Chain drilling jig
Drilling a series of holes separated by the diameter of the drill is a good way to cut slots and openings.in materials. However, it is quite difficult and time consuming to accurately mark and centre punch the metal before drilling can commence. Lack of accuracy can result in the the web being left between two holes being thick and if the hole spacing is not enough then the drill may try to follow the adjacent hole. To overcome these problems I built the simple jig shown above. The jig is a piece of 5 x 14 mm steel strip that has been accurately drilled at 6 mm intervals with holes 3 mm in diameter. The centres of the holes are accurately 6 mm from the edge of the strip. Also shown is the small punch, 3 mm diameter, that is used in conjunction with the jig
In use the edge of the jig is clamped up to the edge to be chain drilled and the small punch is used to transfer the position of each hole to metal below. The jig is then removed and the punch marks enlarged with a larger centre punch and then each centre punch mark is drilled out using a 6 mm drill.
In use the edge of the jig is clamped up to the edge to be chain drilled and the small punch is used to transfer the position of each hole to metal below. The jig is then removed and the punch marks enlarged with a larger centre punch and then each centre punch mark is drilled out using a 6 mm drill.
The strip was a piece of 5 x 14 mm hot rolled steel.
The strip was mounted in the mill vice and a light cut was made with an end mill to true up the edge.
The strip was then mounted in the mill vice and using a centre finder the milled edge of the strip was located. The strip was moved so that the axis of the mill spindle was 6 mm in from the edge.
A centre drill was then mounted in the mill chuck and this was used to make pilot holes every 6 mm along the strip by using the graduated collar on the mill. This ensures accurate spacing.
The centre drill was then replaced by a 3 mm twist drill and each hole was then drilled through 3 mm. The holes were then chamfered on both side using a countersink bit.
The strip was mounted in the mill vice and a light cut was made with an end mill to true up the edge.
The strip was then mounted in the mill vice and using a centre finder the milled edge of the strip was located. The strip was moved so that the axis of the mill spindle was 6 mm in from the edge.
A centre drill was then mounted in the mill chuck and this was used to make pilot holes every 6 mm along the strip by using the graduated collar on the mill. This ensures accurate spacing.
The centre drill was then replaced by a 3 mm twist drill and each hole was then drilled through 3 mm. The holes were then chamfered on both side using a countersink bit.
The punch was made from a 3 mm masonry nail. These are hardened steel nails and they are hard enough 'as is' to use as a punch. The nail was chucked in a hand drill and then, whilst rotating, held up to a grinder, also running, to grind an approximately 90 degree point on the nail. When grinding do not let the nail get hot as this will temper the hardness.
A small knurled collar was made to facilitate holding the punch. This was a force fit on the head end of the nail.
A small knurled collar was made to facilitate holding the punch. This was a force fit on the head end of the nail.
To test the jig a piece of 6 mm steel was taken and the gauge clamped along one edge. The punch was then used to indent the steel all the way along. The jig was removed and the steel centre punched at each indent. The bar was then drilled with a 6 mm drill.
In the photo the first three holes have been drilled. Note the uniform spacing, both from the edge and from each other of the centre punch marks.
In the photo the first three holes have been drilled. Note the uniform spacing, both from the edge and from each other of the centre punch marks.
This close up shows the narrowness of the metal between the holes and between the holes and the edge
The jig shown here was designed for chain drilling using a 6 mm drill. However, the dimensions can be altered to permit other drill size to be used to suit the job in hand.