Metal turning

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  • #1725
    shadoh
    Participant

    So I finally got all the parts together I need to make my “Power Pumper” for my BSA pump. I machined up the head over the weekend but I have a few questions.

    All the steel I bought for this project was out of the cold roll scrap piles of my local metal supply shop (I love that place). This stuff is garbage to turn on the lathe. No matter what I do the cuts end up being rough, at least in my view. Im used to the almost mirror cuts that stainless or ali give me. Is there a trick to cutting this metal or is just because its such a low grade of metal? I would describe the cuts to more of a tearing action than cutting.

    I turned the gear shaft out of this same metal. Its rough but will work fine. I would like to harden it as there will be allot of stress on it. Whats the best way to do this? Do I use water, brine or oil? Also, I dont have a decent torch available to me. Will a propane torch get this hot enough? The gear shaft is 3/4X6 inches.

    Thanks guys

    #35640
    marc
    Participant

    If you use carbide bits use slower cutting speed higher feed and a deeper cut. If your using HSS get used to it. Also using a lot of cooling helps.

    Regards,

    Marc

    #35641
    brushy-bill
    Participant

    Try putting a larger radius on the point of your cutting tool, whether carbide or H.S.S. it will help. Also if using carbide, set your tool just slightly below centerline of the part. Don’t let the H.S.S. get above center line. Use a positive rake angle on both types of tools.

    #35650
    mm123522
    Participant

    Shadoh:

    Cold rolled wont harden. Low carbon steels will not harden. You need air or oil hardening steel. It would be hard to get a piece that big hot enough with a propane torch. It must be bright red to get it hard

    Mark

    #35656
    shadoh
    Participant

    Hmm, I will try running it without hardening. I do have a nice little pile of stainless now. I could remake it out of that. Can you harden stainless? I dont know what type it is though (.

    #35696
    brushy-bill
    Participant

    Mark wrote;
    Shadoh:

    Cold rolled wont harden. Low carbon steels will not harden. You need air or oil hardening steel. It would be hard to get a piece that big hot enough with a propane torch. It must be bright red to get it hard

    Mark

    To all;
    You can most definatly harden Cold Rolled steel. It is a process called
    “case hardening” also known as “pack hardeneng” it can be done with an acetelene torch, as long as you use a carbon material to emerse it in such as “Kasinet” ( get bright cherry red, 1650 -1700 degrees, emerse in the carbon material, and coat well, reheat, and quench. In water or oil. in this “by hand” method, water is better than oil. if using an oven and “pack hardning”, oil is better.)

    Case hardining is very benificial as it hardens the “outer skin” of the material and leaves the inner core ductile.

    Most all machine set-up and layout tooling ( 1,2,3 blocks, grinding vises, angle plates ( steel ) , sine bars & plates, v-blocks) that can be purchased is made from “Low Carbon Steel” which is cold rolled steel and then case hardened. When done in a heat treat oven, the hard case can be up to 0.065 – 0.080 thousandths of an inch deep but usually, 0.035 – 0.040 is the norm.
    Doing it with a torch, you can get up to around 0.015 – 0.020 case depth.
    I have done it both ways, for tooling that I make for myself, ( I have some that I have used for over 30 years) it is sent to our heat treat
    service, if I just want a “wear surface” the torch method works well and is quick.

    Don’t mean to hack on anybody, just wanted to clarify.

    #35708
    shadoh
    Participant

    Could you quench it in used motor oil? Used oil is full of carbon.

    #35714
    cygnus-x-d82
    Participant

    to heat it poor man style, i used my BBQ starter…stacked alot of coals…buried the part 2/3 up an then more coals…fired it up in the bottom…and used a fan at the bottom of the grill starter….took 10 minutes to get it glowing more orange than red….

    #35716
    mm123522
    Participant

    Brushy Bill
    Your right, I didnt consider case hardening, but is it right for a gearshift lever?.

    You could start with 4140 prehard stock for the gearshift lever. Its allready hard (about 40 rockwell “C”), but still machinable.

    Drill rod or air hardening or oil hardening steel will go brittle after quenching. You still need a heat treat oven to temper it.

    4140 prehard stock would be best because it is strong and requires no heat treatment.

    Mark

    #35734
    shadoh
    Participant

    Lol, not gearshift, gear shaft. Maybe I should have said drive shaft? Its a 6 inch rod, mostly 3/4 in diameter. It will have a chain gear on one end and an arm on the other to cycle the hand pump.

    #35748
    brushy-bill
    Participant

    Mark,
    You are absolutly right, 4140 is an exelent steel to work with, it is tough & hard enough, and you can get an excelent finish with it.
    I do use 4140 for alot of personal projects, That is as long as I can “find” it around the shop. Coldrolled steel used for a gear shaft is fine, ( depending on the torq on it.)you would be suprised, just how often it is used simply due to the
    “bargain basement” price.
    Please excuse my poor spelling

    Quenching c.r.s in used motor oil is fine, as long as carbon is introduced during the heating process. The carbon in the oil is not enough to penetrate the material.

    The method using the grill works, I have hardened knife blades this way
    although I was using tool steel. And basicly using it as a forge.

    #35753
    marc
    Participant

    Most driveshafts from cheaper automobiles are made from lower carbon low alloy steels and case hardened for only the outer 3mm. It’s the outer part of the shaft that actually takes the load. No matter if it’s bending stress or torque.

    In school we did a liitle investigation to a broken drive axle from a suzuki swift or alto. Turned out to be case hardened St37. “Lowly” construction steel.

    It broke due to the fact the rubber mandrel it turns in was worn and sand and rust had erroded the case hardened part of the shaft. Reducing it’s strength by approx 40%.

    Just goes to show with the right treatment/protection you can use cheap materials for high load aplications!

    Try the coal horn case hardening technique! gives nice oldfahioned results!!

    Regards,

    Marc

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