_____ is an error due to the irregular form of helical groove on a cylindrical surface.

Concept:

Pitch error

• Pitch error is defined as the total length of thread engaged either too high or too small.
• The various pitch errors may be classified into
  1. Progressive error
  2. Periodic error
  3. Drunken error
  4. Irregular error

Progressive Pitch error:

• The pitch of the thread is uniform but is longer or shorter than its nominal value and this is called progressive error.
• This error occurs whenever the tool work velocity ratio is incorrect but constant.
• Causes of Progressive error:
  • Incorrect linear and angular velocity ratio.
  • Incorrect gear train and lead screw.
  • Saddle fault.
  • Variation in length due to hardening

Periodic Pitch error:

• In this the pitch error causes the errors to repeat at a certain time interval.
• This error occurs when the tool–work velocity ratio is not constant.
• Causes of Periodic error:
  • Un-uniform tool works velocity ratio.
  • Teeth error in gears.
  • Lead screw error.
  • Eccentric mounting of the gears.

Drunken error:

• It is an error due to the irregular form of a helical groove on a cylindrical surface.
• In this case, pitch measured parallel to the axis is always the same, but the problem is with the thread is not cut to its true helix.
• Due to this flank surface will not be as a straight edge, it will be a curved form.

Irregular error:

• These are the errors that randomly take place on threads without any specific reason.
• Causes of Irregular error:
  • Machine fault.
  • Non-uniformity in the material.
  • Cutting action is not correct.
  • Machining disturbances