Re: [CAD_CAM_EDM_DRO] Re: Max feedrate of ball screws?

Very interesting project.
I may be mistaken, but I think you are expecting too much from #25 chain in
terms of a load.
Why not to try chain #40?
The good source for chain sprockets and chain is www.princessauto.com.
For example, 10 feeet of the chain is $12 Cdn, 40 teeth sprocket is $8 Cdn,
Ball - bearing pillow block - $8 Cdn.
Btw, I don't work there.
Regards, Alex

----- Original Message -----
From: <echnidna@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, December 06, 2002 6:55 PM
Subject: [CAD_CAM_EDM_DRO] Re: Max feedrate of ball screws?


> Seth,
> Like you I am a serious woodworker and understand the necessity for high
feed rates, plus the desirability of being able to work with other
materials.
>
> I first looked at leadscrews and discounted them. They dont like dust and
even with the best dust extraction systems we will still get some flour
hanging around. The leadscrew shaft speeds necessary to achieve high
feedrates mean we must use large diameter leadscews to avoid shaft
vibrations and whip which will aggravate resonance problems and may limit
the speed regardless of all else. Or devise a way of mechanically supporting
leadscrews midpoint without impeding the mechanics travelling past the
supports. Large diameter leadscrews also bring into consideration shaft
balancing, support structures and inertia etc.
>
> Then I considered rack and pinion. Dust being a major factor here but
possibly mounting a rack and pinion so the rack is inverted and the pinion
below it may work.
>
> After seaching all the archives (which is very difficult and time
consuming)I found some good information on chain drives which are more than
adequate for woodworking and are described in previous lists as being at
least as accurate as rack and pinion and very tolerant of dust and grit. I
seem to recall accuraccies of .001" are achievable. Which is accurate enough
for a lot of metalworking as well as more than ample for woodworking. Of
course we can still microstep to finer cuts for smooth surfaces but the
repeatable accuracy may be limited to about .001". One of the old lists
described in some detail an old type industrial gantry router (with
excellent reputation) constructed with chain drives but I havent been able
to find it again.
>
> My machine will operate in your desired speed range. I have a counter
shaft across the machine with a #25 pitch sprocket each end of my Y axis.
The #42 Y axis stepper drives the shaft from the centre of the shaft to
equalise torsional deflections of each end of the shaft. I feel for my
purposes #25 pitch chain was the most practical method, it has a tenslie
strength 860 -1000 pounds so I expect it will operate at 10 -15% of its
strength.
>
> It may be more practical considering the economics to have a woodworker
and a metalworker as separate stand alone machines. Lets face it
multipurpose wood working machines are ok but cannot compare to separate
dedicated machines and it may apply to cnc also despite its greater
versatility.
>
> btw my router is a little larger than yours about 4'6" by 2'6" actual
workpiece are but with 3 separate z axis (and 2 more planned).Just like me
its a little odd
>
> Regards
> Bob Thomas
>
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., "dgmachinist" <scsm@m...> wrote:
> > Greetings!
> >
> > I don't suppose anyone out there could tell me the max feedrate
> > of ball screws? The screws that I have in mind are .625 dia., .200
> > lead. I need them to be 60" long. (I'm building a 2'x4' router)
> > They will be supported at each end with the nut moving back and
> > forth. (like every typical gantry) Since the X axis is 60" long, I
> > decided to go with dual screws, motors, etc.
> > I see all of the "commercial" routers are boasting speeds of 400+
> > IPM. How do they acheive those rates?
> >
> >
> > TIA
> > Seth
>
>
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