Monday, October 2, 2017

How much is an "RCH"?

I was putting Zeus out on the line this morning when I saw a hank of corn silk had fallen from the drying rack onto the walkway.

That served as a memory jog.  There is science to be done.

How much is an RCH?
It is unclear if Red Corn Hair (henceforth RCH*) refers specifically to the color of the corn or to the hair, or silk as it is sometimes called.

If in doubt, consult with the skilled trades person you are working with.

The reason that "RCH" is used is because of its near infinite flexibility.  For instance, it can be used as a length dimension, the width dimension of a single item or of an assembly...and the actual dimension will be different!

Not all corn is as healthy as ERJ corn, so the actual dimension that you need to cut off the end of that 24' 2-by-12 might be somewhat less than 5.208 inches.  Consulting with your journeyman is particularly important when cutting expensive pieces or if you have been left with a huge pile of sticks to cut.  It is a sad day when you cut 150 studs too short.

The actual width of a single RCH is 0.011 millimeters or 0.0004 inches.  This is nonsensical in the context of carpenter work because there are no tools that can shave such a small amount off the width.

Unfortunately, there are two answers for the width of an RCH when working with carpenters.  Rough carpenters, also known as framers, use the loose RCH method.  If a rough carpenter tells you to shave an RCH off the side of a sheet of decking plywood he undoubtedly wants you to remove 0.369 inches.  Remember that when working to three significant digits it is important to make allowances for the width of the kerf and the moisture content of the wood.

Wood measured and cut in the morning usually loses moisture throughout the day and will be slightly smaller when nailed into place.  This trend reverses itself if it starts to rain.

Finish carpenters use the tight RCH method.  According to exacting research by the crack, ERJ team the precise dimension of a tight RCH is 0.0245 inches.

I hope you found this essay useful, or if not useful, then entertaining.

*Some people who are less refined than Eaton Rapids Joe use a coarser term than Red Corn Hair. If you are one of those people, I don't want to hear it.  This tries to be a family-friendly blog.


  1. Ha! I thought I had heard a different definition of that measurement at one time.