Re: Ball screws

Trevor,
I am planning on using the dual nut system for the GEM mill myself.
I have been checking all the main suppliers of ball screws, still not
decided though. The 3/4" Kerk screws that I used on the Mill/Drill
were chosen for the load capacity (350lbs). This was the best fit
for nut diameter/load capacity from Kerk. I have since learned that
the thrust generated by a 720oz/in motor using a 5TPI ball screw is
around 1000lbs, nicely matching the 3/4" ball screw capacity.
For encoders, check the last few days of posts about "Cheap
Encoders". Using linear encoders is supposed to be the best method of
knowing where the tool tip is, but I understand there are problems to
this. I don't understand them yet, so not yet interested in the
feedback system yet, though maybe in the future. I do think that if
you know where the table is, not the calculated position of the
table, then you will be able to get your position pretty well.

Allan

--- In CAD_CAM_EDM_DRO@y..., tbrooking@s... wrote:
> Allan:
>
> Thanks for the help, the dwg files look great. I have to check the
> dimensions of my mill to see if they are comparable with yours.
The
> screw sizes on your drawing show a screw with a 3/4" diameter.
What
> criteria made you come to select that size of screw?
> On my machine I would like to use some form of feedback loop that
is
> relative to the table position and not the screw angel. I was
> thinking that way I could lower the cost of the screws by
purchasing
> a rolled screw verses a ground screw. The only disadvantage that I
> can see is that I would have to develop the preload set-up for the
> nuts (two nuts with a spring or solid shim) to minimize the
> backlash. I have seen and heard of some different methods for
> encoding the table position, rack & pinion, cable & pulley,
friction
> wheel. Do think that using a simple method of encoding table
> position like the ones above along with less expensive ball screws
> and still be able to maintain good accuracy (0.001 tol. or better)
is
> practical?
> If you are still looking screws for your machine, ball screw
> manufacturers like Tompson, Nook, and BSA have online catalogue
that
> you can download. They all are similar and most have some drawings
> that you can view (pdf format).
>
> Trevor
>
> --- In CAD_CAM_EDM_DRO@y..., allan_r9@h... wrote:
> > Trevor,
> >
> > I uploaded the .SAT 2.0 file and .DWG Acad14 files as zipped
files
> to
> > the files section. Look under Drill 2HP model folder. The 4
axis
> > file is not mine - don't know how it got into the folder I just
> > created.
> > Before trusting my dimensions, check your machine before cutting
> > parts. I used a tape measure for the larger parts during
> modelling,
> > so 1/16" accuracy. Also, these machines may vary slightly during
> mfg.
> >
> > Allan
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., tbrooking@s... wrote:
> > > I am intersted in your modeling of the screw components. I am
> > > currently using autocad r14 for my cad work, if you could e-
mail
> me
> > > the files in a format supported by autocad r14 that would be
> great.
> > >
> > > Thanks
> > >
> > > Trevor
> > > --- In CAD_CAM_EDM_DRO@y..., allan_r9@h... wrote:
> > > > Hello,
> > > >
> > > > I too am shopping for ball screws to convert my GEM500 to
CNC,
> so
> > > I'm
> > > > interested in the same answers you get. I did convert an
Enco
> > > > Mill/Drill (2HP version) to 3 axis CNC using Kerk Motion
> Products
> > > > zero backlash nuts and screws (not ball screws). I wish I
had
> > gone
> > > > for the ball screws now. I have all the pertinent components
> > > > modelled in 3D solids. If you would like the file, let me
know
> > what
> > > > solids format you can use. The Mill/Drill started with Ah-ha
> > > control
> > > > and Gecko G201 drives with 3 Sanyo-Denki 720oz/in motors,
then
> I
> > > > bought the BDI disk from Paul at the NAMES 2001 show, and got
> the
> > > EMC
> > > > control working. It runs much smoother than the Ah-ha
> control.
> > > The
> > > > EMC system will be used for the GEM500 conversion which will
be
> a
> > 5
> > > > axis machine. The 3d model for this machine with 5 axis
> trunnion
> > > > will be placed on the files list soon.
> > > >
> > > > Allan