Cutting a keyway without a broach

[Robin GrahamParticipant @robingraham42208]

[Robin GrahamParticipant @robingraham42208]

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 ChildsParticipant @ianchilds37813]

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 1Participant @davidgeorge1]

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

[Anonymous]

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

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 LickfoldParticipant @neillickfold44316]

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

[AJWParticipant @ajw]

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 1Participant @michaelcox1]

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 RuddParticipant @johnrudd16576]

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:

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!

[ChrisBParticipant @chrisb35596]

+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.

[HopperParticipant @hopper]

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 PughParticipant @andypugh44463]

With a CNC it becomes quite easy. 

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

[Danny M2ZParticipant @dannym2z]

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 *

[clogsParticipant @clogs]

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

[KettrinboyParticipant @kettrinboy]

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 RobertsParticipant @trevorroberts83547]

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 PughParticipant @andypugh44463]

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.

[FarmboyParticipant @farmboy]

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 PughParticipant @andypugh44463]

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 B1Participant @mickb1]

+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!

[AJWParticipant @ajw]

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

[Robin GrahamParticipant @robingraham42208]

Thanks chaps, as ever. Seems that his is very doable – now I have numbers / pictures for tool geometry I shall grind a tool and proceed with confidence. Well, optimism at least!

Robin.

[peak4Participant @peak4]

Some years ago I had a need to cut some splines on the outside of a gear linkage shaft on the Ducati; I was replacing an old rusty one with a custom stainless shaft.

The method I used was akin to the one shown in Andy Pugh's Historic military Vehicle Forum link earlier.

The machinist there used a home made slotting attachment, but in my case I effectively replicated something similar with the Myford S7 top slide.

I removed the handle, end plate and feed-screw from the top slide, and replaced it with a short section of angle iron; 2 screws fixing it to the top slide casting and with one cross drilled vertical hole in the centre.

That hole then allowed me to use 4 short lengths of flat bar, with a hole in each end and a long length of 1" x !/4" steel as an operating handle, in a similar manner to that shown in the link. ( the operator there used 2 bars and a shackle to link the slotting plunger, handle, and fulcrum point.)

The main pivot point for my handle was a vertical piece of round bar bolted into one of the cross slide T slots. It cut the splines fine, and there was no wear on the saddle rack or handle gear; I locked the saddle for rigidity.

I've since used it to cut slots in pulleys using the same boring bar, still set horizontally in the tool-post but with a square ended HSS insert, rather than a pointed one, as I'd previously used for the splines.
The tool I used was very similar to those shown right at the beginning of this thread by Andrew.

It seemed to me a better way of doing the job than the constant traversing of the saddle with the operating handle.

Also this method allows one to cut slots or splines on a taper, without the need to build a fancy dedicated slotting attachment.

I know a picture tells a thousand words, but the Myford and the slotting handle are about 30 miles away at the moment.

 

Bill

Edited By peak4 on 10/11/2018 00:11:34

[peak4Participant @peak4]

p.s. Just out of curiosity I typed "using top slide as a slotting attachment" into Google and found a post with illustrations on this very forum.

Mine was very similar to that shown in the book, but with the fulcrum on the cross slide.

Finding and linking to that earlier would have saved me a lot of typing.

Bill

[Les Jones 1Participant @lesjones1]

This is a lash up I made to reduce wear on the rack & pinion when cutting keyways.

A block of wood was cut to fit between the slide ways on the bed and a T bracket made from offcuts of angle and box section. This was bolted through the wooden block to two wooden cross pieces under the bed. I might even get round to making proper pivot points some day rather than just bolts. It is also quicker than using the rack & piniion. One other point. Some times I find it better to mount the tool bit so it cuts when moving towards the tailstock rather than towards the headstock. It hase less temdency to dig in.

Les.

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