Author Topic: Oversize crankshaft / undersize flywheel hub.  (Read 436 times)

Offline Gas_mantle

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Oversize crankshaft / undersize flywheel hub.
« on: August 24, 2018, 12:42:30 PM »
Hi all, I'm trying to get back in the saddle with this hobby after a break of a few weeks and have hit a minor snag with a small vertical steam engine I'm building  :(

The crankshaft I have is 12mm dia and the flywheel casting hub I have before machining is about 15mm (say 14mm after machining), I've tried without success to obtain a wheel with a wider dia hub but was unsuccessful so it's a case of working with what I have. Ideally I wanted to attach the wheel with a keyway but think that isn't really practical and even if I adopt a grub screw I'm left with a shaft that is a bit too big for the hub.

I like the style of the wheel and want to use it if I can  :)

I wondered what other members think of as a way forward? The obvious way seems to be to turn down the crankshaft dia at the wheel end to say 9mm but that seems a bit amateurish  :headscratch:

Somehow sleeving the hub sounds a possibility ?

Any thoughts guys and gals ?


Offline b.lindsey

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Re: Oversize crankshaft / undersize flywheel hub.
« Reply #1 on: August 24, 2018, 01:19:43 PM »
My personal opinion would be to turn down the crankshaft. I think sleeving the hub, while doable, would not leave the flywheel looking "original."  Just my opinion.

Bill

Offline Jasonb

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Re: Oversize crankshaft / undersize flywheel hub.
« Reply #2 on: August 24, 2018, 01:27:19 PM »
I did it to this 7" Stuart flywheel, just turn down the hub so it is parallel and bond on a sleeve, blend the spokes in with filler.



Painted up OK



J

Offline Gas_mantle

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Re: Oversize crankshaft / undersize flywheel hub.
« Reply #3 on: August 24, 2018, 01:35:44 PM »
Thanks guys, it's something I need to sleep on tonight as I'd like to make a start tomorrow.

Jason if I stick to existing 12mm shaft my worry is that I haven't a lot of thickness in the existing hub to securely attach the wheel. In your example you still have quite a substantial hub wall to get a secure fastening.

I'll try and take a few photos later showing what I have to work with.

I can see me taking out a mortgage to buy a Stuart casting at this rate  :wallbang:

Online Roger B

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Re: Oversize crankshaft / undersize flywheel hub.
« Reply #4 on: August 24, 2018, 02:38:02 PM »
Even with shipping and possibly customs you shouldn't need a very big mortgage for one of these Flying Wheels:

https://www.rc-machines.com/en/model-engineering/flying-wheels

Best regards

Roger

Offline Jim Nic

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Re: Oversize crankshaft / undersize flywheel hub.
« Reply #5 on: August 24, 2018, 02:51:12 PM »
I'd reduce the diameter of the shaft to accomodate the flywheel you have.   This will allow you to secure it with a key and also give you a positive shoulder to locate against.  As for being "amateurish", well we are amateurs, aren't we.  What you would be doing is using your ingenuity to utilise materials you have to hand  ;)
Jim
The person who never made a mistake never made anything.

Offline Gas_mantle

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Re: Oversize crankshaft / undersize flywheel hub.
« Reply #6 on: August 24, 2018, 03:35:53 PM »
Cheers guys, turning down the shaft does seem to sound the easiest  :)

Roger, that flywheel page you linked to is very useful, I hadn't seen that before but they seem to be reasonably priced and available in sizes I haven't been able to find until now.

I'll see if I can get a postage quote on this as it looks worth a gamble  :)

https://www.rc-machines.com/en/model-engineering/set-of-casting/flying-wheel-cast-iron-o-124-mm