To create the proper undercut diameter, how much material should be removed from the workpiece?

To create the proper undercut diameter, how much material should be removed from the workpiece?

• A. Twice the thread depth
• B. Once the thread depth
• C. Three times the thread depth
• D. The full thread depth

Answer: (A)

The main idea is that the undercut provides clearance at the root of the thread by removing material on both sides of the thread profile. The thread depth is the distance from the major diameter down to the root on one side of the thread. To create a proper undercut, you need to reduce the diameter on both flanks by that amount, which adds up to removing material equal to twice the thread depth. That gives the relief the tooling and mating parts need, preventing interference and allowing the full thread to function properly. If you only remove once the thread depth, you wouldn’t have enough clearance at the root. If you remove the full thread depth, you’d overshoot and weaken the cut, compromising the thread shape. Removing three times the depth would remove too much material and destroy the thread engagement.

The main idea is that the undercut provides clearance at the root of the thread by removing material on both sides of the thread profile. The thread depth is the distance from the major diameter down to the root on one side of the thread. To create a proper undercut, you need to reduce the diameter on both flanks by that amount, which adds up to removing material equal to twice the thread depth. That gives the relief the tooling and mating parts need, preventing interference and allowing the full thread to function properly.

If you only remove once the thread depth, you wouldn’t have enough clearance at the root. If you remove the full thread depth, you’d overshoot and weaken the cut, compromising the thread shape. Removing three times the depth would remove too much material and destroy the thread engagement.