Harold Hall

First Page

Where a larger quantity of parts is to be drilled then stacking the parts enabling more than one part to be drilled at a time would be worth considering and is a definite advantage of the two part jig. This though would depend on the thickness of the parts being drilled, say three off if 3mm thick but only two off if 5mm.

One such area where two part drill jigs are very beneficial is in the manufacture of very small parts. These can be so small that marking them out accurately by hand is almost impossible. Being small, drill sizes will also be small and clamps and drill bushes are unlikely to be necessary.

Photograph 7 shows some parts that were required for a model of a Monmouth cart, Photograph 8. As only ten parts were required a simple flat plate jig would have been more than adequate had they been larger but working at such small sizes the jig seen in Photograph 9 was all but essential.

From the Photograph it can be seen that it consists of a base and a top plate with six pins to locate the part being drilled, that is, one either end and two on each side. The pins are long enough to locate the top plate also. Note that the lower plate is thicker so as to adequately hold the pins.

Working at this size making the jig accurately would still need some considerable skill if made and marked out by hand. Because of this, using the part's dimensions and the diameters of the pins, the co-ordinates of the holes to be drilled in the jig were calculated. With that done the holes were positioned on the milling machine using the micrometer dials on the leadscrews to set the holes in the positions calculated. With that done the parts were placed into the jig three at a time and drilled, with the jig certainly meeting all four benefits that I laid down at the start, that is ease of use, improved productivity, consistency and accuracy. Incidentally, the hole size was 1mm and drilled with my shop made mini sensitive drilling machine, Photograph 10.

Larger Drill Jigs

Larger versions than that above will work similarly but will no doubt need larger quantities to be made to make them worthwhile. If the job in hand requires a quantity of say 20 plus, then making a jig is worth considering, especially if the project requires accuracy and consistency of the part being made. Sk. 3 shows a larger version of that seen above and whilst following the same principles it includes a clamping facility that is preferable for larger parts and holes.

Metalworking

Workshop Processes