Guhring oHG - RT 150 GG

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The Specialist for Deep Holes over 7 × D:
Type RT 150 GN with negative helix

Related topics: RT 150 | RT 150 GG

Fig. 1

Order RT 150 flyer

Chattering may occur applying type RT 150 GG in unstable conditions without a pilot hole and drilling depths over 7 × D - if we take a closer look at the relationship between interabting forces (see fig. 2).

Type RT 150 GN (fig. 1) requires no pilot hole up to approx. 15 × D. The negative helix divides the cutting forces into the elements F_n and drawing force F_Z. The drawing force F_z is therefore on the spiral part, so the tool is being drawn. This has the advantage that slender tools only bend if subjected to considerably higher lateral forces. A further advantage is that the drawing force acts as a pre-loading on the spiral part, thereby increasing its' dynamic stability.

Comparison:

When ploughing a field, the plough has always been drawn. If the plough was pushed, lateral forces caused by the different soil conditions would push the ploughshare sideways, making it impossible to "cut" the earth.

Fig. 2: Analysis of cutting force F_c on drills with different helix angles

The diagram show the normal force F_n as an element of the cutting force F_c causing a vertical load, i.e. lateral on the spiral part of the tool, wanting to buckle the tool. The element F_s is under load when pressure is applied, the spiral part buckles and is "pushed". Extremely slender drills, pushed and exposed to such forces deviate from concentricity at very low lateral forces, chattering is imminent. A negative helix, however, divides the cutting forces into the elements normal force F_n and drawing force F_z. The drawing force F_z is therefore on the spial part, the drill is being drawn. This has the advantage that slender drills only bend when exposed to considerably higher lateral forces.

Tools	Carbide grade	Shaft	Surface	Series #
		HA		*773*

Advantages

no bending, no buckling, as drawing force causes a pre-loading on the spiral part (fig. 2)
more economical (fig. 3), as no pilot hole required up to approx. 15 × D.
high dynamic stability, type RT 150 GN operates with no oscillating movement and vibration-free
good surface qualities and dimensional accuracy of hole

Range of application, manufacturing specifications

similar to type RT 150 GG.

Fig. 3: Comparison of tool life between RT 150 GG and RT 150 GN
Workpiece: Cast iron GG 25, Ø = 10 mm.
v_c = 100 m/min, f = 0.2 mm/rev.
Drilling depth a_p = 80 mm.
Coolant: soluble oil, 50 bar.