• Design the 3d printed parts,
• Print them,
• Assemble everything.

I broke out my favourite CAD tool: OpenSCAD and wrote a bunch of code. I found an openscad library on Thingiverse that can generate GT2 pulleys. My belts aren't quite GT2, but they're close enough.

I decided on 8mm shafts because I have a large number of 608 bearings, and they have an 8mm ID. I sized the pulleys to get the required spacing between the stepper shafts and the first axis shaft, around 27mm OD, which works out to a tooth count of 44. The stepper pulleys have 20 teeth. I made the holes for the stepper motor mounts slotted to allow for tensioning the belts. I did the same for arm 1.

It was a bit of a challenge to design the bottom bearing holder. I can't use the bolts holding the stepper together to mount the bottom plate, since removing bolts from a stepper is generally a bad idea. It's important that the bearing be in the correct place as that determines the belt tension. I ended up making a piece that fits between my steppers with my belt tension. Not ideal, but perfect is the enemy of done.

bottom\_bearing\_holder

This fits between the steppers to hold the bottom bearing in place. The steppers are clamped together by a cable tie.

top\_holder

The steppers mount to this, retaining a bearing in the centre.

shaft\_1\_drive\_pulley

This is pinned to shaft 1 and driven by a stepper via a belt.

shaft\_2\_drive\_pulley

This holds two bearings and sits next on the shaft above the shaft 1 drive pulley. It is driven by the other stepper and drives the shaft 2 driven pulley.

arm1\_split\_base and arm1\_split\_end

The smaller hole is pinned to shaft 1. Two bearings are retained in the big end to hold shaft 2.

shaft\_2\_driven\_pulley

Pinned to shaft 2 underneath arm 1. Slightly taller than the shaft 1 drive pulley to allow for a wider belt.

arm2

Pinned to shaft 2 above arm 1.

If I were ordering these parts for a build I would order at least 20% extra, especially the washers. They're cheap

• Write the software