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Internal keyway on a lathe

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John Hewes04/02/2014 18:34:20
22 forum posts
2 photos

Hi, I need to cut a keyway in the bore of an aluminium alloy pulley for a wood turning bowl lathe drive.

I am planning to do this on my Boxford lathe by making up a boring bar to almost the bore size and fitting an adjustable cutter near to the end so that I can use it as a broach, a little at a time.

Any advice, please as I haven't done this before.

Two specific questions:-

Is it sufficient to lock the faceplate by engaging the back drive as well as the mandrel drive pin?

Do I need a leadscrew handle, or should I just use the saddle handwheel?

Thanks in advance


JasonB04/02/2014 18:41:00
23063 forum posts
2769 photos
1 articles

I've done it several times and just used the saddle handwheel and the lowest gear to hold the chuck. Just take a couple of though at a time and let the spring work out of the tool once you get to depth.

You should not need to move the cutter in the tool once its set just wind the cross slide back towards you.

In alloy the tool should not bee dto be massively thick, I have used a 1/2" boring bar with a 5/32" HSS square tool bit in steel without problems.

Stub Mandrel04/02/2014 19:07:05
4315 forum posts
291 photos
1 articles

Unless your tool shape is very poor, there will be no forces trying to rotate the work, so you don't need heavy duty clamping. Also, once you have started the groove it will tend to guide the toolbit.

A sharp tool is essential as the force to take cuts may be more than you might expect. As Jason says, expect to work the spring out of the cutter.

Also make sure there is plenty of relief on the front of the cutter (the side facing you).


Clive Foster04/02/2014 19:26:32
3173 forum posts
113 photos

Job goes a lot faster if you drill a hole to remove most of the material first so your tool merely has to bring the hole to shape rather than cut it from scratch. Plug the bore with a spigot of the same material and set the drill centre just inside the junction between bore and plug so the part circle hole is a little shallower than the keyway depth.

How close to the keyway width you choose to drill is down to your nerve and equipment capabilities. I find something around the 0.5 mm - 1/32" undersize works fine.

First time though its probably best to draw things out so as to get a feel for relative positions of hole and final keyway. Easy with CAD. Especially if the keyway is shallow th eprocess is not quite as obvious as it appears.


John Hewes04/02/2014 22:20:27
22 forum posts
2 photos

Thanks all for your advice.

I'm not sure Clive that I can drill such a small hole accurately enough though. I suppose I have several tries around the hole if I mess it up!


Les Jones 104/02/2014 22:56:51
2261 forum posts
156 photos

Hi John,
I find it better to have the tool cutting when pulling it towards the tailstock. It is less inclined to dig in.


Thor 🇳🇴05/02/2014 05:24:05
1660 forum posts
46 photos

Hi John,

if you have access to a milling machine and the pulley isn't to large for the milling table you could first mill the keyway before broaching.


IanT05/02/2014 09:24:17
2002 forum posts
212 photos

Or find someone (Club/Friend?) with a Shaper of course!


Brian Wood05/02/2014 11:09:03
2579 forum posts
39 photos

Hello John,

I have in the past made a bush with a sawn out and carefully filed key slot on one side and fitted that to the bore of a pulley for a similar fix. Once the Loctite had set I drilled a small hole on the joint face to contain a locking pin and then turned the bore of the bush to finished size with light cuts.

It saved me hours of planing away using the broaching method and worked just fine


Nigel Bennett05/02/2014 12:42:54
460 forum posts
20 photos

When doing this, I always secure the lathe spindle. Ensure the lathe power is switched off. Stick a chuck key in the chuck and tie a weight to it to take out any movement in the lathe spindle.

John Hewes09/02/2014 10:31:42
22 forum posts
2 photos

Hello again.

Just to let you know that I managed this fine with all your help, Gents, thank you.

Nigel, I took your advice, but used a bungy rubber to hold the faceplate in place.

I now have another question but will start a thread under "beginners".

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