Shop Note

Drill Jig

The block or main body of the Jig is a piece of Plexiglas 3/4" by 1" by 1". It was machined to be square and parallel on all sides. It was also polished for esoteric reasons. The dimensions are .750" by 1.000" by 1.000"

That is called "toolmaking"...... :)

A slot 10 MM ( .394") wide by .125" deep was milled into the block, into one of the 1.000" sides. This was to accommodate the port lid, which is 10 mm (.394). This is a close fit to insure accuracy when drilling the ear holes.

The slot also provides a location, and keying effect for the nylon toe clamp which secures the port lid during drilling.

Drill Jig and Cap Screw

A hole was drilled and tapped for a Cap Screw. The hole is central to the 10 MM slot and 5/16" (.3125") from one end of the block. It is threaded 8-32 to accept the clamp screw, which is a Socket head Allen Cap screw by 3/4" long. The hole is 5/8" deep from the bottom of the 10 MM by .125 slot.

Pressed onto the head of the screw is a commercial straight knurled cap that makes a wrench unnecessary.

Two relief recesses were milled into the block to clear the ears and hinge section of the port lid so that it would sit flat on the bottom of the slot, when clamped.

Two holes for the carbide bushings were bored into the side of the block at .125" by .125" location, in relation to the slot and ears.

The holes are .118" ( 3 mm )diameter. Press fit to secure the bushings by friction.

Drill Jig, Port Lid, and Cap Screw

The carbide bushings are .118" outside diameter by 3/16" long. The inside diameter is .018" . They were graciously donated by the Bulova Watch Co....... :) I worked for the Bulova System and Instruments Division for many years. The holes for the bushings are blind, that is, they are only 3/16" deep, or there would be a conflict with the milled recess for the ears.

The clamp is a piece of nylon .343" by .385" by .875" long. It has a slot cut across the length to provide a heel to bear on when clamping the port lid in place. The clamp also has a clearance hole for the clamp screw. The hole is central to the clamp's width, and 9/32" (.281") from the heel end.

Jig in Use

In use, a port lid is placed in the slot with the ears and hinges in the recessed slots in the bottom of the main slot. The nylon clamp is placed into the slot, the screw is inserted into the clamp and secured.

The block is now placed on one side and an ear drilled.

The block is now inverted and the other ear drilled.

To reduce the chance of breakage of the drill, I placed a right angle stop on the drill press table which orients the drill jig block and lines up the drill with the hole in the bushing.

Works like a charm..........:)
{Jerry G}

Back?