Re: Flexible Couplers on Retrofit?

On my Bridgeport, the original NC converter used rigid couplings
from the NEMA 42 steppers to the screw shafts. The way they added
flexability was overdrill the four motor mounting bolt holes. They
inserted a piece of neoprene tubing. A thin nylon sleeve was
inserted into the tubing (either as a buffer or just as a spacer -
I'm not sure). Then the bolts slip fit through the nylon sleeve.
If the motor is missaligned, there is a little flex in the mounts.
I've never heard of anyone else doing this (but then there's a lot
of uniqueness about this machine's design besides this).

Anyone have an opinion on this scheme?

Jeff


--- In CAD_CAM_EDM_DRO@yahoogroups.com, Steven Ciciora
<sciciora@A...> wrote:

> I assume you know about:

http://groups.yahoo.com/group/hf47158toCNC/ ?

>
> You could try to do a solid coupler, but by the fact that you

asked, I

> would guess you won't be happy with the results. You _really_

need to get

> it perfectly aligned. The fact that commercial machines use flex

couplers

> tells us something.
>
> Something quick and dirty, and on par with the accuracy of the

machine is

> to use a flexible hose between the motor and lead screw, and hose

clamps on

> both ends. Later if you feel it is a limiting factor, you can

upgrade it.

>
> Please read the above newsgroup. All sorts of good suggestions on

how to

> clean up your machine, eliminate friction, back lash, etc. Your

motors

> will be a bit small to do fast rapids (don't expect 20ipm), but

the price

> was right, and the xylotex driver will support bigger motors in

the future.

>
> - Steven Ciciora
>
> At 02:26 PM 1/8/2004 -0500, you wrote:
> >Todd, you need flexible couplers unless you want to break

something - or

> >unless you can (lathe) turn and mount parts with extremely high
> >concentricity. Things will bind if they're out of alignment.
> >
> >If you're strapped for cash, why not consider using a slightly

flexible

> >material like a high durometer polyurethane rod and turn them out

of

> >that? You should still be able to drill and install set screws

if you

> >make the OD large, relative to your shafts. Quite honestly $20 a

pop

> >sounds pretty good to me! My 3 helical zero-backlash couplers

for a

> >Bridgeport sized mill set me back over a hundred each!
> >
> >Cheers, Peter
> >
> >Todd Meidinger wrote:
> >
> > >I am in the process of putting together a CNC retrofit Mill

using a

> > >Xylotex controller and NEMA 23 116 oz./in steppers from Jeff. I

am

> > >putting this on the $279 s axis machine that Central

makes/sells. I

> > >know for this price it can't be the best in the world but I am

not

> > >looking for that right now. I figure I am going to have just

over

> > >$500 into the entire setup when I am done. Get what yo pay for I
> > >guess.
> > >
> > >Will I need flexible couplers from the steppers to the screw? I

was

> > >looking at flex couplers and they are about $20 a pop for the

ones I

> > >
> > >
> > >
> >
> >
> >
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