Machining the ends of ballscrews & ball screw size

[Zumba]

In order to machine the ends of a long ballscrew, e.g. 5 feet long, I take it the only way to do it is to use a lathe that has a headstock with a large enough bore to allow the ball screw to go completely through it.

What's the largest diameter stock that a typical 1236 or 1340 lathe can hold in this fashion?

On a similar note, is there a general formula or rull of thumb for choosing ball screw diameter as a function of length and weight of the component being driven (e.g. gantry)? Also, how is an extra-long ball screw supported, as on the X-axis of a 10' gantry router? Thanks.

[kdoney]

Most of these lathes (import) have 1 7/16 spindle hole or so they say. You can find 13 and 14" lathes with over 2" spindle holes though. It seems to me that it is cheaper to get them machined by the company you are buying the screws from, except if you have a friend.

[NC Cams]

Yeah, especially if the screws are prehardened.

It is one thing if you screw something up when machining it and another thing entirely if a friend does - usually ends it.

However, if the vendor does it, he usually eats it - welcome to the fun, exciting and profitable (???) world of prototype machining.

[Ken_Shea]

welcome to the fun, exciting and profitable (???) world of prototype machining.

[ViperTX]

Well, I'm sure we all have encountered this....."How long should the ballscrew be?" and unless you have designed a prototype well you're not exactly sure....so people like myself buy the unmachined stock....we machine one end and if we mess it up....we cut it off and do it again and then machine the other end.

So, far I haven't messed any ends up....but the opportunity always exists....the biggest problem I've encountered was with threading the end...as most everyone knows 'when you use a die' the 2 or 3 threads that are against a shoulder are not complete threads....so, I turned a spacer that went over the threads and pressed against the shoulder of the ballscrew, so I could preload it.

Problem solved. "What problem!"