Re: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic cylinder

i am thinking on this approach, and like it. what you meen, i could "help" my stepper with a hidraulic/pneumatic cilinder/pair of cilinders.

but what ideas you have for changing the direction of this "help". it is easy to build a thrust in the cilinder in one direction, but you have to change the direction when the movement changes
direction.

vajk

alex wrote:

> There are numerous pneumatic cylinders available, some consisting of
> an outside beam/inside slide with the stoke as long as 10 feet, which can
> become part of the structure of a router, quite naturally, in this case
> small stepper will only serve as an
> interface to the PC.
> Do you think this is workable?
> Regards, Alex Likhterman
> ----- Original Message -----
> From: Van Der Sandt Coert <vandersandtc@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Thursday, November 07, 2002 7:47 AM
> Subject: RE: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic
> cylinder
>
> > If you are going to 'lock' the axis with the worm gear anyway - then you
> > could also use pneumatic cylinders, no?
> >
> > -----Original Message-----
> > From: alex [mailto:telecomt@...]
> > Sent: Thursday, November 07, 2002 1:44 AM
> > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > Subject: Re: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic
> > cylinder
> >
> >
> > Sorry made a mistake - not coaxial but parallel to the drive screw.
> > Force of the cylinder should be applied towards the carriage parallel to
> the
> > screw.
> > Alex
> >
> > ----- Original Message -----
> > From: Jon Elson <elson@...>
> > To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> > Sent: Wednesday, November 06, 2002 12:21 PM
> > Subject: Re: [CAD_CAM_EDM_DRO] Re: replacing feed screw with a hydraulic
> > cylinder
> >
> >
> > >
> > >
> > > Van Der Sandt Coert wrote:
> > >
> > > >What if you had one big pump to keep up the pressure and some kind of a
> > > >rotary valve on each axis that just lets a metered amount of fluid
> > through
> > > >every time its activated.
> > > >
> > > >Alternatively you could have a pump on every axis and calculate the
> pump
> > > >speed so that every axis reaches its goal at the same time.
> > > >
> > > >
> > > And, what is going to drive those pumps? Electric motors? Clutches?
> > > How can this be better
> > > than just driving the machine directly with the motor? If you are going
> > > to hook a servo motor
> > > to a reversible hydraulic pump, then drive the table with a cylinder,
> > > that has to be the
> > > Rube Goldberg method of replacing a leadscrew!
> > >
> > > Just as a reference point, hydraulic systems, especially hydraulic
> > > motors driving a leadscrew,
> > > was a VERY common system on larger CNC machines, in the 1970s. I
> > > believe it was the
> > > most common axis drive system on the larger ones, in fact. Direct
> > > electric drive cam in
> > > VERY quickly after larger power transistors became available. The
> > > makers of big machines
> > > never looked back, and you'll be VERY hard pressed to find any larger
> > > CNC machine with
> > > hydraulic drive today. The only machines still using hydraulic drive
> > > that I can think of are
> > > surface grinders, where they just have a steady back and forth feed
> > > between limit switches.
> > >
> > > The buyers of these machines must have a REAL good reason for making
> > > this choice.
> > > The reason, of course, is they had HORRIBLE experiences with the high
> > > maintenance
> > > costs of hydraulic systems! Another side light, the commercial aircraft
> > > industry is trying
> > > to desing their way away from hydraulics, for the same reason - high,
> > > VERY high, maintenace
> > > costs.
> > >
> > > Jon
> > >
> > >
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