2 questions concerning "pre - heat treating" steps

I have a few questions concerning the "best" way to do this:

What should I do for drilling holes before heat treating. Do you guys drill them one size bigger? Drill them and redrill after heat treat with carbide or some other bit?

As for putting on a bevel / "finished" edge, how much material should be left for heat treating? Is this the final thickness it will be after heat treating too or do you take it down to final edge thickness after HT? (I'm not talking about a sharpened edge, just thickness if that makes sense)

Thanks as always

As far as holes are concerned, I always drill them the size that I need them and leave it at that. So far I haven't had any problems.

Concerning the pre-heat treat bevel thickness, it depends somewhat on the thickness of the steel overall, as well as the type of grind, but typically, leaving the bevel around the thickness of a dime seems to be enough for most applications.

If you need to thin it down a little bit afterwards, that shouldn't be an issue, as long as you're careful not to ruin your temper.

Heck, some guys don't grind at all until AFTER their heat treat, so if you leave a little extra, it might be better than leaving not enough.

The edge thickness deserves some clarification because it can differ with different steel types and thier respective HT methods. An oil hardening steel that is heated in a forge will induce decarb during the HT process and this leaves a skin of soft steel that has to be ground off after heat treating. It is common to leave an extra bit of edge thickness before HT to account for this. Oil hardening also carries some risk of warpage during quenching and a slightly thicker edge reduces this risk to a degree.
Air hardening steels and higher alloy steels (including stainless) generally require higher temperatures and longer soak times during HT and because of this they are usually protected from oxygen during heating by stainless foil wrap, anti scale compound, or an atmosphere-controlled furnace/kiln (otherwise the amount of decarb the process would incur would be prohibitive). When protected from oxygen during HT there is little or no decarb afterwards and so blades can be taken much closer to final finish and dimension before HT.

Justin raises an excellent point. It depends a LOT on the alloy and how it will be treated. Air-quenched vs. oil-quenched, vacuum furnace vs. open coal forge, etc.

I grind my "air-quench" blades (CPM-154, 440C, CPM-3V, D2 etc) VERY close to final dimension (.020" edge at most, 500-800 grit finish), and have them HT'd by a pro shop with ridiculously expensive equipment. Costs me about $10/blade and saves me a lot of hand-work post-HT.

I drill holes nominal and if needed, turn pins/bolts down to fit post-HT.

Having a fuel rich fire in a gas forge will also protect from decarberization. This will produce a carbon monoxide rich atmospher which does not promote the oxidation of the carbon in the steel the way free oxygen and carbon dioxide will. That's why good ventilation is needed in the forge shop. With solid fuel forges you use the low oxygen part of the fuel mass but finding it requires that you obsurve where in the fire you obtain the least scale. Another way to cut down on burning off carbon and fire scale is to use a piece of non-coated steel pipe closed off on one end. You put this in the forge and allow the fire around it to heat it to a glowing red. Toss a few pieces of wood or charcoal into the pipe before you insert your steel and the wood/charcoal will burn and consume any free oxygen inside the tube.

Doug Lester

Ok I will be doing O1 and sending them to Peters HT