Rotating Ballnut - design ideas

[Jonathan]

I have at last started making the rotating ballnut assembly. I've started with one stepper motor mount, it's 100x245mm:





The reason for having such a long cutout for the motor is to allow me to use any reasonable size pulleys without changing the belt, which will obviously be difficult. I CNC milled all except the bearing bore which was bored on the lathe. I had to remove the gap bed on the lathe to do it - the join was painted over so it looks like this might be the first time it was removed! The six holes closest to the bearing will be used to push a ring against the outer ring of the bearing to preload it. The 4 bigger holes are for posts which link this to the other bearing mount.

I'll make some more bits when I've found my caliper :whistling:

[Jonathan]

I've now made all 4 bearing/stepper mounts and one shaft. I will machine the pulley (30 tooth) directly on to the shaft.

When I machined the shaft on the lathe I got only small pieces of swarf, not the long stringy stuff you normally get - see picture below of drilling it for what I mean. It was almost like cast aluminium...but it's not. Must be a strange grade?

Lots of photos, hopefully pretty self explanatory:



















It got 0.01mm bigger after drilling...so now 34.99mm which fits the bearing nicely:







(Hopefully nobody without broadband is trying to view this!)

[Jonathan]

Video here:

http://www.youtube.com/watch?v=mSNFD...=youtube_gdata

Whipping caused it to stall at 15m/min. That be less of a problem when everything is mounted properly.

Some pictures:





At 8m/min I couldn't stall it by pushing on the gantry. Above that I
can, but only by bracing myself against the wall and pushing with both
hands...otherwise it just pushed me along the floor.

After the video I tried adjusting the acceleration. It went up to 3m/s^2 quite happily.