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Deep hole drilling 4140. Annealed or RC43 ?

atex57

Stainless
Joined
Sep 6, 2006
Location
SW Wisconsin
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.
 
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.
 
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
 
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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