Dos and dont’s – threading with dies
• Chamfer: Make a chamfer at the end of the bar at an angle of 45 degrees to remove sudden loading of the leading edges. This has to be done before starting the die or die nut. Also it has to be made certain that the die or die nut is presented to the bolt squarely.
• Tolerance: Major diameter of the bolt usually has large tolerances. Use this to your advantage by reducing the diameter of the bar. Thus, the cutting force will be reduced to a minimum. If tolerance class is not specified, consider tolerance applicable for medium range i.e. 6H and 6G.
• Swarf: To direct the swarf away from cutting area, it is always preferable to use the gun nose type of die.
• Lubricant: The cutting area should always be supplied with a steady flow of the correct lubricant.
• Split dies: To avoid rubbing, the adjustable split die should not open out. Move the adjustable screws equally by say, 0.15 mm to close the split die. If it is done unequally, there may be pressure on one side which may lead to breakage.
• Cleaning: As a norm, dienuts are used for cleaning out existing threads. Usually the process is done by hand. Avoid using die nuts for thread cutting unless it is an exception.
• Rake angle: Large rake angle for long chip formation whereas a small rake angle for short chip formation. Its applicable and or workpiece material isn’t specified, assume it as intermediate tensile strength.