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  1. #1
    Member
    Join Date
    Aug 2019
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    3

    4140 ht on a tl-1

    Hi all,

    I recently decided to give up my day job and take a stab at the American dream of owning and operating my own business. I have been blessed as I am doing well so far. I recently aquired a new customer in the food processing industry and the first job they gave me required 4140 ht. The finished turned dimensions are 2.5", 1.5" and 1" over a 3" length.
    This job and material ate my carbide inserts. Obviously I have the incorrect grade inserts or my speeds and feeds are wrong. My lathe is a tl-1. I tried 3 different inserts. They are the only ones I had on hand. The first insert, an Iscar WNMG 3-1-TF IC20 lasted about 2 minutes before the tip completely melted off. The second insert, Iscar WNMG 3-1-PP IC10 cut okay but needed replacing every part. The last insert was a Mitsubishi DCGT 11T304R-SN. It was prone to edge chipping. I was running at 600 sfm and 0.035 doc. I'm looking for any suggestions that could help me be successful next time this job comes through.

    Thanks,

    Ray

  2. #2

    Re: 4140 ht on a tl-1

    I would reduce the SFM to about 120 and the feed to match. Try a DCMT with a 1/64 nose radius. The DCGT is an aluminum cutting insert, much too sharp of an edge for hard materials. DOC should be about the nose radius. I have found the Shars Tools inserts to be a pretty good value. A good compromise between the expensive name brand inserts and production. I use them in 304 SS and get an acceptable number of parts/insert.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Aug 2019
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    3
    Quote Originally Posted by Jim Dawson View Post
    I would reduce the SFM to about 120 and the feed to match. Try a DCMT with a 1/64 nose radius. The DCGT is an aluminum cutting insert, much too sharp of an edge for hard materials. DOC should be about the nose radius. I have found the Shars Tools inserts to be a pretty good value. A good compromise between the expensive name brand inserts and production. I use them in 304 SS and get an acceptable number of parts/insert.
    Thank you, this will narrow my search. I am surprised at your suggestion to limit doc to the nose radius. I could have sworn that I read somewhere that one should cut as deep as your machine will allow (hp and rigidity wise).

    120 sfm seems a bit slow for 4140, but I have some scraped parts I can try that sfm out on.

    Thanks for your reply

  4. #4

    Re: 4140 ht on a tl-1

    In aluminum and other easy to machine materials deep cutting works great, but sometimes you are limited by the insert. On my machine I can peel about 0.875 inch off of the diameter of aluminum, but in SS I have to be a lot more conservative, not because the machine lacks HP or rigidity, but rather the inserts just don't last long, and I have tried a number of different inserts, including the expensive ones.

    4140HT is pretty tough stuff, if the inserts live at 120 SFM, then try 240 and see what happens. I just experiment until I find the best combination for the job.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
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    Join Date
    Aug 2019
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    3
    Quote Originally Posted by Jim Dawson View Post
    In aluminum and other easy to machine materials deep cutting works great, but sometimes you are limited by the insert. On my machine I can peel about 0.875 inch off of the diameter of aluminum, but in SS I have to be a lot more conservative, not because the machine lacks HP or rigidity, but rather the inserts just don't last long, and I have tried a number of different inserts, including the expensive ones.

    4140HT is pretty tough stuff, if the inserts live at 120 SFM, then try 240 and see what happens. I just experiment until I find the best combination for the job.
    I just realized my mistake. I was calculating sfm for annealed 4140. My new calc for prehardened is 285 sfm. So your numbers are really close. Geez, I have egg on my face.
    My Iscar inserts require a min .039 doc to activate the chip breaker. And according to Mitsubishi's website the DCGT insert should cut alloy steel, but it doesnt mention if prehardened stuff falls into that category . I think I found some new inserts to try per your recommendation. They are ordered and their way.
    Thanks again.

    Ray

  6. #6

    Re: 4140 ht on a tl-1

    I forgot to congratulate you on successfully starting your own business, that is a big step. Great job. :cheers:

    People actually calculate feeds & speeds? I normally use the insert manufacturer's recommendations as a guideline as well as my 50 years of experience making chips, then cut that about in half to start using the feed and spindle override. Then I watch and listen, making adjustments as needed for the first few parts. Then look at the number of parts / edge, and look at the failure mode of the insert. I also stock a number of different insert types so if one insert is not working to my expectations for the job, then I'll change to a different insert(s) to find one that does work.

    I ordered some inserts from my local tool vendor, gave them the operating parameters, and let them decide what was the best for the job, $18 each. I was getting 18 parts out of an edge, well that wasn't acceptable, so I ordered some cheap inserts (~$5 each) in different types and through some experimentation was able to get 50 parts out of an edge. Because of my product mix, I am only working with 304SS and 6061 aluminum on the CNC. Other materials are normally one or two parts and are done on my manual lathe.

    Overall, you just need some experience to learn what combinations work best on your machine and materials, every machine is different, and even the material varies between batches.

    Best of luck to you.
    Jim Dawson
    Sandy, Oregon, USA

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