By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Internal Key-way Shaping

All Topics | Latest Posts

Search for:  in Thread Title in  
Nigel Graham 224/11/2020 00:15:33
921 forum posts
16 photos

Faced with possibly having to cut internal key-ways or splines in some gears:

I know the common dodge of using the lathe as a sort of shaper is poor practice especially on a light machine like a Myford 7; though a Harrison L5 might be man enough to take the widths I need cut, if taken gently. (Up to 1/4inch / 6mm)

I could use my Drummond manual shaper, and I know for such tasks the tool is not pushed through the work on the cutting stroke but pulled, with the clapper-box locked by an upwards extension to the tool-holder. *

Or I could make a slotting-tool rather like a boring-bar to fit a small fly-press. (Broaches are a bit on the pricey side for me...) One possibility I have is to adapt an old boring-head for this duty, so setting the depth for each stroke is simpler. More accurate too as it keeps the cutter itself aligned.

On which, would it be permissible to use the lathe's tailstock to drive said boring-head, which has a matching taper; or will that force an excessive and unbalanced load on the tailstock?

My main question though is the width of the tool assuming 1/4in / 6mm maximum. Would it better to use a thinner tool and offset the work or cutter to widen the slot, or go in with light cuts by a full-width tool?


* The shaper. I do know too that the cutting edge should be under the clapper fulcrum, but learnt that only quite recently, and I have seen and probably been guilty of some very unfair tool-setting on shapers.

Clive Foster24/11/2020 00:24:17
2540 forum posts
83 photos

For a simple single keyway shaping in the lathe is fine if you drill out most of the material first. Sacrificial bung in bore and drill around 1/16" under key size has worked fine for me in the past using a SouthBend lathe.

In steel I'd probably use a needle file to clean out most of the corner too.

Accurate indexing for splines would seem too troublesome in the lathe.


not done it yet24/11/2020 07:21:35
5428 forum posts
20 photos

I remove the complete clapper box assembly on my Drummond, for a duty such as this.

I turned up a new spigotted plate and driiled a hole (central, I think), tapped it, and screwed in a cutting tool holder. Works well but is a bit limited to the length of slot.

David George 124/11/2020 07:51:42
1434 forum posts
459 photos

Hi Nigel I have cut keyways on a small lathe. It takes a while as I only take a thou or two at a time and repeat cut the same cut to make sure that it is not building up a cut and I have dropped a slot drill down the bore on the mill to relieve the amount of material to be cut. I have also relieved the bore with a groove to have a place to stop a keyway to run out to when it can't be cut through.


John Olsen24/11/2020 09:30:26
1126 forum posts
92 photos
1 articles

Clive mentions drilling first, I would agree but I would go much closer to the final size. The bung should ideally be the same material as the workpiece. Fit it flush and centre pop on the joint line. Then drill to close to final size. Maybe 5% under. This takes out nearly 80% of the material. Filing will take out the rest. Although I have shapers, if I only needed one keyway I would do it this way rather than set up to do it on the shaper, which would take longer. Unless it was the one or two sizes that I have already made tooling for of course.


JasonB24/11/2020 09:34:39
19603 forum posts
2150 photos
1 articles

I've done upto 3/16" wide on the lathe but it's slow going and did put a lot of load onto the rack. It's a case of weighing up what it may cost to replace a damaged part of the machine or buying the broach which at £36 would soon be the better option. Assuming you have a suitable press to drive the broach in the first place.

As you have the shaper I would go with that even if you have to do a central 3mm slot then change to a 6mm cutter to widen it which is probably preferable to doing two side by side 3mm slots as tool mat deflect into the first slot.

IanT24/11/2020 10:08:01
1750 forum posts
164 photos

Hi Nigel,

There are often posts on here about cutting keyways - and I'm frequently tempted to say "I'd just use a shaper" - but there's not much point if they don't have one. However, in this case, you do - so why not use it?

Don't worry about the cutting edge being under the fulcrum (most of mine are not) and especially not in this case as the clapper will be locked and the tool needs to reach into the hole. Nor do you need to cut on the 'pull' stroke - although some folk seem to prefer this.

I use a simple 'L' shaped holder, which is a bit bendy so only takes light cuts. Make sure the cutting tool has plenty of side clearance. Don't go too deep with relation to the width of the slot. Not in this case - but in larger holes, you can view an internal slot pretty much like an external slot and there is good advice in Delmar about that type of work. If you don't have Delmar yet - then I'd advise downloading it as your shaper reference bible.

You might also have a look through this (rather long & windy) article that has some good ideas about purpose tool holders and set-ups which you may find useful. A simple 'L' shaped tool holder (welded or brazed) will do for a one-off light duty job but if you intend to do a lot of internal slotting then a direct thrust one will be better. On my TUIT list but not got around to making one yet.

Keyway Slotting in the Shaper



Mike Poole24/11/2020 10:52:46
2857 forum posts
67 photos

Stefan Gotteswinter used the quill of his milling machine to shape a key way, he did make a solid spindle lock to stop any rotation. There are a few key way solutions for the Myford that mount on the cross-slide and completely relieve the rack of any involvement. A shaping machine is ideal for key way cutting and if I had one it would be my first choice, a slotter is even better but they are rare even in tool rooms. My VMC doesn’t know yet that it will be called for slotting duty soon but it will be interesting.


JasonB24/11/2020 11:02:17
19603 forum posts
2150 photos
1 articles

I've slotted with the X3 Mill but only in bronze after drilling out most of the waste which worked well but Would not want to do 6mm wide in steel that way. On the VMC it may be possible to raise the table rather than pull down the quill as I had to.

Mike Poole24/11/2020 11:23:16
2857 forum posts
67 photos

I haven’t tried it yet Jason but the spindle lock will be good for both methods, if the quill objects then the table will be more robust, I suspect either method will be a bit of a workout. I have a broach but the bush is too short so I would need to make a new one, athe moment I don’t have a press but the Meddings drill or the VMC might be capable of pushing it. The job is only a 1/8” slot in aluminium so should be fairly easy.


JasonB24/11/2020 11:26:09
19603 forum posts
2150 photos
1 articles

I drive my 1/8" and smaller broaches with my old Narok drill press which seldom gets used for drilling these days. Works OK on steel and CI

Edited By JasonB on 24/11/2020 11:26:31

Andrew Johnston24/11/2020 11:56:36
5841 forum posts
662 photos

I've used the Bridgeport quill to drive a 1/8" broach in cast iron:


But I was pushing my luck and wouldn't do it again. Although I now have a proper arbor press broaches can still be fiddly:


I cut the internal splines (5/16" wide) on my traction engine gears (EN24) using a home made HSS cutter and a slotting head on the Bridgeport:


This was a trial run on an embryo gear I fudged up. The end of the tool is curved to match the external spline:


Given that a shaper is available there's no question that it should be used.


JA24/11/2020 13:22:26
1061 forum posts
54 photos

I have broached a 5/32" wide keyway in a cast iron flywheel using a single edge tool held in the tool post on a "Big Bore" Myford. I tried to cut 0.001" at a time. It was very hard work. I will have to cut a 3/32" wide keyway quite soon and I am not looking forward to it.

Ian Bradley's book "Myford Series 7 Manual" covers cutting an internal keway. He suggests replacing the lead screw on the top slide by a cross head and slide the top slide backwards and forwards by a lever and connecting rod. The lever fulcrum is clamped to the right hand end of the bed. Obviously the tail stock has to be removed.


Edited By JA on 24/11/2020 13:25:27

Nigel Graham 224/11/2020 21:49:07
921 forum posts
16 photos

Thank you very much Gentlemen -

lots of ideas and experience there for me to mull over.

I must admit I'd not considered using the milling-machine quill as an arbor-press - even despite the obvious advantage of a precision feed. It would be hard work on my mill because the quill is very stiff and I can see no clear, safe way to service it. It also seems a bit unfair on the machine, but I could use an old, hefty bench-drill which just about holds a 10-inch rotary-table on its machined base-plate.


My comments on shaper tooling and their setting come from two sources: A.H. Sandy's Cutting Tools For Engineers, for the profiles; and Ian Bradley's The Amateur's Workshop, for internal keyway cutting.

Most usefully for me from Sandy's book is the information on cutter form. His book was for engineering students, so does assume using a slotting-machine but that's by-the-by. He gives as an example, finish-machining the basic inner and outer shapes of a forged, curved link we would probably see as a steam-engine's expansion-link; using on a heavy-duty slotter with power feed to its rotary table.


L.H. Sparey briefly shows using the lathe for shaping a long external keyway with the tool held in the tool-post, in his The Amateur's Lathe, along with a warning that heavy cuts place considerable strain on the lathe. I wonder if using a back tool-post would ease things by partially balancing the opposing torques - feed effort v. cutting resistance - on the saddle.


Another option has occurred to me, stemming from the advice to drill the bulk of the metal away first; and that is to use cylindrical keys (dowels or similar).

Howard Lewis25/11/2020 12:46:42
4177 forum posts
3 photos

I have cut internal, and external keyways, in steel, on a ML7, using the Slotting Tool designed by the later Peter Robinson.

Possibly College Engineering Supply still do the casting.

It has since been used, on a riser block, in the larger successor to the Myford.

+1 for drilling a hole to remove much of the metal leaving the tool to just cut out the corners.

On one occasion, a tool was mounted in the Tailstock, and the internal square produced using the Tailstock feed, to rack it to and fro, rotating the work, held in a 4 jaw chuck, for each cut.

An alternative method, might be, like Jason, to use the manual downfeed on a vertical mill to drive the tool through the work, whilst putting on the cut with the table traverse feed.

With a tool of suitable form, and the work on a Rotary Table, it would be possible to cut gears, or splines, in this manner.


Edited By Howard Lewis on 25/11/2020 12:47:42

Nigel Graham 225/11/2020 20:59:11
921 forum posts
16 photos

Thank you Howard.

The principle of a lathe-mounted attachment, with suitable dividing method for splines, is attractive by offering the keyway-cutting on the same set-up as the turning.

I think if I use that approach I'd make the attachment to fit my Harrison lathe as that would give a much more rigid foundation than the Myford, and the capacity for larger diameter work-pieces. The drawback is how I would fit a division-plate as the L5 is not designed to carry one, and the primary spindle pinion is small, only 20T, and apparently a permanent fixture.

Nigel Graham 225/11/2020 21:36:19
921 forum posts
16 photos

I broke off to look at the link Ian T offers....

Thank you for doing that, Ian, but...

Oh dear! I gave up on p.7 or 36, put off by the writer's literary style. I consider myself reasonably literate and I made due allowance for the American spelling and (Australian?) material specifications, but just could not follow him properly. At least I tried.

I did though note one point he makes, and new to me, that the cutter must be symmetrical so its corners meet the work simultaneously.

I like the round-square tool-bit adaptors he shows, resembling clock-key shafts. Though trade items I have not seen them advertised, used or demonstrated anywhere here.


Not Done It Yet -

Yes, making a special holder that changes places with the shaper's clapper-box & slide looks a good idea.


I've thought about how to divide a work-piece on a simple shaper not allowing much room for the work-holding.

For most of the few components I am likely to make or adapt with internal splines or flats, there may be no problems in carefully drilling small index-holes in a suitable area of the work itself. This assumes the part will eventually be hidden, that area will be machined down past the holes, the holes will become enlarged as lightening-holes or for a crossed-out gear - or will stay as they are but not spoil the appearance.

I will need make a special angle-plate, bored-out and back-faced, for the shaper; or suitably modify an existing angle-plate.

Howard Lewis26/11/2020 17:13:57
4177 forum posts
3 photos

Nigel, maybe you will need to make up a plate with the required number of divisions, that can be fixed tom the job, so that suitable, (possibly home made ), slotting tool, fixed to the Saddle, can be used.

You will some means of loctating and locking the division plate, relative to the lathe bed. Possibly some form of upward extended sadle stop, comes to mind.



John Hinkley26/11/2020 19:36:24
1015 forum posts
344 photos


When I was making my gearbox, I had a lot of internal keyways to cut and ended up buying a broach. But while researching the different means of machining keyways, I had a look at Stefan Gotteswinter's other video of slotting on the shaper, here.

I didn't go that route, as I said, but did get around to making the tool holder for my little shaper - a motorised Perfecto, like this:

keyway slotter_2

The tool projects from the clapper at a downward angle of 5°, the tool is 12mm in diameter and takes 4 or 5mmØ round high speed steel. It is to a similar design as Stefan's, the beauty of this arrangement being that the back rake is imparted by the down slope of the tool projection. In my case, a previous owner had drilled and tapped a hole in the side of the clapper box, as seen in the photo above, which meant that I could lock the clapper with a suitably sized set screw. The thrust is taken by the enlarged step seen at the join with the clapper box and the tool is retained in the clapper but a couple of grub screws, gripping the rear portion of the tool.

When my current project is complete, I intend trying it out in earnest.


Edited to improve clarity - I hope.



Edited By John Hinkley on 26/11/2020 19:38:05

mgnbuk26/11/2020 19:36:30
910 forum posts
65 photos

Stefan Gotteswinter also did a video of cutting an internal keyway using a shaper here.

Nigel B.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest