Don, Wrong answer, guess again.
The kit supplied allen wrench strips because it is a cheap, low quality tool that can not support the required torque. The required torque is higher than necessary because of the overly tight, tapered, and/or incomplete threading of the set screw hole in the knobs. The concentric knobs are undoubtedly splitting because they are plastic knobs that have the set screw threaded directly into the plastic. That design is a non-starter from a quality perspective and is bound to fail in one way or another, sooner or later. The engineering dilemma with an all plastic knob is that if the set screw threading isn't tight the set screw will strip out the plastic threads before achieving enough force to secure the knob to the shaft. On the flip side if the threading is tight enough to allow securing the knob, it is also tight enough to tend to split the plastic around the set screw hole via radial pressure when torqued. This is why quality knobs are either all metal or have metal inserts for the set screws. Being an old gunsmith, I'm not intimidated by slotted screws and wouldn't hesitate to swap out the allen drive set screws with slotted ones, and probably will if these knobs ever need to be removed. I realize that this is a good solution only if one actually knows how to properly fit and operate a slotted screw driver. The "pinky" tight approach is OK if you are working with a "D" shaft that provides positive indexing. Otherwise, as in the round shaft K3 concentric pots, the set screw has to be very tight to maintain the knob indexing. 73 Jack KZ5A -----Original Message----- From: Don Wilhelm [mailto:w3...@embarqmail.com] Sent: Tuesday, May 11, 2010 5:39 PM To: Jack Brabham Cc: 'elecraft@mailman.qth.net' Subject: Re: [Elecraft] [K3} Help, hex key for split knob Jack, If you stripped out the allen wrench, you were applying more force than is necessary, and excessive force may be the reason some of the newer knobs are cracking (that is just a guess). 73, Don W3FPR Jack Brabham wrote: > Tim, > > I had a similar experience assembling #4169 a few weeks ago. Unfortunately > my stack of assorted allen wrenches didn't include any that small. > > My work around was to grind off the "stripped" portion of the cheesy allen > wrench each time it stripped. > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
