# Cutting taper keyway in fly wheel



## bob shutt (Nov 20, 2013)

Does anyone know of a source for tooling to cut a taper keyway in the fly wheels for the Little Brother hit n miss? It calls for .094 wide with a 1/8 per ft taper? The hole is .312 dia


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## Charles Lamont (Nov 20, 2013)

bob shutt said:


> Does anyone know of a source for tooling to cut a taper keyway in the fly wheels for the Little Brother hit n miss? It calls for .094 wide with a 1/8 per ft taper? The hole is .312 dia



You don't need to buy anything special. You can use the lathe as a slotting machine. Put a tool like a parting blade on its side in the toolpost and wind the saddle back and forth, putting very small cuts on with the cross-slide. I have lever that clamps to the bed for the saddle movement.
The three pics (put there recently for someone else with a similar query) at the bottom of this page show the idea: http://www.charleslamont.me.uk/Seagull/timing_gears.html

For a taper you would need a taper turning attachment, or would need to use the top-slide rather than the saddle, in which case it would be better you could take the feed-screw out and rig up a similar lever for the reciprocating motion.

If you want to do slotting more regularly, a dedicated slotting attachment can be made. There is a kit available from Hemingway Kits.


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## kvom (Nov 20, 2013)

Assuming you mean a 8-1 taper rather than 1/8" per foot, then the angle is 7.1 degrees.  If you can hold the wheel on your mill inclined 7 degrees you can mill the slot with a 3/16 endmill and then square the end of the slot with a file.


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## idahoan (Nov 20, 2013)

The other option which is what I used on my engine would be to use a standard 3/32" A sized broach and make a special bushing that has the proper angle machined into it. The broaches should be available from most the tool suppliers.

Dave


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## Jasonb (Nov 21, 2013)

As Dave says make a bush with the bottom of the slot tapered and use a standard broach. Shars sell reasonably prioced ones.

J

PS it is 1/8" per foot or 1:96


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## abby (Nov 21, 2013)

If the hole is 0.312" dia , presumably this is the small end of the tapered hole ? how thick is the flywheel ? I assume around 1/2" ? 
At a taper of 1/8" to the foot it is virtually parallel so just use a parallel keyway , if the taper is 1:8 which sounds more correct the big end of the hole will be about 0.344". 
A 0.094" parallel key will still give more than sufficient contact , the taper provides most of the the locking force not the key.
Just my view ! why complicate the issue with special tooling and jigs when a simple solution will work.


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## Jasonb (Nov 21, 2013)

Its not a tapered round hole its a tapered slot for the matching taper on the keyway to locate onto.

The taper is used to stop the flywheel moving along the shaft, if it were a plain key this would take the load but there would be nothing to stop the flywheel moving sideways.

If you put a tapered ket into a flat keyway there is a risk of it cocking the flywheel off to one side as the wedging force will only be applied to one edge of the hub


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## MachineTom (Nov 21, 2013)

Cutting a tapered slot is a lot easier than a a tapered slot with a tapered bore. So buy a "A" size 3/32 broach, Make a bushing 5/16 and mill the slot with a taper of 1:100, Depending on your equipment a 3/32 keyway cutter, an indexer set at the taper angle, likely the easiest. 

I'd make the bushing first then make a key to fit the final taper.

look on ebay those broaches are small so not so expensive.


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## abby (Nov 21, 2013)

Ah , I see , I thought it was a tapered shaft and matching hole like a ships propellor fits to it's shaft.


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## bazmak (Nov 22, 2013)

What you have shown is a standard drive key.I cant remember the proper name
The keyway is not tapered and the key has to be filed slightley untill
you achieve a drive fit.The key is tapped home with hammer and removed using the shoulder
with a taper of 1/100 if the key is 2" long the taper is 20 thou.I recall fitting this type of key
was an apprentice exercise.The keys were blued and filed to a good fit.They were/are used on
Large engineering ie ships propellors etc,cant see there use on model engineering
Will somebody please confirm the name of this type of key


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## Jasonb (Nov 22, 2013)

I know them as GIB headed keys but you can also get plain tapered without the gib head


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## idahoan (Nov 22, 2013)

What Jason Said, (Gib Head Key)

All the ones I have seen and worked with on the full sized stationary engines; the key way in the flywheel has the same taper as the key.
This is common practice, at least in the US.

Dave


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## kvom (Nov 22, 2013)

Gib Head Keys:

http://www.mcmaster.com/#machine-keys/=phpq6v


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## Charles Lamont (Nov 23, 2013)

It is a gib-head key, and the keyway in the hub is supposed to be tapered, but that does not mean that in full size it would not be blued up and filed to fit.


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## bazmak (Nov 23, 2013)

If your using a gib head key in model engineering its purely for aesthetics
the small size dictates the taper will only be a couple of thou.Run a file over the keyway
in the shaft and file/fit the key.The small taper is only to lock the key in place


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## MachineTom (Nov 23, 2013)

I believe they are called cotters as a general name, then tapered, Flat etc. MHB of 1952 still referres to them as cotters.


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## Jasonb (Nov 24, 2013)

bazmak said:


> If your using a gib head key in model engineering its purely for aesthetics
> the small size dictates the taper will only be a couple of thou.Run a file over the keyway
> in the shaft and file/fit the key.The small taper is only to lock the key in place


 
Quite likely to be more than a couple of thou', the current engine I'm doing has a flywheel hub that is 1.5" wide so that would need 0.015" of taper as it works out at ).010" per inch.


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## bob shutt (Nov 24, 2013)

Looks like I started quite a discussion. I was able to get a broach. I plan on making a bushing with a taper slot. The engine is the Little brother. Here is the progress so far. The shaft is not the crank shaft yet. That is in the lathe now.


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## gus (Nov 25, 2013)

bazmak said:


> What you have shown is a standard drive key.I cant remember the proper name
> The keyway is not tapered and the key has to be filed slightley untill
> you achieve a drive fit.The key is tapped home with hammer and removed using the shoulder
> with a taper of 1/100 if the key is 2" long the taper is 20 thou.I recall fitting this type of key
> ...



Hi Bazmak,

Let me make a wild guess----------Gib-head key.

This is a very old design. Saw my uncles cutting them on a overhead pulley driven Shaper.


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