Half Round Drills

Half round drills are ordered by specifying drill diameter and flute length. See the Half Round Drill Sizing chart for available diameters, lengths, and driver sizes.

Half Round Drills

Diameter10X SeriesLo20X SeriesLo30X SeriesLoDriver
.1250 -.15622.36*60(110)3.54*90(140)---
.1563 - .18752.75*70(120)4.72*120(170)---
.1876 - .23443.1480(130)6.29150(190)---HA-1
.2345 - .31203.93100(150)7.08180(230)---Dd=16mm
.3121 - .39064.72120(170)7.08180(203)9.44240(290)Ld=40mm
.3907 - .46885.51140(190)8.66220(270)11.81300(350)
.4689 -.57816.29160(255)10.23260(325)14.71360(425)HA-2
.5782 - .70317.08180(245)12.4315(380)17.71450(515)Dd=25mm
.7032 - .81257.87200(265)14.56370(435)21.25540(605)Ld=50mm
.8126 - .96888.85225(295)16.73425(505)24.80630(710)
.9689 - 1.14069.84250(330)19.09485(565)28.34720(800)HA-3
1.1407 - 1.500010.82275(355)21.85555(635)33.07840(920)Dd=35mm
*Drills have V (gun drill) style flutemm
25.4 = inches

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Toll Free: 1-888-338-1049

The Deep Hole Drilling System Setup Procedure

The gun drill and half round drill standard drill point position is offset to 1/4 of the drills diameter. This does not allow the drill to start unless guided by either a gun drill bushing or a pilot hole. On conventional machinery, a pilot hole is usually the most practical.

Should you have any questions regarding materials, speed and feed, machine application or operation, contact Sterling Gun Drills for assistance.

Step 1) Mix lubricant at 10:1 ratio in a separate container then fill up the reservoir.
Step 2) Prepare a pilot hole for the gun drill or half round drill to a diameter of +.001", -0, by 1/2 to 1 diameter deep. If tolerances require, keep the pilot hole diameter closer but NEVER undersize. NOTE: Standard gun drills are not measurable, prepare the pilot hole as above to the label diameter.
Step 3) Secure the drill in a toolholder mounted in the spindle, turret, or toolpost true to the part or spindle centerline. Connect the nozzle from The Spraymist Kit to the male fitting of the toolholder, or transfer block on a CNC.
Step 4) Connect the Spraymist Kit to shop air at 100-120 psi. Select the proper drilling parameters from the Sterling Gun Drills Speed and Feed chart.
Step 5) Insert the drill tip into the prepared pilot hole just short of the bottom. Start the spraymist by opening the slide valve. Adjust the mist jet needle to create a fine mist. (a white ring will be visible at the bore opening during drilling). Caution: NEVER rotate the drill outside of the hole.
Step 6) Turn on the spindle, then start the feed. Chips should clear the bore continuously to depth. If packing occurs, reduce the feed. At depth, back off the bottom slightly if a blind hole then stop everything and remove the drill. Inspect the cutting edge often for wear.