Re: GEM-500PCN bedmill - CNC ready

Ballendo & Smoke,

I think the specs said grade 5 "ball screws" not bearings. I don't
know what that means, is there a system for rating the relative
accuracy of ball screws?

Incidently, I once had to get some precision bearings that were made
in Germany. As I recall the grading system was the opposite of
ours, with the lower numbers meaning higher precision.

Doug

--- In CAD_CAM_EDM_DRO@y..., ballendo@y... wrote:
> Smoke,
>
> Don't electric motors use grade 3? And grade 5 for supporting a
> leadscrew seems ok... Certainly NOT for a spindle, but for the
> leadscrew?
>
> Ballendo (I'd be glad to "test" it)
>
>
> --- In CAD_CAM_EDM_DRO@y..., "Smoke" <gordonr@r...> wrote:
> > Ball bearings are classed as grade 1, 5 7 and 9. These grades
> refer to
> > Bearing tolerances with grade 9 having the most precise
tolerances.
> > Therfore using grade 5 bearings means low tolerance bearings are
> being
> > used...an indication of a low quality machine.
> >
> > Smoke
> >
> >
> >
> > >Jon,
> > >
> > >For this mill as configured with the Fagor control it is slow. I
> > >don't know the price complete with Fagor, but if in 20 quantity
> less
> > >control etc it's $3750 ( I think that's what I read here) then it
> > >must be at least $12K complete in single quantity. For that
price
> I
> > >would expect much better performance, wouldn't you?
> > >
> > >I thought this machine had grade 5 ball screws, whatever that
> means.
> > >So speed limitations of Acme screws are not an issue here.
Also, I
> > >assume it has servos, I can't imagine any machines are still
being
> > >built with factory made controls and running steppers.
> > >
> > >At any rate the specs have errors and are very incomplete which
> makes
> > >me wonder about the builder.
> > >
> > >thanks,
> > >
> > >Doug
> > >
> > >
> > >
> > >--- In CAD_CAM_EDM_DRO@y..., Jon Elson <jmelson@a...> wrote:
> > >> dougrasmussen@c... wrote:
> > >>
> > >> > Guys,
> > >> >
> > >> > I checked out the specs for the above mill. Errors in their
> > >> > specifications!!!! As I mentioned several weeks ago, this
may
> be
> > >a
> > >> > clue as to the overall quality of a machine.
> > >> >
> > >> > They note the feedrate at 2000mm/rev for the CNC version.
Do
> they
> > >> > mean 2000mm/min, which would translate to 79/min? 79 in/min
is
> > >> > painfully slow, if that's the correct value, why can this
> machine
> > >> > only go that fast?
> > >>
> > >> 79 IPM is painfully slow? Talking with Sherline owners with
> > >Microkinetics
> > >> drivers, they were getting 14 IPM rapid feed rates, and at
least
> > >some of
> > >> them thought that was OK. With my stepper rate generator
board I
> > >got
> > >> 25 - 30 IPM. On my servo-controlled Bridgeport mill I can go
to
> > >105 IPM,
> > >> but I rarely take it over 45 IPM because I have a tendency to
> cause
> > >> catastrophic crashes.
> > >>
> > >> Now, for a real commercial shop, they want 400 IPM rapids, but
> most
> > >people
> > >> discussing this and similar machines are not doing commercial
> > >production.
> > >> Going much faster than this may cause real problems with Acme
> > >screws.
> > >> Anyway, with steppers, the power decreases very fast with
> > >increasing speed,
> > >> so that may be the cause of the speed limit.
> > >>
> > >> Jon
> > >
> > >
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