What are typical Rockwell hardness ratings for transmission and axle shafts?
Also, when doing homebrew hardening, is there a certain way to get a certain hardness?

(Our Baja car from last year broke a shaft in its gearbox, and it was just plain old steel and twisted in two.. I want to machine a new shaft and try to case harden it ourselves instead of sending it off to be done)

When I built the rear output shaft for my planetary crawler box, I used a stock cut down 231 output shaft. The stock shaft was 62C measured at many different lengths and diameters. When we hardened the cut and resplined shaft, we put it in a slow turning welding lathe, and got the biggest rosebud tip in the shop. We heated it to 1400 degrees (checked with a Temple stick) with the torch while it was turning. When we got to the temp we wanted, we dunked it into a big bucket of water. I checked it after it cooled, and I measured 58C at many different lenghts, and it was verey consistent all the way around. The depth is tough to measure, but from the end of the shaft it measures about .150 deep. This way may sound crude, but it works, and is fairly close to the factory specs.

I thought dunking it in oil or lime was the best way to harden things?

Brian, it sounds like you know what you are doing but don't you think that dunking the shaft (in water especially) at such a high temperature will create a martensitic grain structure that is very brittle?

I have been wondering on the same topic for some time now. I have a friend that makes tractor PTO shafts and I asked him what he does. He byes pure carbon from the welding place in town and heats the shaft tell its read hot with a torch(or as close as he can get do to size) then drops it in and lets it cool. It sound like it may work but he has no way of checking the hardness. Any thoughts on the process?? Has not had a shaft brake yet, but that dosn't mean it works for a resplined tail shaft ether.

Clark

Fullreversal -- Are you at GA Tech? Good school. Might be worth while in finding who runs the metal labs, to see what stuff they have around there.

On the metal structure when quenching, it depends on the original material. Oil quenching is often done to prevent the
steam pockets from forming next to the surface during the quench.

Kasenit is a "case hardening compound". Original stuff (years back) was a cyanide compound, but that formula is no longer sold,
thankfully. Still good stuff. MSC is one source for it. MSC Order Page (http://www.mscdirect.com/PDF/PDF02/2010.pdf) I use it for wear (shafts) applications, or maching home made punches.

Of the "home made" hardening compounds, there was one of bone meal with carbon. WARNING: OK to use the first time, but after heat & moisture you get Saltpeter (potassium nitrate). Carbon & nitrate is EXPLOSIVE. Pitty the poor home shop machinist who reused the case hardening mixture! :( Guy Luatard wrote about this is one of his "Home Shop Machinist Bedside Reader" Series of books (really a collection of tips, but great tid bits). If you know any home shop machinist, those books are great. You can find them on Guy Lautards Web Site (http://www.lautard.com/)

Tom :usa:

Why not machine the thing out of some hard ass chromoly shaft? I would ask your MET guys around there as they should know about this stuff. We have had problems like that one our axle shafts before.

By the way where do you guys compete East, Midwest, West? I'm with SDSM&T and we will be at the west, getttin it!

Weasel,
Are you in Rapid? I live in Blackhawk during the summer, and I am going to school in Brookings, graduating in May with MET. I am helping the ME guys here with their Mini-Indy car.


liveaxle,
I will have to see if it will be brittle, since there is no way to test it without breaking it. The unit is going in a full size chevy next month, so we will find out. It is tough to get the surface that hard without making the center to hard. If we used oil, or something else to quench it, it would have quenched slower, and not been as hard. I suppose we could have also put it in the oven for 15 hours, packed with carbon, quenched in oil, and put it back in the oven again for 18 hours at a much lower temp. I was VERY pressed for time when I did it.

Brian,
Yeah I'm in Rapid. Going to SDSM&T for ME. I've been on the baja for the past few years. You might have seen me around, I'm the short guy that drove the baja last year on ended up getting first in the hill climb. What are you doing for the Indy?

Weasel,
I am machining some drive train parts and doing the tube work on the back of their car. I don't agree with most of it, they are the engineers. I am using it as an individual studies class and getting 3 credits for it. First I tell them the parts they spent all the time designing and drawing pictures of are impossible to build, then they draw it again and I build it.

Originally posted by Brian E
Weasel,
First I tell them the parts they spent all the time designing and drawing pictures of are impossible to build, then they draw it again and I build it.


Hahaha.....sound like the Indy team. They havn't had a good one in quite awhile. So do you do the work in Rapid or what?

I do all the work in the lab on campus here in Brookings. I will be back there for good in May after graduation. I need to find a job bad, but there isn't much to do with my major there.

Originally posted by Brian E

When we got to the temp we wanted, we dunked it into a big bucket of water.

No doubt it is hard, but it is also brittle and likely to crack just by dropping it on the floor.

If you want to harden steel properly, first you need to know what type of alloy it is. Once you know what it is made of then you can determine how to quench it. After it is quenched you have to heat it up to a certain temperature for a length of time to temper or draw it so that it is also ductile and not brittle.

http://www.anvilfire.com/FAQs/heat_faq_index.htm

Actually im at Auburn University (A BETTER school by the way) LOL :)

Our baja team will be gettin it at east and midwest this year. and the word has come down that I will be doing drivetrain next year! hell yeah

Well if you wanna get your butt whipped come on over to the West Side and we'll show ya how we do it. :flipoff2: :flipoff2:

I wanted to go to west this year, but the school said nope. I hear the weather at the course is absolutely unforgiving right now. I got some email that said wind gusts were up to 78? mph, with extremely low vis.

just a note after hardening it you could have it cryogenicaly frozen to achive more strength.


dont belive this would help ?
go talk to some 0ne with the life time guarenteed
birfields.

I built an adapter a few years back, I married a T-18 trans to a toyota 4cyl Turbo transfer case. I had to cut the T-18 output shaft off and respline it to match the toyota 23spline input. I tested hardness before and after... before it was 64 Rockwell C scale at the surface. I turned it down and then used an OD grinder to finish the surface. It was like 37RC where I cut the splines... If I did it over again I would harden it, but if you want to save some grief, contact a local hardening shop, I did and they said they would toss the shaft in with someone elses batch of stuff and only charge me $50 (the shop minimum). I have hardened metals before at home, but you can't accurately control the temp, nor can you get it evenly heated with a torch. perhaps you could make a small forge by dismantling a propane Bar-B-Q and using the propane system. you would have to install a blower fan from a truck heater system and pipe it to a burn chamber. make a heavy steel frame and get some fireplace bricks for insulation...

hardening compound can be made by sintering any carberiferous material (leather, wood, bone meal, plants, animals [xnay on the animals]).

I would go for at least 45RC minimum, as your shaft is probably made from 8620 steel... if you E-mail me with the dia of the shaft I can calculate how much torque it can hold for you.

cwtoyota@yahoo.com

Originally posted by Fullreversal
I wanted to go to west this year, but the school said nope. I hear the weather at the course is absolutely unforgiving right now. I got some email that said wind gusts were up to 78? mph, with extremely low vis.

Really? Kick ass, that will make for some awesome race conditions!!

i am working on a project that requires linear ball bearings and hardened shaft on which the bearings travel. instead of buying the hardened shafts i was thinking of using some colled rolled steel and heating it up in a charcoal fire then dropping it in a bucket of water. any thoughts on how this would work?

I was a weldor in a protoype aerospace shop for several years and played with oil/ water quenching. From what I saw after hardness testing on calibrated equipment the only benefit is a very shallow surface harden that is inconsistant at best. To do it right you need to know the material the max thickness of part and have a calibrated oven and timer and a wat to control thr atmosphere around the part. Anything else is a crap shoot.

i am working on a project that requires linear ball bearings and hardened shaft on which the bearings travel. instead of buying the hardened shafts i was thinking of using some colled rolled steel and heating it up in a charcoal fire then dropping it in a bucket of water. any thoughts on how this would work?

No, typical cold rolled steel is 1020 and it doesn't have enough carbon in it to be hardenable that way. If you must harden it yourself you could do the kasenit type thing or use some 1045 or 4130 etc. for the linear bearings you really need to have a good surface finish so whatever you do it needs to be straightened and ground after heat treat. case hardened shafts still spall with linear bearings, it is best to use induction hardened or thru hardened shafts, in that application.

Heat treating stuff yourself is a bad idea in general. I have a small box furnace at work and all the capabilites to heat treat small parts correctly, but I don't, I send it out. There is really an art to heat treating to maintain dimensional stability and all that even with the proper equiptment. You really have to have the experience to make it work.

I did Formula SAE in school. We had a ton of problems with parts heat treated in the school lab. Lots of distortion and quench cracks, screwed up threads, and lots of parts missed the hardness specs. The metalurgy profs new the theory just fine but the experience MOJO part of it, only the old guys in the heat treating shops have that...

spend the money to have it done right, or realize there is a good chance you are going to scrp your parts.

Send your work out for hardening.
It's a must!........that you know what kind of material it is to harden it properly. Carbon alloys have so many different heat treat properties it's mind boggling. Oil, air, N2, water, blah blah blah. Some need long drawn down quench times, some need quick quench and redrawn temper.
Low carbons like mild 1018 don't react well with heat treats but will surface harden with case hardening materials. There are many different types of case hardening materials. Usually when you case harden you leave very little room to grind a finished surface and case hrdng will raise the surfaces, ie; spline pitch interferances, thread pitch interferance and bearing tolerances.

A pro heat treater will get it done right after all the work you put into it.

No, typical cold rolled steel is 1020 and it doesn't have enough carbon in it to be hardenable that way. If you must harden it yourself you could do the kasenit type thing or use some 1045 or 4130 etc. for the linear bearings you really need to have a good surface finish so whatever you do it needs to be straightened and ground after heat treat. case hardened shafts still spall with linear bearings, it is best to use induction hardened or thru hardened shafts, in that application.

Heat treating stuff yourself is a bad idea in general. I have a small box furnace at work and all the capabilites to heat treat small parts correctly, but I don't, I send it out. There is really an art to heat treating to maintain dimensional stability and all that even with the proper equiptment. You really have to have the experience to make it work.

I did Formula SAE in school. We had a ton of problems with parts heat treated in the school lab. Lots of distortion and quench cracks, screwed up threads, and lots of parts missed the hardness specs. The metalurgy profs new the theory just fine but the experience MOJO part of it, only the old guys in the heat treating shops have that...

spend the money to have it done right, or realize there is a good chance you are going to scrp your parts.

Dead on Gordon. I've installed heat treat furnaces and foundry stuff for years and the voodoo factor is off the chart. It pays to send the work to the pro's.

If you must harden it yourself you could do the kasenit type thing or use some 1045 or 4130 etc. for the linear bearings you really need to have a good surface finish so whatever you do it needs to be straightened and ground after heat treat.

I'm sure you probably know this already, but just to clarify...

The Kasenit stuff puts a really shallow high-carbon hardened layer on the part. This is good for things that deal with surface contact, but once you scrape that hardened layer off it's done. The actual piece itself has very little hardening. So if you were to case harden a piece using carbon-quenching techniques, and then put a ground finish on it, there's a good chance you will have just removed all of the hardened layer already.

Case hardening is good for things like tools and knives and such, where the outer layer in direct contact needs to be hard to resist chipping and distortion, but the 'guts' of the metal is strong enough without requiring hardening. That process won't really give you much benefit in terms of shaft longetivity or strength capability. You might see less wear in bearing surface and gear tooth contact areas but that's about it.

Everything else...yeah, Gordon's right, as usual.

SAE comps (I did formulaSAE at Pomona) are all about getting real world experience.

In the real world you would almost never do your own heat treating. Might as well lean how to talk to the heat treat guy now.

We got all our heat treating done for free...but there wern't many parts on the car that were hardended. All the suspension stuff (that I designed and manufactured) was normalized after welding. Only axle shafts were hardended (and were Ti till we twisted the splines off).

I used to work in a small machine shop. We did alot of emergency heat treating, parts that didnt have time to be sent out to be heat treated. I n those cases we would use O1 (Drill rod). We'd heat it on fire bricks with a torch untill the carbon scale started to show then quench it in a heavy oil untill cool to the touch. It the needs to be drawn back, heated with a torch on till it turns a light tan color. If its not drawn back the material is too brittle. The hardness would always come out around 52 - 56 RC. O1 is the easiest tool steel to heat treat at home. The next would be A2, its air cooled with fans instead of quenched in oil. Hence the A = air O = oil.

Quenching with water would make the material way too brittle (like glass)

Now I work in a large machine shop, we have a heat treatment furnace.

Brad

Weasel,
Are you in Rapid? I live in Blackhawk during the summer, and I am going to school in Brookings, graduating in May with MET. I am helping the ME guys here with their Mini-Indy car.


liveaxle,
I will have to see if it will be brittle, since there is no way to test it without breaking it. The unit is going in a full size chevy next month, so we will find out. It is tough to get the surface that hard without making the center to hard. If we used oil, or something else to quench it, it would have quenched slower, and not been as hard. I suppose we could have also put it in the oven for 15 hours, packed with carbon, quenched in oil, and put it back in the oven again for 18 hours at a much lower temp. I was VERY pressed for time when I did it.A full size chevy that has a crawler box which contains a homebrew hardened modified 231 shaft...... That reminds me of movies you start to watch, and already know within the first part of the show, how it is going to end.