Threadless Ballscrew Nut (5 degree tilt for 16mm shaft)

thingiverse

This is another design for threadless ballscrew nut. The nut relies on friction from the shaft and bearings to grip and move by turning the nut or the shaft. You'll need: M6 x 47mm screws, three of them; one M6 x 20mm screw; six M6 x 11mm spacers that are 1mm thick; three M6 nuts (or six for extra security); one M6 square nut; and six 626 bearings. To print two identical pieces and attach them back-to-back, insert the square nut in the slot for the adjustment screw, then secure the bearings and tension adjustment screw with screws. Spacers can be made by stacking washers on a screw with a nut, attaching it to a drill, and grinding down the outer diameter. If you don't have a grinder, use sandpaper instead. The spacers should fit around the outer bearing ring to prevent them from rubbing against the printed ballscrew nut. With some support under the bearing, you can tighten the screws more securely, which will keep the nuts in place better. The two screw holes for the fixed bearings are quite tight, so just tap them when you insert the bearings. As a bonus, you can loosen the adjustment screws to slide the nut around the shaft like a quick release on a lathe. The tested nut I printed was able to sustain my full body weight (around 55kg), and it didn't slip even when I applied nearly my full weight onto it. The nut has a 5-degree tilt angle on a 16mm shaft, according to calculations, it should travel about 4.397mm per revolution. With my digital caliper, it traveled around 4.66mm per revolution. I think the error is due to: The play in the bearing; The resolution of the printing (I'm using 0.2mm layer height on a Flashforge Creator Pro); and the cheap digital caliper I bought for like USD$15. Here's the math behind nut movement and revolutions: Let the tilt angle of the ball bearing be θ. Let the diameter of the shaft be D. The circumference of the shaft is C = D x π. The movement of the nut after a full revolution is H. Given the angle θ and shaft diameter D, the movement of the nut per revolution is: H = tan(θ) x D x π. For example: An 8mm shaft with a 20-degree ball bearing angle will travel: H = tan(20 degree) x 8mm * π ~= 0.364 x 8mm x 3.1415 ~= 9.147mm after a full revolution. An 8mm shaft with a 10-degree ball bearing angle will travel: H = tan(10 degree) x 8mm * π ~= 0.176 x 8mm x 3.1415 ~= 4.4315mm after a full revolution. A 16mm shaft with a 10-degree ball bearing angle will travel: H = tan(10 degree) x 16mm x π ~= 0.176 x 16mm x 3.1415 ~= 8.8631mm after a full revolution. Given the shaft diameter D and desired travel distance H, the tilt angle of the ball bearing should be: ϴ = tan^-1(H / (D x π)). For example, you want the nut to travel 4mm after a full revolution with a 16mm shaft. Go for: ϴ = tan^-1(4 / (16 x π)) ~= tan^-1(0.00795) ~= 4.55 degree