Fabricating bronze chainplates and tangs

[Ryban]

Our Westsail's hardware is coming up on the 40-year mark. I haven't pulled a chainplate yet to inspect, but I know I need to preventatively replace a few tangs (there are 2 for the bow sprit, and 2 for the boomkin). I also am thinking of just replacing all the chainplates while I'm at it. This is partly to check it off as an item we don't have to worry about while cruising, and partly because I'd like the machining challenge. I stumbled into owning a small milling machine that is CNC enabled, and having some machining experience from my grad school days.

These threads were useful:
https://www.cruisersforum.com/forums...ngs-31447.html
https://www.cruisersforum.com/forums...es-254157.html

I'm sold on bronze and am not really interested in discussing using stainless steel instead. Bronze has a leg up in almost every way, except for its price, and, subjectively, its appeal (but I prefer a green patina over rust stains anyway).

My main questions are:
1. Silicon bronze bar stock can be hard to come by, Al bronze is a little more common. Are Al bronze alloys suitable for this applicaiton?
2. Bending is a common question/concern that comes up when fabricating chainplates at home, especially with bronze alloys. The largest angle I need to bend is 25 degrees for one of the chainplates, the other is 15, and 0. I have a large vice, and a map torch, but that's about it. Are these angles safely achievable?

[Jammer]

The originals would have been cast, yes? Why not do that?

[Ryban]

Casting is an option, and PTF can provide castings -- they quoted me at around $1500 for the 6 chainplates, including the drilling. So about $250/ea.

I briefly considered casting them myself, but I trust myself far less to produce strong castings, then to machine down wrought metal. I just worry about introducing unseen casting defects.

[Bowdrie]

Originally Posted by Ryban

My main questions are:
1. Silicon bronze bar stock can be hard to come by, Al bronze is a little more common. Are Al bronze alloys suitable for this applicaiton?
2. Bending is a common question/concern that comes up when fabricating chainplates at home, especially with bronze alloys. The largest angle I need to bend is 25 degrees for one of the chainplates, the other is 15, and 0. I have a large vice, and a map torch, but that's about it. Are these angles safely achievable?

Silicon Bronze has a very high copper content and bends more easily than the other bronze alloys, it's easy to work with, no surprises or drama.
There are a few alloys that are commonly called "Aluminum Bronze".
I had a rudder heel fitting cast from "Nickle Aluminum Bronze", another name for it is "Navy M".
Extremely tough, a "sticky" metal, even with the proper speeds/feeds, and cutting angles, all of the machine work was harder than I expected, and coolant was needed.
Of course, I wouldn't want to try to do any bending on a casting, the bar stock might be ok.
I'd talk to someone who works with bronze.

[deblen]

https://marinesalvagemaine.com/


Don's Marine Salvage https://www.facebook.com/wegotboatparts/


Reverse engineering bronze casting-Youtube
https://www.patriotfoundry.com/services/

[Benz]

I was able to bend 1/4" silicon bronze plate and bar with a vice and a big lever; 3/8" thick required a hydraulic press I luckily had access to. I made each bend only once to prevent fatigue, and was careful not to have to bend back.

[SVTatia]

Originally Posted by Ryban

Casting is an option, and PTF can provide castings -- they quoted me at around $1500 for the 6 chainplates, including the drilling. So about $250/ea.

I briefly considered casting them myself, but I trust myself far less to produce strong castings, then to machine down wrought metal. I just worry about introducing unseen casting defects.

Just curious, are your current chanplates SS or Bronze?

[Bowdrie]

Whether you do the drilling or have it done, make d**n sure that there is lots of offset where the pin hole is for the toggle/turnbuckle.
Somebody just a short time ago, in another thread, posted the table from Skenes Elements of Yacht Design that gives the offsets.
Don't make the amateurish mistake of only having 1/2in of metal above the hole for a 1/2in pin, it wants more than that.
And adding a bit more for bronze is always a "no harm/no foul".

[Ryban]

The current ones are all SS.

If 3/8" chainplates require a hydraulic press to bend, then I'll probably have to outsource that part of the fabrication. I wonder if it could be done with appropriate heat and a long lever though. Maybe I'll poke around.

The quote I got from Atlas Bronze for 3/8" silicon bronze (C65500) plate dimensioned 24" x 16.75" (enough for all the chain plates and at least a few tangs) was $915. If I used all the material to make chainplates, that works out to about $114/ea.

Aluminum bronze (954) cast bars 3/8" x 2" from Online Metals are $106/ea. But casting is not ideal here since I want to bend them safely.

[Jammer]

I would imagine that if you heated the bend line with an oxyacetylene (or oxypropylene) torch and put the chainplate in a large vise you could easily bend it over even without a long lever. I would think that would lead to less work-hardening and therefore a safer, stronger part than cold bending it.

[peb]

https://www.northerntool.com/product...B&gclsrc=aw.ds

I fabricated 1/4 inch silicon bronze chain plates with the above tool. I also used it for a gammon iron made out of 3/8" silicon bronze bar. Also used it for a 5/8 inch bronze rod to make a mainsheet horse for a gaff main.

Bronze is different than steel when bending. You work it cold, and it hardens as you work it. Sometimes you have to reheat it and quench it to soften it again.

Not hard to do, but takes some practice, which can be expensive.

[deblen]

https://www.iyrs.edu/workshops/cleat...KOV0lXXomouz80

[Cheechako]

Originally Posted by Ryban

The current ones are all SS.

If 3/8" chainplates require a hydraulic press to bend, then I'll probably have to outsource that part of the fabrication. I wonder if it could be done with appropriate heat and a long lever though. Maybe I'll poke around.

The quote I got from Atlas Bronze for 3/8" silicon bronze (C65500) plate dimensioned 24" x 16.75" (enough for all the chain plates and at least a few tangs) was $915. If I used all the material to make chainplates, that works out to about $114/ea.

Aluminum bronze (954) cast bars 3/8" x 2" from Online Metals are $106/ea. But casting is not ideal here since I want to bend them safely.

Checking out some bronze flat bar recently on line I discovered what you have. Totally strange to me for flat bar stock to be cast. Anyway, I would not want to use cast bar if I need to bend it.
I think most of Cape Dory's bronze fittings are silicon bronze IIRC. I used a number of their things on a boat I built many years ago.
I wonder is the bronze foundry in Port Townsend WA still in business?

I would prefer wrought material myself though, but I know bronze cast has been used for chainplates in the past.

[NRosenthal]

Port Townsend Foundry is in business
https://www.porttownsendfoundry.com/

[OneBoatman]

You have some good pricing at $1500 for all six. Why not be done with it? The problem with cold working it yourself is that it will take quite a bit of force to bend say 3/8" bar stock where you have basically two problems: one being difficulty getting grip and leverage on a short subject without galling, and two, repeatability. Because silicon bronze readily work hardens you don't really get a second chance if your mandrel and set up isn't firm and repeatable. You don't want to get into needing a full anneal and straightening. This temp for silicon bronze will be ~1300 F and you may recognize a propane torch in air burns at roughly 3600 F. I expect there is minimum bend radius info available for cold working, and the vendor of the alloy should be able to provide this.