Brilliant work, mate! Like form & function met and fell in love.
I'm guessing you spend at least 30-40 minutes machining each fitting, even with a system worked out to repeat the same job multiple times. Trouble with trying to make such things (by hand) for sale is the time factor.
The advantage is that you could produce fittings for different rail spacings. And the look of the thing, so much finer than cast NRS fittings.
You might scroll through the "More Games with Frames' thread, that has lots of discussion on fabrication and aluminum welding. Here's a copy of my post on oarstands.
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Scrap to Oarstands
Couldn't find oarstands for 1.05 OD frame tube (I'm building a superlight play frame with single side rails). Thought about drilling extra holes in the NRS towers. But instead I dug around in the bin of 6061 at the salvage yard and found some nice T-rail, flat, and square billet stock (about $2.50 for a boxful).
Shaped the parts with a hacksaw, drill press, and various files. The holes were already drilled in the T-rail so I cut that piece to use them. The two holes in the strut are for carabiners, rescue bag, etc. The bevels on the oarlock socket are to allow the welder to get a decent bead.
Definitely shop around for the welding job. $85
— think I got gouged, but the guy is a boater and I like his dogs.
Here's the end product, with two 1/4" x 1-1/8" u-bolts for grip on the single rail.
Here's the pair. Cost $98 plus 4 hours of my labor.
Just found out that Sawyer makes Mini-Cobra locks with 1/2" shanks that weigh about half what the full-size ones (with 5/8" shanks) do. So I'll look for a bushing I guess.
Anyhow, I like doing this trash-into-treasure thing.
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Ugly and crude compared to your work. You should try a pair of oarstands next (hint, hint).