Deep hole drilling 4140. Annealed or RC43 ?
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    Default Deep hole drilling 4140. Annealed or RC43 ?

    I need to drill an 1/8" dia 4" deep in 4140. I only have 2500 RPM lathe and spray mist through tool available. What would you recommend, annealed or heat treated to RC43? What should I look out for? Done a bunch of 5/16 and 1/2 no problem. From the drill mfg web site it looks like .00015 feed and all the RPM I've got.

    Thanks, Ed.

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    Quote Originally Posted by atex57 View Post
    I need to drill an 1/8" dia 4" deep in 4140. I only have 2500 RPM lathe and spray mist through tool available. What would you recommend, annealed or heat treated to RC43? What should I look out for? Done a bunch of 5/16 and 1/2 no problem. From the drill mfg web site it looks like .00015 feed and all the RPM I've got.

    Thanks, Ed.
    Definitely annealed is the way to go.

    I would drill in stages, drill as deep as you can with a regular, brand new, jobber drill, then switch to your long skinny drill to finish.

    I would use coolant, not oil, and clear swarf often.

    And for god's sake, keep that bit sharp.

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    I guess I did not specify that it is a gun drill (deep hole drill) being used.
    Thanks for the info.

    Ed.

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    You will need to start and keep the hole going straight, I use a end mill for the first 1/2 inch or so to make a good straight hole, then short bits until I have to use the long one.Drill the hole first then do the rest of the job so a backup is not a big deal when the bit jams up from chips and snaps off...Phil

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    How straight does it need to stay? 4140 likes to move during heat treat.

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    I would do a test with samples of both material tempers, if possible. While annealed will be "easier" to cut, a gun drill usually does not have a free-cutting tip geometry, and so might actually have an easier time making smaller, more easily removed chips with the harder alloy.

    Keep the mist at a rich level, and as much air pressure as you have. Set up a deflector cone/funnel on the drill to cut down on the mess.

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    You're running 32xD without through coolant?

    Can I come watch??

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    Quote Originally Posted by ChipSplitter View Post
    You're running 32xD without through coolant?

    Can I come watch??
    You have never watched gun drilling? 32xD is easy!

    Ed.


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