Re: [CAD_CAM_EDM_DRO] Re: Bridgeport ballscrew retrofit kits and prices

cnc_4_me wrote:

>>So what do you think is the best bet?
>>
>>Scott
>>
>>
>Same question i have been asking myself...
>
>For myself there are 2 clear choices, Rockford ballscrew with rolled
>ballscrew with .002 or .003" error and made with custom ends...This
>would give you a very nice installation...I could have one end
>machined for a handwheel for manual operation and the other end
>machined for bearing support, motor drive pully and encoder...
>
>

I wouldn't bother with rolled ballscrews, especially since the ground
ones are so close in price. The ones I mentioned from Machine Tools
Direct are ground, and cost $600. The maximum lead error on my screws
was 0.000466 for the long one, and 0.000233 for the short one. (yes,
that's just under 1/2 of a thousandth, and 1/4 of a thoudsandth)

You don't need custom ends to use a handwheel on one side. The standard
ends have a long shoulder on which a handle OR a pulley can be mounted.
I'm trying to figure out how to get both on one end (I would like both X
handles, and a Y handle), but that probably won't happen. There is a
bearing journal on both sides, and it's needed on both sides. You
should have dual angular contact bearings on one side (the motor side),
and one double-row angular contact bearing on the other side. The
single bearing on the "far" end doesn't fill the space inside the
bearing bracket, to allow for thermal expansion without bending the
screw. The thread on the end of the ballscrew is used on both ends.
I'm still designing, but I think this will be the stack-up on my machine:
nut | washer | spacer | pulley | spacer | bearing pair | ballscrew shoulder
On the other side, just replace the pulley with a handwheel, and the
bearing pair with a single wide bearing, and you're all set.
These screws are just a little long for my 9x42 table - though they
might not be if I had official Bridgeport bearing brackets. (My machine
had a power feed on X, which isn't compatible with the ballscrew, so I
bought a clone mill bearing bracket off ebay)

The only thing I had to do was to bore out the pulleys to 0.625. I had
a hard time finding small pulleys that already had a wide bore. I did
find one company that can customize the pulleys, but they wanted $75
minimum for the job - it didn't seem worth it for 4 pulleys.

>Second choise would be ground ballscrew from hiwin...For a couple of
>hundred dollars more than rolled screw you get a .0005" error
>screw... And the bragging rights that go with it...But you have to
>live with the standard ends...
>
>

See above - standard ends are fine. The ground screw is still way less
accurate than the control resolution - my machine will have 40000 steps
per inch - the screw will be 20 counts of error. (though this is
correctable with EMC and others)

>What i would like to know is how everyone else has made do with the
>standard ballscrew ends...How did you work out the opposed bearing
>mounts...You need a thread on the shaft between the pully and
>bearings to tighten up the bearing assembly, but standard screws do
>not have this thread...They only have the end of shaft threaded to
>hold handle on...
>
>

You don't need any extra threads. You just make spacers so that the end
nut holds everything.

>Wally
>
>

- Steve