Re: [CAD_CAM_EDM_DRO] Some basic questions...

Peter Moreton wrote:

>Hi,
>
>I'm starting down the CNC route, and would like to ask some questions
>regarding my plans, before I make too many mistakes! If I list out the
>salient points below, perhaps lister's could comment upon my thinking...
>
>1. I have acquired 3 large stepper motors, they are 'Oriental Motor
>VEXTA' devices, model number 3056-9412, rated at 2.9V / 3.3A and are 1.8
>deg/step. Size wise, they have 70mm mounting centres and are 63mm deep.
>A bit small , I know, but I'm not looking for speed. Probably about 300
>oz/inch?. Question, The steppers are marked as '2-phase'. Could
>anyone explain to me the significance of this?
>
>

Most steppers are "2 phase". That means they have currents in 2
windings that
are 90 degrees out of phase. This is needed to tell the motor which
direction
to turn. (Oriental Motor also makes 5-phase motors, that perform
better, but
need their own brand of special drivers to power them.

>2. I have a Bridgeport series-1 mill, in good condition. Do I really
>*need* to buy zero backlash leadscrews, or will the CNC controller
>software be able to calibrate out the backlash in the existing
>leadscrews?.
>

No, the software can not correct for a gap between motor motion and table
movement. If you will only do positioning work, ie. drilling holes as
certain
locations, then the software can do this. But, consider making a round hole
by orbiting the table (circular interpolation). This requires that each
axis
comes to a complete stop and then reverses very smoothly. With that
backlash,
the motors would have to move at very high speed to get to the other side of
the backlash, and then instantly slow down to nearly zero speed to pick up
the desired movement at that point. It seems doable, but it just
doesn't work.

>3. On the topic of the Bridgeport, does anyone have a view on how best
>to make the mechanical connection from the stepper to the X,Y,Z axis. I
>am expecting to use a toothed belt system, and wonder if there are any
>commercial kits of parts to simplify the attachment of the steppers?
>

I think thare are kits, but they may be expensive. Anilam probably has
such stuff. The ball screw makers probably also have part or all of this.

Jon