Constructions and Application of Drifts in Drilling Machine

Drift is a key made out of a flat sheet and tapered at one side it is used for driving out sleeves and taper shank drills and drill chucks from the drilling machine spindle. The drift is introduced into the slot of the machine spindle or into the slot of larger size sleeve. The wedging action of drift forces the drill to come out. The wedge has a taper of 11/14 inch per foot or an angle of 80 and 19’. The tang of sleeve and the tang of taper shank drills have or turned to an included angle of 1630 22’ to suit the taper of the drift.

Causes of Breakage of Drills

The drill is liable to break if proper care is not taken while using a drill. The causes of breakage of a drill are as follows:

(a) Selection of Drill. The type of drill is to be selected as per the job. While drilling sheet metal preferably straight fluted drill is to be used. Likewise for drilling deep holes single fluted or oil tube drill is to be used. If selection of drill is not proper it is likely to break.

(b) Selection of Speed and Feed. Speed and feed of drill plays a vital role while drilling. It depends on material and size of hole to be drilled. Speed must be more for light materials and for small drills and vice versa.

(c) Drills Not Ground Properly. The different angles of drill depend upon the material to be drilled. Softer the material more the clearance angle and lesser the cutting angle and harder the material lesser the clearance angle and more the cutting angle.

(d) Centre Pop Not Marked. Before starting the drilling operation, hole location must be marked. A clear pop mark is required to be made at this marking to avoid wondering of drill. Otherwise it is likely to break.

(e) Pilot Drill is Not Used. While drilling larger size holes pilot drills must be used. The hole can be drilled to the required size and there will not be much pressure on drill. If pilot drill is not used maximum load is likely to generate and it may lead to breakage of drill.

(f) Drill Not Taken Out for Chip Clearance. When smaller size drill is used, drill is to be taken out of the hole frequently to remove the chips from cutting zone to avoid any blocking of chips in drill flutes. This will also allow the coolant to reach the cutting zone and cool the job and the job.

(g) Coolant is Not Used. While drilling a certain amount of heat is generated at the cutting edge by friction of drill and the work piece. If coolant is not used the drill will get over heated and likely to break. While drilling in the softer or ductile material the material is likely to adhere or stick on the cutting point. For example, while drilling aluminium and its alloys the coolant kerosene must be used to clear the chips and prevent sticking.

(h) Blunt Drills Not Ground. While drilling, certain amount of heat is generated and the cutting edge becomes blunt. In that case drill is to be ground with proper cutting and clearance angles. If blunt drills are forced into the work piece the drill is likely to break.

(i) Feed is Not Uniform. If feed of the drill is not constant or the drill is fed with jerk it is likely to break.