[SwissBeast]

I am going to be attempting to gun drill a 1mm (0.0394'') diameter hole 3.1" deep. The material is 440A and the gun drill is solid carbide. I have a descent experience with gun drilling on this machine but I have not attempted a hole this small in diameter. The machine is a Citizen M3-20 with Y-axis on the turret. The hole is 78.74x the diameter. I can supply 2000psi of high pressure which should be plenty considering that tiny through-hole can't flow very much. The only thing I can not achieve per drill manufacturer is the sfm. A recommended 125sfm puts my main spindle at 12k rpm. My spindle max speed is only 10k. Feeding at .00014 ipm. I am feeding out of the guide bushing, gun drilling with my turret. Positioning the gun drill about 0.100" from the face of the guide bushing and feeding the material over the gun drill which is stationary. Just wondering what to expect out of a such a small gun drill? I had a little bit of difficulty with an 0.061 but at the end of the project I had it dialed in and running successfully.

[underthetire]

One of my old customers used to gun drill, holding the drill in the sub spindle and running the chucks in reverse. They had it dialed in pretty well. I built a 3500 psi coolant system for them for that application, but it worked best about 2200 psi.

[chet470]

Swiss Beast,

Do you mean .00014IPR or IPM? Your experience will be a tremendous asset....Max your spindle at 10,000, make sure you bore your pilot hole .001" smaller than the gun drill. I would try in the range of .0001 -.0002 IPR. I recently used a .041 gun drill in stainless and ended up around .00018IPR and she ran like a swiss should.....flawlessly!
You will have to experiment with feeds, I would start at .00012" IPR and maybe tweek it as you go.

[SwissBeast]

Yeah the feed is in IPR not IPM. And as far as the coolant pressure I think that the 2000psi should be plenty. My main coolant related problem is the incredibly small diameter of the coolant through hole on the gun drill. No matter the psi that I can supply the tiny hole can only flow so many gallons per minute. I could possibly be loosing some pressure at the turret head and turret slide from the plunging brass high pressure connection, but once again the main cause of a leak there would most likely be caused by the limited gun drill coolant flow. However I am interested in the theory of the pilot hole being bored at 0.001" smaller than the gun drill. I would think that it would lead to the gun drill snapping the tip off when you turned on the spindle? Maybe I am wrong. Could you elaborate on this?

[beege]

I remember talking to an El Dorado tech about gundrilling on an L20. He gave recommendations about coolant psi (oil, not water soluble), start feedrate and pilot hole conditions (depth, diameter). I think the diameter was .0002-.0005 over... it was ten yrs ago, but it's what I remember. El Dorado is a great resource.

[SwissBeast]

Yeah El Dorado is who I normally go to for any questions I have. I mainly use DME gun drills, but this go round it was from a different supplier. The drills I received were out of tolerance per manufacturers specs. They had a runout at the tip of around 0.100". I checked them in the spin fixture on our OC. The drill company checked the other 4 drills in this diameter that they had in stock and all of them were out of tolerance. The wait is about 10 weeks for the next batch from Europe. In the meantime I was wondering if anyone on here had any advice or experience with the small diameter gun drilling.

[chet470]

My apologies, I meant .001" over the drill size for the pilot. Of course with a drill of that size I would reduce that to maybe .0005" like the other gentleman mentioned.

Good luck.