Re: [CAD_CAM_EDM_DRO] rigid coupling, stepper to leadscrew

At 21:42 11/07/2006, you wrote:

>Again on the subject of the KT150 table conversion:
>
>http://www.indoor.flyer.co.uk/kt150conversion.htm
>
>I was wondering exactly how bad an idea coupling the leadscrews (2mm
>pitch 10mm diameter ACME) directly to the screws would be?
>
>The screws are unsupported at the other end.

Its not a great idea unless the setup is such that the two shafts are (and
continue to be) co-axial, which is unlikely to be the case if the screw is
unsupported at the other end.

>Obviously the motors would take end loads

DO NOT assume that steppers are capable of handling end loads. All of the
ones I have dealt with are not - their shafts are generally biased to the
front by a spring washer at the back of the motor. If the end load is
comparable to the spring force, the motor shaft/rotor will simply get
pushed 1-2mm back into the motor housing.

>but they have bigger
>bearings than I would use for thrust bearings even on the small ones I
>have, they are also dirt cheap. Endplay is had to detect but then I'm
>only pulling and pushing on them by hand.

You have to fit thrust bearings to the leadscrews - there isn't a short cut
here.

>Alteratively what is the shortest and thinnest method of adding a
>bearing to the end of a screw? I'm considering two thrust bearings
>and a needle roller to make the machining super simple (just one hole
>for the needle roller).

That would work fine - as would a pair of back to back ball races.

Regards,
Tony