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Boring Tools and their Makers


 
  "Mephisto" Bits - How They Are Made - American Machinist,
Vol. 2, January 1, 1920.
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Crimping or twisting the blade is illustrated in Fig. 4.

Fig. 4 - Twisting the bit.

The cutting end of the hot blank is inserted in the "buck A, the rear end of the blade being supported in the fork B while the square on the shank is held by tongs in the operator's left hand.

With his right hand, the operator turns a crank connected to the spindle of the machine. Twisting is continued until in the judgment of the operator the number of turns and the lead are correct, no hard-and-fast rule being followed. Operators on this work, however, become so expert that the results are very uniform.

Bits for boring treenail holes in wooden-ship construction and for other deep-hole work are not twisted but are crimped between dies in a machine of the bull-dozer type. Such bits must have the bottoms of the crimps accurately formed so that the chips will be brought out of the hole and not clog the bit.

After twisting, the bit is reheated at the end and headed. In this operation, both the cutting and scoring lips are formed in dies, the action of the machine being similar to that of a bolt-heading machine.

The next step is to even up the twist between dies in the lever-operated fixture, Fig. 5, after which the bit is cold-straightened.

Fig. 5 - Evening the crimps.

The blank for the leader screw is hollow-milled to size and shape in a hand lathe and the outside diameter is ground to size.

In this latter operation, the bit is held in a chuck in the live head of the machine, Fig. 6, and supported at the other end by a female center into which the blank for the leader screw fits.

Fig. 6 - Grinding to size by a friction wheel.

The action of the machine is similar to that of any cylindrical grinding machine except that the actual grinding is not done by an abrasive wheel, as would naturally be supposed, but by a steel wheel running at a very high peripheral speed. The removal of metal from the bit is by friction. There seems to be little wear on the wheel which is evidenced by the fact that the wheel now on the machine has been in constant use for about 17 years.

Fig. 7 - Grinding the clearance.


 
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