Re: Z axis Peter

--- In CAD_CAM_EDM_DRO@y..., Peter <prenolds@s...> wrote:
> Where are folks posting newsgroup pics these days? I tried to
upload a
> couple but the yahoogroups system says the storage area is full for
this
> group... I'm sure this has been disussed, but the group is so
chatty -
> I can't find a reference to this topic in 9000+ messages I have
> accumulated. (Plus I got side tracked reading messages I had
previously
> skipped...)
>
> Thanks, Cheers, Peter
>
>
>
> mjf462001 wrote:
>
> > Peter,
> > I am glad to hear that. I would love to see the pics.
> >
> > Matthew
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., Peter <prenolds@s...> wrote:
> >
> >>I drive the knee on my CNC mill (BP Clone) and can report good
> >>
> > results
> >
> >>although it took a lot of fiddling to get things set up
correctly.
> >>
> > I
> >
> >>posted questions on alt.machines.cnc and received many of the same
> >>helpful suggestions described earlier - i.e. gas springs and/or
> >>emergency brake to stop the knee's weight backdriving the ball
> >>
> > nut. I
> >
> >>really appreciate having 16" of vertical travel under computer
> >>
> > control.
> >
> >>My machine started life with an acme screw for Z but when I drove
> >>
> > the
> >
> >>knee up and down at my stepper's top speed (yielding 24 IPM on Z
> >>
> > axis)I
> >
> >>got horrible gib vibrations which I couldn't really eliminate
with
> >>
> > gib
> >
> >>adjustment. (It would just return at different speed.) And I
still
> >>
> > had
> >
> >>a backlash problem if I ran at full speed - so I installed a ball
> >>
> > screw
> >
> >>& nut to see if that would solve the problem.
> >>
> >>I also purchased two $14 gas springs (75lb each) from McMaster
Carr
> >>
> > (p/n
> >
> >>9416K403 - mounting fittings are extra)and installed them at the
> >>
> > front
> >
> >>of the knee. I'd probably suggest a pair of slightly stronger
gas
> >>springs (say 125lb) but a combined 150lb of gas spring stops any
> >>movement of the knee - even with the stepper motor removed.
> >>
> > (Though I
> >
> >>wouldn't stick my hand under it without wood blocks to support
> >>
> > it...)
> >
> >>I can post a couple of pics tomorrow if anyone is interested.
> >>
> >>Cheers, Peter
> >>
> >>p.s. I've had an excellent experience dealing with Rockford Ball
> >>
> > Screw.
> >
> >> They are very well organised.
> >>
> >>p.p.s. I've also been dealing with Flashcut for a couple of years
> >>
> > and
> >
> >>love their little controllers (I have 2 cnc'd machines) and PC
> >>
> > software
> >
> >>- they just don't break!
> >>
> >>
> >>
> >>Jon Elson wrote:
> >>
> >> > mjf462001 wrote:
> >> >
> >> >
> >> >>--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> >> >>
> >> >>>mjf462001 wrote:
> >> >>>
> >> >>>
> >> >>>>Hugh,
> >> >>>>
> >> >>>>Thank you for the link. I am still not sure weather
> >> >>>>I should drive the quill or the knee. When I get around to
> >>
> > making
> >
> >> >>>>
> >> >>up
> >> >>
> >> >>>>my mind I will at least have some pics to reference to.
> >> >>>>
> >> >>>If you use the machine to drill holes, or if you have some
slack
> >> >>>in the vertical ways for the knee, like mine, then I think you
> >> >>>
> >> >>should
> >> >>
> >> >>>go with the quill. My knee sags out, toward the operator,
when
> >>
> > you
> >
> >> >>>lower it. I can't tighten the gib because there is a worn
spot
> >>
> > on
> >
> >> >>>
> >> >>the
> >> >>
> >> >>>ways.
> >> >>>
> >> >>>Jon
> >> >>>
> >> >>John
> >> >>I saw a pic of Dan's setup. The way he drives the knee, I
would
> >>
> > say
> >
> >> >>it looks pretty rigid!
> >> >>
> >> >>Without having to do the math I wonder how much torque a guy
> >>
> > needs
> >
> >> >>so he wouldn't have to gear down (slow down) the z axis drive.
> >> >>The mill is new and without any wear.
> >> >>
> >> >
> >> > I'm not saying it isn't rigid, just that you are moving a LOT
of
> >>
> > iron to
> >
> >> > poke
> >> > a 10 gram drill bit into a workpiece. On a Bridgeport Series-
I
> >>
> > size
> >
> >> > machine,
> >> > you are talking about moving about 1000 Lbs of iron up and
down
> >>
> > every
> >
> >> > time. It certainly will work, but it may cause much more
rapid
> >>
> > wear
> >
> >>on the
> >> > knee slide. You should note this is the most highly stressed
> >>
> > way on the
> >
> >> > machine, as the weight is completely off to one side of the
> >>
> > slide.
> >
> >>Worse,
> >> > it puts the load on the dovetail, rather than on the flat!
> >> >
> >> > I think it is unreasonable to try to CNC the knee without a
> >>
> > ballscrew
> >
> >> > retrofit. And, after a ballscrew, you'd need a safety brake
to
> >>
> > prevent
> >
> >> > the table from dropping when you go to E-stop, or lose power.
A
> >> > reliable counterbalance, either weights and pulleys or gas
> >>
> > springs,
> >
> >> > would help out, but then you'd definitely need a ballscrew, or
> >>
> > the
> >
> >> > backlash would show up, without the knee weight.
> >> >
> >> > Jon
> >> >
> >> >
> >> > Addresses:
> >> > FAQ: http://www.ktmarketing.com/faq.html
> >> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> >> >
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> >> > URL to this page: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
> >> > bill,
> >> > List Manager
> >> >
> >> >
> >> >
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> >> >
> >> >
> >> >
> >> >
> >>
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
> > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> >
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> > bill,
> > List Manager
> >
> >
> >
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> >
> >
> >
> >