Re: [CAD_CAM_EDM_DRO] Stepper performance

> You will only get 70 V from that arrangement. The factor is 1.414, minus
> a bit for diode drop.

Actually what I meant was I could set a tap on the transformer to give
25 vdc, 50 vdc, 75 vdc, or 100 vdc (the actual steps are I think
around 18 vac). The 75 VDC tap strikes me as uncomfortably close to
the limit of the Gecko's, although I do not expect much in the way of
deceleration 'generator' effects.

> > To ease the friction loads I'm probably also going to add
> > needle-roller thrust bearings to the leadscrew mount, and hanging a
> > cheap ballscrew on the back of the bed is within possibility -
> > especially as it would save wear on the leadscrew.
>
> The roller bearings are most likely insignificant compared to the
> friction of an Acme screw. Anyway, it is DEFINITELY insignificant
> compared to the cutting loads, unless your leadscrew is REALLY
> stiff!

Considering the cutting loads increase the friction on the thrust
bearings (right now quickly faced cast iron pulley on cast iron
leadscrew bracket... ugh) I'm not sure I think they can be ignored. I
think overall the friction dominates - especially during a rapid.
That's part of why I am giving serious consideration to a ballscrew
that would mount in blocks that clamp to the rear V-way. Any idea if
I could leave it mounted all the time and backdrive it (with timing
belt removed) when operating the lathe manually? That plus an encoder
would get me a DRO... Otherwise I'll have to unbolt the nut bracket
from the apron.

And then of course there is the question of how long an end-supported
length of 5/8" ballscrew material is acceptable, vs going to 1" for
slightly over twice the material cost.

Chris