Paving Breaker forging & heat treating 101

[Nakedanvil - Grant Sarver]

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.

Edited June 20, 2009 by nakedanvil

[HWooldridge]

And I'm not trying to "sell" your induction units but I think they would be perfect for this type of work. I've done a few pavement breakers on my 100lb hammer with the propane forge and they came out OK but not perfect. I typically draw them pretty soft with the intent I'd rather have one mushroom during use rather than break. I do pinch and cut as you have described rather than try to beat it back out to a point.

[JNewman]

I will have look into getting some re-pointing work. The construction industry is one of the few that is pretty busy right now around here. I appreciate your opservation skills.

[Nakedanvil - Grant Sarver]

I've seen (and done) the big demolition points and chisel by a few different methods. I've seen people machine them in a mill, very time consuming and wastes a lot of carbide. I've seen (and done them) by forging, a real man-killer. After many years I settled on sawing as just about the best all-around. Of course this takes a pretty big saw, but I've seen it done well in some of the vintage Wellsaws too. I settled on an angle iron fixture set at 15 degrees that sits on the out board side with the vise holding the fixture. Just put kind of a “C” frame over it with a single “T” handle screw down to hold the bit. Use a torpedo level on the notch to get it oriented. Then use the level on the previous cuts as you go around.

You’ll learn from experience (and expensive blades) which bits are too hard to saw. When they come in, you want to stick the end in the forge and draw them back a little (maybe that silver after blue). Usually we saw off the first 2-3 inches of beat up end to get away from the work-hardened part and get rid of the rounded edges on a chisel so the new one looks near-perfect. It also needs to be cut back so you can take a decent cut without skidding out. Always start the cut slow so that the blade goes down straight.The finished bit should have a small flat on the end anyway. On a 2-1/2 it should be about 1/4 –3/8”. On a four inch about 1/2 –5/8.

The “little” 2” bits bring $35.00-50.00. Bit of a chore to handle, but the monster 5” and over go for $200.00 and up.

Edited June 24, 2009 by nakedanvil

[JNewman]

I went to 4 rental shops looking for sharpening work. 1 gave me 25 points and chisels to sharpen, and they will send me more next time they need about 50 sharpened. Using Grant's information above I sharpened them in about 2 hours. I need to get a little faster and find some more shops that will send me more points. Unfortunately there is a shop in Toronto that is sharpening them for $3.75. I can't see doing them for less than $5 ea unless they have several hundred to do.

[Nakedanvil - Grant Sarver]

Good production rate is 40 - 50 per hour sharpening points and chisels. That Indian smith in the video could do that, Ill bet. I always had guys who would tell me they can't forge any faster (not sharpening, but similar) and I'd tell it's not when you're forging that matters it's when you're not forging. They'd take, say 20 seconds to forge something (3 per minute) and then only get a throughtput of 50 parts per hour. You gotta look at where all the other time is going. Save steps, keep the work area tight, feed the fire at a rate that always has a hot part just ready for you, it's an art. Learn to do simple time/motion studies on the fly.

Now in sharpening, $3.75 could work, IF the customer is dropping the tools off and picking them up. Good luck John.

[JNewman]

Getting them hot is where my holdup was. I was being cautious (probably too cautious) in keeping the short heat so I was often waiting for stock to heat up. I did my nipping under my hydraulic press with a spring cutter which didn't have quite enough power nipping the chisels especially if the cutter didn't quite line up. If I start getting a lot more of this work I will have to set the press up a little better with a dedicated cutter or set up a cutter on my small hammer.

[Nakedanvil - Grant Sarver]

Part of the benefit of nipping is that you can chop the end off at a point that gives you just the right length of heat.

[Mills]

I am trying my hand at this, started today. I am using some scrap stock to work out the steps. I went to the trouble of fabbing spring tool to get the correct angle. Nah that pretty well sucked. next was free hand on flat dies and a taper tool, way too slow.

I have taken some pictures of the results but the files are too large and I am unable to find the resolution adjustment on this software. Will try again later.

I am curious on what tooling ya'll use to do this work. I understand (I believe) about the nippers and removing the end. What of actually forging the point?

[JNewman]

I just used a bottom taper tool on flat dies for the forging of the taper.

Edited October 22, 2009 by JNewman

[JNewman]

Here is the bottom tool I used to forge the points and chisels. It just slips over the bottom die

[Mills]

Thanks for the picture. I think I'll give that a whirl. I see some other uses for that as well. Will let you know how I fare.

[jason0012]

I used to some breaker points from time to time. It never was very big business here, most rentals just send the dull bits out over and over! I had a few good customers who would send me a few hundred chisles a year to repoint, but they are all out of business now. For the last few years when I have aproached any contractors about tool dressing they have expressed a preference for simply replacing dull bits! I have worked on a few of the bigger ones too, up to 5". Those big points are a huge pain, just for the weight. These big monsters come in the shop so seldom as to not be worth the trouble. I have to locate a die I haven't used in 8 months and rearrange the whole shop to get the crane in....= barely worth the hassle.(The money on those is pretty good, but I see such bits so rarely ) Tool dressing is really good work, I would like to do more, there just isn't any demand around here. Is there any way to scrape up more of this type of work? Ive been through foundries, boiler companies, paving contractors and rental companies. The local utilities seemed promising but have a contract with someone else that has him working at about 20% of my cost!( $1 per point!) A few things I haven't seen mentioned is those bits that aren't worth sharpening. I did work once for a boiler company. Their previous experience with a tool smith was with someone I happen to know and trust did a first rate job for them. They complained quite a lot about his bits breaking and being substandard ect. I knew better but took the job anyway, about 400 chisles 5/8&78 size. About 120+ were so badly cracked and stressed that i clipped and clipped and could not find sound material in them. These bits i brought to the customer and explained that they were unserviceable. the customer would not accept that this was not my fault or that of the other smith. I should mention that many of these bits were bent past 20 deg, and almost all were mushroomed quite badly. I have no idea what was done to these bits in their service life but by the time they came to me they were pretty much done. That customer was one of only two who I ever found truly angry with the service I rendered. Frustrating since there really wasn't much I could do.