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post #13 of Old 02-17-2013
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Re: casting Bronze porthole rings

I agree with you there but casting is just one of those super steep learning curves. Even with more forgiving materials such as lead and aluminum there is a pretty steep curve.

CNC can be quite involved. I would start by making a paper blueprint that I would take back to my old college professor to get one of his students to translate into G code which I would then help set up and run on one of the schools CNC machines to machine the part I want. I would then either sandblast or acid etch the part to obtain the desired semi rough finish on the outside (the casted look) and then I would install the part on my boat knowing that the allow was properly mixed.

The thing most people dont know about alloys and 1960-1970's rudder shafts are an excellent example.

Stanless steel has a content of nickle in it to help keep the steel from having its normal brittle sheer characteristic (Since a lot of force is sometimes exerted on rudders) this gives the rudder shaft some spring to be able to flex and bend as opposed to twist and break.

Nickle and steel are VERY hard to get mixed evenly into a good alloy. during the 70's and prior that alloy was hand mixed and hand casted. They have lasted very well but for anyone who has had the misfortune of owning one that someone did a bad cast on the result is that the nickle content is higher and lower in different portions of the shaft, the eventual result is you trying to figure out 1. how you catch your rudder thats floating away and 2. how you are going to get back to your slip/mooring.

We should all know that portholes are one of those areas that can sink a vessel when a storm becomes bad enough that you have to close up the cabin. Not the kind of an area where I would want to risk it.

Not when I can use materials already on hand to cut machine a part where the alloy will be as close to perfect as one can humanly make it.
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