TREPANNING TOOLS AND THEIR APPLICATION
Why trepanning cutters?
If large holes are to be made in sheet metal with twist drills, the hole will be out of round and jagged. This is because the thickness of the sheet is insufficient to guide the drill point and to resist the cutting forces.
One way to overcome this problem is by using trepanning cutters. Instead of cutting away all the metal in the hole as swarf, the trepanning cutter merely removes a thin annulus of metal. This leaves a clean cut hole in the stock and a disc metal slightly smaller than the hole.
If large holes are to be made in sheet metal with twist drills, the hole will be out of round and jagged. This is because the thickness of the sheet is insufficient to guide the drill point and to resist the cutting forces.
One way to overcome this problem is by using trepanning cutters. Instead of cutting away all the metal in the hole as swarf, the trepanning cutter merely removes a thin annulus of metal. This leaves a clean cut hole in the stock and a disc metal slightly smaller than the hole.
Fly cutter:
The simplest type of a trepanning cutter is shown in above Figure. This is the traditional cutter. Another type of trepanning tool shown in Figure 2 is also used.
For both cutters, first a small hole to suit the pilot is drilled For both cutters, first a small hole to suit the pilot is drilled at the centre of the required hole. The adjustable arm can be set so that the edge of the cutting tool produces the required size of hole. This may require a number of trials and adjustments before the correct size is reached. The pilot is located in the pilot hole and as the tool rotates it is fed through the work. (Figure)
Hole saw
Another type of trepanning cutter is a hole saw. It is used where a number of holes of the same size have to be cut.
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