Rotating Ballnut - design ideas

[m_c]

Personally, if space wasn't an issue, I'd take your top design, replace one of the normal bearings with a pair of angular contact bearings, and put a lock nut onto the shaft to adjust play out the bearings. That way endfloat is adjustable, the normal bearing provides extra support for the belt tension, and it allows for smaller pulleys.

I got my bearing and locknut from www.simplybearings.co.uk (for locknuts, click bearings on the front page then scroll down).

As for thread cutting, sharp tool (I bought a HSS insert one from greenwood tools, but I see chronos/glanze have them listed now), slow speed, and remember don't disengage the leadscrew feed once you've made the first cut when doing metric! Reverse the lathe back to the start.

[Jonathan]

Personally, if space wasn't an issue, I'd take your top design, replace one of the normal bearings with a pair of angular contact bearings, and put a lock nut onto the shaft to adjust play out the bearings. That way endfloat is adjustable, the normal bearing provides extra support for the belt tension, and it allows for smaller pulleys.

By a pair of angular contact bearings are you referring to something like 2 of 7207, or a single 3207? Either way that's getting a bit expensive, plus cost of threading tool though I would use that for other things. I don't want to compromise on the design due to cost, but there are limits. Another thing with that design is since the bearing supports are separate pieces I've got to get the centre heights very accurate, and mount them on a good flat surface for the bearings to be concentric. Bear in mind I'm probably going to be machining this on my mini lathe, which isn't great.

How much end float can I expect in a 5207 bearing if I went for the other design? These are the cheapest I can find:

http://cgi.ebay.co.uk/5208-ZZ-DOUBLE...item53e20e2fe6

This is the other design modified for no thread cutting:



Thanks for the link to the lock nuts, I'll get them if necessary.

Decisions decisions...