Drilling Jigs:
Drilling jigs are used to machine holes in mechanical products to obtain positional accuracy of the holes harden drill bushes or jig bushes are used to locate and guide drills and reamers etc. In relation to the work piece these guide bushes are not essential but these prove to be economical and technically desirable. The position of the jig into which the harden bushes are fitted is called bush plate. Drilling jigs are either clamped to the work piece in which holes are to be drilled or the work piece is housed and clamped in the jig body. If more than one hole is to be drilled , the drill jig is made to slide on the table to drilling machine. Such a drill jig is moved by hand into position under the drill so that the drill radially enters the bush. During the drilling operation the jig is held by hand. If the drill size is large enough to produce a high torque , either stops should be provided or the drill jig is clamped to the table of the drilling machine. A drill jig is provided with feet which rest or slide on the table of drilling machine. These feet should be outside of the cutting forces, thus providing solid support. Drilling jigs make pysible the drilling of holes at higher speed with greater accuracy and with less skilled worker. Then is possible when the holes are laid out and drill by hand. Also they produce inter changeable parts because each part drilled in a drilling jig should have the same hole pattern as every other parts.
It is clear that during the drilling operations burs will be produced. The bur produced at the short of the hole is smaller than that produced at the end of the hole. The first type is called minor burs and second type is called major burr. (when the drill makes through the material). When designing a drill jig these two types of burr should be taken into consideration since they may cause difficulty in unloading the work piece from the jig after a hole has been drilled.
