Thread and Forum Title Floating plunger pickups
Prepared by Tommy Day Originator Ian Middleditch
Ian - Feb 23, 2018 at 2:09 PM
Since I posted on the Slater plunger pickups thread I have had lots of requests for more details of my solution to pickups. I am not claiming this is my original idea but it’s how I go about making virtually invisible pickups which do not restrict sideplay.
I have taken some photos of the set up on an industrial tank, Barclay 0-6-0T which is currently on my workbench. A scale is included which gives you all the sizes you need. A note of caution though, I work in S7 so those of you who favour fine standard need to make compromises for the reduced back to back and narrow frames.
I use 1/8” brass tube and 3/32” plastic tube bought from K&L metal centres at shows or model shop. The plastic telescopes inside the brass. The principal is the same as that used in toilet roll holders! The pusher brass tube has one end closed off with a bit of etch waste soldered on and a hole drilled, 0.8, in the centre. The spring needs to be light and about 5mm long, I use Slaters buffer springs. Sometimes I have glued a short stub of wire into the inner end of the plastic pusher tube to locate the spring but in practice it isn’t needed.
The solder tag is a bit of etch waste and is positioned such that it takes the thrust from the pusher both ends. Use a fairly light flexible wire.
The guides are the same material. Cut a bit of the brass the full width of the outside of the frames plus a wee bit for trimming. Solder firmly to both frames and then cut out the bit in the middle, the piece removed makes the pusher, use a cutting disc in the drill. Doing it this way ensures that both guides are directly in line and it is easier to position for soldering. You will need to shorten the piece you removed but that can be done when you are filing the ends square. Glue a short piece of the tube into each guide, use an epoxy as it fills any gaps. When set file off the outside flush with the frames and run a drill through to give a sliding fit for your plunger wire, in my case it is 0.7 straight brass.
Before fitting the plungers from the inside, square off the working end of the plunger and smooth on fine emery paper. A slightly domed working surface is better than a point. The springs are from Slaters buffers, they sell spares in packs of 12. Adjust the tension by filing the plastic pusher a little, better to make them too tight initially and ease them off . You want the pressure to be enough for good contact but not too much to brake the wheels. Also permit a bit of sideplay so that the whole assembly follows the wheelsets if they are displaced on a curve.
You will note that the feed wires are not yet soldered on. I leave that until the final erection.
If you ever need to clean the pickups they can be removed without taking the wheels off but just watch out for the springs when you remove the pusher, they can fly for some distance!
Ian.
SimonD - Feb 23, 2018 at 2:25 PM
Thank you for sharing this, Ian.
I’m quite keen on floating plungers, and following DLOS’ scheme have made a few, using the coupling springs from Premier Components. These work well, but I suspect your design might be simpler/easier to make. I shall try, when the opportunity arises.
Best
Simon
Thompson21380 - Feb 23, 2018 at 3:39 PM
Thanks Ian,
I think we did discuss this on the Slaters plungers thread a while back?
I made up a trial set and now have all the materials available so I think I might try this on my Sans Pereil Nelson build.
The only thing I did different was to use a Brass crankpin bush to close off the Brass floating tube and use proprietary plastic rod for the inside telescopic bit.
Bob
Ian - Feb 23, 2018 at 4:20 PM
It was discussed but I have been asked for drawings and sizes which were not on the Slaters thread. I thought it best to start a new one with a more appropriate title.
The beauty of my method is that everything is made from easily obtained, inexpensive materials which most modellers will have to hand.
Ian
Bob Alderman - Feb 23, 2018 at 4:28 PM
Ian
I'm not clear where the spring is in the assembly Any chance of a sketch section of the assembly?
Bob
Ian - Feb 23, 2018 at 5:31 PM
Bob,
The spring goes into the brass tube and is trapped between the closed end and the plastic pusher rod. By compressing same the ‘miniature toilet roll holder’ fits between the two wire plungers and provides equal pressure to both.
Hope this explains the arrangement.
Ian.
Bouch - Feb 26, 2018 at 10:50 PM Ian, How does this work on the axle with the gearbox? I don't see this “toilet paper holder” in place, and it looks like the gearbox would interfere with its placement. Mike
Ian - Feb 27, 2018 at 11:13 AM
Mike,
The pickup pusher and the gearbox do not interfere. It’s just a matter of planning before drilling the guide holes.
With care you can even work round inside cranks and a gearbox as in the example below viewed from above. The piece of pcb is there to bring all the wiring to one place.
Ian.
Martin Long - Feb 27, 2018 at 2:21 PM
Thank you Ian for explaining this so clearly that even a duffer like me can understand how these are fabricated and work. A simple idea well executed. Thank you for sharing.
Martin
End of thread