Re: [CAD_CAM_EDM_DRO] Ball-screws

James Owens wrote:

> Hi All,
>
> Bill and I have, for a few weeks, been looking into the possibility of
>
> fitting Ball-screws to my Bridgeport like machine, him in the States
> and me
> in the Britain.
>
> The machine will be retro-fit with CNC using DC servos.
>
> I know there are those of the opinion that what is being done is a
> waste of
> time and money and that a CNC machine should be bought and mine
> shipped to
> the scrap heap. This is not an option for the simple reason of where
> it is
> and the amount of time it took me to install it. I really don't want
> to do
> it again.
>
> If I fit Ball-screws manufactured in this country the cost is
> something in
> the order of £500 an axis, $750 in your money, and they would be
> metric 25mm
> with a 5mm lead. The dials would all have to be changed.
>
> The travel on the X axis is 29" and the Y is 12". The lead-screw
> fitted at
> the moment is 1" with a lead of 0.200" and 0.035" of backlash in the
> centre
> and almost none at the ends.
>
> Between us we have come up with just two possible companies that have
> answered email and the phone.
>
> 1) McMaster-Carr
>
> 1" dia. 48" ball-screw in the two lengths, 0.004" error/foot and a
> lead of
> 0.250" including Qty. 2 ball-nuts = $166.00.
>
> 2) Rockford
>
> 3/4" dia. 48" ball-screw in the two lengths, 0.003" error/foot and a
> lead of
> 0.200" including Qty. 2 ball-nuts = $423.00.
>
> 1.150" dia. all the rest the same as above = $511.00
>
> All are ex-stock and I believe have 50um repeatability.
>
> Why such a difference in cost? If it is quality does the difference
> add up
> to $257 worth on an elderly machine.

Are both of these anti-backlash ball nuts? Typically, the nuts cost
more than
the screws! These are not very accurate screws, that's for sure.

You should also check with Thompson (the linear bearing people) who
bought
Saginaw steering gear, who made a Bridgeport retrofit kit.

Also, try Ball Screws and Actuators, who make a kit for a number of
machines,
and HiWin, who also have kits. HiWin may have a higher precision kit
that
comes in cheaper than one of the above sets you already priced.

Jon