Inside Squares and Hexagons
Internal squares, hexagons and other shaped holes require special attention and consideration by the part designer, draftsman and producer.
Space must be allowed for the chips and burrs produced by the tool used for the special shape. Squares and other shapes are produced inside a hole by broaching, and the chips are pushed ahead of the broach.
A hole size should be selected to allow a minimum of material to be removed, as shown in Figure 3. Industry practice is to use a hole 3 to 5 percent larger than the distance across the flats for hexagons, and 10 to 15 percent larger for squares.
Space for chips is provided by making a hole deeper than the distance required for the square, hex or other shape. If a deep hole can be used, as in Figure 1, a recess is not suggested as in Figure 2.
The use of a recess in a hole makes it possible to broach nearer to the bottom of the hole, but adds an operation and will increase cost.
If not detrimental to use of the component, wedged-in chips should be allowed in the bottom of the broached hole. If wedged-in chips must be removed, this should be stated on the print. Removal may add to cost. If wedged-in chips are acceptable, this, too, should be stated.