Tough Shiny Annealed 4340 Help
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  1. #1
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    Default Tough Shiny Annealed 4340 Help

    So there's this part we turn, face drill with axial-facing live tooling and cut off in a Hardinge T42. We spec 3/4" round cold drawn annealed 4340. All is well. From time to time we get ground material in...probably just because thats all the supplier had in stock. Then my operators claim when we get the "shiny" material none of the tooling holds up. I thought they were crazy and making up stuff in their mind just because the OD of the material looked "different", but sure enough the drill and cut-off go to shit very quickly...the drill is the worst - like less than 10 parts (.140" X .5" deep hole). We use a general purpose Guhring 730 series drill (150SFM, .003IRP). We tried going both ways on the speed and feed but no dice, so we put in a high speed drill, slow it down and it works okay. This has happened several times over the past couple years - "cold drawn" (i.e. gray) finish = good, "ground" (i.e shiny) finish = bad.

    I got my hands on the chemistry report and attached it. Does anyone see anything out of the ordinary that would make the material unusually "tough" that I can maybe try to spec out moving forward?

    Thank you!

    chart.jpg

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    Do you have a Rockwell tester handy?
    How does it act when you slap a file on the stock?
    Even 4340 PHT isn't hard to machine if they happened to mix up the materials. So I'm leaning toward a totally different material altogether.
    It's definitely not Thompson shafting, right?

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    Thompson Rod/Shaft is Hardened on the OD, but if you are getting it in short lengths pre-sawed (sawn?) then the ends would have about .05"-.100 of Case Hard, so drilling would slow, Carbide Drills at 150 SFM would eat the casing up, but the inside of T-Rod is some gummy shit. So maybe the change in conditions.

    So Nerd are you getting it in lengths or are you sawing it?

    What happens to the Drill? How is it failing?

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    Quote Originally Posted by Mtndew View Post
    Do you have a Rockwell tester handy?
    How does it act when you slap a file on the stock?
    Even 4340 PHT isn't hard to machine if they happened to mix up the materials. So I'm leaning toward a totally different material altogether.
    It's definitely not Thompson shafting, right?
    Yes - hardness is in line with what the report claims (~20HRC). I don't think it's too far off because the parts get heat treated and they are heat treating "as 4340" at least...otherwise I would expect the heat treater to be all, "are you sure this is 4340?..."

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    Quote Originally Posted by litlerob1 View Post
    Thompson Rod/Shaft is Hardened on the OD, but if you are getting it in short lengths pre-sawed (sawn?) then the ends would have about .05"-.100 of Case Hard, so drilling would slow, Carbide Drills at 150 SFM would eat the casing up, but the inside of T-Rod is some gummy shit. So maybe the change in conditions.

    So Nerd are you getting it in lengths or are you sawing it?

    What happens to the Drill? How is it failing?
    Material is 12' lengths...so we barfeed it. I thought about some case hardening being the issue but the drill is done axially in Z on the face of the part , not radially from the OD in X. The lips get chewed up until the drill breaks off as if the feed was too high, but we tried backing off on the F and then backing off more and then more, down to like half of what we normally feed but no luck. I wondered if maybe the collet wasn't set right in the nut so the drill wasn't rotating concentric or something but that doesn't hold water because we checked that and, again, it drills just fine on the "cold drawn" surface material.

    I'm not familiar with this "Thompson" material you speak of. Is that a trade name I could ask the distributor about? We usually get the material from seemingly-reputable suppliers like EMJ, Castle, Also, etc.

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    Quote Originally Posted by Nerdlinger View Post
    I'm not familiar with this "Thompson" material you speak of. Is that a trade name I could ask the distributor about? We usually get the material from seemingly-reputable suppliers like EMJ, Castle, Also, etc.
    Pretty much yes a trade name. It's 60Rc case hardened steel that is ground on the O.D.
    Since you're barfeeding this stuff, this rules out Thompson shafting.
    https://www.thomsonlinear.com/websit...dard_shaft.php

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    They are prolly jacking these parts up somewhere from 32-39Rc depending on the need for strength (done a lot with this stuff).

    Your cert looks good & the reported 226/233BHN number is the best range for easy machining. If the guhring drill is uncoated carbide you need it running in the 370-420 SFPM range and a bright HSS should play well around 60-65 SFPM. The .003”IPR is good for both (could get 10-25% bump up with a split point).

    I don’t get the shiney vs dull thing making machining harder either. I can’t remember ever working with 4340 in a “pump shaft” condition (basically TG&P like 1045), usually hot rolled or forged. So no specific knowledge here…

    Normally all the 4X40’s all work well around 95-105 SFPM for turning and about 55-65% of that speed for twist drilling. I’d then upconvert those to carbide speeds if that was what I was using (or use the tool Mfg’s #’s if available).

    Don’t worry about the thompson rod, if you’d sent it to the saw man they’d likely have come back & beat you with it.

    Good luck,
    Matt

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    Are the heat numbers still on the bars or was the bundle tagged?

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    After the Rc check, I have to think it is some cut parameter.

    OR, is it moving in the bar-feeder? If the OD is nice and shiny, is it possible that the bar is not doing what you would like it to? Have you been chasing lengths a little? Have you double checked Collet/Chuck pressure on the different bars? If it's spinning a little, while Drilling that little tiny hole that would fuck up your Drill too.

    Just guessing obviously, but the Diameters and Roundness' of the bars are different.

    R

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    I have had 4140 P/H T&P push back in the Tornos, but it's only got a spring acctuated collet closer on it. The T42 should have a good closer on it, but if it is hard and smooth, and you were running smooth pads - short parts could happen. Not sure that I could blame premature tool wear on a slippery bar condition tho?

    Kind'a makes yuh wonder if that cert matches that bar doesn't it?
    $100 and you could verify for yourself....


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    Ox

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    If its precision ground material, there's a good chance it started out as hot rolled or cold finish instead of the cold drawn you spec'd.

    Could hot rolled/cold finish vs cold drawn be some of the difference you're seeing?

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    It looks like that material came from Spain. I haven't seen much material from there. How does this cert compare to material that worked well?

    I have seen similar differences in finish from different manufacturers in DOM tubing.

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    I'm going with littlerob1 in that the material may be slipping in the collet. Even if the lengths are consistent it could still be slipping radially. This explains the chewed up drill edges.

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    Quote Originally Posted by Tonytn36 View Post
    I'm going with littlerob1 in that the material may be slipping in the collet. Even if the lengths are consistent it could still be slipping radially. This explains the chewed up drill edges.
    Note that OP said that the cut off was failing prematurely as well. Radial slip certainly seems like a reasonable explanation.

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    Quote Originally Posted by litlerob1 View Post
    After the Rc check, I have to think it is some cut parameter.

    OR, is it moving in the bar-feeder? If the OD is nice and shiny, is it possible that the bar is not doing what you would like it to? Have you been chasing lengths a little? Have you double checked Collet/Chuck pressure on the different bars? If it's spinning a little, while Drilling that little tiny hole that would fuck up your Drill too.

    Just guessing obviously, but the Diameters and Roundness' of the bars are different.

    R
    That's a good idea, but it doesn't sound like it - lengths were fine and the closer on the Hardinge is pretty nice. Plus, this has happened maybe 6 times (where we get this material that is difficult to run) so like I could see one bad set up but since it is a predictable pattern I think it has something more to do with the material.

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    Quote Originally Posted by Matt_Maguire View Post
    (or use the tool Mfg’s #’s if available)
    Guhring says 195 for this drill/material, but I've only got 4k in the live tooling so 150 is the best I can do those parameters DO work fine with the "dull" material, though. Of course I don't actually think the "shininess" of the material matters but rather some OTHER difference that for whatever reason shares a correlation with the TG OD

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    Quote Originally Posted by mjk View Post
    Are the heat numbers still on the bars or was the bundle tagged?

    This last happened like a month ago so I can't remember, but maybe if I'm organized enough I can try to see next time and compare the tags on the mtl to the cert provided upon request from the distributor. I BELIEVE the heat numbers are on the EMJ tag...

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    Quote Originally Posted by Ox View Post

    Kind'a makes yuh wonder if that cert matches that bar doesn't it?
    $100 and you could verify for yourself....


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    Ox
    Yeah, I could definitely send it out for testing...$100 you think? It's just weird (or helpful?) that it happens "from time to time". I was hoping someone would look at the chart and be like, "oh my god, there's way too much kryptonite in there!" or something.

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    Quote Originally Posted by ManualEd View Post
    If its precision ground material, there's a good chance it started out as hot rolled or cold finish instead of the cold drawn you spec'd.

    Could hot rolled/cold finish vs cold drawn be some of the difference you're seeing?

    That's a possibility. I have very little experience with HR but I would think by the time you get 10% of diameter (or whatever) past the OD it would be the same? The .140" hole is .236" from the center of the .750" diameter material so I would THINK that far into the core there would be no difference.

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    Quote Originally Posted by robert123 View Post
    It looks like that material came from Spain. I haven't seen much material from there. How does this cert compare to material that worked well?

    I have seen similar differences in finish from different manufacturers in DOM tubing.

    As obvious as that may seem I have NOT done it yet but I will...we're running the "dull" stuff now so I'll get a copy of the cert and compare.

    We have another job where we do some forming of 1020 DOM tubing...some worked fine and some cracked. It turned out that the steel killed in America is done with Aluminum and overseas was done with Silicon. Both "kill" the steel but when it's done with Al it leaves the steel much more ductile than when it is done with Si, so maybe Spanish 4340 has something goofy in it. Thanks!

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