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Re: synchronous gap help (fwd)

---------- Forwarded message ----------
Date: Wed, 11 Jul 2007 17:57:47 EDT
From: FIFTYGUY@xxxxxxx
To: tesla@xxxxxxxxxx
Subject: Re: synchronous gap help (fwd)

In a message dated 7/9/07 10:46:02 P.M. Eastern Daylight Time,  
tesla@xxxxxxxxxx writes:

>I'm planning to use a 3/8 " g10 rotor 8" in diameter with 4 1/4 "  tungsten 
electodes held on with

>shaft collars (the disc is pinched between the collars). A sheet  metal ring 
connects these 
>electrodes. I have two stationary electrodes (one gap). My motor is  a 
Teletype 1/12 hp motor, 
>synchronous, and runs at 3600 rpm. Any tips on how to balance, cut  the g10 
(i've heard its hard to 
>cut), motor arbor, or anything else I should know? 
    I last night I put the center hub hole in my  piece of G10. I'm using a 
US Tsubaki "Power Lock" KE keyless hub to lock the  rotor to its shaft. The hub 
part number is PL-5/8KE, since I'm using a  5/8" shaft. Rotor on its own 
shaft, timing-belt driven from the  motor. This hub requires a rotor hole ID of 
1-3/16" (1.1875"). 
    I clamped my piece of 3/4" thick G10 to the table  of an old Bridgeport 
vertical (knee) mill. I cut the hole with a 1-1/8"  six-flute center-cutting 
endmill (held in an R8 collet). The endmill was High  Speed Steel. Definitely 
hardened, because I had to turn the shank down to fit  the 7/8" collet. The 
point where the shank hardness changed was very  abrupt!
    Anyhow, I had previously read the TCML archives  warnings on the subject 
of machining laminates. So even though I was using  steel tooling, I made a 
point to take my time. I cut for only two seconds at a  time, before I withdrew 
the endmill. My goal was to reduce heat build up on  the cutting edges. It 
only took a couple of minutes to completely and cleanly  cut through the G10. The 
opposite side delaminated for an area 1/16" past the  edge of the hole, but 
for only one layer of fiberglass. Very minor.
    The endmill was almost brand new when I started,  but it had dulled 
significantly by the time I was done. I'm sure it would have  made another hole in 
G10 just fine, but the wear was obvious. No oxidation of  heat coloring, and 
no melting of cutting surfaces. It looked like the original  clearance and rake 
angles had simply been abraded to new, flatter angles
    I used a shop vac with the pickup right at the  hole, and wore a dust 
mask. No noticeable itching or dust problems at all. And  no visible airborne 
dust, either. 
    Finished the hole to size with an expandable HSS  hand reamer.
    Now I'm making a fixture (1-3/16" bar stock  welded to plate) to mount 
the rotor plate on to let it spin. I'll attach the  plate to a band saw table to 
cut the disk from the square. Then I'll lay out  the flying electrode holes, 
and bolt the plate to the drill press to spin the  rotor to each electrode 
hole. At least the holes should have the same  radial distance. I may put the 
disk in the lathe, and use live tooling to  grind the electrode holes, and index 
the disk to position with the lathe's  bull gear indexing holes. I've got a 
chucking reamer to finish the electrode  holes to size.
    The archives have been very helpful. Thank you to  all who have been here 
before me, and shared their experience!
-Phil LaBudde
Center for the Advanced Study of Ballistic  Improbabilities

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