Monday, May 9, 2011

Better than a wet finger

When last we talked about our fat bird problem, I had completed the Mark 1.5 version of the replacement wind vane, using brass rod, sheet, and a PVC pipe cap.  You may remember that I was concerned about the weight of the Mark 1.5 version, and that I was going to see if I could make one using aluminum.

It's done.  I found that small pieces of sheet aluminum are available in the hardware store as flashing - I cut the vane itself from one of these sheets.  In order to lighten the design, I made the vane considerably larger than in the Mark 1.5 version, and positioned it closer to the pipe cap.  The net result was that I needed one third less counterweight on the front, making the entire assembly considerably lighter.

The only tricky part of the aluminum manufacture was attachment of the vane to the aluminum rod.  Unlike with brass, I couldn't solder the vane to the rod.  Instead, I made two close-together folds in the bottom edge of the vane such that, viewed end-on, a triangular space was created - one a little too small to accommodate the rod.  Then I applied epoxy and wedged the rod into that space.  It's solid.

Glue-up jig
For final assembly, I wrapped the sensor body with enough tape (that's the blue layer in the picture) to make a snug fit into the pipe cap - this made sure that the assembly would go together centered.  I treated the inside of the pipe cap with acetone to soften its surface and then added some 5-minute epoxy - enough to form about a 2 mm thick layer.  I lined up the registration marks I had made on the sensor, and using a carefully constructed glue-up jig (ha!), I assembled it and waited for the epoxy to cure.


Mark II Vane
The final product looks good.   In order to protect the pipe cap from the ravages of solar UV, I cut and applied some aluminum tape to it.

It works!
And then on Friday, while we were anchored in Eagle Harbor, I climbed the mast and installed it.  Almost unbelievably, the calibration turned out to be spot-on!  Hopefully the short length of available perching space on the rod will discourage obese birds from using this as a lounging spot.  But if it doesn't, I'll drill a small hole into the top and glue in a heavy plastic bristle from a shop broom (I don't want to make a lightning rod here!).
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2 comments:

Dylan said...

Great post. I lost my vane in a storm...I will try your method and see how it works.

bob said...

Dylan -

Mine is a Standard Horizon WS-1. I don't know anything about other masthead sensors - I have never had another. But even if yours isn't, maybe some part of this could be useful to you... My learnings:

o weight is important.
* Aluminum is better than brass
* Making the vane bigger and moving it closer to the pivot retains the wind leverage but reduces the amount of counterweight needed: lower total weight.
o You can do this with inexpensive materials from the hardware store.
o Think long and hard about calibration.

bob

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