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Difficulty: MediumScrews and Threads

A woodworker is selecting a replacement spindle for a workbench vise. They have four options with identical handle lengths and spindle diameters. Arrange the vise spindles in order from the one that applies the MAXIMUM clamping force for a given amount of effort, to the one that applies the MINIMUM clamping force.

  1. 1Spindle with 12 threads per inch (TPI)
  2. 2Spindle with 8 threads per inch (TPI)
  3. 3Spindle with 5 threads per inch (TPI)
  4. 4Spindle with 3 threads per inch (TPI)

Answer

The correct sequence is: 12 TPI, 8 TPI, 5 TPI, and 3 TPI.
The mechanical advantage of a screw determines how much clamping force is produced from a given effort force. It is inversely proportional to its pitch (the linear distance between adjacent threads). Threads per inch (TPI) is the inverse of pitch, meaning a higher TPI results in a smaller pitch. A smaller pitch creates a shallower thread angle, which maximizes the mechanical advantage and produces the greatest clamping force. Therefore, the spindle with 12 TPI applies the maximum force, while the one with 3 TPI applies the minimum force.

Step-by-Step Solution

1
Identify the relationship between Threads Per Inch (TPI) and pitch.
Pitch is the inverse of TPI. A higher TPI translates to a smaller pitch (distance between threads).
Understanding pitch is necessary to determine the mechanical advantage of the screw.
2
Relate pitch to mechanical advantage and clamping force.
A smaller pitch means the screw advances less linear distance per revolution, acting like a shallower inclined plane. This increases mechanical advantage, resulting in greater output clamping force for the same effort.
The question asks to order the spindles by the amount of clamping force applied.
3
Rank the spindles from maximum to minimum clamping force.
Maximum clamping force corresponds to the highest TPI. The correct order is 12 TPI, 8 TPI, 5 TPI, and 3 TPI.
This establishes the final required arrangement.

Key Concept

Mechanical Advantage of Screws Based on TPI
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Topics

Screws and Threads

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