What kind of steel is this? (lathe tool)

[matthew-s]

I purchased a craftsman 6x18 lathe from the original owner. I think he has it since the 50’s. It came with some tooling. Most of it was obviously HSS 1/4 x 1/4 and 1/2 x 1/2.

The other day I needed a boring bar for a small diameter hole. I found these “L” shaped tools that were ground on one end.

I decided to grind the straight side. I think I made a good tool, but I did not cut. It actually rolled a burr on the cutting edge.

I found I was able to scratch these with a file.

So, what is this material? Is it intended to be hardened after grinding? It’s not clear to me you can harden at home - I’m lead to believe you need to control the tempering over a good amount of time, no?

 

[coffmajt]

Without better info its tough to really know what the material is, but if it is HSS then you can harden and temper it if you have some simple equipment. To harden HSS you must heat and quench. Tool steels can be Oil, Air, or Water quench designed. As small as the boring bar looks I would start with an oil quench. You need to heat the tip you will be cutting with to at least 1850 degrees F. An easy way to know you are hot enough is to use a magnet ( usually orange white in color but ambient light can sometimes fool you) When the material is no longer magnetic at the hot end you are ready to quench. I use old motor oil in a can, just drop the bar in and let it stay for several min, then fish it out and check it with a file. If the file wont cut it good to go. If it did not harden the I would try water next using the same process. If not try Air. If none of these work you probably don't have tool steel. Good luck == Jack

 

[Cooter Brown]

In South Bend's how to run a lathe No. 15 they talk about forged carbon tooling, maybe that's what you have. It does look kind of funny.

The 3rd picture is from South Bend's how to run a lathe No.41. A spark test will be a good test.

 

[mikey]

If I had to guess, I would think that material is carbon steel. It will cut but it won't hold an edge. You can try case hardening it with Kasenit or Cherry Red but I suspect is is going to take more effort than it is worth. An option is to harden and temper tool steel as Jack suggested.

 

[Technical Ted]

Touch one of your know HSS tool bits to a grinder and then do the same with the unknown. Are the sparks the same color? If I remember correctly, carbon tools will give off a brighter, lighter colored spark and the HSS a deeper red (only going off memory so you might want to verify this). I'm sure you can also find a spark color guide chart on the internet.

Edit: In re-reading, I see I missed Cooter Brown's post where it basically says the same thing in the South Bend book.

Ted

 

[matthew-s]

Thanks. The guy I bought it from seemed like he knew what he was doing. There we even a couple of loose blank rods. I hoped I was just missing a simple old-timers trick.

It does seem like more trouble than it’s worth. I ordered a few 1/4 square HSS blanks and will try to make what I need.

I need to bore a hole to 0.308 in stressless steel to prepare it for a reamer. I have not found a boring bar this size yet.

 

[ericc]

I have one of these, and it sparks as HSS. It is only hardened on one end, like HSS twist drills.

 

[Dorn]

.... Tool steels can be Oil, Air, or Water quench designed. ... == Jack

Oil, Air and Water quenching tool steels are not the same as HSS. You need to go through a special high temperature hardening, quenching, tempering procedure to get the full benefits of HSS (mainly that it can get very hot before loosing hardness.)

My guess is that these L-shaped boring bars are some kind of high carbon steel that was either never properly hardened or that was softened by overheating while grinding. In that case the classic home shop machinist -- heating, quenching, tempering process -- will probably harden them enough to allow them to hold a cutting edge. Since the tool is so small in cross section (so it will cool fast) it probably doesn't much matter whether or not you use water or oil. Also, if you only need to use it a few times, I'd probably not even temper it. There is too much chance that you would over temper it and you would be back to a soft tool again.

Another possible problem with these L-shaped boring bars is that they are just too flexible. If I have a broken/dull endmill that is just a little smaller than the hole to be bored (say a .250" endmill in this case) I much prefer to grind it into a D bit single point tool. Of course that might not work if you need the hole to be quite deep.

If you don't know what a D bit is, look at this discussion
http://www.practicalmachinist.com/vb/general/d-bits-154906/

 

[benmychree]

Carbon steel tools would not have been hardened on the non used end, only the working end would have been hardened, that is why it does not hold an edge on the back end; it would if you hardened that end by heating and water quenching it and drawing the hardness back a little by re heating to a light straw color. High speed steel is hardened entirely differently, by a process called the Taylor White process in which the tool is preheated to a full red heat for a period of time, then the temperature is raised quickly to nearly the melting point, then placed in a current of air to cool. Before the era of high speed steel, carbon alloy steels were used, such as the well known (in the day) Mushet Steel; in reality, it was a form of HSS, that when hardened similarly to carbon steel, was sort of a high performing carbon tool steel; it was by accident that F.W. Taylor and his assistant Maunsel White discovered that by doing the two stage heat treatment with high heat, that the whole structure of the metal was changed, and it had the property of red hardness and could be run faster than carbon steel by a considerable factor without softening and the tool failing. In fact, once HSS is hardened, it takes a complicated and very time consuming heat treatment to anneal it; just heating it red and burying it in lime as is suggested for carbon or alloy steels has very little effect on its hardness.
Taylor started his experiments in cutting metal so he could write a book detailing how workmen could have speeds and feeds and depth of cut dictated to them for production work; he experimented for about 18 years, finally coming out with a book in 1897 or 1898, I think, titled "On the art of Cutting Metals", then later on came out with the intended book titled "Shop Management" in 1911.

 

[benmychree]

I have one of these, and it sparks as HSS. It is only hardened on one end, like HSS twist drills.

Twist drills are hard only on the working end, because the material on the chucked end is a welded on piece of lower grade steel. this saves tool steel, and if the tool were all hard, it would be difficult to hold in the chuck without slipping under torque.