Key types - any advantages?

I've got to make a replacement countershaft for my ML10 lathe. This shaft has Woodruff keys at either end for the drive pulleys.

I see that the cost for the correct Woodruff key milling cutter is pretty steep... most especially when considering that this is essentially for one-time use.

Would an alternate straight, 'feather key' work just as well in this situation?  This is something that I could mill out much more easily with the tooling at hand.  (see illustration)

Edited By Ignatz on 10/08/2017 08:15:44

A feather key would be ok if fitted correctly

After all it's what youv'e got on the motor

Edited By roy entwistle on 10/08/2017 08:43:09

John Stephenson replaces them at every opportunity and any job that comes to him has straight keys put in as a matter of course.

​That would seem to be a good endorsement by someone with long practical experience.

​Brian

I assume woodruff keys are fitted as it easier to manufacture for mass production work, but tend to be weaker as they take out more material than needed.

I prefer straight gears as you only need to remove a minimal amount of material from the shaft.

Woodruff keys are often used on tapered shafts where it is easier to machine than setting the work at and angle to mill the slot and the taper takes the load and key just acts to locate the item on the shaft such a timing gears/pulleys.

I seem to remember that the Austin Seven had this arrangement on its halfshafts.

Either type of key seat can be machined on a vertical mill but the straight key way would perhaps be more difficult on a horizontal mill.

Woodruff keys and cutters are readily made in the amateur workshop.

I assume that model makers would aim for authenticity of key type.

PS Excellent illustration, Ignatz!

Edited By ega on 10/08/2017 11:02:24

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Motorbike flywheels and timing gears often have such as they may house the ignition sensor magnets. Quite common for such an engine to also have a 'wasted spark' in the cycle.

Nick

Can,t see how it would make much difference,the key is not going to fly out anyway once the pulley is locked in place,is it?

I suspect Woodruff keys are just easier and cheaper to make/

problem with Woodruff is that they weaken the shaft more than a flat key, but reduce the possibility of stress fractures caused at the ends of the flat keyway slots. Another problem with Woodruf is that they can 'rock' whilst the pulley is fitted to the shaft which can be a nuisance during assembly.

If they are being used as I mentioned above purely to locate the part on the shaft and not to transmit any power then they can be far smaller than a straight key that has to transmit the load so may not take as much out the shaft as the straight key.

Suppose it all comes down to using the right thing for the job in hand and designing the shaft to allow for what is cut away

I lost the Woodruff key for my electric motor. In desperation I just bolted up the pulley wheel very tightly and ran the machine sans Woodruff key. It stayed that way for weeks until I sourced the correct Woodruff key. On disassembling, there wasn't any sign of the pulley wheel having spun on the shaft!

So I reckon your solution would do fine. Before people berate me for being idiotic. I was desperate to get a job done and it was worth sucking and seeing.

Andrew.

Thanks, everyone, for the feedback. I think that i can safely alter the design of the replacement countershaft to use those captive straight 'feather' keys. There is a tiny bit more fuss-n-bother making multiple passes with a small slotting end mill, but the end result should be far easier on the pocketbook.

PS  Illustration prepared using Blender 3D software with a few adjustments in the Photoshop.

Edited By Ignatz on 10/08/2017 14:56:26

Woodruff cutters are easily made by grinding down an end mill to the correct thickness. I used to use cutters that had maybe chipped a tooth but who,s flanks were still in good condition. They work well.

If a key is needed PURELY for alignment, a short stud set into the shaft can be used. (Example: Stanadyne Fuel Injection Pumps) but ONLY for alignment; precious little use for transmitting torque.

Howard

That's what I did for my dividing attachment

Money spent on a woodruff cutter is not necessarily wasted, they have other uses, such as cutting horizontal slots using a vertical mill.

Neil