How to reduce the diameter of an oversized chapter ring

Hello world, I just wanted to show the quick and easy way I came up with to very slightly reduce the OD of a replacement metal chapter ring for a Seiko Samurai.

Due to not being able to easily source the the exact replacement, I found a very similar one, but made of metal instead of plastic like the original. The original chapter rings OD was something like .35 mm smaller than the replacement, and as such would not fit in the the watch case. I would need to use either a fine flat file, or medium grit sandpaper glued to a hard flat surface to keep the edges crisp while reducing the diameter ever so slightly.

I didn’t want to make a super glue chuck because the heat or acetone that would be needed to remove the part from the work holding fixture would more than likely damage the printed indices on the ch ring, and i also didn’t want to waste my aluminum bar stock on a fixture I’d probably only use once at that size. Inconveniently, I also didn’t not have any plastic or acrylic round bar stock on hand to turn up a quick friction fit work holding fixture that could be held in my Sherline’s 4 jaw chuck….

What I DID have though, were a bunch of watch crystal press dies, many of them being unneeded duplicates. So I chose a convenient size and cut it down on the lathe carefully to a diameter that would friction fit the ch. ring nicely, in order to snugly hold it for reduction without any adhesives. The following shows the set up:

After setting the rpm’s to an adequate speed, I ended up using a strip of 400 grit sandpaper glued nice and flat to a tongue depressor (basically a large popsicle stick for you youngsters out there), and held it perfectly perpendicular to the piece and was able to reduce the part down roughly the .35 mm I needed to fit it into the watch case. This method allowed me to do this without messing up any of the paint or printings on the visible side of the chapter ring, and was able to do it in a precise and controlled manner. Just be sure to sand in short bursts, don’t set your rpm too high, and sneak up on the target OD, and stop an check your digital caliper or micrometer frequently.

Hope this helps any hobbyists or watch modders out there that may be stuck with this issue. If you find yourself with this problem but with no lathe to speak of, feel free to message me from my contact or estimate page, and get it sent over so I can quickly knock it out for you and get it sent back. I do simple services like these for watch modders pretty frequently, and inexpensively.

Hope this helps!

-Dustin Williams

Abstrakt Time Works