Re: [CAD_CAM_EDM_DRO] Machining Ball Screws

Carl,
That's a really interesting solution to a problem, at least it's much
cheaper than buying a new lathe. Why don't you post some pictures of your
rig, to make it easier for us to visualize.

Marv Frankel
Los Angeles

----- Original Message -----
From: "Carl Mikkelsen, Oasis" <Carl.Mikkelsen@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, September 30, 2002 5:39 AM
Subject: Re: [CAD_CAM_EDM_DRO] Machining Ball Screws


> Graham,
>
> First, some random thoughts on your problem, then I'll talk about what I
do.
>
> 1) The balls roll on the inner track of the threads. If the outer edges
> were marred by the lathe chuck, it *MIGHT* not matter.
>
> 2) Chucking the screw by the outer surface will have one of the potential
> (unproven) problems of the solution I use to reduce ball screw diameter.
>
> 3) I always have trouble finding the exact center for my lathes tailstock.
>
> 4) The inexpensive ball screws I get from McMaster-Carr look like they are
> black-oxide finished, appear to be at least case hardened.
>
> 5) I am concerned about applying strong radial forces to the ball screws,
> as I don't want to bend them.
>
> So, with this in mind, I was machining a ball screw yesterday.
>
> I need to turn the 5/8" ball screw down to 1/2" for a coupler and bearing
> assembly. My toy lathe is not nearly good enough for this, so I'm using a
> bench grinder and a fixture I welded together.
>
> The ball screw lies in a piece of 1"x1/8" steel angle, which is supported
> on one end by an attachment point to the grinder's tool rest, and at the
> other by a clamp to the worktable to which the grinder is attached. There
> is a notch cut in the angle for the grinding wheel. There is a stop in
the
> angle to limit the length of the cut.
>
> To grind down the ball screw, you must rotate it slowly in the angle
> trough, and move it past the grinding wheel. Grind it gently, taking off
a
> couple of thousandths at a time, especially at you approach your target
> diameter.
>
> I realize that this is a kludge, that it only approximates a centerless
> grinder, and that the precision is limited by several factors:
>
> 1) evenness of the operator hand pressure compounded by stiffness of the
> fixture
> 2) concentricity of the outer (uncontrolled and unspecified) part of the
> ball screw with the true axis of the threads
> 3) surface finish
>
> The prototypes I've ground are good enough for my purposes, however.
>
> I've done this with the inexpensive McMaster-Carr rolled ball screws, and
> with "hardware store" threaded rod. I haven't work with premium ground
> ball screws.
>
> Again, I'm certainly not claiming this is ideal -- maybe not even good or
> aesthetic -- but it is working for me.
>
> -- Carl
>
>
> At 10:59 AM 9/30/2002 +0000, you wrote:
> >I am about to start working proper on a CNC coil winding project I
> >have had in mind for a while now. I recently discovered that
> >McMaster-Carr do nice ball screws that they sell by the inch. This
> >seems perfect as I need only a very small length.
> >
> >One question I have concerns machining the ballscrew ends, one for
> >the stepper and one for the support bearing. I have a flexible
> >coupler for the stepper motor end but will need to reduce the
> >diameter of the lead screw. What is the best way to hold the lead
> >screw in the lathe while it is being turned down. I assume it
> >shouldn't just be gripped as is. I considered just putting a length
> >of heatshrink over the threads but getting it wrong and damaging the
> >threads would be costly in time and money.
> >
> >Any advice appreciated.
> >
> >Graham
> >
> >p.s. Does anyone have any leads on short (<10") ballscrews with 1mm
> >pitch at low prices? Also cheap lead screw support bearings.
>
>
> Carl Mikkelsen
> Oasis Semiconductor, Inc.
> 201 Jones Road
> Waltham, MA 02451
> (781) 647 8775
>
>
>
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