Re: Ball Screw Machining

John Ross wrote:

> From: John Ross <johnr@...>
>
> Hi I'm new (as of today) to this list, and I have a question about
> machining hardened ball screws. I have been converting my Mill Drill to
> ball screws as the article in HSM. Dan Falck has been giving me some advice
> on how he did this conversion. As Dan had did on his conversion I heated
> the ball screw in a lathe at its slowest speed (60 RPM), to a Straw color
> then let it cool before machining them.

The measurement of temperature by color is quite tricky. I think you will have
to get the screw hotter. I have done some work on fully hard screws with
C-6 carbide tools, and they will cut it. But, drills and taps will never hack
that until it is well annealed. Don't get too scared of damaging the end of the
screw with too much heat. You may also have to use some technique to
allow the end to cool more slowly.

> They are still extremely hard.
> I've tried reheating them but have had no better luck. Drilling the #7
> hole for a 1/4 20 center screw was darn near impossible and my tap won't
> even start to cut a thread. The ball screws I'm trying to use are from
> McMaster Car and they list them as "induction hardened to Rockwell 56-60C".
> Does anybody have any ideas as to how to soften these up so I can machine
> these beasts. My fathers suggestion to grind them is a little pricey
> considering I don't own a tool post grinder.

A Dremel or similar tool can make a poor man's substitute. Any grinding
will be a lot slower than cutting. You won't find it possible to grind internal
1/4-20 threads, anyway.

Jon