The waterjet idea is a good one in this instance - I'd forgotten about that. They will need a CAD file which is easily created. Most waterjet houses in the US will supply the material as part of the service. And you can have round corners if you like .
I do that on all backing plates I make up. I also radius all the edges and polish them just to make them purty.Any reason why keel bolt backing plates/washers always seem to be square with hard corners?
I would think that radiusing the corners would prevent stress concentrations, would hardly be much extra work?
Yet I never see it...
These work surprisingly well on stainless plate. Go slow, keep lubed (Anchor Lube), maintain pressure.A 1" twist drill in anything but a very heavy drill press is fairly dodgy. Any 1" drill you can afford is a Silver and Deming, having a reduced shank, and is way too long to be rigid. Poking that through SS plate is a tough assignment. The annular cutter will work better, but still needs a pretty rigid setup.
You still need a metal shopThese work surprisingly well on stainless plate. Go slow, keep lubed (Anchor Lube), maintain pressure.
Rotabroach Hole Cutters | Blair EquipmentRotabroach Annular Cutters, cut clean, burr-free, round holes fast, in sheet metal and thin plate materials.www.blairequipment.com
This is the key, but saying is easier than doing. 316 in the annealed state is softer than mild steel, and will cut more easily. Unfortunately 316 is a badly work hardening material, so if you don't cut around 0.002" or more per edge, it will work harden and the next edge runs into hardened material. To keep even a 1/2" drill cutting properly takes around 200+ lbs of pressure - impossible with a hand drill. That's why people try stepping the hole diameter up using larger drills, at each step the edge engagement is small and you can get enough pressure, but it causes other problems. The annular cutter has less edge engagement as it is just a thin ring, but still takes good pressure or the same things apply.The key to stainless is to keep cutting quickly. I'd try it.
I did it on a 43' years ago. I had a machine shop drill the S/S "floors" simply by providing the center spacing of the bolts (10"). I think you'll find the bolt spacing will be a nice round number and all the pairs will be the same distance apart but measure all of them to be certain.Thanks for all the tips.
I went to the boat and had a quick look today and the curvature of the plates isn't nearly as bad as I remembered, there is a bit of an optical illusion going on, it is not an issue. The plates were probably 10 mm when they were new (the rust and subsequent work makes it difficult to be precise) and I'll put in 10 mm. I'm torn between DIY in mild steel 1 at a time vs get them made up in stainless - if the latter I'd have to send away and get them all done at once, I'm not, yet, aware of a local suppler. Will proceed in the new year.
Sure looks like 'rust jacking' discussed early in the thread. How deep is the divot in the hull, especially compared to the relevant cup in the plate?It isn't clear to me whether the backing plate was curved as it tried to conform to the hull or whether it might be showing the 'cupping' that is normal for washers?