GUHRING - Ружейные сверла - 2008 EN

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Precision of single-uted gun drills

Basic tolerances                                                     Alignment accuracy
The application of single-fluted gun drills can achieve a            Because brazed single-fluted gun drills always have the
lower basic tolerance, as the cutting forces at the cutting          precision carbide head brazed on to a flexible tube, the
edge are absorbed by the supporting strips, unlike twist             tool achieves very accurate aligned holes remaining unaf-
drills where the slightest deviation of the two cutting              fected by possible concentricity errors.
edges causes a larger hole.                                          However, extreme material fluctuations and other influen-
                                                                     cing factors can impair the alignment accuracy.

      Achievable                       normal                                         0.06
       tolerances                      conditions                                     0.05
                                                                                      0.04
Copper, nickel, zinc                                   optimal                        0.03
   and their alloys                                conditions                         0.02
        Al-alloys                                                                     0.01
                                                                     Alignment in mm
 (acc. to Si-content)
Heat-treatable steels

        Cast rion
   Nitriding steels
   Stainless steels
   Structural steel
Case hardened steel

                            11 10 9 8           76          5                                                 250 500 750                                        1000
                                                                                                                        Drilling depth in mm
                                  Basic tolerance grade IT

Surface quality                                                      Deviation from concentricity
The forces at the cutting edge are absorbed by the support           When a hole is produced with, for example, a commercial
bushes, which in return burnishes the surface.                       twist drill, the quality of the point grind affects the con-
Lubrication between the supporting strips and hole sur-              centricity of the hole. An imbalance of forces is created at
face is therefore very important.                                    the cutting edges. With gun drills, these cutting forces are
The better the lubricant, the better the surface quality.            absorbed by the supporting strips, resulting in excellent
                                                                     concentricity.

Achievable                                                                                                    stationary workpiece - rotating tool
  surface                                                                                                     anti-clockwise rotating workpiece - rotating tool
  quality
                                                                                      1.0
Twist drills                                                                          0.8
                                                                                      0.6
Pilot holes                                                                           0.4
                                                                                      0.2
Reaming                                                              Deviation in mm

Honing

Deep hole drilling

Average peak-to-valley  25  12,5  6,3  3,2 1,6  0,8 0,4         0,2                                           250 500 750                                        1000
     height Ra in µm              N9   N8 N7    N6 N5           N4                                                      Drilling depth in mm
                                                                                                                                                                    5
Peak-to-valley height N11 N10                                                                                         Gun drills
         class N

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