Advancing Manufacturing, Tomorrow and Today

Deep-Hole Drilling on Swiss-Types

Modulation-assisted machining—achieving rapid peck drilling using a modulation unit from M4 Sciences—was the key to solving a gundrilling challenge at Alphatec Spine. However, the solution involved more than just installing the modulation unit. The company’s Hector Acosta and Frank Phan also experimented with a number of variables in order to optimize the process. Here is some of what they learned:

Type of drill. In this application, solid carbide gundrills, rather than drills with carbide only at the tip, offer performance that justifies their cost premium. The tools featuring a coolant passage with a crescent-shaped cross section, instead of circular holes, seem to provide better coolant flow. Because of this feature, Alphatec uses drills from Drill Masters–Eldorado Tool and Guhring. For the coolant itself, the shop uses Blaser Swisslube’s Vasco vegetable-based fluid.

Collet quality. The integrity of the collet’s seal is vital to ensuring that coolant flows only through the drill, not past the drill and out the collet.

Pilot drill. Just prior to gundrilling, the machining cycle places a pilot bore. Three times diameter seems to be sufficient depth for this.

Speed. The machines performing the gundrilling are capable of 10,000 rpm or higher. While Alphatec does not max out spindle speed, the shop routinely runs these drills at 8,000 rpm.

Frequent filter change. Modulated drilling has an impact on machine maintenance. The tiny chip size allows much more of the material to be carried away by cutting fluid. As a result, coolant filters have to be changed frequently.

Pressure. Coolant pressure that is too low won’t permit efficient gundrilling, while pressure that is too high can cause the drill to wobble. In its modulation-assisted process, Alphatec has found the best pressure to be between 850 and 1,250 psi.

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Advancing Manufacturing, Tomorrow and Today