Cerrated hard jaws for second op with ph4140?
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  1. #1
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    Default Cerrated hard jaws for second op with ph4140?

    Hello.
    Stupid question. I need to cut 2 parts asap for a client and would really not like to switch chucks. Can I clamp a solid finished bar with cerrated hard jaws and expect an unmarred finish and decent run out if I use cerrated hard jaws in a 3 jaw Chuck for the second op. Most of my work is 3j collet chuck so I never used the 3 jaw that is currently installed on the machine for the 1st op. The part is 6 inches long coming out of pre hardened 4140 I need to od about 2 inches. The part I will be holding is solid with a 32mm diameter.

    Thank you.

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    I've done it a few times on shit that don't matter, put an indicator on it and see how true it spins. If your serrations are to a bit of a point then yeah you'll leave marks on it. If the serrations are kinda flat should be alright. Don't hog and you should be able to use a little bit of pressure, I've made things under a 100psi many times.

    Brent
    Last edited by yardbird; 11-08-2019 at 01:39 AM. Reason: Edited post

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    Gripping with all the jaw will be the least amount of flex in the master jaw, flex will make marks. Remember rpm will work against you with low chuck pressure, I'd keep the R's down to a mild roar and not a bazillion mph. Best thing to do grip up on a chunk of 4140PH stock then check the runout. Then see at what chuck pressure you start getting marks that can't be tolerated. Then machine accordingly.

    Brent
    Last edited by yardbird; 11-08-2019 at 01:41 AM. Reason: Fixed stuff

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    I'm not a CNC lathe guy, just a mill guy.

    But in high school, we had a bunch of Leblond lathes. Ran em a lot. Was told to wrap parts in emery cloth, or with shim stock, if we needed to not have marks in the parts.

    Works okay, it isn't perfect.

    I'd say cut a piece of .010" or .015" shim stock and clamp on that if you can. Should at least reduce what you can see by "smoothing" the teeth bite out a bit.

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    Just build a precision split ring out of Aluminum. .

    I don't use shim stock, unless I need to. I can't seem to get the part to run true with shims.

    R

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    Quote Originally Posted by litlerob1 View Post
    Just build a precision split ring out of Aluminum. .

    I don't use shim stock, unless I need to. I can't seem to get the part to run true with shims.

    R
    I second this. Shims are unreliable by nature.

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    Quote Originally Posted by yardbird View Post
    I've done it a few times on shit that don't matter, put an indicator on it and see how true it spins. If your serrations are to a bit of a point then yeah you'll leave marks on it. If the serrations are kinda flat should be alright. Don't hog and you should be able to use a little bit of pressure, I've made things under a 100psi many times.

    Brent

    Worked great. Thank you.


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