Re: [CAD_CAM_EDM_DRO] Re: CNC coil winder traverse

Graham Stabler wrote:

>Looking at the common lead errors I didn't think the accuracy would
>be up to it without direct feedback. The backlash also has to be <
>0.01mm and I have not seen many ballscrews with really low lead and
>backlash errors.
>
>

Oh, they most certainly exist, but you can't buy them from McMaster-Carr.
Ground machine tool positioning screws can be had with extremely low
error, and backlash as close to zero as you can measure. I have zero
backlash, high precision ground screws on my milling machine. I cannot
find any deviation in the screws with a stack of gage blocks and a
tenth-reading dial test indicator, over a distance of one foot. (I ran
out of gage blocks, so I couldn't go any farther than that.)
You might look on eBay for used or surplus machine tool screws.

Oh, for low-load positioning, you can get anti-backlash screws and
sliding nuts from BS&A with any degree of precision you need. I
wanted just one screw for a laser photoplotter, and they hand selected
a screw for me with extremely low error over the length I needed (2 feet).
It came with a chart showing the deviation at hundreds of points along
the screw. I used a cheap Saginaw rolled screw and single nut to prove
out the machine, and then got the BS&A screw when I found the error
and backlash were a problem.

Jon