It's certainly possibe to make your own broaches from silver steel especially that sort of size.

Clickspring did a reasonable video to get the idea.

**LINK**

regards Martin

I've got a 1/4 sq push broach, and you're right they do cost north of £100 a kick. BUt if you would like to PM me with details of what you want done I'll consider doing same for a small fee to charity.

Quantity, material, length of hole, any orientation requirement, any thing else relevant. Can't remember the size of pilot hole offhand but approx 6.5 mm – it's slightly larger than the across flats dimension of the square hole. Broach cuts dead to size 0.250 across flats IIRR.

Where are you – I'm in W Glos UK. Forgive me if we don't meet up, present restictions as you know, but if you can post me the bits I'll make the hole and post 'em back

Best rgds Simon

I have bought broaches from Steelman, in the past, they don't seem to have online ordering anymore but worth an e-mail they were cheaper than the DuMont ones from MSC

Many years ago when I was an apprentice I had a job which required a square hole. This was achieved by drilling a pilot hole just undersize followed by marking out each side with the square shape. Corners were removed by careful filing and the the final square was achieved by using a 1/4 in square HSS tool bit as a broach. The "broach" being pushed through the hole using an arbor press.

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I've not used a broach but have looked at obtaining and using small ones, but only in steel. I think I would be very wary of using a 1/4 inch push broach in cast iron, I would imagine that there is a danger of fracturing a corner at the outgoing end.

I stand ready to be educated by those with experience.

Jim

Quote from Simon Williams 3 – "Can't remember the size of pilot hole offhand but approx 6.5 mm – it's slightly larger than the across flats dimension of the square hole. Broach cuts dead to size 0.250 across flats IIRR."

Just checked my DuMont 1/4" square broach and the pilot hole size is inscribed '17/64"' (or 6.74mm). For preventing 'break out' damage on CI I have in the past used a sacrificial plate of aluminium. You do need a good arbor press with these broaches – using a vice or anything which is 'flexible' is guaranteed to break the broach.

Martin

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Try the used tool and machinery dealers,or give Tracy tools phone call. I have cut a lot of keyways in cast iron gears and pulleys,no trouble with break out.I use a hydraulic press,cut cast iron dry,

If you can keep the spindle of the mill from rotating you can use it as a slotter by chucking up an appropriate shaped cutter. The cutter needs a degree or so back clearance. Typical feed is a thou or two per stroke. Cut out one quadrant at a time. I used half a drill blank ground square at the end and having 1* back taper. Avoid making the cutting tool too large or you will have trouble pushing it through the work. My tool was about 3/16" square.