View Full Version : Shaft extension with internal keyway. Anyone tried doing it like this?

04-19-2008, 05:26 AM
I want to use this motor in a winch, but I need to extend the shaft.

I'm thinking about getting a piece of 4130 tubing, chucking one end, and supporting the other end in the steady rest while I bore the ID to the shaft diameter. Then, I'll use the mill to cut a slot to clear the key. Last, I'll slide on a sleeve to cover the "keyway", and tack-weld the end to hold it in place.

Has anyone ever done a keyway like that?


04-19-2008, 06:03 AM
If I am reading correctly, I think that slotting the tube all of the way through, to clear the key is going to cause it to spring open as soon as you make the slot.

I think a better option, lacking a keyway broach or shaper, would be to simply file cut a keyway. I have done this a few times over the last few months with good results.


04-19-2008, 06:31 AM
never done it as a shaft extension, but have done it as a method of internal keyway

why don't you just broach it on the lathe?

You make up something like this


then put it in the carriage, use your lathe as a shaper, slide carriage back and forth, taking off a thou at a time

04-19-2008, 06:35 AM
Sounds like a good solution to me, given there are no restriction on 'tidiness' or the o/all dia. Go for it

oil mac
04-19-2008, 08:06 AM
One of the products made by a firm i once worked for used to make a similar type of coupling on a motor shaft, to connect to another shaft, This is an old idea, called a Muff - Coupling Make sure you have plenty of body in the coupling wall and a couple of pinch screws might not go amiss bearing on the top of the key Should your driven mechanism, and motor be securely bolted down that nothing moves axially you should have a safe enough assembly

04-19-2008, 08:21 AM
I've done it before,but you don't need the extra sleeve.Just slot through the side wall stopping short of coming out the end.Then slip the part over the shaft and insert a piece of key in the slot so it bottoms out in the shaft.Put a couple center punch marks at each end so it holds tight,slide the whole assembly off the shaft and weld the key directly into the adapter.

It won't shrink the bore down since the key is in there and it returns the bore to being a soild piece.If you want insurance against shrinkage make up a dummy shaft with key way to match the motor and do the welding with the dummy in the bore.

You just need to take care that the key slot is machined dead on center.

04-19-2008, 02:54 PM
"Just slot through the side wall stopping short of coming out the end....."

Thanks for the excellent suggestion. Even if I don't weld the key in, it'll be useful to keep the tube from opening up.