TABLE OF CONTENTS Previous chapters dealt primarily with conventional workpiece materials such as aluminum and steel. Other metals were discussed and speeds and feed data were presented for several metals. The following paragraphs present the issues faced by a variety of materials beyond those already described in the earlier chapters. Countersinks are used in many materials other than metals and particularly today composites present a unique challenge to all machining processes.
If one desires to countersink with a center reamer in a drill press, chatter can be an issue. Backing off the cutting edges to leave a cylindrically ground margin 1/32 in. [0.813 mm] wide will diminish this problem (Anonymous 1952).
As described in Chapters 4 and 6, the COFA design tool (Style #77) requires different spring stiffness for different materials. The material effect on the tool is defined in Table 4-8. As seen there for most applications the standard spring identified only as an "H" can be used. For easy cutting materials such as aluminum a softer "W" spring is recommended. For hardened materials or special alloys a special stiffer "Z1," "Z2," or "Z3" spring is recommended.
Wood is easily machined by countersinks; countersink research unique to wood has not been found. Sharp tools clearly provide the smoothest surfaces. Hard woods machine better than the soft materials. The issues common to drilling wood also apply to countersinking. Since the countersinks are largely covered by screw heads,...
