• Thread rolling is the forming of a thread on a workpiece with a die by exceeding the yield point of the workpiece material and flowing the material into the thread roll to take on the mirror image of the form in the thread roll.
• Thread rolling is done at room temperature.
• Thread rolling is a chipless operation.
• Thread rolling is typically run at speeds about 3 times that of cutting.
• The minimum practical speed for rolling is 100 Surface Feet per Minute or 31 Surface Meters per Minute. Lower surface speeds may produce threaded parts but roll life will be extremely poor (the reason is the material will not easily flow into the rolls and can work harden to the point where material flow stops altogether). Higher surface speeds are feasible with mild, ductile materials.
• To calculate proper RPM for 100 Surface Feet per Minute use the following formula: 

             Surface speed (Feet per Minute) x 3.82       
RPM = ----------------------------------------- 
                   Thread Diameter (inch)
• To calculate proper RPM for 31 Surface Meters per Minute use the following formula: 

              Surface speed (Meters per Minute) x 318.3       
  RPM = -------------------------------------------- 
                     Thread Diameter (mm)

• Thread rolling is possible if the workpiece material has an elongation factor of 12% or higher.
• Thread rolling typically increases the tensile strength of the workpiece because of the work-hardening that goes on during the roliing process.
• Blank diameter is normally the pitch diameter when rolling a 60 degree thread.

Blank diameter (mm) = Pitch diameter (mm) = Thread Diameter (mm) - 0.65 * Pitch (mm)

Blank diameter (inch) = Pitch diameter (inch) = Thread Diameter (inch) - 0.65 / TPI

• Chamfers on the blank prior to rolling should be 30 degrees or less. A 30 degree chamfer will become approximately 45 degrees after rolling.
• The greatest cause of thread roll failure is over-rolling. The thread roll can only hold material equal to volume of the groove on the roll. If more material is forced into this space because of an oversize blank, something must give and that is the thread roll.
• Thread rolling dies are very strong under compressive load but relatively weak under axial loads (like over-rolling or improper chamfer on the blank).
• Coolant should be designed for the extreme pressure of thread rolling, otherwise, as the material flows into the die there is metal to metal contact and die life is greatly reduced.
• Water soluble works the best at removing heat. Watch the concentration, though. Make-up solutions should be weaker to keep the ratio correct in the sump. Use a refractometer to check concentration regularly.
• Oil will give the best looking thread but it must have an extreme pressure additive to do the job correctly.
• Rerolling of parts with high carbon content will greatly shorten die life. The higher the carbon content, the more the material work hardens.
Infeed and Through Feed Thread Rolling Machine Terminology
Infeed and Through-Feed  Dies
• Infeed - Spindles are set at zero degrees. The part does not feed through the dies. The length of thread rolled is limited by the maximum width of the dies. These dies are always helical.
• Through Feed - Spindles are normally set to an angle other than zero. The workpiece feeds through the dies. The length of thread produced is unlimited. The following is a description of various types of Through Feed dies:
• Annular - The dies have annular rings, they do not have threads spiralling down them. They have zero helix. The angle of spindle tilt is the helix angle of the workpiece. The workpiece advances one pitch every time it makes one revolution.
• Speed-Up - The dies have helical threads. The angle of spindle tilt is greater than the helix angle of the workpiece. The workpiece advances more than one pitch each time it makes a revolution.
• Slow-Down - The dies have helical threads. The angle of spindle tilt is less than the helix angle of the workpiece. The workpiece advances less than one pitch each time it makes a revolution.
• Flat Throat - An entrance design on the die where the minor diameter of the die is constant. The major diameter is truncated at about a 3 degree angle down to less than the pitch diameter of the die so the workpiece may be fed into the die and the thread progressively formed.
• Form Ground Throat - An entrance design on the die where the entire thread form is stepped down at approximately 3 degrees to a diameter that is less than the pitch diameter of the body of the die. This allows the workpiece to fed into the die and thread formed progressivley.
• Form Ground Relief - An exit design where the entire thread form is stepped down to attempt to alleviate over-rolling caused by the dies springing closed as the workpiece exits the back of the dies.
• Through Feed Die Set-Up Tip - Look at your machine from the side and note the location of the pivot that the spindles move about when they are inclined to an angle other than zero. This is the spindle pivot point. During set-up, try to have the center line of the die in line with the spindle pivot point. Do this with the use of spacers (make sure the spacers are flat and burr free). 

End Rolling Dies	Straddle and Bump Rolls