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Hi, Mike, Well, the fact is that the age of any particular piece of steel just isn't a meaningful factor in its machinability or weldability..... the "analysis" and "heat-treat" are the factors which make the difference. So....I'm going to take a guess that by "old steel" you mean miscellaneous oddments of material you have on hand, which could range from common mild steel, to various and sundry parts which are one or another high-strength heat-treated material. Drilling mild steel is pretty obvious, actually....you can find plenty of information on the internet about how to correctly grind your drill points, speeds and feeds, coolants, etc., etc. Drilling, turning, or milling heat-treated material is a different tin of worms entirely. There are quite a few different steels which will be found as "salvaged" material. Old truck axles, for example, will often be "4140", a chrome-moly steel, with "40 points" carbon, and "through hardened", which can be drilled or turned readily enough if one is careful. Occasionally, one will find a part which is "case hardened", a process which imparts a "hard skin" to the steel, leaving a softer core. (old mauser receivers are a good example) It is possible to drill case-hardened steel if you first grind through the outer "skin" to expose the soft steel core....the "case" varies with the application....often it is only a few thousandths deep, sometimes, on heavy gearing, as much as 1/16" When drilling some of the hard, tough steels you may find, such as, for example, "Max-el", the "secret" is to use a best quality drill, (any of the standard American makes, preferably "cobalt" flavoured) with a correctly ground point, with, if anything, a bit lesser point angle than the standard 59deg., run slowly, and in a good heavy, rigid drill press. The common cheap drills and drill presses sold for woodworking and very light-duty metalworking simply will not do..... Use a suitable cutting-oil. My own preference is to mix one part of best quality black "sulfur" cutting oil with one part of "Rapid-Tap", a commercial tapping oil. Feed pressure on the drill is all-important when drilling hardened alloy steels, or the stainlesses. Allowing the drill to "rub" or "skate" on chrome-nickel steels will "work-harden" or "glaze" the surface of the steel, so you must apply a heavy feed pressure to keep the drill cutting at all times (reduce the feed ever so gently as the drill comes through the workpiece, obviously) Trying to weld steels of unknown analysis is fraught with problems.....it can be extremely difficult to get a good sound weld on some of these steels, even using a "TIG" or "argon-arc", and 316 stls filler-rod. It will sometimes happen that one can get a "pretty" weld, but the part will fail in the "transition-zone" between the parent metal and the weld deposit..... "TIG-brazing" will sometimes work well when welding does not.....but every job is its own individual situation.... If you haven't a lot of background in welding, I'd suggest, if I may, that you stay with mild steel for weldments, or, if you must try welding alloy steels, make certain that no one will be hurt if the weldment fails in service.... cheers Carla
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