Assuming that it's a through-hole ..

Pull Broaching would be the obvious choice.

Something along these lines would be nice.

MichaelG.

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P.S. … I recall you suggesting that someone else should outsource his job:

This looks very much like a case where you might take your own advice.

… As you will see; it's very easy with the right kit.

Have a look at Michael Cox's web page he shows a really simple method of broaching there

http://www.mikesworkshop.weebly.com

cheers

Bill

I could send them out and have the hole wire eroded or buy a push broach which are a bit easier to put through than a pull one if you don't have a puller. Not the cheapest though you would need to offset the cost by the time you will spend making a tool. Hex broach at 7mm from someone like Steelman's is £240.

You can make similar tools from Silver steel, 7mm dia lead pin on one end tapering out to 7mm AF and then turn grooves to form the teeth and back clearance.

Hi Graham,
As the material is aluminium I would try to make a broach from a long Allen key. Using a carbide tool I would turn a number of grooves spaced a little over 12mm apart They only need to take the points off the hexagon. I would then turn the first section to 7mm dia and the following sections to slightly larger diameters until the last section was the full hexagon. It should be possible to force this through a 7mm round hole as each step would only be removing a small amount of metal and only one groove would be cutting at a time. This is only an idea – I have never tried it.

Les.

Can you be sure a wobble broach won't make a twisted hole on such a long run? I suppose there's only one way to find out.

Neil

I did one by planing it in the lathe, using a square tool wide enough to create the flats, and gradually moving the cross-slide out until I'd got a full flat. Indexing the job round 60 degrees isn't hard if it's in a 3-jaw chuck. Yes, it was tedious but it ended up OK. Bopping a suitably-sharpened hexagon down a slightly undersized planed hexagon hole might be a better way of ensuring consistency. Don't take too much out, or if you do or it'll look bad when it bursts out. Countersinking the hole beforehand would help.

Does the specification require a perfectly formed hex hole?
I assume the part or parts slide on a hex shaft of some sort.

If you were able to enlarge the hole slightly it would greatly reduce the force required to push or pull the broach through the hole. You often see this on mass produced parts. The centre part of a hex nut sliding on a shaft has very little influence on the load carried by the part or the accuracy due to the geometry, it is at a tangent to the imaginary circle located at the mid points of the flats on the hex shaft.

Regards
John

Suggest sending it out to a water jet company or laser cutting if you need better finish on the edges. Will

Just tried it and its not a problem to do.

Took a spare 6mm allen key as I could not be bothered to search for a 7mm one, hacksawed off a 1" length, faced and then turned the end slightly hollow.

Drilled a 6mm hole in some ali bar, applied a bit of tapping fluid and pressed the key into the hole using the bench vice.

Not too shabby

If doing it again for a proper job I would cut a slightly steeper cone into the end of the punch, make two punches, one with the corners turned off so the first punch will remove 50% material and the second take it out to size and lastly make a simple guide to keep the punch true while pressing it in.

J

Good result

I stand happily corrected.

MichaelG.

I recently purchased a proper rotary broach from Ruforth! 20quid!!

Its showing some signs of abuse but works ok, anyhow it came with one tip 1/8th fitted and it works a treat, however I would like to get hold of a couple more tips, anyone know of a UK supplier, I can find loads listed on ebay but they are all located in the US, postage will be more than the bits, I suppose I could make some but I cant be bothered right now as I'm putting all my efforts into getting the project bike finished which should be this coming week.

Cheers

Shaun

More recently than that, about two issues ago. Issue 241 Mike Cox has an article on making a simple rotary broach for hex holes.