Foot Rope Fixture directions:

"The Main Runner is a piece of maple wood, as is the rest of the fixture except for the hardware.   The purpose of the Main Runner is to provide a means of aligning the traveling clamps/guides.   It is machined from the solid and can be built out of separate pieces if you don't have a milling machine.

There are two slots to allow the traveling clamps/guides to ride the rail machined into the base runner.   The rail of the Main Runner keys in the clamp blocks for longitudinal alignment.

All the dimensions of the fixture are nominal, meanng one inch is exactly one inch, etc.   The reason being, that if you place a scale (6" ruler) and measure any amount, it will be that size, for example 1/4" will be .250".   So if you ever have to add anything to the fixture, it can be done independent of the fixture, and not require fitting and assembly or dissassembly.

That is called "Toolmaking"

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