Gundrilling Tools

Vertival Line

TBT DIVISION
NAGEL Precision Inc.

288 Dino Drive
Ann Arbor, MI 48103

Tel: (734)-426 5650
Fax: (734)-426 5649

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Vertival Line

TBT Automotive Division

Tool Technology

Even though the gundrilling system consists of more than just to tool, it is the basis for the process. Traditionally, the gundrill is a single fluted cutting tool. More recently, double cutting tools have been developed for short cutting materials. Independent of being a single or double lipped drill, the tool consists of three main components which are brazed together:

· Drill head: full carbide or with carbide inserts
· Shaft
· Driver

tool

The drill head has a couple of characteristic features: V-shaped clearance; Oil passage opening; Support pads and nose grind.

The V-shaped clearance in the drill head defines the principal rake or cutting face. The clearance allows the chips and coolant to return to the chip box. Logically a reduction in the size of the V-shaped clearance will reduce the capacity of the tool to transport chips out of the workpiece.
This is exactly the reason why double lipped drills do only work well with short chipping materials such as cast iron. With long chipping materials such as aluminum the chips will get stuck and the tool breaks. If we compare single and double lipped drills we can see that the latter have only 1/3 of the clearance per side in comparison to a single lipped drill.

chip clearnace

The oil passage opening can be in the form of one or two round holes or a kidney. The kidney provides a larger clearance, but reduces the strength of the tool. Consequently, the kidney is only used for smaller diameter drills.

In order to provide stability for the cutting tool, support pads have been ground into the outer diameter of the tool. At the same time, these pads create friction between the drill and the bore, thereby executing the burnishing effect that is so characteristic for the gundrilling process. The exact position and form of these pads have a great influence on the drilling result. A wrong form can cause the tool to get "jammed" in the bore, overheat the tool, ream the bore or increase the bore run-out. Your TBT specialist will define the exact tool geometry that is most appropriate for your process.

pads

The nose grind of the tool is defined by the type of material to be drilled. The nose grind influences the bore quality, chip form, feed rate to be achieved, bore run-out and process stability. There is a large number of "standard" grinds available for different workpiece materials. In praxis many deviations from these "standard" grinds are made in order to optimize the drill process.