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Forging a cut off hardy out of a jackhammer bit


Pug}{maN

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The steeper the angle the faster it will cut, but too steep it will ripple. I usually grind them steeper than they should be for myself then use them then it usually ripples and then I grind it again and it holds up perfectly. When I make them for someone else I grind them less steep because they cut quicker than most people are used to so they don't hit their hardy with their hammer as easily. I have never measured the angle, but you can look at pictures that have been taken of my hardies and measure them yourself. If you are just cutting round stock, a straight cut is fine, but if you are cutting square or flat stock a curved one is definitely better because of the surface area contact. I would suggest making it curved because you'll probably be cutting all kinds of stock and it will cut round stock more efficiently also. Everyone assumes that it will slide off the curve, but that is just an assumption. I don't know who came up with the straight hardy, but I'm pretty sure it was not a blacksmith. If you are cutting hot material, you do not need to harden it. If you are cutting cold material, you need to harden and temper it. If you cut large stock, you would just lose your temper, so there is no need to harden. Learning to make, use, and maintain tool is to your advantage, so don't try to "plow" with your hardy. Hot cuts are thin tools, so move your material after every hit and your tool will cool off quickly just like it will heat up quickly if you do not move it.

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Cold chisels are generally ground to 60 degrees. Hot chisels should be ground to an angle more acute than that. You kind of have to feel it out as to how tin you can get away with. It depends on your skill the kind of steel the hot cut is made from and the thickness of the steel being cut. As far as hardening and tempering it is somewhat a matter of debate. if the tool gets over heated the heat treatment is lost though the tool preforms better when it is heat treated. I do heat treat my tooling, others don't, but I also forge my hot cuts out of S7 a steel with good hot working characteristics. This steel will withstand elevated temperatures better than say 4140 or 1045. Many jackhammer bits are made from 1045 though not all. I personally don't use a lot of 1045 for hot work tools as I find it to be a bit soft for tooling that will be used in a professional high volume shop. If I am going to put the work into making a tool by hand I want it to be as durable as possible. I tend to grind hot cut hardies straight but I have used curved as well. I really don't see the difference in performance in general work. Though with thicker steel the curved edge is more efficient though on flat stock a curved cutting edge is harder to use. All of this bring said everything Brian said above is completely valid. I just wanted to present an alternate strategy that is also employed by many smiths successfully.

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The curve is not that much on any hardy I have seen and a curve works great to get a cut started and then walk it down the length of a large item without starting multiple mis strikes.

I like my hardy tough not hard as it's a lot easier to zip it sharp on the angle grinder than to regrind and perhaps even re-heat treat a hammer that some student has slammed onto a hard hardy edge. I also like my cutting edge pretty thin, easier to cut and less deformation when used.

Mine was made from the broken off chisel end of a pavement breaker. All I really did was to forge the shaft end to fit a 1" hardy hole and thin the worn cutting edge a bit, got over 25 years of use in it and it's still going strong.

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I followed Francis Whitaker's advice and made my hardy into what he termed a "straight side hardy." It has the vertical side and a bevel on the other side. It just makes it a little easier to get a straight cut depending on which side of the hardy is facing you. You can get a 90 degree cut on what you're holding or on the piece which is cropped on the other side of the hardy. You can also get beveled cuts of various angles. The same can be done with an included-angle hardy by raising or lowering your holding hand, but the single bevel simply helps a little. The anvil hardy has a straight cutting edge. It is an old manufactured hardy that has been drawn out a couple of times. It is probably 60 point carbon steel. The home made little hot cut of S7 has the curved edge and an included angle. Both tools are dressed at a 45 degree angle. The angle could be more acute for finer work.
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I my self use 4140 have great results. I do not heat treat check the edge sharpen with a file curved or straight I have both large stock over 3/4 I use the curved one. my very first one was made of rebar did great and still use it from time to time made it to fit my old anvil. I have used A-2 (air hardened).

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I had used a straight hardy until being exposed to the rounded hardy. The straight was one of Grants (4140 and Ht'd i believe) and the rounded was forged from 1045 and not Ht'd.Having both I can cut faster and more accurately with the rounded top. I find it better for flat as I can roll it around all the sides and mark or cut to center.
Just the experience of a non professional smith with not near the experience of Brian or Timothy.

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Timothy will it scar a hammer face at the heat treat you are using it at?

(And yes I use H13, S7 and S1 for many of my cutting/slitting and punching tools)
As far as I know It will not scar my hammers. I have gotten to the point that I don't often hit the hardy with my hammer. I prefer my hammers a bit on the harder side as my struck tooling is a hodgepodge of old, new, self made, manufactured, properly hardned tool steel and unknown scrap. I don't like to have to dress my hand hammers all the time because I struck something harder and it left a mark. My go to steel for hammers is 4140 and W1 as a second choice. I do also use 1045 for hammers that will only strike hot steel or nonferrous materials. I should also say I started making my hardies out of S7 because I was forging a lot of stainless and silicon bronze I needed something more high performance than what I had been using. I think prior to that I had been using something made out of an old truck axle or 4140 I have made many hot cuts because I like to make tools and I swap anvils from time to time because I'm fickle. I needed to be able to make a cut at the end of a heat to make time so the material was often cooler than it should of been. It was destroying my hardy in short order. The edge was just upsetting into a blunt edge. I found with the S7 I could cut at lower temperatures (red heat) and still keep a thin keen edge. Every once and a wile I will need to sharpen the edge with a smooth file in my vise really just a few strokes rarely grind. The vise is only a step away so its a really quick thing. I was doing hundreds of cuts in a day. I have never had to draw out the hardy to date. I also found with the S7 I could have the edge ground for hot work and still cut soft steel cold with minimal damage to the edge. Remember I'm tiring to do volume and I have a 65gk air hammer. It would be a difficult job to forge a hardy from S7 by hand and the steel in not cheep when compared to other options. So take my advise only as a way that works and not "The right way" etched in a stone tablet on some mount up high.
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And I'm teaching a couple of classes a semester as well as at demos and re-enactments so I have little control over the hammer control of the person who may be using the hardy. I tend to like students using a bit softer hammers as it helps preserve my anvils and tools. (and have a dead soft french crosspeen for particularly egregious ones that can't hammer like lightening as lightening *often* hits the same place twice! If any of them read this they'll know what it meant when I handed them "frenchie" and said "here try this one!" actually it's a good size for a new person anyway...)

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Yeah I was thinking about just making both types in seeing which 1 I like better

Pug}{maN, if you give me your address in a personal message, I will send you one of my hardies so you don't have to make that one. Make or buy the other type and post the results on this thread. I don't expect anyone to believe me. You have to see things for yourself.
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I say take Brian up on his generous offer and hammer to your hearts content. I'm often confronted with, "should I or should't I" thoughts. I really have to go it alone here and the only place I've learned much is on this site and some books. Don't get me wrong, I've learned plenty. With the unselfish contributions to this site by all the smiths here. This is a treasure for the blacksmiths community. I am a strong proponent of "just do it". If I don't get out there and hammer, I won't learn a thing. I learn from my mistakes and failures. There have been plenty. The closest help, I've been able to find, is close to 400 miles away. But thats what I get for living where I live. So, I try my best to do as much as my bad knees will allow. In my experience breaker bits make good tools.

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It's nice to have the *luxury* to learn from other people as few of us are young enough to make all our the mistakes on our own. Starting out in pre internet days I was pretty much standing around with The Modern Blacksmith in one grubby hand and a hammer in the other. It's amazing how much faster the learning curve can be taken if you have *someone* to point out where you are going astray!

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When I just resharpend my regular hardy, (Garage sale,an Atha made for 7/8, WOO HOO!!) I started the process of rounding the cutting edge on the grinder. Might take another sharpening or two to get a real pronounced round. Got a chance to use that style at a conference and rolling the cut across the edge is a breeze.

My first hardy was a jackhammer bit with a welded collar, bought off of fleabay, that I want to reforge to a straight sided cutting edge, mostly to use a a butcher to start tenons, probably will leave that one square topped.

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