Without commenting on what others are posting
above here's my normal dissertation on chainplates:
Type 316 is an ideal choice and for thru-deck type chainplates should be the only one seriously considered but it is not the only choice. Type 304 is certainly acceptable for external chainplates that have been well polished and are well maintained. Aluminum
of sufficient grade and thickness can also be used and in some production cases is used to great effect. Refer to "Skene's Elements of Yacht Design" for scantlings.
If you are making simple strap type chainplates purchase
bar stock the width you need. Do not cut or drill your stock until 95% of your polishing work is done (see below). Chop saws with abrasive bits make the quickest work with bandsaws being a close second if you have access to a bandsaw with a deep enough throat. You can (regardless of what you may hear) cut stainless with a hacksaw. Use the best quality blade you can find and mount it to a high tension saw. Lubricate the cut frequently and you will not have any issues.
There's a world of misinformation out there on stainless drilling. It's an easy material to deal with if you use the correct technique. Best choice is a drill press (well, aside from a mill) set to it's slowest setting but a good hand drill will be able to do it. I've drilled a 3/8" hole through 1/4" stock with a black and decker hand drill from walmart. The key is a variable speed drill operated as slow as possible. One you are set to drill get on it and commit. Do not stop to check your progress. If possible, use a steady stream of actual cutting fluid but in a pinch any cooling
, lubricating fluid will work. If you burn up your drill bit you are generally stuck with a hardened hole you'll never get through so you generally get one chance. Do not rush the job and you'll have no problems. Also, while a high quality bit is nice it is by no means required.
DO NOT use square holes. This applies to chainplates, holes in masts, etc. Corners are a stress nightmare. Countersunk fasteners in external chainplates aren't great either.
Mounted belt sanders and hand angle grinders are your friends. I've had much more luck with sanding
discs on a grinder than I've had with a stone. I wouldn't necessarily duplicate your old plates just because that was the original equipment
. Just because it was original doesn't mean it was correct. Try Skene's again to get general dimensions for the top end of the chainplates. I believe there is also a copy of the Skene's table in Brion Toss's "Riggers Apprentice"
Cold bending should be able to take care of most of your needs. Ideally a press and a jig you make up for the task is the way to go but it is possible to get acceptable results with a vise and rubber mallet. Any bends need to be made before you drill.
Mill finish bar stock is heavily pitted from the rollers the sheet stock is pressed through. It's also frequently slightly cupped. Step one is getting down below these imperfections. Using drywall screws edge-screw your bar stock to a work table.
Now hit with a belt sander armed with 60 or 80 grit. This is the singlemost time consuming and mind-numbingly boring part of the whole job. Keep the belt sander orientated the same way and work the metal over slowly and consistently until you've sanded away the last of the pits.
Cool the metal with water frequently or you'll burn through the sandpaper and scorch your table. A belt sander really is the only tool aggressive enough to do the trick but it's easy to screw up. Keep it flat or you'll gouge the metal.
After you get a good consistent finish with the coarse paper drop to 120 grit and sand again until you get an even dull look. After the 120 grit it's time to switch to a buffer/sander with 220 grit also worked with a flat tool (do not pick it up to edge sand no matter how strong the urge). 400 grit on that same sander is the last step before the buffing wheel. It's at this stage that you are ready to cut,bend,and drill your stock.
Chances are you'll need to touch up areas after you drill. The little spirals of metal coming out of the holes tend to scratch up the area around your holes. Hit these with the buffer/sander again with the 400 grit if they are light enough or the 220 followed by the 400 if they are deeper.
Buff with white rouge on a bench grinder or angle grinder fitted with a buffing wheel. Mount and enjoy. Seal with 101 or other polysufide based sealant
All of this represents a good saturday's worth of work and is certainly within the realm of do-it-yourself. It's not unusual to the able to buy the stock AND the tools and do it yourself for less than buying
a set of chainplates and then you have the basic toolset for doing 99% of the custom metalwork on your boat (linkplates, tangs, backing plates
, etc.) and a good bit of experience to boot.