[R-390] Torque and Clamps

[Tom Bridgers]

After over tightening clamps on my R-390A's for several monthsyears ago, I gradually learned to get it right by feel.  After that, I had no other clamps break.  But the first few made me pull my hairout, which is why, today, I am slightly bald.
Tighter is not always better, and tightening clamps on an R-390Ais one of those situations.
I have used the Xcelite bristol blade for over 10 years.
I'd be interested in learning more about the more logical andengineering approach of  the Utica Adjustable Torque screwdriver.
-Tom  KE4RHH

> To: r-390 at mailman.qth.net
> From: wa4aos at aol.com
> Date: Wed, 7 Nov 2012 16:19:56 -0500
> Subject: [R-390] Torque and Clamps
> 
> Hi Group,
> 
> 
> For years I have used a Utica Adjustable Torque screwdriver @ ~6 in/lbs to tighten the Bristol screws on the clamps in the R 390 series receivers that I restore. I never found any official torque specification but ~6 in/lbs is very snug without being too tight. I have never broken a clamp in this range, since using a torque screwdriver, and never had a receiver come back for a broken or lose clamp.  Using a torque screwdriver certainly takes the guess work out of not having some clamps too tight or too lose.  
> 
> 
> I carefully inspect all clamps after they come out of my ultrasonic cleaner under a bright lamp and magnifier lens. I have tried the, " dry penetrate test,"  but that turned out to time consuming and costly, although I did find flaws from time to time that were not visible under my bright lamp. Most of the time I will find at least 1 clamp per gear train that is questionable or bad. 
> 
> 
> So, three questions:
> 1) Does anyone know if there was ever an official specification of tightness of these screws?
> 
> 
> 2) Anyone have experience with methods of identifying small cracks and fatigue points in metal  parts that is less costly and time consuming than the aforementioned, "dry penetrant test,"  I have used in the past?
> 
> 
> 3) In the past, I once found a company that sells an almost identical clamp as used in the R 390 series receivers, of course with an Allen bolt. The unit price was around $9ea and I am near the end of that inventory. Does anyone recall the company that sells/sold those clamps. My purchase was logged on a system that had a hard drive failure before I did my backup and this vendor has slipped through the cracks.
> 
> 
> FYI: In case anyone is interested, I use Xcellite 9966 Bristol blades with the 99PA adapter to mate the bristol blade to my Utica Torque Screwdriver; this works out VERY WELL.
> 
> 
> 73,
> Glenn WA4AOS
> DSM Labs dot com
> 
> 
> 
> 
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