Why are flywheel keys square?

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Why are flywheel keys square?

This topic has 10 replies, 7 voices, and was last updated 4 May 2012 at 15:15 by John Wood1.

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24 April 2012 at 15:19 #2337
John Wood1
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@johnwood1
There must be a reason!
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24 April 2012 at 15:19 #89656
John Wood1
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@johnwood1
I am currently building the Redwing engine and have got to the flywheels. The keyway has to be broached but I don't have a proper broach and therefore have to use a square ended tool and 'plane' the metal away. The problem is the casting is so hard thet I struggle to take any metal off at all. I have made a cast iron plug to fit snugly into the centre and drilled through at the intersection, this removes most of the metal and I have now managed to get a decent square groove,

It occured to me that if one used a round key then all this fuss would be avoided – wouldn't it? I know one would have to use a round nosed cutter to mill the corresponding groove in the crankshaft but I reckon that's easier than broaching.

I bet there is something I have not realised so would someone please enlighten me?

Thanks, John
24 April 2012 at 15:27 #89657
John Stevenson 1
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@johnstevenson1
Because there is no sudden change in section like you get when you come across the wall of a key, the round type is gradual and in time will roll over and extend the 1/2 hole.

John S.
24 April 2012 at 16:00 #89658
Engine Builder
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@enginebuilder
Hi John, This a method I use for my flywheels.

Flwheel is held by a collet with dummy key.

Edited By David Clark 1 on 24/04/2012 21:01:30
24 April 2012 at 16:50 #89659
JasonB
Moderator
@jasonb
They must be very hard castings if you can't plane them after drilling. I've used the planing method for keyways 3/16" wide and 1" long in steel without drilling first, just 1 or 2 thou at a time and its soon done see this

Though I have now bought a set of miniature broaches from the states at a very reasonable price its a minutes work to press them through, don't think I will be going back to planing.

One of the reasons for a square hole is that the gib headed key can have a slight taper in its height so it tightens up as pushed in, you won't do that easily with a round hole.

J
24 April 2012 at 17:28 #89660
Russell Eberhardt
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@russelleberhardt48058
John S is right of course, however I have used round keys with a bit of locktite to overcome the tendency to roll and never had a problem. If you can drill both the wheel and the axle with it assembled you can get a good fit easily.

Russell.
24 April 2012 at 20:20 #89673
Sub Mandrel
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@submandrel
For small bores (say 1/4" to 5/32&quot I use a 'top hat' shaped filing guide with a slot in it and a square file.

Neil
25 April 2012 at 09:23 #89694
Russell Eberhardt
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@russelleberhardt48058
Posted by Stub Mandrel on 24/04/2012 20:20:33:

For small bores (say 1/4" to 5/32" I use a 'top hat' shaped filing guide with a slot in it and a square file.

That must be a tiny file. What size key do you use on a 5/32 shaft!

Russell.
26 April 2012 at 01:56 #89749
russell
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@russell
very neat flywheel fitting (and engine). But some future engine restorer is going to have a b…..r of a time removing them!

russ
28 April 2012 at 16:19 #89874
Sub Mandrel
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@submandrel
well perhaps I meant 5/16"

Neil
4 May 2012 at 15:15 #90217
John Wood1
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@johnwood1
Many thanks for the posts which have helped me get my head around the subject. Also thanks for the other ideas, all useful info.

Cheers John
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