Cutting keyway in pulley

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Cutting keyway in pulley

This topic has 15 replies, 9 voices, and was last updated 16 November 2015 at 16:00 by Michael Gilligan.

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15 November 2015 at 18:55 #212476
David Brown 9
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@davidbrown9
I have a step pulley from my drill press, which I don't use much since I got my mini-mill. I want to fit it to a motor I have.

The motor has a 14mm shaft and 5mm keyway. The pulley is slightly too big for the shaft-around 15mm inside diameter. It does not have a keyway.

If I want to cut a 5mm keyway in the pulley I assume I need a 5mm broach. Can I do this in the milling machine (Sieg SX2) by hand, by putting the broach in the chuck? What size keyway bushing do I need?

How exactly do I do it? Also, will it work given that the internal pulley diameter is slightly bigger than the shaft on the motor? The pulley is just the size I want, so it would be a pity not to use it.

Also, how do I add pictures to my post?

David
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15 November 2015 at 18:55 #7871
David Brown 9
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@davidbrown9
15 November 2015 at 19:07 #212477
Neil Wyatt
Moderator
@neilwyatt
You will need a bush whatever you do, so incorporating the keyway in the bush will make life easier.

If you can mount the pulley in your lathe, I would bore it out to 19mm and fit a 19mm OD by 14mm ID bush in it, with a 5mm slot cut for a keyway in the bush. use a strong retainer and you should be OK.

Neil
15 November 2015 at 19:09 #212478
JasonB
Moderator
@jasonb
Sleeve the pully down to 14mm which you will have to do anyway then broach the pully complete with sleeve using a 14mm bushing.

You will need a tall mill if you are going to use it to push a 5mm broach through, if the pully is aluminium then a drioll press will just do as the broach can go through the hole in the table

You could save yourself £50 on a broach and bush by doing it with a simple tool in the lathe, these 4 3/16" (4.7mm) one in steel were done that way

J

How to include photos

Edited By JasonB on 15/11/2015 19:12:10
15 November 2015 at 19:10 #212479
John Haine
Participant
@johnhaine32865
Well, first you will need to sleeve the pulley to match the motor, otherwise it will be impossibly unbalanced. (Or sleeve the motor shaft to fit the pulley!)

You don't need a broach. I cut a 3/16 keyway in a steel bushing for a pulley by…
- Mounting the bush concentric in the lathe (actually it was already there having been turned and bored to size) – so likewise mount the pulley concentric in the 4J
- Making a shaping tool to fit a substantial boring bar I already had which gfaced the "wrong way", i.e. the cutting edge faced the headstock and was the right width for the key
- Fitting the boring bar to the carriage at centre height
- Using the lathe as a shaper, locking the headstock and cutting the keyway by using the rack to apply the cut and slowly applying the feed on the cross-slide.
It took a long time but worked fine and the keyway was perfect. It now applies the drive from a 3 phase motor fitted to my VMB, the bush being loctited into a larger hole in the pulley.

You could probably replicate this by mounting the boring bar in the mill chuck, the pulley on the table, and using the manual rack-and-pinion drilling feed to apply the cut, moving one of the table slides to increment the depth.
15 November 2015 at 19:46 #212484
David Brown 9
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@davidbrown9
I don't have a lathe.

How do I sleeve the pulley to match the motor shaft?

I would need to buy a boring bar, but I am sure it would come in useful. Should I use the R8 taper on the mini-mill? I have added some pictures-they are rather big!

David
15 November 2015 at 19:53 #212486
David Brown 9
Participant
@davidbrown9
OK, I guess it's obvious how to sleeve the pulley, I use a bush as Neil Wyatt advised. Bore out the pulley to 19mm and fit a bush, cut a 5mm keyway in the bush. I presume I can do this using 2 different sized boring bars in the mini-mill?

Would I need boring bars exactly 19mm and 5mm? Obviously I don't know exactly how they work!

David

Edited By David Brown 9 on 15/11/2015 20:04:11
15 November 2015 at 20:10 #212496
John Olsen
Participant
@johnolsen79199
There is a simple way of cutting a keyway that does not need a broach. Having to fit a sleeve might make it harder to do, but the idea is that you turn up a slug of the same sort of material as the pulley and fit it into the hole, flush with the face of the pulley. Then you make a centre pop mark and drill through with a size just a little under the desired size of key. Take out the slug from the centre, now you have half a hole where you want the keyway. Next you take a small square file and file out the corners. As you get closer to the size, use a piece of key steel to gauge the fit.

The idea of using a slug of the same material is that it stops the drill running off, as will happen if you use a piece of steel in an alloy pulley.
15 November 2015 at 20:10 #212498
Chris Evans 6
Participant
@chrisevans6
If you have R8 on your mill, mount the bar say 20 mm in a collet and a lathe type tool in the machine vice on the mill.. You can now turn the outer diameter to 19 mm for the desired length. Cut and face off, bore your pulley fit the bush and bore to 14 mm slot as required. I would just look at the cost of a new pulley first as it may be a cheap option.
15 November 2015 at 20:12 #212501
JasonB
Moderator
@jasonb
Easiest way without a lathe is to get a bit of bar, lets say 3/4" as that the nearest to 19mm if you can't turn it. set up a length in the mill pointing upwards and drill/ream or drill/bore a 14mm hole down the middle.

Now mount your hollow bit of bar horizontally in the mill vice and mill a 5mm slot right through it on ctr line so its like a "C" shape.

Now set the pully onto the mill table and bore out to fit the piece of bar

Loctite bar into new larger hole

Edited By JasonB on 15/11/2015 20:18:30
15 November 2015 at 20:18 #212505
Bazyle
Participant
@bazyle
I'm not sure why the suggestion was 19mm specifically. The key point was to avoid difficult keyway cutting. If you had a 19mm outside, 14mm inside bush you can, before putting it into the pulley, mill lengthways a 5mm gap right through the wall, maybe as a slot leaving a bit each end to hold it in shape. Then you glue it into the pulley and hey presto a keyway is formed. Depth is (19-14)/2 or 2.5mm.

You can make the bush in the mill if you have a boring head (not a boring bar) and can firmly hold a bit of rod vertically. Don't forget a boring head can just as easily machine the outside of a vertical cylinder as the inside of a hole. Other options exist if you have a rotary table and no boring head but if you have a mill you will have to get both some day.

Edit: looks like Jason drew a 'hole' picture in the time it took me to write.

Edited By Bazyle on 15/11/2015 20:22:30
15 November 2015 at 20:27 #212507
Neil Wyatt
Moderator
@neilwyatt
Posted by JasonB on 15/11/2015 20:12:47:

Easiest way without a lathe is to get a bit of bar, lets say 3/4" as that the nearest to 19mm if you can't turn it. set up a length in the mill pointing upwards and drill/ream or drill/bore a 14mm hole down the middle.

Now mount your hollow bit of bar horizontally in the mill vice and mill a 5mm slot right through it on ctr line so its like a "C" shape.

Now set the pully onto the mill table and bore out to fit the piece of bar

Loctite bar into new larger hole

That, I think, is what i suggested in the first place.

Here's a drawing:

Yyes where did Jason's pic come from!

Edited By Neil Wyatt on 15/11/2015 20:28:56
15 November 2015 at 20:38 #212512
JasonB
Moderator
@jasonb
Yes Neil same as yours now that I know David does not have a lathe, mine assumed he had a lathe.

J

PS my drawing came from somehere better than yours
16 November 2015 at 10:23 #212586
Ian S C
Participant
@iansc
Jason's method is the one to go with, and if all else fails, the slot can be cut with a hacksaw, and filed to 5 mm. I remember someone came up with this in a letter in Model Engineer, probably in the 1990s. I'v used it for a repair on agricultural machinery, the inserted bush was hardened inner part from a bearing, so the slot was cut free hand with the angle grinder, 5 or 6 years on its still working well.

Ian S C

It was the drive on one of these machines for feeding out large hay bales.
16 November 2015 at 11:21 #212610
David Brown 9
Participant
@davidbrown9
Thanks for all the advice. Amadeal in London do a 2 inch boring head set, 9pc 1/2 inch boring bars, for a R8 holder, would these be the right size?

I realise buying the pulley would be cheaper, but I can use the boring head set again and again in the future! I am making a mirror grinding machine and will need more pulleys etc so the boring head set is likely to get used again.

David
16 November 2015 at 16:00 #212649
Michael Gilligan
Participant
@michaelgilligan61133
Posted by David Brown 9 on 16/11/2015 11:21:01:

I realise buying the pulley would be cheaper, but I can use the boring head set again and again in the future!

.That's the attitude, David

MichaelG.
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