Re: [CAD_CAM_EDM_DRO] Re: Re: Belt vs. Direct Drive

Granted - climb milling is a special case. I remember I broke a mill bit
even on
a huge hydraulic mill - don't remember what make, it was 25 years ago.
(this contributed to my search for a new career).
It probably can be avoided in a CAM. Don't think Bridgeport will do climb
milling.
This requires extremely rigid machine.
Alex

----- Original Message -----
From: Tim Goldstein <timg@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, January 04, 2003 1:38 PM
Subject: RE: [CAD_CAM_EDM_DRO] Re: Re: Belt vs. Direct Drive


> Maybe on all issues but climb milling. The spindle is pulling you to one
> side of the lash, the table motion is pushing you to the other. Short of
> a closed look linear encoder how are you going to have any idea where in
> the range of play you are? With a closed loop you can have severe
> stability problems and it sure defeat the cheap approach.
>
> This is not to say that it is not worth building a cheap crude machine.
> It can be a great starting point for a biginner. Just don't expect any
> miracle in software will turn it into a precision unit. Vaporware does
> not count.
>
> Tim
> [Denver, CO]
> Sherline products at Deep Discount
> Mach1 & DeskCNC with credit card ordering
> www.KTMarketing.com/Sherline
>
> > -----Original Message-----
> >
> > At 02:36 04/01/2003 +0000, you wrote:
> > >No. You still have the problem of the backlash when you
> > climb mill and
> > >it never works perfect when you do circles.
> > >
> > >Tim
> > >[Denver, CO]
> > >Sherline products at Deep Discount
> > >Mach1 & DeskCNC with Credit Card ordering
> > www.KTMarketing.com/Sherline
> > >www.KTMarketing.com/DeskCNC
> > >
> > >----- Original Message -----
> > > > In this respect I wonder if it is possible to build a very crude
> > > > machine, with a worst possible screws and backlash everywhere and
> > > > try to compensate for it in a software to the point of an
> > accurate
> > > > machine? Alex
> >
> > Tim -
> >
> > That is only because the crude approximations to backlash
> > compensation
> > start with the assumptions that:
> >
> > (a) a given program will not do both climb milling and
> > "normal" milling, and
> > (b) the backlash is constant over the travel of a given leadscrew, and
> > (c) the backlash value is accurately known.
> >
> > It would be possible to provide sufficient information to the control
> > software to allow it to do a significantly better job of backlash
> > compensation than most controls manage currently; however, the real
> > question is whether it is a worthwhile thing to do, given the
> > alternative
> > of building a better machine to start with.
> >
> >
> > Regards,
> > Tony
>
>
>
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