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Thread: Hardening a drive shaft

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    Default Hardening a drive shaft

    I have a drive shaft that I needs to re-harden after I heat treated it to remove it temper so I could TIG weld a grove that the oil seal cut into it. It's 8 inches long and approximately 2 inch diameter. The front haft is solid metal.

    The problem I'm having it I can not re-harden the shaft. I do not know what the carbon content of the metal is and that is a big problem when trying to harden it.

    Using a electric kiln I pre heated the metal to 1400*F (760*C) then went to 1436*F (780*C) with a hold time of 1 hr. I then quench it in cold water. It appear to have no effect on hardening the shaft.

    I then tried 1450*F (790*C), with a hold time of 1 hr. again no effect on hardening the shaft. My last attempt was 1550*F (843*C) for 1 hrs hold time and this time I quench it in a salt brine again there was no effect on hardening the shaft.

    The shaft was very hard before I started messing with it, any suggestion on what I should do nexts?

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    Hmmm What the heck is the application of this shaft? Automotive usually uses 4041 and similar which would have been glass hard after a 1559 dunk in water. But there are other alloys like high speed tool steel designed to take more heat and can require up to 2200f to harden so I would continue creeping up as you have been until you get the butter zone.

    Couple slight mods to your method I would recommend are . . .

    1> Quench in oil first, a dunk in oil won't harm a water hardening alloy but quenching an oil hardening alloy in water can cause micro stress fractures that ruin your part . . . so try oil before water, if it won't harden in oil then try cooling faster with water. Just cheap motor oil, some say used thinking you get some case hardening from the carbon in it but it doesn't need to be and in fact I don't like used. Important that it's in a metal container that you can lid off in case of fire but fire risk is lo so long as you use enough oil to cover the part a couple inches deep.

    2> Get yourself a strong magnet on a stick to reach into the oven and check, when she goes non-magnetic go another 50-100f and soak. It should harden then, try in oil and if it doesn't harden then clean and re-heat and try water.

    If that doesn't do it I'd suspect it may be some very low carbon stuff that they cryogenic heat treated quenching in something like liquid nitrogen and you may be out of luck . . . likely you just need more heat though.
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    Too late now but you should have just tigged it. You could wrap the shaft in wet rags to keep it cool.

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    Thank you Adfield for your help.
    I was hopeing not to use oil because of the smell and fire danger. But if that what I need to do I will follow your instruction. I read do not use multiply grade oil like 10-30 and cooking oil is OK. I wonder if there any problem using old cooking oil? I know it a dumb question but I don't want to buy 3 or 4 gallon of cooking oil and use it one time. Unless I have to.

    The shaft is a drive shaft for a low rpm hydraulic motor. I've believe it a low carbon steel, but it only a uneducated guess.

    I read about using a magnet to test for a non-magnetic field and I think I have a strong enough magnetic.

    It will be a couple of days before I can used the kiln, by then I hope to find some oil and work out any problems using the magnetic.



    Dogfish, I took the shaft to a machine shop to be TIG welded and machine. He told me if it was welded it would be so hard it could not be machine. That why I decided to try doing it myself.

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    I know a blacksmith that uses old fry oil, that is usually peanut oil I think. A cooking oil with a high flash point should work.
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    Quote Originally Posted by Dogfish View Post
    Too late now but you should have just tigged it. You could wrap the shaft in wet rags to keep it cool.
    I assume he needed it annealed for the lathe work to refresh the seal surface after the welding buildup.
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    A toolpost grinder or carbide would have taken care of that. I have machined welded parts before, they are not hard.

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    I hate it when someone ask for help and them keep every one hanging. That said, I've am having a hard time finding use Vegetable oil in Anchorage. So if anyone knows where I can get some please let me know.

    All I need is 3 or 4 gal, by the time I clean it up I think it will take 5 or 10 gal.
    MacGyver

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    Quote Originally Posted by Dogfish View Post
    A toolpost grinder or carbide would have taken care of that. I have machined welded parts before, they are not hard.
    Grinder would take forever to clean up a weld, coated carbide will get you to maybe 50Rc but usually leave a poor finish that you'd need to grind. Ceramic inserts will get it done to around 90Rc but who keeps those around.

    My fix would have been to ether turn it down and make a press fit sleeve or build-up with spray weld or plating.
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    Quote Originally Posted by ADfields View Post
    Grinder would take forever to clean up a weld, coated carbide will get you to maybe 50Rc but usually leave a poor finish that you'd need to grind. Ceramic inserts will get it done to around 90Rc but who keeps those around.

    My fix would have been to ether turn it down and make a press fit sleeve or build-up with spray weld or plating.
    Speaking of a press sleeve. After I remove the temper I was talking to a friend about what I was doing. He told me about a product called SKF Speedi Sleeve that is a very thin S.S. that is design to go over a drive shaft with a problem. If I had known about it sooner I could have fix my problem a long time ago.

    I don't know how smooth 50Rc or 90Rc is what I do know is any imperfection under the seal will destroy it in a very short time. The surface must be polished to perfection, I don't know how that could be done if the surface is extremely hard.

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    You can still put on the Speedi Sleeve, That would solve your finish problem.

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    Quote Originally Posted by Gerberman View Post
    You can still put on the Speedi Sleeve, That would solve your finish problem.
    I realized that two week ago and decided I would see if I can fix the shaft by TIG welding and tempering. If not your suggestion will be my backup plan H.

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    Quote Originally Posted by Gerberman View Post
    You can still put on the Speedi Sleeve, That would solve your finish problem.
    I realized that two week ago and decided I would see if I can fix the shaft by TIG welding and tempering. If not your suggestion will be my backup plan H.

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    Quote Originally Posted by MacGyver View Post
    I realized that two week ago and decided I would see if I can fix the shaft by TIG welding and tempering. If not your suggestion will be my backup plan H.
    You need to harden it back because if you don't it won't last very long doing the job, otherwise they wouldn't have hardened it to start with. I would guess is that it has splines someplace and they won't last long soft, unless hardened the mating set will eat them up pretty quick.


    The Rc numbers are for hardness not surface finish. The "R" stands for Rockwell standards and the "c" means the "c" scale the Rockwell standards . . . there are "a" through "g" Rockwell scales and "c" is for most hardenable steels. Sometimes you see it like "HRC" (hardiness Rockwell scale C) and sometimes Rc and sometimes just R or Rockwell and the "c" scale for steel is assumed.
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    For a good finish even on a hard surface, take it to an auto machine shop that grinds crankshafts. They have a belt sander designed for polishing cranks. You're probably going to need to have the shaft rehardened by someone that specializes in hardening steel and then have it polished.

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    Quote Originally Posted by ADfields View Post
    You need to harden it back because if you don't it won't last very long doing the job, otherwise they wouldn't have hardened it to start with. I would guess is that it has splines someplace and they won't last long soft, unless hardened the mating set will eat them up pretty quick.


    The Rc numbers are for hardness not surface finish. The "R" stands for Rockwell standards and the "c" means the "c" scale the Rockwell standards . . . there are "a" through "g" Rockwell scales and "c" is for most hardenable steels. Sometimes you see it like "HRC" (hardiness Rockwell scale C) and sometimes Rc and sometimes just R or Rockwell and the "c" scale for steel is assumed.
    Yes, it has splines inside the shaft and I know I need to be hardened it other wise it will not last like you said, that why I'm keep trying to get it right.

    I gave up looking for used cooking oil and bought 3 gallons of canola oil for $17. Some of the things I do to save a buck is just dumb. LOL

    I fired the shaft for the fifth time today. I had planned to go up in steps to find where it gos non-magnetic and then add 50* to 100*. Before I new it I was at 1505*F and tested it with a magnetic and it was non-magnetic. Not knowing where it lost it magnetism I decided to let it soak for one hour at 1550*F and quench it in oil.

    Well it did not work so tomorrow I will do it again and follow your instructions.

    MacGyver

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    Quote Originally Posted by rbuck351 View Post
    For a good finish even on a hard surface, take it to an auto machine shop that grinds crankshafts. They have a belt sander designed for polishing cranks. You're probably going to need to have the shaft rehardened by someone that specializes in hardening steel and then have it polished.
    I never thought about a auto machine shop that grinds crankshafts.

    I did get it polished using strips of sandpaper. I may have to take your advice and have someone do it right after another ten tries. LOL

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    Quote Originally Posted by MacGyver View Post
    Some of the things I do to save a buck is just dumb. LOL
    LOL Yea me too . . . just last week I went and paid $20 for a Harbor Fright bearing separator that broke then $145 for one made by OTC to press off a bearing when I could have just paid Napa $15 or $20 to press it off for me. But, for some stupid reason I'd rather do it myself and now I have the tool for next time . . . a year or two from now.
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    I repair anything I can myself and end up buying a lot of tools for just one job but they usually end up paying for their self in the long run. I would rather spot weld a hard shaft than remove temper and try to re temper. I have used quite a few redi sleeves with good success and that would probably be my first attempt. At this point it will need to be re tempered but how is above my pay grade.

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    I'm beginning to think I may not be able to harden the shaft using oil or water. I did find out the non-magnetic point is 1425*F and after a 2hr soak @ 1550* I still failed to harden it in oil.

    So far I could not find any shop in town that does heat treatment.

    I'm reading up on case hardening using air or box carburising any suggestion are welcome.

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