Author Topic: Cutting keyways without a broach.  (Read 997 times)

Offline Gas_mantle

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Cutting keyways without a broach.
« on: December 23, 2017, 08:10:00 PM »
Hi,

I wondered if anyone here has tried cutting a flywheel keyway without a broach by steadily advancing a parting tool through the bore ?

This video shows the kind of thing I mean :-


I'm wanting to fix the flywheel on my current build using something a bit more realistic looking than the usual grubscrew method but don't have any broaches so I have considered trying it. At the moment the flywheel I have is a cast iron 'Lady Stephanie' wheel that is already reamed at 8mm to fit the crankshaft.

I'm probably going to replace the wheel with a better looking one shortly so if I did make a mess then it's not the end of the world but I'd prefer not to damage it if I can.

Anyone got any thoughts / comments etc ?

Thanks
Peter  :)

Offline Jasonb

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Re: Cutting keyways without a broach.
« Reply #1 on: December 23, 2017, 08:27:29 PM »
Wot like this



Though I prefer to use a bar with a small HSS toolbit, similar to this



Works quite well, the four in this steel part are 3/16" wid eand 1" long.



As Muncaster called your project his "simple " entablature engien I kept true to that but nothing wrong with adding More details.

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #2 on: December 23, 2017, 08:32:57 PM »
Yea that's the kind of thing I meant.

I'd like to have a bash at it as I want to try and get away from using grubscrews. Does about 2mm wide sound about right for an 8mm bore ?

Ps - crosshead nearly done  ;)


Offline Jasonb

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Re: Cutting keyways without a broach.
« Reply #3 on: December 23, 2017, 08:41:55 PM »
1.5mm or 1/16" would be plenty big enough.

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #4 on: December 23, 2017, 08:50:02 PM »
Ok thanks.

I'll have a bit of a play around on a bit of scrap over the next few days, I'll need to experiment with the depth of cut

Offline Steamer5

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Re: Cutting keyways without a broach.
« Reply #5 on: December 23, 2017, 10:59:03 PM »
Hi Gas mantle,
 Have a Google there are calculators that will tell you how deep to go. Ive used them on shafts & they worked great!

Cheers Kerrin
Get excited and make something!

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #6 on: December 23, 2017, 11:02:58 PM »
Thanks Kerrin, I'll take a look  :)

Offline Art K

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Re: Cutting keyways without a broach.
« Reply #7 on: December 24, 2017, 03:28:27 AM »
Peter,
If I wasn't on vacation I'd go out in the shop and give you the formula. I used to work at a shop that made gearboxes. Back in the day I did a lot of internal keyways and had it memorized. Wow, that was 22 years ago, no wonder I forgot it. :lolb:
Art

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #8 on: December 24, 2017, 03:49:37 AM »
Cheers Art,

The engine I'm building is small and the flywheel is unlikely to see any significant loading so if I'm a bit out with my guesswork skilled calculations then it's not really going to matter.

I kind of thought that a depth of cut in both the wheel and the shaft equal to the key width sounded about right ?

Offline 10KPete

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Re: Cutting keyways without a broach.
« Reply #9 on: December 24, 2017, 06:30:00 AM »
Peter, here's a handy one for establishing the keyway depth in the hub. The rest you can figure out....
 'H' is half the key size.

http://www.cncexpo.com/KeywayArc.aspx

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline Jasonb

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Re: Cutting keyways without a broach.
« Reply #10 on: December 24, 2017, 07:37:41 AM »
As as simple rule of thumb most keysteel is square so total depth in shaft and hub is equal to key width.

Offline pgp001

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Re: Cutting keyways without a broach.
« Reply #11 on: December 24, 2017, 08:57:11 AM »
Peter

If you are fitting a gib key, then you should really taper the keyway through the hub to match the key.

Merry Christmas
Phil

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #12 on: December 24, 2017, 11:57:46 AM »
Many thanks guys,  Pete's calculator above agrees with Jasons square suggestion so I'll aim for that  :)

Phil, I take your point about cutting a tapered keyway but as that isn't really practical in my case I was intending to have just a very shallow taper on the key.

Merry Christmas all.

Offline Jasonb

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Re: Cutting keyways without a broach.
« Reply #13 on: December 24, 2017, 01:22:34 PM »
How good a fit is the crankshaft in the flywheel bore, if it is a bit looks and you use a tapered key in a straight keyway it may act like a wedge and kick the flywheel off, a matching taper in the hub means the key contacts all the way along and pushes evenly against the hub. 1:100 is the right sort of taper.

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #14 on: December 24, 2017, 01:27:37 PM »
Hi Jason, I'd say the fit is good but I guess that's relative to who is judging.

Maybe this isn't such a good idea afterall  :(  I thought a tapered key gently tapped in would hold without problems.