Re: My ballscrew / bearing block design.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "afogassa" <afogassa@y...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, fj62@s... wrote:
> >
> > A couple more questions...
> >
> > I picked medium preload because light went from 0 to X lbs of
> preload. I
> > wasn't sure that would guarantee no backlash. Will a light preload
> > generate a no backlash setup?
> >
> > I'm sure I learned about shrink fits at some point in my machine
> design
> > class but that was 15 year ago...If I shrink fit a piece on the
> ballscrew
> > and then machine it will it "loose its grip and slip" (obscure
> reference
> > to 'you ain't got a hold on me' - AC/DC)?
> >
> > Is there a technique for getting the required surface finish for the
> > seals? I was also wondering about the hardness required for them.
> I was
> > contemplating just putting speedi-sleeves on these portions of the
> shaft.
> >
> > Thanks,
> > M
>
> machine it size to size than heat it up to red and put it in place
> very quick, don't press it or it will deform and expand taking the
> shape of the shaft and do the AC/DC thing.
> I've sent a ballscrew to a machine shop to do the same thing,asked
> to machine it size to size, they sad no...it must need to have
> interference or it will slip later on.
> Well, they made it smaller heat it up than press it in, guess what?
> it expanded took the shaft shape(diameter) and came out losse on the
> first try. Asked to do it again, size to size this time they agree
> with me and it still working.
> Eaving If you don't have backlash you still have elastic
> deformation on the nut and bearings.If it is for a large load than
> you should go for a bigger bearing.
>
> Fogassa.
>

I am not experianced with such applications, but I had thought that
generally speaking, that steel will expand about 0.001" for each
degree F ? That would mean one could machine it undersized about
0.001", heat it oil smoking hot, and it should slip on with no
resistance.

Chilling the shaft and heating the bearing often makes a slip on
assembly where otherwise it would be a press fit.

Am I close on this ?

Also, Les mentioned to pin the shaft. I looked at pins and drills and
realized that if you have a small shaft, say, 1/2 inch, you cannot put
in a 1/4" pin. you remove too much of the shaft.

of course a 1/8" pin is small and can shear.

Is there any rule of thumb or formula ?

And, then (mini rant) pins can be really expensive. a couple $$ each
or you have to buy 50 for $5.00 to $10.00 bux.


Dave