Harden Boxford Main Spindle Key?

I need to replace the key that locates the sliding gear on the main spindle on my CUD. The old one is fairly worn and it ocurred to me that it might be worth hardening the replacement. I've bought a piece of key steel and I found a post in the forum suggesting the material should harden ok. Any reason not to?

Edited By William Chitham on 27/06/2019 10:57:48

Hi William, personally I wouldn't. good key steel should be tough enough to be used as is. If you harden it and you have a jam-up, it could do damage to the key way in the shaft and/or the gear. In all my professional day job, I've never come across a harden key.

Regards Nick.

William, its better that the key wears, or breaks that you damage the spindle key way, or the gear, keys are cheap.

Ian S C

I agree with the above. By the time you have hardened it and tempered it you might well be back to its supplied hardness. Better to check the keyways and make a stepped key, if necessary.

Thanks all, I'll leave it as is, it seems a bit of a weak spot in the design though. That key has to transmit all the driving torque to the spindle as well as having to slide back and forth in the keyway and it has no direct means of lubrication. And for some reason it is only about 2/3 the length of the keyway slot in the gearwheel.

William.

Key steel is tougher than mild steel, Boxford must have had a reason to use an unhardened one. If you make a close fitting replacement, which can slide with the minimum of play, it should be fine. Make a couple of spares, and maybe use a little moly grease when re assembling.

A sliding key like that is sacrificial, like brake pads and clutch plates. It takes all/most of the wear so it is easy and cheap to replace.