I own a 200 year old goban that a friend is refinishing. Its dimensions are a non-standard 17.5" x 16" (444.5mm x 406.4mm).

We're thinking about laser-etching a grid with an 8mm border having traditional line thickness (1mm) and star point sizes (4mm).

I am wondering:

• What diameter of black and white stones would be best?
• What grid dimensions should we use?

The picture below shows 19 black and 19 white stones set upon the board. The black stones are too small relative to the white stones. A grid to fit the white stones wouldn't leave much of a border between the grid and the edge of the board. We're going to exchange the black and white stones (i.e., get a new set), but deciding on the ideal dimensions has been a challenge.

It seems to me a good size for the margin would be half the distance between lines. So, the line spacing ("on center") would be 1/19 the height and 1/19 the width. That would make the line spacing 23.395 mm vertically and 21.389 horizontally. That would make the margins 11.69 mm and 10.695 mm.

To determine the stone size, I was thinking of using a table of sizes used for a standard board in Wikipedia, and reducing the stone size proportionally. The table gives a stone diameter of 22.5 mm, which is 5.30% of the width of the board. Using the same ratio for your board, you would have a stone size of 21.56 mm. This would make the stone diameter slightly larger than the column width, so the areas of the board might look crowded late in the game. I'm told this is common, and the WP table supports that.

The WP table gives only one stone diameter. However, further down in the article, it states the black stones and white stones have slightly different diameters. It doesn't say what the difference is.

In measuring for placement of the lines in the board, I would suggest finding the center, and measuring from there. That way, the margins will "absorb" the errors. If you start from one side, you increase the chance that a margin on one side of the board is noticeably different than the margin on the opposite side.

I notice the WP board has an aspect ratio of 1.071 (or 0.933, rotating 90 degrees). Your board has an aspect ratio of 1.094 (or 0.914). So, your board is going to have a slightly more elongated look.

Your board is 95.8% as wide as the WP standard board, and 97.8% as long as the WP standard. So, if you like, you could make the width of the lines either 0.96 mm or 0.98 mm.

P.S. Looking at the picture you provided, I would say the white stones are the about the right size for that board. You could make them a tiny bit larger in diameter to make a more crowded look. Or, you could base the column width on the size of those white stones. You could adjust the width of the columns to get the look you want, making the margins larger or smaller.

There is some useful information on Sensei's Library: http://senseis.xmp.net/?EquipmentDimensions