axminster mills

[richb77]

I've been working on my chassis/platform.

So far any comments? Any glaring issues (bear in mind its not complete)

I am getting confused over the ball screws ends and fixtures. Any suggestions to what goes where?

Cheers

[irving2008]

rich,

Depending on a number of factors, leadscrews (ball or otherwise) need to be supported in one of the following configurations:

- none: Only suitable for very short screws and low power environments where endfloat/backlash isnt an issue - the stepper motor sets the endfloat as its rigidly coupled to the leadscrew. the stepper experiences reflected axial and radial loading and so its specs determine the maximum work load that can be tolerated.

- far end: use for longer screws (length >20 * dia) where whip at speed is an issue. Usually the bearing just provide radial support. Endfloat still set by the stepper with a rigid coupling, although its possible to use back-to-back angular contact bearings to provide both radial and axial support/control. Stepper will still experience radial loading reflected from the workload though.

- near end: rarely used on its own, but provides a means of decoupling the stepper so the bearing block controls the end float and therefore removes axial and radial loading from the stepper.

- both ends: the best but most expensive option. The far end controls whip, axial and radial loads and uses back to back angular contact bearings to control endfloat. the near end is a sliding fit on the leadscrew and controls radial loading only allowing a sliding coupling to the stepper. Used for maximum loading environments and large screws where temperature-related expansion may be an issue.

Most hobby CNC use none, far end or both; near end rarely seen (bet I'm going to be proved wrong now)

Note: backlash in the workpiece movement is a combination of endfloat in the leadscrew mounting and axial backlash in the nut (movement from one face of thread to other on directional change) and radial backlash in the stepper to leadscrew coupling.

[irving2008]

I've been working on my chassis/platform.

So far any comments? Any glaring issues (bear in mind its not complete)

I am getting confused over the ball screws ends and fixtures. Any suggestions to what goes where?

Cheers

Rich, looks good so far... but suggest you start a new thread in the DIY Machine Building forum