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Cutting a keyway without a broach

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Robin Graham08/11/2018 20:19:47
438 forum posts
82 photos

I need to make a keyed fitting between a 19mm shaft and a steel sprocket wheel. I'm thinking a 5mm square key, looking at the keys on my lathe changewheels. I can mill the way in the shaft OK, but don't have broach for the internal way in the wheel. Or a press for that matter.

I think I've read that this can be done by 'planing' on the lathe. Can anyone advise or point to advice about tool geometry/DOC/feed for this process?

Robin.

Ian Childs08/11/2018 20:30:36
11 forum posts

The way I did this was to make a tight fitting dolly, centre punch the line in the required position and drill through both the edge of the hole and the dolly, remove the dolly and then file the half round hole square to fit the key. This was in a sprocket too although the hole was a bit bigger. Think I did it three times like this.

David George 108/11/2018 20:38:26
avatar
510 forum posts
184 photos

Hi robin you can rough out the internal keyway using a slot drill in a mill then transfere it to a lathe and finish it with a tool ground to the correct width taking small slices untill corect depth. I have a piece of silversteel cross drilled with a 6mm hole and a grub screw in the end to clamp the has tool bit ground to suit the key size like a part off tool on its side.

David

Andrew Johnston08/11/2018 20:47:13
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4155 forum posts
502 photos

You just need a toolbit that looks like a short parting tool. Like these:

slotting tools.jpg

These tools and bars are actually intended for use in a slotting head on the vertical mill. But they could just as easily be mounted in the toolpost on the lathe and moved back and forth with the saddle.

Andrew

Neil Lickfold08/11/2018 20:53:34
467 forum posts
89 photos

If the tool is sharp, you can push through 0.001 inch depth of cut to about 0.002 inch depth of cut, from 0.002 inch diameter to a max of 0.004 inch diameter. Metric 0.05mm to 0.1mm max on diameter. The blade or cutting wants to be around 5 deg or so . If you make it too much like a chisel, it will pull the cross slide in and try to keep making a deeper cut. Having the tool face , the one in line with the bore, if that is set so it is about 1 deg clearance, this will also help to stop the tool digging in. Any material taken out before hand, dramatically reduces the cutting loads. Even if you hand file a rough slot , and then use the tool in the lathe for finishing the key slot works well. HSS works really well for lathe key slot cutters.

Neil

AJW08/11/2018 21:00:04
121 forum posts
54 photos
I have cut keyways in a couple of flywheels using Andrews method, it worked well.
I pushed it through in small stages with the tailstock.

Alan
Michael Cox 108/11/2018 21:59:27
486 forum posts
27 photos

Here is an easily made adjustable broach:

http://mikesworkshop.weebly.com/small-hole-slotting-tool.html

I would suggest that you remove most of the material by drilling or milling first and then use the adjustable broach to clean up the slot.

|Mike

John Rudd08/11/2018 22:14:33
1242 forum posts
57 photos
Posted by Andrew Johnston on 08/11/2018 20:47:13:

You just need a toolbit that looks like a short parting tool. Like these:

slotting tools.jpg

These tools and bars are actually intended for use in a slotting head on the vertical mill. But they could just as easily be mounted in the toolpost on the lathe and moved back and forth with the saddle.

Andrew

Excellent!

ChrisB08/11/2018 22:51:09
202 forum posts
87 photos

+1 for Andrew's method.

I did something similar but in a much simpler crude way. Drilled a steel bar to take a drill bit radially, locked in position by a screw. 20181006_142735[1].jpg

Hopper08/11/2018 23:26:50
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2969 forum posts
50 photos

I've done a few Myford change gears the abovementioned way, converting early pin-drive gears to the later keyway type. I just used the regular boring bar with toolbit in effect turned sideways. Racked it back and forth with the carriage handwheel, taking one to two thou cuts. Tool geometry was as described above, about 5 degrees back rake, plenty of clearance on the sides and front, and honed razor sharp. It's a rather tedious process but you get there. I would not like to do a full set of change gears like this in one sitting! But fine for a one-off.

Andy Pugh09/11/2018 01:31:30
43 forum posts

With a CNC it becomes quite easy. 

Edited By Andy Pugh on 09/11/2018 01:32:28

Danny M2Z09/11/2018 04:34:22
avatar
652 forum posts
265 photos
Posted by Michael Cox 1 on 08/11/2018 21:59:27:

Here is an easily made adjustable broach:

http://mikesworkshop.weebly.com/small-hole-slotting-tool.html

I would suggest that you remove most of the material by drilling or milling first and then use the adjustable broach to clean up the slot.

|Mike

Brilliant Mike, I like the fact that it is adjustable. Maybe that's why I should visit your site more often

* Danny M *

clogs09/11/2018 06:59:30
416 forum posts
12 photos

I've never bothered,

I use the mill to slot the shaft and again the mill to slot in the pulley etc.......as for the pulley, as long as the slot is deep enough, at least 1.1/2 times normal keyway depth, I leave the slot with a rounded top......custom make the key from flat stock.......can't justify buying special tools for the odd job and besides the keyway is usually covered with a nut and washer anyway.....

it's not a perfect world.......I'm sure this'll create trouble on the forum but life is to short........

this has been my go to method for years and it has been sucsessfull on high horse power items used on tractors etc.....clogs

Kettrinboy09/11/2018 09:31:36
64 forum posts
17 photos

I,m with clogs on this one as I said in another thread a few days ago ,if you want it to look pleasing to the eye its easy to make a rounded top key from some flat stock by using an edge rounding milling cutter, so say for a 6mm wide key a pass either side with a 3mm rad cutter forms the round top and a bit of fitting with a file fits it in the keyway , so compared to the lathe method it takes a bit longer to make the key but way less time to do the keyway.

regards Geoff

Trevor Roberts09/11/2018 09:39:40
6 forum posts

Have a look at this link.

**LINK**

 

Clickspring is an interesting site. There is a link to him using the cutter, I think t is him making a keyway in a pulley.

 

Regards

 

Here is the link to the pulley

https://www.youtube.com/watch?v=e4apNy_2AB8&t=0s&index=3&list=PLZioPDnFPNsHepuEmjmiRiuXYZrHnu7QY

Edited By Trevor Roberts on 09/11/2018 09:42:47

Andy Pugh09/11/2018 10:11:31
43 forum posts

I haven't seen a mention yet of a hand-slotting attachment for this task.

One is mentioned and shown in a photo here:

**LINK**

(That forum, especially the pre-ww2 section, has a number of fascinating 12" to the foot models being built.

Farmboy09/11/2018 11:33:43
99 forum posts
8 photos

I have successfully planed a keyway in an aluminium pulley with a home made bit in a standard boring bar mounted in the toolpost.

I also have fond memories of watching my late father cut a perfect 1/4" keyway in a steel shaft with a cold chisel.

Now, this is probably a silly question but, in my ignorance, I am wondering if/why a key really needs to be square. Taking an earlier suggestion about mounting the pulley on a mandrel ( or perhaps its own shaft ) and drilling on the join line before filing square, what would be wrong with just fitting a cylindrical key? Obviously it would only work on the end of a shaft. The crucial area would seem to be the interface between pulley and shaft, where the shear effect on the key would be concentrated. Is the shape of the body of the key important?

Mike.

Andy Pugh09/11/2018 12:50:33
43 forum posts
Posted by Farmboy on 09/11/2018 11:33:43:Now, this is probably a silly question but, in my ignorance, I am wondering if/why a key really needs to be square

They don't. Tangential keys, used in pairs, are (or were) sometimes used:

**LINK**

Of more relevance here, you suggest cylindrical keys. These work well, but why limit yourself to plain cylinders? threaded keys into tapped holes half-and-half drilled can work very well and are very secure.

There were a couple of examples on my Harrison milling machine.

Mick B109/11/2018 13:08:40
767 forum posts
47 photos

+another 1 for Andrew's method.

I was actually taught to do it this way at the Government Training Centre where I learned the lathe in '75, and it was one of the exercises. Broaching was for batches of tens to hundreds.

I've used a similar technique to shape out square through-holes in the lathe from round - at some cost in blistered palms!

AJW09/11/2018 17:25:10
121 forum posts
54 photos
This post spurred me on to put the keyway in my otherwise finished flywheel!
Using Andrews method, I fitted a length of shaft into the bore secured with a dab of picture on the end, just enough to hold it in position.
I then drilled down through the joint line with a 3/32 drill which was then opened up to 3mm.
Shaft tapped out I adjusted the broach to remove about ten thou per cut. Could almost be tapped through by hand although a hide mallet was used.
Came out well and didn't take long.

https://www.model-engineer.co.uk/albums/member_photo.asp?a=49026&p=816425

If photo doesn't work it is in my photos!

Alan

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