Author Topic: Need a little help  (Read 345 times)

Offline ozzie46

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Need a little help
« on: July 21, 2022, 11:16:26 PM »
I wonder if some one would sell me a couple of pieces of mild steel and broach a 3/8 square hole in them. They are the crank cheeks for a 9 Cyl radial. the 2 pieces are bolted together and the hole broached so that they are in alignment. Attached is a pic of the dimensions. The steel parts are .500 x 1.625x 3.218.

Pls let me know if you can help and how much it will cost. I cant see spending almost $200.00 on a broach I will only use once.
Thank you
Ron

Offline crueby

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Re: Need a little help
« Reply #1 on: July 22, 2022, 01:07:30 AM »
Hi Ron,
Not a direct answer to your query, but an alternative method:  I have done the same kind parts for crankshafts, but rather than the square holes I'll do a round one (a little smaller than the shaft so there is a shoulder to help hold things), assembled them with high strength Loctite, then drilled/taper-reamed for a small taper pin that is driven in and cut/filed off flush.  Not quite the same look as the square hole would give, but plenty strong and cheaper to do.
Just a thought!Chris

Online Jo

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Re: Need a little help
« Reply #2 on: July 22, 2022, 06:45:04 AM »
I think you are underestimating the art of the possible. I have seen fantastic broaches made in home workshops that are as good as any that can be brought. Here is Steve's write up of making a 1/8" broach:  https://modeleng.proboards.com/thread/14818/home-keyway-broach

For what you need use some 3/8" square silver steel, turn the end round to 3/8" (9.53mm  :) ) then turn a long shallow taper along it for a few inches - the longer the taper the less each tooth has to cut. Cut teeth along the tapered bit, making sure they are deep enough to catch the curls of swarf. Hardened and tempered to dark straw in the usual way.

The biggest problem I can see is keeping the two cranks identical so I would be using a square pin through the crank holes and keeping them together while working on them back to back. Drill a 3/8" hole in your two pieces of steel add lubricant and push it through one at a time. You may also want to put a hole through a third plate so you can keep the holes square to the edges by using that as a jig while machining the two.

Nothing ventured, nothing gained...

Jo
« Last Edit: July 22, 2022, 06:51:36 AM by Jo »
Enjoyment is more important than achievement.

Offline ozzie46

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Re: Need a little help
« Reply #3 on: July 22, 2022, 11:58:21 AM »
Crueby: the crank must be able to come apart. so the pressed locktite method is not viable. crank fits together witha push no shake fit
so the master rod can come off. Thanks for the input.

Steve Hucks has kindly stepped up and is helping.

Jo thanks for that info that's some thing to keep in mind.

Ron