Making oldham couplings

As part of my mf-70 cnc mill conversion (upcoming post), I needed to couple the nema23 motors to the axis leadscrews. I decided to make some oldham couplings. They’re quite simple, two metal discs that are clamped to the axes, with a groove in each. A piece of acrylic between can slide, so no translational forces can be transferred.

32mm steel bar
10mm acrylic sheet

M6 tap
various drills/endmills
m6 bolts

Start by cutting the steel into two short lengths (I used about 12mm, doesn’t matter too much). Drill a hole all the way through lengthwise, to match the shaft diameters (I think I used 7mm and 5mm). Next, drill a 5MM hole through the side, about 3/4 of the way through. Tap this to M6, and insert a holding bolt. Next mill off about 8mm of each side, to about 3mm deep. The steel parts are done now, so sand any rough edges.

Next, mill the acrylic center. I used cambam to produce the gcode. You have to flip the disk to mill the other side, try to get the other cut at exactly 90 degrees. You can even just use polymorph (low temperature melting plastic), just heat it, push the metal disks in at 90 degrees and let set.

Just push the pieces together into a stack, and the axes will run smoothly (might want to add a drop of oil). The advantage of this type of coupling is you don’t need to align the shafts much at all, which makes a bodged solution like you see in the picture possible.

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