[R-390] How are your knobs ?

[quartz55]

I agree with everything you've said.  Sounds like a good plan.  Yes, I 
did cut the bushing .1" too short, but that is not necessary to do, the 
mentioned bushing will stick out as far as the original fingers fully 
inserted in the drilling if it's cut right, at about .9". I've moved the 
knob to the MC position and am running it end to end at least once a 
day.  So far it feels like a real knob.  The other thing I messed up was 
not lining up the slots with the web, so the clamp probably doesn't work 
to it's most effectiveness.  Just sloppy work on my end, I wasn't paying 
attention when I glued it in.

I'm sure these bronze fingers are not as brittle as the pot metal of the 
original, so 'honking' should be allowed, but I don't think it's 
necessary, like I said less than 1 turn on the bristow screw tightened 
it sufficiently, but I have a pretty smooth gear train in both the KC 
and MC on both RXs.  But when I get to the end it stops agreeably.

Yes, I replied to you, not the list, I'll do better.  Isn't it great 
when this crowd sourcing works out?  I can only hope it benefits others.

Dave

On 5/25/2014 4:25 PM, Charles Steinmetz wrote:
> [offlist -- I think your message came to me direct and was not posted]
>
>> Unless the repair bushing is custom made, I doubt if we could achieve 
>> Charles' ideals.  The bushing was a good, but not tight fit on the 
>> shaft, it easily slid on and off the shaft
>
> I was thinking mostly of the next refinement, for the owner with 
> access to machine tools.  I think you did a great job with what you had.
>
> It is possible to form the ID of the fingers into a parallel fit with 
> the shaft freehand (without machine tools).  With the knob off the 
> shaft, tighten the clamp lightly onto the flute portion of a drill bit 
> that is the same size as the shaft.  Run the drill, tighten lightly, 
> run the drill, tighten again..., using the flutes of the bit as a 
> reamer.  Do this a few times.  When you see that you have cleaned up 
> the first 1/4" or so of the bore, you are done.  You shouldn't have to 
> remove more that 0.005"--0.010".  But again, this should not be 
> absolutely necessary for it to work satisfactorially.
>
> The reason for my seemingly obsessive attention to optimizing this 
> interface is to maximize the chance of getting a good, non-slip fit 
> without needing to honk down so hard on the clamp screw, which can 
> lead to failure of the clamp and/or the knob fingers.
>
>> I would think that one would want all the glue and depth possible to 
>> give the most grip and load.
>
> I presume you are referring to my comment re: not necessarily seating 
> the bushing to full depth?  Yes, optimally one would cut the bushing 
> to the length that will bottom in the bored hole and leave enough 
> protruding to pass fully through the clamp with a bit extra (perhaps 
> 0.050").  But having cut it short, I think it would be better to leave 
> more protruding (so it passes fully through the clamp with the bit 
> extra) rather than seat it to full depth and have the clamp hanging 
> off the end.  But, as I said, I have every confidence that your repair 
> will survive to the radio's end and beyond just as it is.
>
> Best regards,
>
> Charles
>
>
>
>
>
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