DIY Chainplates: Polishing the Stainless

12 Jun

A while back I wrote up the first two thirds of how I made my own chainplates (I and II). Finally, here’s the last part- polishing.

The polishing was by far the most difficult, frustrating, and time-consuming part of building my chainplates, and not something I ever want to repeat. Unfortunately, it is necessary to do at least some polishing as a polished finish is integral to the ‘stainless’ properties of SS, but as I mentioned before I think that this step could be avoided by simply buying pre-polished stock. Certainly, polished stock would be more expensive but I suspect even the added cost would be cheaper than the money I spent on polishing medium while trying to figure out my technique and certainly the result would be a finer finish. With that said, here’s how it went down.

I did virtually all of my polishing after I had finished machining the stock. Here’s a shot of pieces in various stages of the process:

The two pieces in the middle are as I bought them in an unpolished mill-finish state, the other have some polishing. As you can see, it was a long way from mill-finish to nice and shiny!

The first issue with polishing rolled barstock like I had is that the stock comes off the rollers slightly cupped. This means that when you try to sand/polish you are contending with high and low spots rather than a flat surface.

You can see that the chainplate on the right has been sanded a little and is shiny on the edges but not in the center. This is because the concave shape let by the rollers makes the edges higher than the center so they get hit first by the sanding medium.

My first try at polishing was gleaned from this forum post where someone recommends to start by belt-sanding each plate flat to eliminate this cupping. The chainplate on the left in the photo above is the only one I sanded with this method. As you can see it worked quite well but behind-the-scenes this is not such an elegant solution:

Here’s a brand new belt on my sander after a very short time sanding stainless steel!

Maybe my stock was more cupped than most but I quickly gave up on this strategy when I calculated how many expensive sanding belts it would have taken to get each piece perfectly flat. Instead, I decided to work with the shape of the stock and polish as best as I could without flattening it.

There was still plenty of work to do as the rollers that turn out the bar also leave significant scale and pitting. To combat this I took out my trusty 4-1/2″ angle grinder, maybe the most-used tool in my shop. I tried a bunch of different sanding mediums looking for the best compromise between being too aggressive and scratching the material versus being too soft and taking an inordinate amount of time. I found that sanding discs were too coarse but flap wheels, being a bit less aggressive, worked very well and were able to take the shape of the material enough to sand uniformly. Unfortunately, they are also far more expensive, at around $8 a pop, and don’t last long at all. I compromised by using only the handful of 120-grit flap disks I had already bought before moving onto less expensive sanding mediums.

Here is my friend Wesley doing initial sanding with a flap disc.
And a chainplate after the initial 120-grit sanding.

The process for each chainplate differed a little as I honed it down but in the end I found the quickest way to get a good finish was a progression of sanding from 80-800 grit. I started with a coarse 80-grit disc on the angle grinder to remove scale and heavy pitting but this left marks which were far more visible than those left by the uniform abrasion of the belt sander. Next I used my 120-grit flap discs to get a smoother finish before moving on to a 220-grit sanding disc. In order to use cheap hook-and-loop type discs on my grinder I made this flexible backing pad.

I got a pad for the repair of hoop and loop sanders and an old heavy-backed sanding disc

These were glued together to produce a backing pad which would securely hold sanding discs while being flexible enough to conform to the shape of the material.
I cut a hole in the middle of the pad so that it would fit on a grinder and a similar hole in each sanding disc so it could be installed and removed easily.

This system worked well enough to finish up the chainplates but it was not perfect. The speed of the angle grinder is too aggressive and I found my discs would rapidly disintegrate at the edges. I used this technique for sanding with 220 and sometimes 400-grit paper which was followed by 600 and then 800-grit paper on the less aggressive random-orbit palm sander. After I was satisfied with the results at 800-grit I moved to my bench grinder using a polishing wheel and 1000-grit polishing paste.

This resulted in chainplates that were quite shiny, but still certainly not a mirror finish:

I call it a blurry-mirror finish. It’s to allow modest guests to avoid having to take too close at look at themselves when boarding the boat from a dingy.

 Actually it turns out shiny steel is quite difficult to photograph and the chanplates did come out better looking than this photo would make it seem. Still there are certainly imperfections. I discovered that the problem with my step-sanding method was that it was difficult to tell which scratches were coming from which grit and so some marks were still left from coarser grades of sandpaper which I thought were only minor imperfections that would come out in the polishing. In retrospect I think it would have been much more effective to do less sanding – say to 400-grit and then polish with a rougher grade of compound, maybe finishing with the 1000-grit for shine.
All-in-all this was one of very few projects on the boat where I felt like I was often wasting money and vast amounts of time by doing things myself instead of turning to a professional for at least some of the work. Still, I am proud to say I made my own chainplates from scratch and though they don’t have a perfect mirror finish they look pretty damn good all the same! Plus the total cost in materials and supplies for all seven chainplates was well under $400.

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder


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