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

Mine uses a special hub that is keyed and set-screwed on the end of the ballscrew. On this hub is a taper that the timing pulley with a standard tapered bore is drawn on to with bolts through a flange on the same hub. Then there is a shoulder where the handwheel/dial resides and beyond that, threads for the standard Bridgeport serrated ring nut to lock the handwheel. The shaft then has room for a handcrank which I didnt use and were substituted with a sleeve spacer then the nut on the very end secures everything tightly. Keys don't chuck. If they do they need to be replaced. Or the keyway in the shaft or the sheave is damaged or was never machined properly to begin with. In this arrangement the hub cannot be secured until the preload on the bearings has been achieved because it needs to be able to slide so the nut on the end of the screw can pre-load the whole assembly. Then the setscrew is secured. The Z axis knee uses the same hub however it is threaded inside to screw on the shaft
and is then roll-pinned to secure. I'll answer this before it's asked: I don't have any drawings or dims of that hub. I'm going to disassemble one and get the dims eventually, just haven't had time.

Ron

cnc_4_me <cnc4me@...> wrote:

> You don't need any extra threads. You just make spacers so that

the end

> nut holds everything.
> >
> - Steve

Well, that is the problem... The end nut has to hold everything...It
has to tighten up the bearing pair thru the pulley...This means that
the pulley now cannot be pinned and probally not even
taperlocked...This leaves only setscrewing the pulley to the shaft
after the nut is tightened...For the kind of torque we are talking
about i am not sure setscrewing will hold up...


Also using the standard end does not address how to put a encoder on
the end of the ballscrew or if you want to put a handle on after the
pulley like you would like to do...This is why a custom end is so
desirable.

Wally




--- In CAD_CAM_EDM_DRO@yahoogroups.com, Stephen Wille Padnos
wrote:

> 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

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