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Thread: 4140 tool steel

  1. #1
    myford7type is offline Member
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    I got a bunch of 4140 tool steel for free and was wondering what you guys think of the stuff any suggestions on machining it?

  2. #2
    Tumbleweed Tim is offline Stainless
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    I have a job this week that requires 2 fixtures made of 4140 annealed and I am wondering how it grinds, and if it is hard to tap. Rockwell is 25-32c. I know you can get a good finish milling, but I have limited experience with it on some old worn out equipment. Nice stuff to get for free. Thanks for bringing up the subject.

  3. #3
    Ray S is offline Junior Member
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    Use a lot of 4140 and don't have any problems drilling or tapping. Just use a good tapping fluid like tap magic.

  4. #4
    dwo
    dwo is offline Junior Member
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    I've had the pleasure of using this stuff in my Machine Tech. class. I've milled and turned it, and getting a good finish is nearly fool-proof. One part I made for my lathe required six tapped holes 10-32 about 1/4" deep (not blind). I "babied" the first two, then realized I could do it much faster and not break the chips as often. I also had to tap six 5/16-24 holes about 1" deep. I just power-tapped these on the mill with no problems at all. I used Tap Magic, by the way.

  5. #5
    Pazuzu71's Avatar
    Pazuzu71 is offline Hot Rolled
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    4140 is very easy material to work with. No problems drilling, milling, tapping, etc.
    It's great for general, all purpose, machinery uses.

  6. #6
    msrm is offline Member
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    4140 or Break Die is a pretty good material
    to work with BUT it will work harden in a
    second. Use plenty of cutting oil/coolant
    when machining and use sharp tools. I use
    heat treated (with a torch) to make fast
    replacement die blocks and for short run dies
    You can't weld it very easy (it cracks).
    You might be able to preheat for welding but
    I've never tried. Again I wish I could find
    the places that give away tool steel and the
    cheap but perfect SB lathes at auctions.

  7. #7
    E-Stop is offline Cast Iron
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    I worked with 4140 on a daily basis for almost 11 years. Run about 75 SFM on your drills and end mills. About 20-25 SFM on taps. I brush the tap with 40 wieght motor oil to lube it and keep plenty of coolant on the other tools.

  8. #8
    charlie is offline Plastic
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    4140 is a pleasure to work with. In addition to what these other gentlemen have said about it, it is very stable material; it won't distort too much when removing a lot of stock as long as it is kept cool. I recommend air blast, no coolant for carbide tooling, and heavy chip load, .005-.007 per tooth with indexable tooling. Monitor the indexable edges, as workpiece will get warmer as edges wear.

  9. #9
    Forrest Addy is online now Diamond
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    Probably should define a few things.

    4140 and most other low alloy steels aren't "Tool steels" They haven't the hardenability nor the edge strength to serve in cutting tools.

    You see a lot of low alloy steels like 4140 in tooling (shanks and bodies for carbide tooling for example) but the term tool steel as I understand it is intended for steels that directly cut, form, draw, or otherwise shape work in process.

  10. #10
    E-Stop is offline Cast Iron
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    Forrest Addy is correct. 4140 is NOT the same as tool steel. Tool steel is much tougher. I've used 4140 to make my own tool bodies to hold a carbide or cermet insert and it works fine on light to medium cutting.

    I made a custom size insert drill out of 4140 and although it cut well, as the chips evacuated they erroded a path in the tool body and eventually the tool failed.

  11. #11
    Tumbleweed Tim is offline Stainless
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    Cruising right along. Cutting at 75 and .002 per tooth on Lagun with Prototrack. Fine tooth M42 end mill finishing with carbide at 95. My buddy (moonlighting) is on identical equipment next to me running much faster, but edge breaking down quick. Leaving about .01 for finish on profile, some deflection of small end mills in corners. Taking 1/8 off surface with face of rougher not a problem and gives good finish. Got to grind now and I will let you know how the Norton SG wheels work on this steel. Kind of worried about it being soft, but I do not think it will be a problem. Have a nice day.

  12. #12
    T
    T is offline Plastic
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    Grinding is going very, very well. Neet stuff. Looks like gage blocks when ground with out even trying. I better go oil them. Fixtures will be black oxide when done. Good Night.

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