RepRap: Blog

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: http://www.thingiverse.com/thing:2009

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)

Labels: ball chain, gear, Mendel, reprap, small

The Z drive was tested by connecting it to Phoenix and using the Arduino electronics on there (you can see the Y stepper controller on Phoenix's frame lower far left). The Y and X axes were tested by engaging my electric screwdriver in the adjustment slot at the rear of the motors, and whizzing it back & forth. Not a full-on electrical test, but the mechanics should do the job.

I have also properly fitted the NEMA17 motor to the X axis on the now fully-assembled Phoenix, and that checks out okay - and I printed an ABS cat. All in all a very busy weekend.

Vik :v)

Labels: ball chain, reprap, shiny, stepper

The Ponoko-inspired lasercut RepRap is now hopefully in its final iteration. I've built most bits at least twice, and I have tried to remain compatible with Ian Adkins' lasercut RepRap at BitsFromBytes as well as the original Darwin. I've taken the best from both in true Open Source manner, so we have:

• No routing needed. No hand-tooling of any of the plastic bits, in fact (if I've got it all right).
• The extruder is now swappable and is compatible with the Darwin swap design (if I've got the measurements right on this one too).
• I have put 2 extruder mechanisms on the sheets so you have something to change.
• The Z motor can be replaced by a GM3-type gear motor and rotary encoder. I've made the Z motor bracket so it can use opto sensors and a variety of other gear motors too.
• There is now a capstan that can be fitted to the top of one of the Z driver rods. This can be moved by the head, allowing the carriage to move the Z platform up and down at <0.1mm>
• The DIY bearing races have been put in. You can still use the skate
  bearings if preferred.
• Ball-chain is used in place of all belts. The larger 4.5mm chain (either of 2 variants) is used for the Z axis, X and Y can use either 3.3 or 3.5mm ball chain.
• X & Y axes can be fitted with NEMA17 steppers.
  
• The Y opto flag can be placed on either side of the X carriage so we remain compatible with Ian's design.
• The X carriage may be removed without disassembling the carefully-aligned frame.
• The corner bracket parts that Ian reported his clients broke a lot are now cut from 8mm acrylic instead of 4.5mm - and I've included a spare.
  

Just submitting them for the Final Cut (thank you Pink Floyd).

Vik :v)

Labels: ball chain, lasercut, ponoko, reprap

This movie shows an X axis using ball-chain instead of drive belt. I built it on a design based heavily on Ian Adkins' lasercut RepRap, which I decided to attempt to simplify a little bit. As you can see, it appears to work. I'll do another run and tidy up the X axis - I just subverted part of Ian's design that looked handy.

One fly in the ointment is that I can't yet print the neat little lasercut toothed gears on my RepRap, though the new Arduino boards should help.

You can't see it here, but I had to elongate the holes for mounting the X motor into Ian's bracket. I'll do a quick redesign so that it can take the motor Ian is using and the ones I've got - plus anything between.

Vik :v)

Labels: axis, ball chain, lasercut, reprap

I've put a Z axis together using some ball-chain and 4 gears printed on my Darwin in PLA - I needed to fit a new motor anyway for testing with Arduino code. It appears that "4.5mm ball-chain" is a standard of some kind. It's a bit bigger than that normally used for keychains and biro bondage at the bank, but is I believe widely used by makers of window blinds and vents.

I have put the experimental ball-chain gear AoI files in the SVN on Sourceforge. You may need to re-scale the rim using AoI depending on how thick a line your RepRap/RepStrap extrudes. With mine the chain fits well up to about 110 degrees around, then gets too tight. Fortunately I only need 90 degrees, so that's OK.

Turning the motor by hand makes the platform go smoothly up and down. Now to build some drivers for it.

Vik :v)

Labels: ball, ball chain, chain, 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