Re: [CAD_CAM_EDM_DRO] Re: Driving a Bridgeport Knee

The knee due to its mass and precision of the acme screw is far more accurate than the X and Y will ever be. And there is zero backlash. The Z mechanism is twice the resolution of X and Y i.e. 1 rev equals .100 opposed to the .200 per rev of X and Y. A ballscrew is not needed. Backlash in the bevel gears can be removed by shimming or compensate for it in the software. The major drawback to driving the knee is slower acceleration due to the weight and the need for a larger servo to power it. The quill wouldnt be any more accurate. Probably not as accurate.

Ron


Polaraligned <polaraligned@...> wrote:


Well, I don't think they get it very much below .001". You will
have backlash to contend with. But the bigger question is how
accurate are those gears anyway? People get ground screws over
rolled ones- yet settle for sloppy bevel gears? I just like the
idea of driving the leadscrew directly and saving the bevel gears
for manual operation of the machine. I may even get a ballscrew
for the Z axis, but I have not really decided if this is just a waste.
As it is all commercial conversions (that I have seen) drive the quill
because it is more accurate. To each his own...

Scott

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnc_4_me" wrote:
>
> Well for what it is worth, the people i talked to about driving with
> bevel gears said to shim them and take out the backlash.
>
> Wally
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
>
wrote:
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnc_4_me"
> wrote:
> > >
> > > I was wondering if this was feasable also, if my machine wasn't
> > > buried under a ton of stuff i would investigate further. While i
> do
> > > not have any answers i do like hearing your ideas or anyone elses
> on
> > > the subject. One thing i am affraid of with usaual methode of
> > > driving the knee, is breaking the bevel gear with to much
> > > horsepower...
> > >
> > > Wally
> > >
> >
> >
> > I really am resistant to driving through the bevel gears as they
> > are very sloppy. I also like to be able to move all axis by hand
> > should the need arise or for the "quickie" machine job. My machine
> > is currently completely apart for a rebuild, and I can see no reason
> > why this won't work. Just can't bring myself to drive through
> > the damn bevel gears....
> >
> > Scott
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
> > >
wrote:
> > > >
> > > > I am thinking about driving the knee with a pulley just below
> the
> > > > bearing on the Z-axis leadscrew. I would machine the leadscrew
> down
> > > > to accept the pulley. The motor would be mounted on the side
> of the
> > > > knee, and to get the timing belt out I would cut a rectangular
> slot
> > > in
> > > > the side of the knee.
> > > >
> > > > Advantages:
> > > > Motor is out of the way.
> > > > I can still use the handle to move the knee via the bevel gears.
> > > > (can't leave the handle permanantly attached!)
> > > >
> > > > Disadvantages:
> > > > Lose about 2 inches off the bottom of the knee travel
> > > > Changing belts would be a real pain in the you know what.
> > > > Permanantly alter the knee with hole (which does not bother me)
> > > >
> > > >
> > > > I think the motor will have no problem with clearances.
> > > > Does this sound good? or am I missing something.
> > > >
> > > > Scott





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