gun drilling in cnc lathe ???

We have 4 pcs of 1 1/2 dia. 4140 PH x 25 inches long. I need to drill a 6mm hole thru the part. Can drill from both sides. (open tolerance). Best would be to send out for gun drilling, but dont have time to wait for an outside service, not to mention getting a quote for 4 pcs. Anyone do this in their cnc lathe? I have 300 psi only. The drills are crazy expensive to "attempt" to do this. Anyone have any luck with this scenario??

Any help one way or another would be appreciated.

Thanks,
Gary

Did some gun drilling on a Swiss on the last job working for the man a little over 20 years ago. Approximately .125 diameter 4 inches deep in Titanium. I was involved with the custom made application. Until we bought a high pressure pump that had a 1,000 - 2,000 PSI range we could not get close to the bottom of the hole without snapping the expensive drill bits off no matter how slow the feed. Also the drill had to be dead on in all directions, getting it to sit straight, flat and on center was a bear. It took a lot of trial and error which added up to a lot of time and money, but was worth it as the family of parts that were assembled together in the ordered quantities equaled over a $1 million. For 4 parts going over 100x deep SEND IT OUT TO A SPECIALTY SHOP. If need pay an expedite fee. You will be sorry if you attempt it yourself. Just my opinion.

You can get twisty drills that will get you half way through.. 4 pieces, I'd try it...

Stepping up in drill lengths. 12.5", thats only 50:1..

I go 4" deep with a 3/16 all the time, and they meet in the middle really nice.. Scale is off
a little, but I know my lathe is SQUARE..

And that's the key.. How is your lathe??? Are your turning less than a .001 taper over a foot??

The lathe has to be square... Round tool holders HAVE to be on center.. I'd try it.. I'd try it on
some scrap first, but I'd give it a shot.

If your lathe is a bit off.. Take some time and get it all squared up.. Makes your life so much easier
doing everything else.

I used a high pressure car wash pump to get the coolant up to 2000 psi. Had no trouble at all in my hardinge CHNC lathe.

Found a local guy that can drill all 4 holes, for what I would spend on 1 drill. 3 weeks lead time though. Going to push my customer out a bit.

Thanks for the replies.