For self steering builders

[Chrisc]

I am building (yet another) windvane and had a bit of an idea - it may be old hat, but for what its worth to my fellow constructors...
Windvanes of course have to be aligned into the wind and this mechanism tends to be a bit troublesome. Usually, it is a disc on a plate with some sort of clamping arrangement from a simple G clamp to holes around the perimeter of the disc with a peg inserted to the ultimate toothed gear type ring. All are tedious to construct. I thought a bicycle chain ring might be the answer. The big ring on a typical 3 ring cluster have 48 - 52 teeth with gives incrementals of approximately 7 degrees. Apart from the really budget steel ones, they are fabricated from hardened aluminum and are cheap, even in NZ where we like to tax the living daylights out of everything. In fact most bike shops would have old ones lying about that they would give you.
It would be simple to make some sort of spring loaded pin arrangement, perhaps similar to a barrel bolt for adjusting the vane.

[s/v Beth]

Like to see how you use it. For me I am back to fabricating the spindle on which to rotate the windgear apparatus. Some type of bearing will be involved, which I can remove the bolts and the windgear automatically switches to align with the wind.

[model 10]

It would be a shame to not use every tooth as a stop, Perhaps a spring loaded pawl kind of like an Aires. It would be kind of a combination Aires and Monitor in that regard.

[seandepagnier]

good idea, just don't use a regular bicycle chain on it.

My arrangement works well... First a 5:1 reduction chain, then lots of friction on this wheel, so I can still overcome it manually slowly, but it never slips.

[Andrew Troup]

Chrisc

As I understand it you're planning to use it as a indexing plate, like the way the Aries uses a gear.

Not as a sprocket, hence no chain.

Seems like a smart way to get a ring of holes easily ... clever fellow !

Just be aware, though, that most high strength alu alloys (in fact, all of them I'm aware of) fizz away fairly rapidly in salt water. And the others would make a crappy sprocket.

It doesn't stop the latest Optimist masts being made of one of them (7075, IIRC) so it's not immediately fatal, but it might pay to try and get several sprockets the same, to have a spare, once you've decided on what size, and how many indexing teeth.

My only other thought is that it would be easier on the brain to go for, say, 72T, so each increment is exactly 5 degrees. Then if you want to change course 60 degrees, you just go twelve holes.

If you have a drill press, I can describe a crafty, and easy, way of drilling a ring of holes at any increment you want.

[holmek]

Yes, please describe your way of drilling holes using a drill press.

[Snowpetrel]

Good idea. I wonder if you wrapped a bit of stainless rod (about the same Diameter as the notches in the sprocket) around a pipe and into a spiral if you could make a sort of worm gear, and by rotating the worm gear you could infinitely adjust the unit, like a Hasler gear?

[Andrew Troup]

I sketched up the geometric principles.

I've run out of time for a comprehensive description but you'll no doubt be able to puzzle it out from a brief one >

Mark out first two holes as shown (alter proportions to suit), bolt two locating pegs to a baseboard (cotton reels cut in half?). Baseboard needs to be clamped to the table when you drill the second and subsequent holes

Drill the hole at bottom left through into the baseboard, and fit a dowel protruding slightly.

After you drill each new hole (which is the one in the middle between the cotton reels), move it onto the (bullet nosed) dowel.

Rinse and repeat.

Order will gradually emerge from the chaos but it will never be entirely symmetrical until you reach the last hole.

If the starting angle is as shown, you end up with 72 holes. The errors will not be cumulative. Every fifth hole will correct the previous four errors.

(or something like that, haven't had time to think it thru carefully)

[msponer]

Originally Posted by Andrew Troup

I sketched up the geometric principles.

Way cool, thanks! I've helped make ginormous sprockets, and knew of no way to avoid cumulative error other than to use a rotary table. It's rare to have access to one as a guest in a shop:

Drilling the Sprocket - YouTube

[Boulter]

Hi:

I vaguely recall there is a way to get an engine lathe with threading capability to cleverly index. Then you just need a tailstock mounted drill of some sorts ... It has been years since I have done any machining, and even then wasn't much.

Boulter