Tuesday, November 8, 2011

Making an Exhaust Chuff Cam

In my last post I mentioned that I would explain how I make exhaust chuff cams for my locomotives so here is a technique that anyone can do.
1. Place the loco upside down in a cradle.
2. Connect power to the loco and clean the rear of the rim of the most likely candidate driving wheel, this is usually the rear wheel on the left, looking towards the front and with the loco upside down.
3. Apply power to the loco while it is upside down in a cradle and bring the side rod crank of the wheel uppermost (where it would normally contact the rail).
4. Make two marks on the rear of the rim wheel three spokes apart (the crank is usually aligned with a spoke) with a very fine marker (0.5mm line width).
5. Move the wheel to the next quarter position by counting the wheel spokes and make the next three spoke set of marks and follow through with the last two sets.
6. Using a sharpened toothpick carefully apply ACC glue (Super Glue) between the three spoke marks at each quarter location and allow to set for a couple of days.
7. Mount a piece of printed circuit board (PCB) to the under side of the chassis either with a suitably located chassis screw or with glue, if glueing the PCB, clean any oil from the chassis thoroughly.
8. Solder the cam wire from the sound decoder to the printed circuit board.
9. If using a chassis screw to mount the PCB ensure that the copper of the PCB where the wire is soldered on  is not in contact with the screw head or chassis by removing copper between the screw and the decoder cam wire.
10. Solder a piece of phosphor bronze wire or strip to the PCB near the decoder cam wire such that one end bears against the rear of the rim of the wheel with the ACC insulated segments. I used Slaters 0.12mm (0.006") phosphor bronze strip on the Austrains C36 but I have also used phosphor bronze wire.
11. With power applied to the loco rub the point of a 8B graphite (lead) pencil to the rear of the rim, this smooths the tracking of the wire/strip.
12. Place the loco on the programming track or main and set the sound decoder to use the cam, this is easily achieved using JMRI Decoder Pro.
14. Adjust the strip/wire to lightly touch the rim until a good clean chuffing sound results.

Here are some photos showing the C36 installation.

If you have followed the above you should now have a loco that chuffs four times for each wheel revolution.
If you have a slightly uneven beat then one or more of the ACC glue segments is a different length but this is not an issue a locos may have a slightly different beat with one chuff being slightly longer/louder than the others. Of course if the chuff sound is really out of balance then you will have to scrap the ACC glue off and redo it.


James McInerney said...

Very clever, Ray! Much simpler than fitting a Soundtraxx chuff plate on the back of the wheel. Won't the superglue wear through eventually though?

Ray P said...


I have had one working now for about 3 years without any problem so far.


James McInerney said...

Tried it out on my latest conversion (Mansfield 5184). Works beautifully! Great idea Ray, thanks!

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