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Old 04-19-2019, 08:21 AM   #22
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Originally Posted by Bob Gardner View Post
Chamfered offered by Dave is probably the best term in the Anglo-Saxon aviation litany for the shaping of the central bore-hole in the hubs of wooden propellers.

Bob, as a woodworker I reserve the use of "chamfer" to an angled bevel cut on the edge of a piece of wood. It is not rounded, but rather is a flat cut (or bevel) between two other flat surfaces.

If you look closely at the photo in a post above you'll notice that what we are agreeing is the intrados side of the hub is where the hub plate is attached to the hub shaft (with a "fillet") . It's labeled with an arrow pointing to an "R" which I believe refers to the "radius" of the quarter round bit used to shape the intrados edges of the center bore. The use of the word "chamfer" isn't offered by me. It was in the diagram on the side PM calls extrados. On that side of the construct a chamfer is used, I believe, to simply "ease the edge" to prevent splintering of the edge as the hub shaft is passed through the center bore. (One problem with splintering is that it removes the varnish protection and can allow water to seep into the wood.) On that side (PM's "extrados") the hub plate is not fixed to the hub but "floats" in and out to allow compression of the plate against the wood.

In both cases, the shaping of the edge of the center hole serves a purpose, but on the engine side it's to allow a space for the metal hub fillet and on the "nut" side of the hub it's simply to protect the edge from splintering. It stands to reason that the wooden hub is sculpted to reduce the amount of dead space between the wood and the metal, and I can see how a rounded edge on one side (intrados, closest to the engine) and a small chamfer (under the floating metal hub plate) would accomplish that.

I'm guessing that at some point the manufacturers realized that the chamfer cut on the "extrados" was overly technical and could just as easily be a rounded edge. That saves a step in the production process, and to my knowledge all modern propellers are constructed that way.

I think we should just credit PM with the application of the term "intrados" to indicate the side of the hub that attaches to the fixed plate on the metal hub, because as he points out that can be an important distinction in identification of a pusher vs. a tractor installation, at least on some of the early propellers.
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