Re: Rotary gaps -- machine work

In a message dated 96-08-07 01:02:51 EDT, you write:

<< reetings,
 I've been working on a rotary gap for a while now (5 minutes at a time).  
 The problem I'm having is making the disc run true.  The disc consists of 
 two aluminum hubs with a 1/2" thick x 12" dia. disc of G-10 epoxy 
 After reworking the hubs, they are sitting in the 3 jaw chuck.  A dial 
 gauge shows that they have been faced so that there is much less than 
 0.001" runout(?).  I then put the disc on the faced hub and put the dial 
 gauge on it.  It shows about 0.002" at the center, and about 0.020" or 
 more out of true at the edge.  Looking at the motion of the dial, I can 
 see that the disc isn't just out of true, but is actually slightly warped 
 or something. The needle indicates one "major" high point, and one 
 "minor" high point.  These high points are not 180 degrees apart either.
 After a little shimming, I can get things a little better, but not good 
 This leads me to the reason for the posting.  How to true up the darn 
 thing?  The three ideas that I have are 
 1) Face the G-10.  I don't like this too much because it may weaken, or 
    at least make it all fuzzy.
 2) Build up a rim of epoxy on both sides and face that.
 3) Ignore the out of true on the disc, put on my brass acorn nut 
    electrodes, and face the points of them.
 Does anyone have any thoughts or suggestions?
 Chip >>


I had a similar problem with my rotary wheel.  The wheel itself is Lexan, and
like yours wasn't perfectly true to begin with.  After mounting the stainless
steel acorn nuts, with star washers under each one, I noticed an even bigger
problem.  All the nuts are not exactly the same height.  I assembled the
complete unit, set the fixed electrodes for about .005" clearance, rotated
the wheel and some other nuts would hit the fixed electrodes.  I tried
measuring and selecting different nuts for different positions for a while
then gave up.  I now run with about .020" average clearance between the nuts
and the fixed electrodes.  This gap increases after running the gap for an
hour or so as the nuts definitely get burned down, requiring periodic
readjusting of the fixed electrodes - which are tungsten.

Ed Sonderman