US 4,052,132 AGranted

Method and apparatus for drilling fine holes in frangible workpieces

OwnerWilliam L. Oatesinventor

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Abstract

A drilling system and method for use on thin frangible workpieces, such as watch crystals and the like, in which the speed of rotation and pecking motion of the drill are programmed to execute a preset schedule of changes with minimal human intervention. In a preferred embodiment, the drill is mounted over the workpiece, which is pneumatically clamped on the work surface in a shallow water bath. The vertical pecking motion of the drill is under the dual control of a primary cable tensioned by weights on one end under control of a solenoid; and a secondary cable, the tension of which is responsive to the rotation of a master cam. The latter also initiates relay action for sequential operation of controls. The drill operates at an initial, relatively low rotational speed and a brisk pecking motion. At a preselected point near the lower end of the drill hole, the rotational speed of the drill is shifted to "high", and the pecking motion is slowed. Simultaneously, weights are lifted from the end of the primary cable, releasing the drill bit for the final slow descent through the remaining portion of the workpiece, reducing the possibility of breakout.

Claims16

Dependent claims

A drill system which operates in accordance with a preselected program to drill an opening or indentation in a frangible workpiece which comprises in combination:

a work surface,
means operable to clamp said workpiece on said work surface,
a rotary drill comprising a drill bit disposed above said work surface constructed and arranged to drill said opening or indentation in said workpiece,
a first driving means operable to drive said drill bit to rotate about its axis,
dual control means operable to impose a pecking action on said drill bit in relation to said work surface comprising:
a first gravity operated pecking control means including weights mechanically coupled to impose a preselected pressure on said drill bit in relation to said work surface,
a second pecking control means mechanically coupled to said first control means, and including a master cam and a second driving means operable to drive said master cam to rotate to control the cycle of the pecking motion of said drill bit,
and relay means responsive at preselected points in the rotation of said cam and the excursions of said drill bit to initiate one or more functions in accordance with said program,
said relay means being constructed and arranged to operate when said drill bit progresses within a preset distance from the breakout point of said frangible workpiece to trigger said relay means:
a. to shift the speed of rotation of said first driving means from an initial low rate to a high rate,
b. in synchronism with (a) to remove weights on said first pecking control means to lessen the pressure on the said drill bit for the final descent thereof into said workpiece,
c. at a point in the final descent of the drill bit just prior to contact with the workpiece, to shift the speed of rotation of said master cam from a brisk initial rate to a relatively low rate for the critical breakthrough period at the end of said program, and
d. to return said drill system, including said drill bit, to condition for reoperation.

10 more elements

A method of drilling holes or indentations in a frangible workpiece in accordance with a preselected program which comprises the steps of:

clamping said frangible workpiece on a work surface beneath a drill having a rotatable drill bit,
driving said drill bit to rotate about its axis,
operating dual controls to impose a pecking motion in said drill bit in relation to said work surface, wherein one of said dual controls raises and lowers said drill bit in vertical motion applying pressure in relation to said work surface by a combination of gravity and the addition and subtraction of weights, and the other of said dual controls drives a master cam to rotate in mechanically coupled relation to modulate the vertical motion of said drill bit,
the rotation of said cam and the excursions of said drill bit initiating relay operations to perform one or more functions in accordance with said program,
wherein the said relay operations include the following functions:
a. shifting the speed of rotation of said drill bit about its axis from an initial low rate to a high rate,
b. in synchronism with (a), subtracting weights in said one dual control to lessen pressure on the drill bit for its final descent into said workpiece,
c. at a point in the final descent of said drill bit just prior to contact with said workpiece, shifting the speed of rotation of said master cam from a brisk initial rate to a relatively low rate for the critical breakthrough period at the end of said program, and
d. returning said drill including said drill bit to condition for reoperation.

6 more elements

Dependencies are inferred from the claim text.

Facts

Application: 05/630,189Filed 10 Nov 1975
Granted: 4 Oct 1977
Term ends: Not estimatedThe source records don’t support an estimate.

Classification11 codes

B23B 41/14
Boring or drilling machines or devices specially adapted for particular work ; Accessories specially adapted therefor: for very small holes
B28D 5/0058
Fine working of gems, jewels, crystals, e.g. of semiconductor material; apparatus or devices therefor: accessories specially adapted for use with…
B28D 5/0064
Accessories specially adapted for use with machines for fine working of gems, jewels, crystals, e.g. of semiconductor material: devices for the…
B28D 5/021
By rotary tools, e.g. drills: by drilling