Making Square Broach

I remember another way to ht A2 without scaling in an oven. I did not have any wrap left and needed to HT a piece. An old timer told me to go over to the large vertical miller and pick up enough cast iron chips to cover the part in a small stainless pan that was under the oven. By packing the part in the chips it keeps most of the air from getting to the part and thus no scaling. Worked like a charm. Part came out the right ht and no scaling what so ever.

These guys use a square file as the broach with an arbor press:

In

Billh50 said:

I remember another way to ht A2 without scaling in an oven. I did not have any wrap left and needed to HT a piece. An old timer told me to go over to the large vertical miller and pick up enough cast iron chips to cover the part in a small stainless pan that was under the oven. By packing the part in the chips it keeps most of the air from getting to the part and thus no scaling. Worked like a charm. Part came out the right ht and no scaling what so ever.

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the shop where I apprenticed, we packed all the work in a covered stainless box filled with crushed peach pit charcoal, it worked well; after I left they could no longer find peach pit charcoal, and went to using crushed coke. I suspect that crushed mesquite charcoal would work as well. I always wondered if the carbon penetrated the steel and gave a case hardening effect, but I think that the limited time at heat, usually one hour, and at a temperature below case hardening temperatures, that there would be any significant effect, and besides most all that treated work would be finish ground after HT, removing any superficial effected zone.

Making steel from iron by heating in a closed container packed with carbon bearing material was a common practice before the advent of modern smelting practices. The ingredients were closely guarded secretes and some carbon bearing materials used were manure, straw, virgin's blood. Swordsmiths staked their reputations and sometimes their lives on their ability to make a superior steel. Japanese swordsmiths are one example.

This was essentially the process used to make blister steel. The biggest problem with steel made in this way was the inability to make steel with a uniform composition.

I have used a process like this to convert mild steel to a spring steel. I embedded the steel in a bed of hot coke in the forge for a working day. I wouldn't claim to have sword quality steel but it made fairly decent spring steel.

These are guitar tuning gears, so not very thick and possibly brass. This is a small hole requiring very little material removal. I have literally broached (punched?) a 5mm blind hex in steel using an Allen wrench. The wrench was cut to about 1-1/2 long, hand ground on the end to create sharp edges, held in a chuck in the tailstock of the lathe and forced into a 5mm dia. hole. The cutting forces caused it to self center. For a hole as small as 4mm, I would make a 4mm square broach/punch from some O-1 drill rod, flame harden it and sharpen the end. At least that's where I'd start.

johnreese said:

Will a rotary broach work? There are a lot of drawings available on hobby/home workshop forums. Can be used in a lathe or a mill.

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Yes but the pilot hole needs to be pretty big. Check a broach mfg. for appropriate relief hole sizes.