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Gun drilling on a manual mill


Oct 26, 2012
griffin, ga
Has anyone out there ever done any gun drilling on a Manual bridgeport mill? I've got some deep water channels to drill that are 3/8" by maybe 15" deep. I was thinking of setting up these on my prototrak mill with a angle head and use the X travel to drill the holes this gives me the travel I will need for the deep holes. I've got an Idea for a running coolant and also could set up some kind of drill bushing fixture to support the drill.

Before I make the investment on the drill and tooling needed. I wanted to see if you guys see any roadblocks that I might run into by doing this setup?

BT Fabrication

Nov 3, 2019
will probably run into travel issues on a bridgeport. a part that long plus the tooling brings that awefully close to over the travel length once fixtured. gonna need someone else and outsource it.


Cast Iron
Jun 21, 2019
Gun drilling requires slow feed ( .0003"-.0005" for that drill size) and high OIL coolant pressure, minimum of about 500 psi to keep chips clearing.

I actually have one to do today 19-1/2 deep 1/2 dia in 4140 on my American Pacemaker lathe, I have special gears to make the feed rate work. I have drilled at .0015 per rev. before I had the special gears but I was always wondering when it was going to twist off in the hole.

If the holes have to be very straight you will also need a support half way up the drill as they do flex pretty easily.

By the way what material are you drilling? There may be better options.

Good luck.


Hot Rolled
Jun 22, 2008
I have a rotary coolant inducer that would work in a mill but I try and do all my gundrilling in the lathe, for the required travels it seems easier. As as posted above you need to support the gundrill in the middle or sometimes more often. Having gundrilled at home vs using a actual eldorado gundrilling machine at a previous employer, I'd farm it out.