[R-390] Torque and Clamps

[Glenn]

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