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View Full Version : Oil, Water, Air Hardening Steel for Turning Tools



EddyCurr
02-21-2012, 08:02 PM
Who here is routinely making turning tools from Oil, Water
or air hardening carbon steel in place of using HSS, brazed
carbide, inserts or other?

Is oil hardening your material of choice?

Do you shape the cutting face before hardening?

Could you give one or two reasons for choosing OWA hardening
material over the other types of turning tools.

Thank you
Ken R.

Jpfalt
02-21-2012, 09:36 PM
O W and A hard tool steels are usually not used for turning tools for one main reason. They can't take the heat generated by turning at modern feed and speed rates.

The rule of thumb is that for a carbon steel cutting tool, if the chips come out blue temper color, the tool edge is wrecked. For high speed steel, the edge is wrecked if you get a glowing orange chip. For carbide, the edge is wrecked if you get a spark out of the cut. Ceramic tools are capable of holding an edge even if the chips come out as sparks.

High speed steels were first introduced during world war 1 in Germany. Cast iron runs at about 90 surface feet per minute with HSS. With carbon steel tools, you are limited to about 30 suface feet per minute.

Mcgyver
02-21-2012, 09:58 PM
for specialty tools its a very valid approach, do it often for milling cutters. I think I'd probably profile grind a hss tool if possible, but I don't know what you have in mind. Obviously a waste of time if its a straight up rectangular tool as Jpfalt suggests

I've always used oil hardening tool steel - regular old oil hardening drill rod. It works and is easy to heat treat with propane or O/A. Cheap and available in the rack and any industrial supply place. I always thought W1 was lower cost but quick check of MSc shows it comparable to O1. Air hardening is more than twice the price so would be for special cases where O1 would be likely to crack

One difference between the three is the that the faster the quench required (ie W1 requires the fastest quench) means the hardening won't be as even through out - the inside will be less hard for W1 than for O1 for example - an advantage with some tools where a less brittle core is desirable.

running any carbon steel cutter, obviously slow waaaay down; point of contact temps are primarily a function of surface speed and carbon can't take much

EddyCurr
02-21-2012, 11:33 PM
Thanks for the replies. Sounds like this isn't a wide-spread practice.

I have thought about using so-called Ground Flat Stock (starting with
a square profile, say 1/4" x 1/4") and either grinding a profile after
hardening or roughing a profile before hardening and then finalizing the
shape after.

One application that came to mind was manually threading short lengths
of small diameters to a shoulder. A job that could seem dicy at insert speeds
might be more leisurely accomplished at speeds appropriate for O1.

Also, there is a claim that O1's greater hardness and finer grain structure
makes for a better edge and better finish than HSS. Is it sufficiently better
to offset the increased trouble/expense of preparation and decreased cutting
speed ?

It is easy enough to try it out firsthand. I think I'll have a go once I
round up the rest of what I need to properly harden O1.

.

beanbag
02-21-2012, 11:58 PM
Minor threadjack.

Is O1 or even 4140 good enough to use as a profile turning tool in aluminum and plastic?

JCHannum
02-22-2012, 06:32 AM
Carbon steel turning tools were used successfuly for years before the development of HSS and more exotic alloys. in the good old days, every shop had at least a small gas forge tucked away somewhere where the machinist formed his tools as needed. The older books detail the process of making various cutting tools. In my wanderings, I have accumulated quite a few of these, many made from other worn or broken tools such as files, letter punches and broken taps and drills.

I have also made profile tools from O1 flat as described. I shape first, harden and stone to sharpen. They will not take the speeds HSS will, but are another tool to be used as needed. One more tool and technique to be added to your tooling arsenal.

1200rpm
02-22-2012, 06:38 AM
i make my own boring bars out of 01 - i seldom turn faster than 600 or so rpm and they work fine in everything i`ve tried them on. here`s some of my bars- oh, also good for internal threading tools.:) i don`t temper them, if one get too brittle i`ll just stick it in the oven at 450 deg for about an hour and that seems to do the trick.
http://i1136.photobucket.com/albums/n495/iwananew10k/1324298053.jpg

rythmnbls
02-22-2012, 06:56 AM
Minor threadjack.

Is O1 or even 4140 good enough to use as a profile turning tool in aluminum and plastic?

Yes, it works quite well for aluminium. The photo below shows a piece of scrap angle iron used to create a radius in 6061.

http://i87.photobucket.com/albums/k142/madluther/Turbine%202/t2_diffuser1.jpg

Steve.

1200rpm
02-22-2012, 07:01 AM
ha,ha! i like it!(the above post)
it only has to be harder than what you`re cutting...right?;)

SGW
02-22-2012, 07:55 AM
Sure - I've occasionally made carbon steel cutters for special jobs. I sometimes mill the shape before hardening. A tapered end mill of 5 to 7 degrees per side is a very convenient way to mill relief angles.

Carbon steel can indeed take a keener edge than HSS, although you would have to use a fine sharpening stone after grinding, I think, for it to make much difference. The only real drawback to carbon steel cutters is their lack of resistance to heat. Slower speeds and feeds and some kind of coolant are in order, but as long as you use them within their limits, they're fine. The ability to make your own cutters is a useful skill that expands your work capabilities beyond what you can do with what you can buy off-the-shelf.

Mcgyver
02-22-2012, 10:33 AM
Thanks for the replies. Sounds like this isn't a wide-spread practice.

I have thought about using so-called Ground Flat Stock (starting with
a square profile, say 1/4" x 1/4") and either grinding a profile after
hardening or roughing a profile before hardening and then finalizing the
shape after.

One application that came to mind was manually threading short lengths
of small diameters to a shoulder. A job that could seem dicy at insert speeds
might be more leisurely accomplished at speeds appropriate for O1.
.

if its not widespread practice, its not because it won't work its because unless its a special shape its just so easy and inexpensive to grind a hss tool to suit that its not worth it.

I hear Carbon steel us supposed to take a finer edge, but probably the low hanging fruit is in putting a great edge on hss - something i get the impression few do. If you're putting a mirror on hss and its not keen enough for your tastes i can't argue with wanting to try carbon steel....but if you not already doing a proper job of stoning hss, indeed pushing the envelope, going to carbon won't improve things (if it even does with the perfect edge).

For say a specialty mill cutter, usually you machine the piece then harden and stone. With a lathe tool, one tends to use the bench grinder - that is one big disadvantage of carbon steel, its sooo easy to temper it with grinder temperatures. In many many cases (taps, scraping tools, etc - even single point thread tools like you're considering) the tool will NEVER be used at speeds where hss has any advantage over carbon...the advantage of the hss is that its easy grind without wrecking the temper.

To make a threading tool that goes to a shoulder, just take a hss blank and grind the V, with appropriate clearance, so its oriented way over to the left side. Stone the final profile using a fishtail gauge (like you'll have to for carbon). Other than just wanting to try it for your own curiosity (which is reason enough) i can't see any advantage and there are several disadvantages in doing this in carbon vs grabbing a hss blank and being done in 5 minutes

RussZHC
02-22-2012, 12:12 PM
Perhaps, and this is with no background to definitively state, the one advantage I could see would be in making some of those "old school" lathe bits that are bent/curved.

I am working my way through a few books published around the time my lathe was new, so late 1930s/1940s and they illustrate a few situations where an off-set tool, accomplished by bending, is used.
I am not certain I truly see how the bent tool is needed, still...again, not sure, have not tried or experimented but I don't think trying to bend the HSS in a home shop situation is going to work whereas with the carbon steel IMO the chances would be better.

IIRC the place I see them most is for internal threading...to get the off-set you need to clear the work as you go deeper into the bore, you have to start with a considerably over-size "bit to be" and grind away or braze on a piece to obtain the off-set but a bend can accomplish the same thing

Edit: like the home made boring bars !

wierdscience
02-22-2012, 02:01 PM
I use A-2 frequently to make form cutters for the lathe.

I has some advantages actually.It's air hardening,it doesn't generally warp or change dimension during heat treating and it comes soft so shapes can be milled and stoned instead of having to be ground from solid.

Additionally it's fairly abrasion resistant which helps with edge breakdown and it's better at absorbing impact than HSS.

I needed a 10mm radius cutter awhile back.Making it was simple as putting a 3/4" sqaure piece of A-2 in the mill vise tipped over 5* in both directions.Plunged in the radius with a 20mm endmill,stoned the mill marks smooth,heat treated it ,stoned it again and put it to use.Whole process took maybe 20 minutes.

lazlo
02-22-2012, 04:50 PM
I use A-2 frequently to make form cutters for the lathe.

Additionally it's fairly abrasion resistant which helps with edge breakdown and it's better at absorbing impact than HSS.

+1. A2 has excellent wear resistance and it's pretty tough for a tool steel. But like Jpfalt says, the common "drill rod" tool steels don't have high red hardness, so the edge breaks down quicker than HSS in use. Even then, A2, O1 or my current favorite: D2, will hold up a lot longer than carbon steel, which is 1095.


One difference between the three is the that the faster the quench required (ie W1 requires the fastest quench) means the hardening won't be as even through out

W1/W2 is a shallow hardening steel. That's why knifemakers love it -- it makes beautiful hamons, which are a surface hardening effect.

This is a choji hamon on a kat I made from W2:

http://i164.photobucket.com/albums/u15/rtgeorge_album/Katana/IMG_0535s.jpg

philbur
02-22-2012, 05:46 PM
As others have said it's convenient for special form tools etc.

I often use silver steel (drill rod). Mount it in a 3 jaw chuck on a semi universal dividing head on a mill to cut the various angles. Heat treat it then stone the top face to put the edge back on.

Phil:)