From: James P Crombie 
To: Atm List , david_margrave{at}yahoo.com
Reply-To: James P Crombie 


Dave
  On my 3.75" spherometer I used a set of 1/8" carbide balls I got from
a hobby shop, (they are used in the clutch of a model race car) and
silver-soldered them into the head of a SS socket head cap screw. I used a
collet chuck to bore a small chamfer on the lip of the hex to make sure the
recess was in-line with the axis of the threads.   I had the
holes spotted, drilled and tapped on a Jigbore we have at work just in case
:-)  and then checked the location using a CMM (coodinate measuing machine)
which showed the feet were all within a .001" band at a 3.750"
dia tolerance .  Of course this overkill but it showed the principle works 
 The only problem with using steel ball bearings is they are
usually case hardened and require carbide drills.  You will also have to
chamfer the hole back a bit to expose the softer steel enough as not to
catch it with the tap.  Oterwise the tap may break or dull prematurely.
 If you have a mill with digital readouts available, you can usually get
better results than using the rotary table by trig-ing out the locations

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James P Crombie

Summerside                   Machinist
Prince Edward Island         Amateur Astronomer
Canada                       3D Designer

E-mail                       jpcrombie{at}pei.eastlink.ca
Astronomy webpage            http://users.eastlink.ca/~jpcrombie/
Rhinoceros 3D webpage        http://users.eastlink.ca/~jpcrombie/rhino/
Mirror Grinder page          http://users.eastlink.ca/~jpcrombie/pics/
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