Protecting areas from case hardening.

I occasionally make crank pins for motor cycle crankshafts. Often these are tapered pins and they are drawn into the taper in the flywheels with nuts that are tightened up with plenty of torque. In order to prevent too much depth of thread becoming hardened and consequently too brittle I usually make a couple of spare nuts and cover the threads with them so that the case hardening is not so severe over the threads. Is there a simpler more reliable method that can be used?

When silver soldering, I paint Tippex onto parts that I wish to keep safe from an overrun of flux/solder. It works well and certainly stands up well to red heat and washes off with water. Might be worth a go.

Mick

Bob copper plating will stop the carbon dissolving into the threads but using sacrificial nuts is probably a simpler way and of course you can use them several times providing the thread is the same.

Fire clay would probably also work but I have not tried it and it may be difficult to remove it -- suck it and see on a test piece ! Tipex well again it might work, it certainly does on silver soldering so it's worth a couple of test pieces, try threaded and plain sections and see what happens.

Regards John

Why don't you carburise in your usual way before you cut the thread. Then cut the thread which will remove the high carbon layer on the threaded section. Heat and quench to harden and you are there.

regards Martin

Good Idea Martin I will give it a try.