Recently, a close friend of mine reached out about a challenge he was facing at his startup company. They needed a way to securely grip to the inner wall of a long section of pipe or tubing in order to rotate it as a particular protective coating was applied. The goal was to have a single tool that would be able to securely grip internally both ends of a pipe for a wide range of internal diameters.

I accepted my friend’s challenge and set to work on a preliminary design.

Based on the same basic engineering concepts as a scissor car jack, the internal tube gripper I designed was intended to be simple, lightweight, and structurally rigid. A screw down the middle would drive the “fingers” of the gripper evenly apart until there was firm contact with the walls of the pipe.

After the first iteration of gripper was designed, the need for greater range of movement was identified as a key area of lack. This first iteration had short links connecting the fingers to the end blocks. Because these links were short, they could only provide a small amount of variability in movement. Also, the width of the cylinder where the rotation would be driven into the tool (the “chuck”) was quite large for the typical use case.

This lead to the next iteration of gripper that worked to address these issues. A slimmer chuck was designed and longer links to the fingers were developed.

This intermediate design resulted in a longer overall assembly. However, it still did not fully reach the entire range of smallest internal diameter to largest. In order to continue down this road of lengthening the links, the assembly would soon grow too long to be manageable.

In order to make the links the needed length, and at the same time mitigate the overall length of the assembly, the pivot points were located more centrally on the fingers. The fingers were kept the same length to provide the same amount of contact surface with the pipe. The result is the current final design.

In the near future, this conceptual design will be mocked-up in a working physical prototype. Stay tuned.

In the meantime, enjoy this kinematic animation: