Keyway cutting

Any good easy ideas for cutting an inner and outer slot for a keyway?

What size keyways and what size hole & shaft??

Brian

The quick (and silly) answer Malcolm is a shaper - but if you had one available, then you would have known that already.

Obviously, external slots can be milled (or flycut) in a lathe or mill.

However, internal slots need some form of linear cutting tool - in industry a slotter or shaper - which essentially move a cutting tool in and out of the bore to cut the slot. This can be done on the lathe with a tool held in a boring bar mounted on the cross-slide and by racking the saddle too and fro to make the cut. Not ideal but it does work. There have also been several designs published for slotting tools that fit on the cross-slide that make things easier.

Hope this helps.

Regards,

IanT

Edited By IanT on 02/05/2017 23:51:40

YOu can hold the shaft in the toolpost at the right height, the end mill cutter in the lathe chuck and machine it that way. Then do the internal as described above, using the lathe as an impromptu shaper or slot cutter.

That's what this is for

I'm sure we have discussed this before...but anyway, assuming you don't happen to have a slotter or a shaper lying around, make a plug of the same sort of material to just fit the hole. Loctite it in, flush at one end. Make a centre pop mark on the line where the two materials join just where you want the keyway. In the drill press, drill a hole just under the size that the keyway is supposed to be. Knock the plug out, using heat if necessary, and now you have about 75% of your keyway done. With a suitable file, file out the corners to make it square, trying the key frequently until you have a good fit.

You can do them on a shaper, and since I have three shapers I have done this, but if you only have one or two to do it is faster to do them by hand as described above, since otherwise you have to mess around making up the right tooling for the shaper.

For the shaft, a slot drill as described earlier is good, but otherwise they can be done by hand too. You drill a hole at each end and then chisel out the material between with a small cold chisel. The old millwrights did a lot of them this way, since the shafts were often not readily removable to take to a machine.

John

Buy or make a

broach?

Thanks for your suggestions

Malcolm

Dunno if you have the proper sizes to hand but working to a measured dimension is much easier than sneaking up by cut'n try.

This link gives imperial sizes :- **LINK**

and this one metric sizes :- **LINK**.

With a bit of care and accurate drilling you can arrange matters to leave very little metal in the hub to be filed or slotted out. A CAD program is a great help when sorting out exactly what size drill to use and where to put it. If you plan to file and have a suitable size piece of tool steel its worth arranging a single tooth fixed depth broach on a round bar made a nice sliding fit in the bore. Only good for a couple of thou each side but will clean up the slot really nicely.

Milling is by far the best way to put the slot in the shaft. Quite easy with the dimensions to hand.

Clive.

I'm interested in general regarding cutting internal keyways, but not sufficient to buy a set of broaches for my occasional use. But I saw this video ( https://www.youtube.com/watch?v=XcU0LTavzDM ) where a single cutter held in a lathe toolpost is fed into the component held in a stationary lathe chuck, with the cross-slide and saddle being used to make the lengthwise and depth cutting. I'm guessing this is what IanT alluded to above. IanT also alluded to DIY designs for this tool - does anybody have diagrams for such a tool?

There is no need to buy a set of broaches, only the size that you need and make your own guide bushes. 3mm keyway broaches are available from $29 on ebay, 6mm for $43. I have a couple and good enough for hobby work. Larger sizes get more expensive.

You will need a lathe for makinging the bush, milling facilities for cutting slot in bush and shaft and a means of pressing the broach thru the bush. (before I had a hyd press, I used a drill press to push thru a 3mm slot)

Paul.

Thanks Paul - even at that price (and it is higher in the UK) it's still greater than I would like to pay for something that I might never use. However, the ability to grind my own HSS tool to suit - if the need arises - appeals to me. And as I have both lathe and milling machine - the machining aspects are not difficult. I just need some idea of cutting angles for the HSS tool. I could even regrind a parting tool to provide the pushed cutting edge - after all the video shows the tool acting just like a wood plane does. It may take longer than broaches - but I have the time and the items I envisage I might need to keyway will be small and one-offs.

You could perhaps save time (edit: and the strain on the lathe) by starting the keyway with a small slot drill so that you only have to remove the corners from a D shaped slot?

Brian

Edited By Brian G on 25/01/2019 12:27:12

This is a very crude thing I made to move the saddle backwards and forwards for slot cutting in the lathe. It avoids putting too much load on the rack and pinion.

The lever pivot part is clamped to the lathe bed with blocks of wood and lengths of threaded rod.

Les.

If you have access to the archives there was a plan for a slotting attachment in issue 6 August/September 1991 which would meet your requirements

Mickyt

Here are the things I have made to do internal keyways:

http://mikesworkshop.weebly.com/toolpost-slotting-tool.html

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

Mike

No need to waste your time and materials knocking up special tools just a suitably sized HSS toolbit in your toolpost will do. Or if you want a boring bar with a tool mounted on it's side.

Edited By JasonB on 25/01/2019 13:05:57

Needed to do a couple of keyways in some new drive pulleys for my mini lathe. Milled the slots under size then filed them to fit. Depth is not critical and width can be controlled with a small file easily enough. Both now fitted and lathe back working.

… 'For the shaft, a slot drill as described earlier is good, but otherwise they can be done by hand too. You drill a hole at each end and then chisel out the material between with a small cold chisel. The old millwrights did a lot of them this way, since the shafts were often not readily removable to take to a machine'.

John

Ahh my apprentice days. Also did the famous hacksaw, chisel, file, scrape a 1" cube out of 2" round stock. If you did anything wrong you would get a clip 'round the 'ear'ole, job thrown down the shop followed by a few 'choice words', hurt at the time but never did me any harm. Can't do that these days, would be charged with verbal & physical abuse, too many snowflakes & millennials. 'Work ethos' has gone out of the window for some, fortunately not the many but quite a few in my 55yrs engineering experience.

George.

George.

Thanks to everyone - the drill out with a slot drill to ease the strain on the lathe is good idea. I will also investigate the archives and follow up Michael Cox and JasonB suggestions.

I think this is all I need to know to start to practice keyway cutting - thanks to everyone again. Will suggest that my input to this thread is now answered.