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Gun Drills

Gundrilling Guidelines:
Gun drilling on a CNC or Manual Lathe or Mill File: Gundrilling guidelines
Operating Parameters:
For hole depths greater than 40 diameters deep, we suggest a shorter drill / longer drill combination
that will allow the drilled hole of the shorter drill support the flute of the longer drill.
On a lathe or milling machine, a gun drill bushing to start a single flute gun drill is generally not
practical. Drill supports, chip box, etc., are also unnecessary.
Start a gun drill with a pilot hole drilled, reamed, or bored to the gun drill diameter +.0005” (+.001”
max.), -0 x ½ to 1 diameter deep. The shape at the bottom of a pilot hole is of no consequence.
Use oil, or oil based, high “EP” water soluble coolant at 10-12% concentration. NEVER use a
synthetic coolant as these provide no lubricating action.
General guidelines: Dia. Ideal psi Min. psi [email protected] ideal psi
.125 1500 500 1.0
.187 1150 400 1.6
.250 925 350 2.5
.375 675 300 4.5
.500 525 250 7.0
.625 450 200 10.0
.750 400 175 14.0
 1.000 300 150 20.0
 1.250 250 125 28.0
 1.500 200 100 36.0
We offer our DM2000 / DM3000 Spraymist Kits as an alternative to high pressure coolant.
Operate with 100-125 psi air pressure. Start with a spindle speed the same as “Min psi” above

Enter the drill tip into the bushing or pilot hole dead spindle to just off the bottom.
Start the oil, coolant, or mist from our Spraymist System.
Start the spindle.
Drilling is continuous to depth.
At depth, if a blind hole back off the bottom slightly, stop everything and remove the drill.
NEVER rotate a gun drill outside of the hole.
Note wear at the tip’s outer corner and flank to establish a re-grind interval. Proper tool life will
depend on material type, hardness, correct coolant type, pressure, and speed & feed.
Special nose grind / Contour combinations are available for very deep holes, cross holes, interrupted
cuts, special shapes, steps. 
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