2010 Full-Line Drill Catalog - Desanto

Precision of single-fluted gun drillsBasic tolerancesThe application of single-fluted gun drills can achieve alower basic tolerance, as the cutting forces at the cuttingedge are absorbed by the supporting strips, unlike twistdrills where the slightest deviation of the two cuttingedges causes a larger hole.Alignment accuracyBecause brazed single-fluted gun drills always have theprecision carbide head brazed on to a flexible tube, thetool achieves very accurate aligned holes remaining unaffectedby possible concentricity errors.However, extreme material fluctuations and other influencingfactors can impair the alignment accuracy.AchievabletolerancesCopper, nickel, zincand their alloysnormalconditionsoptimalconditions0.060.05Al-alloys(acc. to Si-content)Heat-treatable steelsCast rionNitriding steelsStainless steelsStructural steelAlignment in mm0.040.030.020.01Case hardened steel11 10 9 8 7 6 5Basic tolerance grade IT250 500 750 1000Drilling depth in mmSurface qualityThe forces at the cutting edge are absorbed by the supportbushes, which in return burnishes the surface.Lubrication between the supporting strips and hole surfaceis therefore very important.The better the lubricant, the better the surface quality.Deviation from concentricityWhen a hole is produced with, for example, a commercialtwist drill, the quality of the point grind affects the concentricityof the hole. An imbalance of forces is created atthe cutting edges. With gun drills, these cutting forces areabsorbed by the supporting strips, resulting in excellentconcentricity.Achievablesurfacequality1.0stationary workpiece - rotating toolanti-clockwise rotating workpiece - rotating toolTechnicalTwist drills0.8Pilot holesReamingHoningDeviation in mm0.60.40.2Deep hole drillingAverage peak-to-valleyheight Ra in μmPeak-to-valley heightclass N25 12,5 6,3 3,2 1,6 0,8 0,4 0,2250 500 750 1000N11 N10 N9 N8 N7 N6 N5 N4 Drilling depth in mm319