Re: [CAD_CAM_EDM_DRO] Digest Number 2823

At 16:27 03/01/2003 +0000, you wrote:

>I'd also like to see a picture as I can't visualize it yet.
>
>Garry
>
> > Hoyt,
> > I'd really like to see a photo of that arrangement, if if you have one
> > available.
> >
> > Marv Frankel
> > Los Angeles
> >
> >> > which I made in one op for good concentricity. The motors just
>overhung
> > the
> > > screw ends, right out in space. The motors were drag-linked to the
> machine
> > > frame using a stay from flange to the anchor point. The stay can be
> > > slightly flexie from side to side as long as it doesn't stretch or shrink
> > > when torque is applied. This is the most rigid arrangement possible for
> > > transmitting torque, and the motor and screw bearings have no trouble
> > > supporting the motor weight. Try it, it's clean, simple, quick and very
> > > effective.

OK - try this:

If you were to simply couple the motor shaft to the leadscrew with a plain
sleeve with set screws at each end, and not bother to bolt the motor mount
flange to anything, then the motor would be supported on the end of the
leadscrew just by the sleeve. However, when you stepped the motor, the body
of the motor would be as likely to spin as the leadscrew, as there is
nothing stopping the motor body from rotating, so this wouldn't get you
very far. So, to stop the motor spinning, you bolt a stay between the motor
mounting flange and a suitable anchor point on the machine. The stay needs
to be at right angles to the motor shaft, and tangential to the motor body,
in order to do the best job of stopping the motor spinning. Even if the
coupling sleeve is not perfectly concentric, there is enough "give" in this
system to prevent the lack of concentricity from ruining the motor bearings
(i.e., the motor will be free to "wobble" slightly as it rotates).

In other words, it is just another example of a coupling that is tolerant
of misalignment, and (assuming that the stay is neither compressible nor
stretchable) one that doesn't contribute any significant additional backlash.

As Hoyt says, it can work just fine. However, unless you take steps to
protect the motors with some kind of cage or shield, I wouldn't like to
contemplate the consequences (to the motor shaft, coupling, or leadscrew)
of accidentally dropping something massive on one of the motors. So
personally, it is not a method that I would choose to use - what you gain
in simplicity of construction of the coupling you lose in the need to
protect it from harm.


Regards,
Tony