RepRap: Blog

I've got the Z axis going on the Mendelssohn design. In the picture here (RepRap is tilted so the bottom faces the camera) you can see the ball-chain drive connected up to the two Z threaded drive bars. The shiny pulley is a 608 bearing with some great big washers either side of it. Side note: If you put M4 nuts on an M4 bolt, the exterior diameter of the nut is 8mm and it fits perfectly as the axle for a 608 bearing.

The 4.5mm beaded chain gears are the same as used on the RepRap Child/Phoenix machine that built Mendelssohn. Printing a gear with a grub screw and captive nut was too hard, so I devised a clamp-on gear that fastens onto the NEMA17 shaft using an ordinary hose clamp. The tensioning pulley makes installation of the Z drive chain much easier on this prototype than the Darwin.


If you want to see it in operation, here's a video of it. I've stuck a mole grip on the X axis to add a bit of weight, and in case you can't see the ammeter it's running at 250mA. It ran like this for 20 mins, cycling up and down without overheating the motor or the EasyDriveV3 stepper driver. The OLPC is just powering the Arduino board - though some magic is needed to stop the OLPC powering down its USB ports at inconvenient moments. Once that's sorted I'll be able to power a RepRap using Ralith's minimalist RepRap command line utilities.

Vik :v)

PS I've since made the Y axis move back & forth using helicopter belt but need to print new bits to do it properly. People are asleep now, so I'll leave that for tomorrow.

Labels: Mendel, Mendelssohn, reprap, z axis

I've been away for much of the weekend, and crook yesterday so I've not had much time to work on RepRap. Next weekend is a 2 day chainsaw course, so I'm working on Wedgewood whenever I can. Here you can see the beginnings of the Z axis mounting scheme, using the PLA bearing holders I printed earlier to anchor the Z axis studding (one on the top that's hidden from view, and one on the bottom). I've removed the deposition bed so you can see the bearing holder.

The two nuts in the middle of the studding will be held captive by the X axis mountings. Given the weight of the head and X axis, it is unlikely that I'll need any anti-backlashing but it can be done if need be.

For the moment I'll use 2 tin can stepper motors to drive the Z axis, which neatly eliminates the need for a chain or driveshaft to link the two halves and gives me more torque where it is needed most. I've only got 2 of the Jaycar YM2751 steppers as the depot ran out of stock, so we'll see if they get stock before I can finish the Z axis.

The object of the exercise? To see if the Z axis on a Wedge design is going to need guide rails or not.

Vik :v)

Labels: wedgewood, z axis