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Alan H

Brazing bronze that will be under water

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So one of those truisms we all know is "don't mix metals underwater".  You set up galvanic corrosion thattaway.

OK, so on my Piper, the rudder/keel shoe is bronze.  I have no idea what KIND of bronze...silicon bronze, phosphate bronze, machine bronze, aluminum bronze....no clue.

 

There's a fitting that's supposed to be screwed/bolted to the bottom of the rudder, which is essentially like a pintle.  In essence it would be like this..

 

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---except the pin would be about an inch long instead of three inches, and the straps would be wider and shorter.  OK, so I could make a plastic or wood model of the part I want and take it to a foundry.  I can hear the cash register ringing, even through time and space....

 

I could also get some aluminum bronze "hollowbar".  A 3-inch piece in this size is about $30

https://www.onlinemetals.com/merchant.cfm?pid=14185&step=4&showunits=inches&id=758&top_cat=850

 

Then get some 3-inch, 1/4 inch thick aluminum bronze flat bar and bend it around the hollowbar.  Then,  I braze the two pieces together.  I've been wanting to learn how to braze anyway.  but here's the thing...  you can braze bronze with a pretty cheap MAPP torch (plain old propane isn't hot enough, apparently, and I don't want to spend the $$ for an oxy-acetylene setup) but the rod you use is nickel-silver.  You can get bronze brazing rod but the melting temp is higher than MAPP will generate.   

 

So....bronze plus nickel-silver, underwater? ...  Thoughts?

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I was also thinking that this is a pretty small rudder.  It's about the size of a Pearson Ensign rudder. I might be able to bend the bronze strap about the hollowbar

 

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and then use 5200 to lock it in there.

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If you're thinking of going down that route, could you just get some solid bronze rod and hold the strap in place with a few bronze machine screws tapped into the rod?

Not much turning force on the strap at the rudder heel, its really there to keep the rod (pintle) in place.

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37 minutes ago, jgbrown said:

Tig weld it.  Get compatible filler rod. 

Yes.  Filler rod can be really expensive but TIG and bronze will work nicely.    I recently welded an adapter for my galley sink drain in bronze- piece of cake.

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14 hours ago, Alan H said:

So....bronze plus nickel-silver, underwater? ...  Thoughts?

I'd like to see you get that assembly hot enough for brazing with a Mapp torch. Very much doubt it'll happen. It's not only the temperature, it's the rate of heat transfer in/out on biggish assemblies.

The bar you pictured is bearing bronze for sure, I use a lot of it making bushings etc. Don't think it's suitable.

Frankly you're way out of your depth and need to go see a metalworker. Personally I'd probably MIG weld it but I've got 12kg of bronze MIG wire to hand. Or I'd get it cast & pay what it cost. Nobody ever said boat parts were cheap.

If you want a cheap solution, make it out of stainless steel. It won't look right, but it'll be cheap. If you paint it, nobody needs to know.

FKT

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I should in fact probably buy the stuff, drill and countersink the strap, bend it all....

 

....and then take it to someone who know what the hell they're doing. **sigh**

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17 hours ago, Alan H said:

I should in fact probably buy the stuff, drill and countersink the strap, bend it all....

 

....and then take it to someone who know what the hell they're doing. **sigh**

No shame in subcontracting parts of building you don't do, especially when dealing with structural bits!  It's a smart choice.  Talk to them BEFORE you start too and they can probably either sell you the right alloy or at least point you in the right direction.  Make it clear you want to do the layout and make the pieces but will be hiring them to do the welding.

Rough cast bronze isn't THAT bad when you make your own wax or plastic one off first.  They can just dip your one off in ceramic shell, burn it out and pour it, chop the sprue and hand it over.   IIRC used to cost me about 3$/lb in consumables +cost of bronze to pour.  So call a foundry too. 

 

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