Sunday, November 9, 2014

Canopus: Biting The Bullet

So I've finally bitten the bullet and permanently attached the coupling rods on Canopus. The good news is that everything still seems to turn freely under power so it doesn't look like I've messed anything up..... phew!

The instructions say to use solder to affix the retaining nuts in place. Experience from building the Quarry Hunslet suggests this doesn't work very well. The problem is that you need to fix the nut before snipping off the excess pin and filling the nut thickness down. When soldering the nuts the solder doesn't penetrate all the way through the nut which means when you start filling it down the first thing you do is file off the solder and the nut becomes loose. On the Quarry Hunslet I secured the coupling rod in place with superglue but still found this difficult as you get so little time to check and adjust things.

For Canopus I took a slightly different approach and have used LOCTITE 243 medium strength threadlocker. This gives me (according to the datasheet) 5 minutes fixture time (that's for brass, it's 10 minutes for stainless steel). Also unlike superglue it is designed to be reversible, assuming you can supply 26 Newton-metres of torque. I used a slip of paper to try and stop the stuff getting anywhere it shouldn't as well as ensuring that I didn't over-tighten the nuts. This seems to have worked well although removing the last bits of paper was a bit of a pain.

I haven't yet removed the excess crank pin or filled down the nut (this was as much stress as I wanted today) but having had it on the rolling rod everything seems to be working nicely. You can tell that the threadlocker is working as previously running in one direction would cause the nuts to work loose which is no longer happening. Now I've got past this point hopefully progress will pick up a little.

7 comments:

  1. I was wondering what had happened to Canopus.

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    1. I was scared of doing this step and messing it up!

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  2. Loctite is perfect as long as you don't want it transmit torque. It breaks with a crack of heat. It is great for racing car undertrays.
    I would use solder and watch for it running through the threads, use an acid wash before using a lead/silver solder. Don't ever be tempted by multicore solders. Have fun and try it over and over first until you have learnt the art.

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  3. Good news! Hopefully we'll see further developments on Canopus. And maybe some hand-made track to run it on...

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    1. Just ordered track and sleepers so now just have to wait on it arriving. In the end I opted for the Code 60 NS flat bottom rail from PECO that's designed to be used to model conductor rail. I decided that the difference between code 55 and 60 would be small and this way I'd get NS rail rather than steel.

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  4. Very interesting and I am very pleased that you are making progress. I have never had much success soldering coupling rod pins and nuts, although I have used threadlocker on bits of my 4x4 with success (nuts that were prone to vibration creep). It does take quite a bit of getting off, so I think your con rods will be fine!

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    1. From a brief test they do seem really well attached!

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