The 4mm plunger pick-up saga.
The original 7mm plunger pick-ups for the 57xx disintegrated when I stripped the chassis. A friend who models 7mm scale had fitted 4mm plungers to a loco, so I thought I would have a go. The make is a mystery, as there is nothing on the instructions revealing who was responsible. As is the way, they did not assemble as per the instructions. If the insulated wire was soldered into the nickle-silver plunger, the little spring would not fit over the wire insulation…. So, instead, I solder 0.4mm phosphor bronze wire into the plunger.
The next problem was the hole in the frames. The sleeve the plunger fits in required a 2mm hole, but the hole in the frame was 3.2mm. I had previously made the pick-ups for my G6 using 3mm OD / 1.5mm ID semi rigid plastic tubing. 7mm lengths were cut off and glued into the frames using super glue gel. A homemade jig was used to maintain alignment.
After a couple of hours, to ensure the glue is fully cured, rapid setting epoxy was used on the inside of the frames to build up a ‘shoulder’ around the sleeving.
When fully cured, a 2mm drill was run down the sleeves and then a tapered broach was used so ease out the hole, so that the plunger assembles were a snug, but not over tight fit. The outside face of the sleeve was filed down so that it was 0.5 – 0.7mm proud of the frames. Experimentation showed that with the wheels fitted, contact was maintained with the backs of the wheels, but no binding was occurring. A Vernier is helpful with this job. I find that a Vernier and Micrometer are useful tools in 7mm, as one is moving into the realm of engineering with this scale and away from bodgit modelling!
Edited by PD&SWJR, 09 January 2014 - 12:51 .