Jackhammer bit heat treating....for a rental yard | Heat Treating | Forum

Seeing how it was my post, I think it's all right to re-post here:

First, I don't give advice, I only relate what I've observed to work well (disclaimer). The shops I've seen that have the best results i.e. hold up well and don't break do the following: Take a VERY short heat, cut the junk off the end (even to the point of beating some cold steel at the back end) and forge out the point, nip off the end, grind and quench in #2 heat treating oil. Simple, right?

Why does that work so well? By far the worst sin in sharpening is taking too long of a heat and screwing up the temper farther up the shank. The second is forging it and laying it aside to HT later. This causes the same problem, the heat in the point migrates up the shank and ruins the temper. Quenching off of a forging heat is frowned on, but seems to be the best solution. "Book" recommendations are not talking about anything like this situation. The only thing better is forging, normalizing the whole tool and re-heat treating.

What do I mean by nipping, you ask? For a small number of tools you can use a double “V” spring cutter. This will leave a near perfect chisel bevel on the end. For production I would set up an old 10 – 15 ton punch press with double “V” cutters and stop blocks at each end. The cutters are simple 1” square bar (tool steel) set on the diamond. I like to center drill both ends and use set screws through the stop blocks to hold the cutters. The cutters are set in “V” grooves in the holder. I’ve used 1” square high speed tool bits for this, but they often break. I settled on 1” cold drawn 4340. just cut to length, drill the ends, heat treat and you have four cutting edges on each.

Having this machine right next to the hammer is best. When you come out of the fire with a tool, you nip off almost the entire old point prior to forging. This gets rid of any gouges, mushrooming, and cracks, etc. It’s also important not to try to get too many sharpenings from one bit. The nipped end also prevents piping of the end. Nipping also allows you to get just the right length of heat for the new point.

These bits undergo enormous poundings and bendings in use and accumulate strains in the shank. The shank also becomes worn so it flops around too much in the chuck. If the blacksmith only re-draws the point each time, the bit will probably fail and the blacksmith will certainly be blamed. Now EVERYBODY is unhappy. The user has a broken bit (and might get hurt), the rental manager is mad at the blacksmith and the blacksmith is in the dog-house and may have to replace the bit with a new one. All because he tried to get more service from the tool than was reasonable. The customer pays $15.00 - $20.00 for the bit, sharpening is $5.00 - $6.00, he should be happy with 5 or 6 sharpenings.

If you’ve nipped off the end, you now have kind of a blunt chisel. Even when forging a chisel, I like to forge it as a point until its almost done and then stomp it hard on one side to spread it into a chisel. Better than forging it as a chisel, where it keeps fanning out and you keep chasing it back. This is the basis of what we call pre-forming in forging, you get the metal volume symmetrically where you need it first.

The above heat treatment seems to work very well on a wide variety of tool brands. From experience you may find some brands that require post tempering.

With good nippers you can produce a perfect chisel bevel (90 degrees for paving breaker tools). Points usually require a little grinding after nipping. I’ve seen a lot of different Points done. Some like to grind a four sided pyramid point, some just spin it against the stone and produce a cone point. I really like the look of grinding a sort of parabolic curve so the bevel blends into the taper. You can do this on an open wheal with the pointed downward. This is actually easier to do and looks the best (IMNSHO). Because of the time required to grind, it's often necessary to re-heat the last 3/4 inch of the point before quenching, this only takes a few seconds.

DO NOT try to heat treat the entire tool. You cannot do a proper job of that. And if it upsets in the hammer you'll not be making friends. They might be ok. Yes, B&L is a modified 1045. Even if you can't nip them off, you want to keep as short of a heat as you can. What sort of hammer you got? Did you see the tool John Newman made?

Hi all
Yeh I have found that I can teach an apprentice to forge out a nice point or chisel in a day, teaching them how to heat treat the suckers takes a couple of years though, not quite but you get the drift. Forging is the easy part, getting the heat treat right so as they don't mushroom or break 4" back from the point is the part that takes some skill and experience.

Grant is pretty close to the money, but we have old blokes here in Newcastle that have been doing this kind of work for many years and they swear by water quench and draw a temper. I have never had any sucess with water, and I have sharpened 1000s of moils. I have found that quenching off the forging heat in oil, then burning the oil off later (flaring) with the oxy torch to temper them. Main thing is to keep your heat short and not get it to hot when you forge it, forge it, grind it, quench it, in the same heat, aim to quench at a dull orange running to red.
One problem I did have was my blokes would get a different quench temp in the morning compared to the afternoon, this was caused by the quench tub being on the western side of the workshop near a window, in the morning it was darker there, in the arvo the sun would come through the window and they would miss judge the heat and quench the moils hotter, I could not work out why one batch of moils was good the next ones shit, the answer finally dawned on me, I put an old sheet over the window, and problem solved no more broken point or chisels.

Phil

All good information. Thanks all. I used to visit a shop in town that what they called bull points is all that they did. They even had a couple of power hammers that were built specificly for doing them. It was kind of a clam shell hammer. The whole unit foot print was about 26" square and only about 40" high. So it looked like a big chunk sitting there. The upper 4" raised off of the rest with two cylinders and across the front was the tooling that was referred to earlier. A double cut off, a tapered die and I don't remember what if anything else, but the whole top raised up and down. They had a stack of tools in the coal forge taking a short heat, to the power hammer, snip and draw out, next to a grinder and then right to the tank. They had a heat treat tank that had oil that was circulated and a rack above it that held the resharpened tooling so that about 3" to 4" was in the oil and that was it. He could do a point in about a minute. Pretty slick operation. Wish I had a picture to share of the hammer, but that was before the digital cameras.

The shop was in Reading, PA, and originally was a farrier and forging shop. These guys bought it and set it up for the bull point business. Originally it had two brick forges, but for this work they had a metal forge in the back. That sounds like the hammers they had. They were run off of a large compressor in the basement.