Keyway Cutting

Glad afternoon,

I am currently building an Upshur horizontal farm IC engine. The plans call for a 5/16” crankshaft. I would very much like to cut a keyway in order to secure the flywheels but cannot find a supplier for the broaching tool.

Can anyone help with the name of a supplier or offer a reliable method for cutting asmall keyway. In the past I have used Grub Screws but they are at best, problematic.

kind Regards

Tom

Loads on epay? What width are you thinking of? They can be cut using a shaper, mill (vertical or horizontal) or lathe. I would think the size of broach you may be thinking of is a very fragile piece of kit

Please clarify that the diameter fo the crankshaft is 5/16".

Keyways are normally designated by their width, which has some, but not a 1:1 correspondence, with the shaft diameter into which they are cut. Hence you need to tell us what size keyway you want to cut. Search for 'British Standard shaft keyway' or similar and you will find dimensional information.

The broach is used for the pulleys. The keyway in the shaft can be cut by numerous methods, probably a slot drill is easiest, but you can chain drill, chip out some material with a cape chisel and finish with a file if you want.

Let us assume the desired keyway is 1/8". You can then search for "1/8" keyway broach" and select a supplier that meets your requirements. You will need a bushing and shim or two to complete the setup as well as something with which to push the broach. Check the equivalent or closest standard metric size as that might be cheaper than an imperial one.

If you want to buy it, the key itself is made of 'key steel', usually available in 12" lengths.

Arc do a 2 and 3mm broaching set **LINK**

You would have to make a bushing to suite. The alternative is to slot the flywheel with a topslide slotting gizmo. A lever action one is easiest but for a very small key then just winding the topslide would do, if somewhat tedious.

Rod

For the Flywheel it is perfectly possible to cut a keyway by planing in the lathe. For a reasonable sized bore a crossdrilled bar in the tool post at centre hight with a suitable cutter held by a grub screw would work. Cut is put on with the cross slide and the cut is made by racking the saddle back and forth. For the crankshaft a small slot drill would do the buissness.

I'm sure Jason has some other ideas, I'm sure he's done more than me.

regards Martin

or any of the above wot was written as I was posting.

Edited By Martin Kyte on 02/09/2022 18:49:44

usually the keyway is 1/4 the diameter of the shaft so a 2mm broach will do nicely, ARC as Rod says do them at a reasonable price. Available separately here

If you look at some of the posts over the last few weeks in the Princess Royal thread lots of talk about keyways, and keys.

I broach my flywheels to match the angle of the gib head keys, plain milled slot in the shafts and not had one fall off yet out of about 25 done that way. No grub screws used either. Before getting some broaches I planed my keyways with the lathe moving the carriage in and out with a 1thou cut per pass, tilt the flywheel in the chuck or pack on the faceplate to get the seat angle.

Edited By JasonB on 02/09/2022 18:53:38

Edited By JasonB on 02/09/2022 19:19:11

I would be careful if doing it by racking the carriage - some lathes may not like too much of that. Better to get/make one of the sliding tools designed for the job.

are there any plans available for a lever action cutter ?

Yep, that works - but use gardening gloves or suchlike, else you'll get blisters on your palms from repetitive working of the handwheel. You can guess how I know...

I agree with all of the above, but one thing that I found when cutting the four internal splines of the 'carden' shaft of the Radford worm-wheel hobbing attachment was that the first tool I made, admittedly only in mild steel, to hold the cutter tended to flex. I made another tool to the same diameter as the bore and advanced the cutter by slackening the end retaining screw and putting on another 0.005" cut. You can do this by feel/guesswork or with a micrometer. It actually didn't matter in this case how deep, within reason, the splines were cut because the external diameter of the male part did not require to be in contact with the end face of the internal spline. The bore holds the cutter in contact with the spline/keyway being cut so no flexing of the tool shaft can occur.

Gentlemen,

Thank you for your time and for your advice.

I’ve done a bit of reading and placed an order.

kind Regards

Tom

Keyway tool. Here's one I made earlier.

I cut all my keyways in bores using the Hemingway keyway slotting attachment. It is pretty much the same design as the picture above but using castings. Quite easy to build and very useful. The beauty of it is you can bore your holes then cut the keyway without removing the work from the lathe.

That might be why you haven't done it yet. Tools are there to be used, not preserved.

Martin

I use mine, without abusing them.🙂 They still do the job they were designed for. When over 50 years old, new spares are not readily available. I actually use my Drummond shaper to cut most keyways - it was designed for jobs such as that.

Well actually that s what I do. However the OP seemed to be starting from scratch and needing to only cut one keyway. Once you have an idea of the cutting action most people can make the leap to a better configuration of essentially the same thing. I've seen ideas that rack the topslide back and forth with a lever and linkage clamped to the bed and a similar set up to rack the saddle back and forth. I don't think much harm would come to any lathe by hand pressure on the carriage hand wheel unless your both your parents were gorillas.

regards Martin

I would favour locking the saddle (carriage) and use a lever operated tool, it would also have much better feel.

I'm surprised that nobody seems to have mentioned doing the keyway in the flywheel by drilling and filing. The technique is to make a piece of shaft to fit the hole in the flywheel, then locktite it in place with one side flush with the face of the flywheel. It is preferable for the dummy shaft piece to be of the same material as the flywheel. Make a centrepop at the desired location of the keyway on the joint line, then drill through with a drill the same as the desired keyway. Knock out the dummy shaft and now you have a half circle through the flywheel. This can then be filed out to match the key, not too hard a job since nearly 80% of the material has already been removed and the half hole give guidance for both width and depth.

I have three shapers here, but for small shafts especially, I would mostly do the keyway in the flywheel as above, since it is quicker than making up the tooling to do it in a shaper.

John

Hard to imagine that light keyway cuts put more axial load on the carriage than the oft-recommended large-depth cuts when turning using carbide tooling.

Well John, the last keyway I cut last month was 128mm long in a Ø22 bore. I wouldn't want to drill and file that. I used a piece of Ø19.05 (3/4" ) bar with a HSS cutter mounted in it in a QCTH and drove the carriage along the lathe bed to cut it. I was able to press the key steel into the slot with my fingers and hold up the part with the friction between the key and the part by just holding onto the key so I was happy with the result.

It's the middle item with the small sprocket on it here Facebook 

Martin C

Smiley edited out

Edited By Martin Connelly on 07/09/2022 16:42:16

Edited By Martin Connelly on 07/09/2022 16:48:30