Hi Andrew

Quote Originally Posted by Andrew Wilding View Post
If you would like some ideas or a rotating nut you can look at my mill build log.
That did get my attention - I was going to post but hadn't finished thinking!

Quote Originally Posted by Andrew Wilding View Post
I have just uploaded some pictures showing the assembly of the rotating nut. I used 2 AC bearings and preloaded with a nut. I bought a double AC bearing from EBAY but was not happy with the amount of clearance between the balls and the race so I resorted to 2 seperate AC bearings.
It is interesting what you say about the bearings. I was indeed intending to get them from eBay, two of these to be precise:

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

I'm hoping if I press fit the bearing onto the shaft that should expand the inner ring, and tighten the bearing up nicely. Similarly with the outer ring, except if I follow m_c's excellent suggestion of boring it slightly oversize and clamping it then that's not going to happen. Did you get the single row angular contact bearings on eBay, and what size are they?

The problem I've got is that I don't have the constant force applied to my bearings due to gravity, unlike on the various milling machines that have a rotating nut.

I'm really not at all sure what to do now. I've said already two single row angular contact bearings is a lot of money...and yet it looks like that is certainly the best way to do it. Having said that there's someone on CNC zone who has done it with two standard deep groove bearings.

If I could get away with a 16mm. 10mm pitch, ballscrew then I would save so much on the screw, that I could easily afford the cheaper smaller bearings. However I would prefer to have the 25mm screw just in case it fails completely and I have to spin the screw.