Re: [CAD_CAM_EDM_DRO] Re: PIC Based DRO

jguenthe wrote:

> So given the cost difference between rotary encoders and linear
> encoders and
> the desire to have DRO functionality on a small lathe or mill in a
> home shop
> (at a cost that is not multiple times the cost of the lathe or mill).
> Then
> could we not achieve reasonable accuracy with rotary encoders mounted
> such
> that they are driven by the axis that we wish to watch. The drive
> could be
> by timing belt, cable, rack and pinion gearing or friction. I know,
> there
> are drawbacks here also but I would be willing to live with them in
> order to
> have a reasonable accurate DRO without the expense of glass linear
> encoders.
> Let's face it, the logic behind putting an $1800.00 + DRO with linear
> scales
> on a $500.00 mill or lathe is difficult to comprehend at best.
>
> Since the least accurate method of attaching a DRO to a small mill or
> lathe
> is using rotary encoders on the lead screws, the least cost method
> appears
> to be rotary encoders driven directly by the movement of the table /
> saddle
> / cross slide / head we want to measure.

This may not be completely true. If you replace the acme leadscrews
with anti-backlash
ballscrews, a shaft encoder driven by the ballscrews can be quite
accurate. Most
commercial retrofits use this, and many low to medium-cost CNC machines
(Bridgeport
E-Z Trak and a host of clones) use this technique. Small to medium size
ballscrews
with anti-backlash nuts appear quite often on eBay for very affordable
prices.
I'm still looking for a TINY one to put on the cross slide of a 12"
lathe, but I've got
the 43" one for carriage travel. I think it was a Bridgeport BOSS
series X axis
screw, and it looks to be in superior condition.

Jon