Need to broach a square hole...

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Mike Walsh
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Need to broach a square hole...

Post by Mike Walsh » Fri Nov 08, 2019 7:39 am

Hi all,

I'm working on a electro-pneumatic semaphore signal for a railroad. I've been asked to machine new bushings for the shaft.

My issue is the shaft is a 3/4" square shaft. I am trying to determine the best way to broach this opening.

The bearing will be 1-3/8" in length, which is a pretty substantial length to broach. If it was shorter I might try machining the square bore, but that is not the case here.

I've found that the broach is $500 from McMaster Carr.

I am far from a real machine shop - I just have a lathe, vertical mill, and a horizontal mill, and I don't need this 3/4" broach after these few bushings.

Does anyone have any ideas on how to achieve my goal? I have found that some outfits offer hardened steel bushings with square bores, but I need a bronze material.

Alternatively, if anyone has a 3/4" Broach and would be willing to broach the material that I provide, I would appreciate any help you can provide.


Thank you in advance,
Mike Walsh

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Re: Need to broach a square hole...

Post by carlquib » Fri Nov 08, 2019 9:45 am

Drill a hole to the diameter across your flats and then use the lathe carriage to shape the corners. If you put the work in a four jaw you can use the jaws to index the part. It actually goes pretty quick, if you only have a few parts to make. I generally just grind a tool from high speed steel for these jobs.

My name is Brian and I'm a toolaholic.

Bob D.
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Re: Need to broach a square hole...

Post by Bob D. » Fri Nov 08, 2019 9:48 am

Layout your square hole. Drill out the corners with say a 1/8 drill. Put in the lathe, drill/bore 3/4” center hole. Use the lathe as a shaper to broach out the remaining indexing the chuck 90 deg. with a HSS tool. Finish up with some filing.
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Russ Hanscom
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Re: Need to broach a square hole...

Post by Russ Hanscom » Fri Nov 08, 2019 10:22 am

Make two channel shaped halfs, 3/8" deep and 3/4" wide, using the mill, then silver solder together.

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Re: Need to broach a square hole...

Post by LIALLEGHENY » Fri Nov 08, 2019 12:33 pm

Try V W Broaching Service in Chicago Il.

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Re: Need to broach a square hole...

Post by Harold_V » Fri Nov 08, 2019 4:08 pm

You might consider the use of a square holed sleeve (assuming it is available in bronze, that is!). Depending on your design, it may serve the purpose.

Wise people talk because they have something to say. Fools talk because they have to say something.

armscor 1
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Re: Need to broach a square hole...

Post by armscor 1 » Fri Nov 08, 2019 4:23 pm

Drill the 3/4" hole and grind a lead on a piece of 3/4" HSS and press the tool through the hole, recently did a 3/8" mm square hole and came out perfectly.

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Re: Need to broach a square hole...

Post by whateg0 » Fri Nov 08, 2019 5:28 pm

Not sure if it's worthwhile, but the Clickspring guy showed how to make a square broach. Not a lot of material involved. Probably faster to do it on the lathe or mill, though. You can use the quill the same way as the carriage on the lathe, except that you get control of x and y on the mill.

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