Re: Pointseries gaps 'vs' other types

To: tesla-at-grendel.objinc-dot-com
Subject: Re: Pointseries gaps 'vs' other types
From: Chuck Curran <ccurran-at-execpc-dot-com>
Date: Thu, 15 Feb 1996 19:53:20 -0600
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Cc: scotty-at-westnet-dot-com

Hello Scott:

  I appreciate your quick reply to the questions I posed on 
rotary/series gap design.  My hope was to save a bit of time and 
gain from others experience in this area. Happy it is working!  I 
believe my next step will be to get some details on the G-10 
phenolic material you mentioned(or equivalents), specifically the 
ultimate tensile and yield strengths. I already have data at work on 
glass filled composite plastics, used for molding structural parts, 
since this was part of a project I started.  This goes back a ways, 
but as I recall the tensile strengths with short glass fibres was in 
excess of 22,000 psi--I'll look this up tomorrow.  I was considering 
replacing some die cast aluminum parts at the time.  Hope the G-10 
stuff is equal to or exceeds this glass composite level.  It will be 
pretty straight forward to determine if a reasonable safety factor 
is present or not.

>But the larger the diameter, the greater the mechanical stress and 
>the greater the need for dynamic balancing.  The pressures on a 10" 
>disk's edges are incredible at 10,000 RPM.  We are talking about 
>several thousand PSI, depending upon material choices.  (Am I 
>making you ill yet?)   It will probably be neccessary to get the 
>assembly dynamically balanced for speeds in excess of 6,000 RPM.  
>There goes a couple hundred bucks (ouch).  

No, I'm not sick yet(green!!)--just becomes another item to review, 
learn about and resolve.  One of our products at work is a line of 
servo motors which have provided some real interesting 
manufacturing challenges.  Specifically, we have rotor assemblies 
that weigh up to 64 lbs. and do instant reverses at 5,000 RPM.  
These units have magnet segments (12) attached to a 2.600" diameter 
shaft--the customers would get real upset if one of these came 
flying off at speed(none have).  We use 2 plane dynamic balancing as 
one of several steps in a process to prevent failures, so I'll save 
that couple of hundred bucks and get the spark gap rotor assembly 
precision balanced on one of the shop balancers.  I better set some 
quarters aside for buying the skilled operator some coffee--I'd 
screw it up!  The way I'll be mounting the disk to the shaft will 
also allow me to adjust the assemly runout--Ihope to bring the total 
indicator reading down to less than .005".  This assumes the 
purchased material is flat.  If not, plan 2 will have to be 
developed for T.I.R.
  I don't plan on running this at an excessive speed until well 
proven.  I got many unanswered questions yet at this point with 
sections of this coil project and I need to move with care.  I'll 
keep posting the results and when things start going together--I'll 
make some photo's available if there might be any interest.  I have 
sure learned alot through others tests and trials that have been 
posted, so I will make both my mistakes and successes available.  
Again, thanks for the tips!


Chuck Curran