Re: Ball bearings
Tesla List wrote:
> Original Poster: Neon John <johngd-at-bellsouth-dot-net>
> Tesla List wrote:
> > For the record, I have tried annealing bearing balls with the
> intent of
> > drilling them. The project was a total failure!
> I would expect that. Bearing steel just doesn't anneal very much.
> I have drilled it using solid tungsten carbide bits but it's kinda
> like pushing string - neither much fun nor very successful.
> >Think the EDM would
> > work well, but didn't think it was a high-voltage proposition. Details
> > please? Think Lindsay has a book on EDM, and should probably pick it
> > up.
> John De Armond
> Neon John's Custom Neon
> Cleveland, TN
> "Bendin' Glass 'n Passin' Gas"
As a tool $ die maker involved in the trade for almost 30 years, I have
been following this Tesla unrelated thread with some amusement.
Ball/roller bearings are made of a high molybdenum steel which is an air
hardening tool steel not unlike A2 or D2 or many of the other modern air
hardening molybdenum/chromuim/nickel tool steels used in industry today.
The hardness is somewhere in the range of 65 on the Rockwell C scale
(almost file hard). In the hardened state, it can't be drilled with
cobalt drills, which are only slightly tougher than regular M7 high
speed steel, or center punched. It can ground easily, conventional EDMed
easily or drilled with great difficulty using carbide ball end mills,
which are quite expensive and don't last long when used this way. I have
used carbide tipped masonry drills to enlarge holes in flat tool steel
slightly less hard than ball bearings with success, but never tried a
ball bearing. I suspect the results would not be encouraging.
As for annealing, air hardened tool steel MUST be annealed in a special
timed oven that can take the bearing or whatever up to above the
original hardening temperature, usually 1200 to 1600 degrees F. and
slowly return it to room temperature over a period of from 12 to 24
hours to return it to the soft state.
The reason heating to red heat and letting cool in air doesn't work is
because this is the way air hardened steel is designed to be hardened in
the first place! Each time you heat it and let it cool in room air, you
are rehardening it! :^(
All this said, the best strategy to obtain balls for spark/safety gaps
would be to buy tooling balls, which are quite cheap, or predrilled and
tapped brass balls which several other list members have already
mentioned sources for. Or...if you really MUST have ball bearings, take
them down to your local welding shop with some bolts and have the bolts
heliarced to the bearings.
Ed Wingate RATCB