Author Topic: Cutting keyways without a broach.  (Read 2639 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
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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.

Offline Jasonb

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Re: Cutting keyways without a broach.
« Reply #15 on: December 24, 2017, 01:33:41 PM »
More than likely it will in this case so give it a go.

When it comes to making the key leave it on the end of a length of bar while you fit it as that makes it easier to pull out.


Offline Alyn Foundry

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Re: Cutting keyways without a broach.
« Reply #16 on: December 24, 2017, 01:56:55 PM »
Hi Peter.

Seasons greetings.

Your tapered key in a parallel key way will only “ bite “ at the point of contact.

It would be better to place a packer behind the back of the flywheel and broach/slot a tapered way through the boss.

I remember years ago restoring an EEC gas engine for a customer, this engine had been fitted with taper pins instead of the usual gib head key and way. It was a rather neat way of fixture, I’ve never seen it done on anything since!

Cheers Graham.

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #17 on: December 24, 2017, 02:16:01 PM »
Hmm, I think it's time for some of this  :DrinkPint:  to help me think about it  :)

Offline pgp001

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Re: Cutting keyways without a broach.
« Reply #18 on: December 24, 2017, 05:05:45 PM »
Peter

I have a 1/16" broach and the bush to fit a 5/16 hole which would probably be OK for an 8mm, I could put the keyway in for you.

Phil

Offline Gas_mantle

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Re: Cutting keyways without a broach.
« Reply #19 on: December 24, 2017, 05:38:51 PM »
Thanks Phil, that maybe something I'll take you up on  :)

I would like a set of broaches but they are expensive for the limited use I need so I can't really justify the cost.

Happy Christmas and thanks for your help.

Offline Alyn Foundry

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Re: Cutting keyways without a broach.
« Reply #20 on: December 24, 2017, 06:24:33 PM »


I would like a set of broaches but they are expensive for the limited use I need so I can't really justify the cost.

Happy Christmas and thanks for your help.

Hi Peter.

Whilst I agree with your sentiments a couple of broaches of the sizes needed in most ME applications has done me for well over 35 years and they’re still ready for the next engine.

All the best, Graham.

Offline Bobsmodels

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Re: Cutting keyways without a broach.
« Reply #21 on: December 24, 2017, 10:22:17 PM »
Hi

I finally made up a set of tapered sleeves for the broaches I had.  I have attached a file showing how I made a Master block.  It was then used to cut the angle in sleeve and make keys.  The only critical dimension is 1/8" in 12" taper.  Even that is not critical, just get your Master close and make everything using the Master block and all will fit together.

I got tired of always making do especially since I was going to making more flywheel engines.

Enjoy

Bob

Offline 10KPete

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Re: Cutting keyways without a broach.
« Reply #22 on: December 24, 2017, 10:27:21 PM »
I've always wanted a 'set' of broaches but the cost is prohibitive. So I have three small size ones that do all the model size stuff and I make a bush when needed.

I don't find I want a 'set' anymore! Not runnin' a job shop here.....

Pete
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