvements, reprap