View Full Version : Drilling deep holes

patty boy
04-27-2009, 08:08 PM
I need to bore through holes 5/64" in diameter and about two inches deep in 4130 annealed steel. The hole must be straight +-0.010". Is there a preferred type of drill for such work? Is there a preferred procedure to aid in keeping the hole straight. I'll do the drilling with a lathe.

04-27-2009, 08:36 PM
Lotsa luck. I don't envy you one bit.

Others may have more definitive ideas, but I'd suggest:

1.Buy the absolute best-quality drills you can find, and don't be afraid to switch to a new one if the drill you're using seems to be getting dull.

2. Take pains to start the drill as true as possible. Chuck up on the drill to leave only a small amount projecting to start, then gradually pull it out as the hole gets deeper.

3. Withdraw the drill FREQUENTLY to clear chips.

4. Use a good cutting oil.

04-27-2009, 08:52 PM
I know there are cannon drills...AKA D bits.

04-27-2009, 08:52 PM
You might tray a gun drill, they are designed for the application you described.

04-27-2009, 10:51 PM
I saw the deep hole drilling process described on a forum some time ago. It was along the lines of what is described in the book below. A gun drill isn't common in a home shop so I assume you're looking for a way with tools available in a typical home shop. I can write down what I recall of the procedure if that would be helpful; it was fairly involved and would be slow but likely quite accurate - might be practical for a modest number of holes if time weren't critical.

The book "Deep Hole Drilling" is on the net as a pdf here:


Robin R
04-27-2009, 11:25 PM
This video is the best demo of deep drilling I've come across. http://www.youtube.com/watch?v=q6-4oyIoku4&feature=channel_page

04-27-2009, 11:29 PM
Any chance of drilling the hole first, then turning the O.D. of the part between centers?