Should I harden a key?

Ive just remade a 4mm section key to fit the end of my lathe leadscrew for attaching changewheels. I had to make it from mild steel and file it to an exact fit as I'm
not sure if the key was originally slightly undersize or the shaft keyway was a little oversize (it hasn't had too much use eitherway, so shouldn't be wear & tear!) so needed to make the new key minutely oversize, rather than just use 4mm stock. Question is - should I case harden it (with Casenit) before use, or do you reckon it will last OK without?
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Make another at the same time.
Use the first unhardened as you suggest.
Although not ideal it will outlast you and the next two owners in sequence of your lathe. Remember that everything we do is almost a prototype so we don't know until we try things out whether they will work.
However, if it does wear quickly, then harden the other one before use.
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i don't think so .. i don't think the gears are under much stress until you crash ..then you do want something to give .
my smart and brown 1024 has a shear pin in the gear train ..the shear pin is tiny .2mm diameter....ive only broke it once when the tool dug in ..
think mild steel on its own will be OK ..as long as its a nice fit .
all the best.markj
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Thanks for the thoughts chaps. makes sense - I'll leave it as is (unhardened) and see how it goes.
Mind you, I bought this small tub of Casenit some years back at an exhibition thinking (as you do) 'That'll come in useful'... have never had cause to use it since so I am almost looking for an excuse to use it on something! (its never been unsealed - I don't suppose it 'goes off ' does it ?)
regards Mike
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wrote:

If you ever have cause to make any T-nuts for the lathe or mill, case harden them. The threads will last much better DAMHIKT!
Mark Rand RTFM
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