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[<6>]
====== What I want to accomplish ======
  * Determine how to mark the lines on the board.

====== What I've done ======

=== Experiments ===
Other people have used V-shaped router bits to gouge the circles and lines into the board, then filled them with paint. I did a few experiments with that technique and found it hard to get reliable results. If it goes wrong the entire top board is a write-off, so I was very nervous. If the pivot point moves by a tiny amount the circle won't meet up at the end of the sweep, and that would be unfixable. The specification calls for the lines to be between 1/16" and 1/8". It didn't take much slop in the system for the depth and cleanliness of the cut to be significantly affected.

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I attached a bolt to the side of a router dremel attachment, thinking the smaller tool would give me more control, but I didn't have good success here either. Though I got nice clean grooves cut in scrap wood when freehanding, I couldn't get reliable results when drawing big circles. It was too easy for the pivot to jam slightly, or the dremel to tip, and ruin the groove.

Instead I decided to go with a black permanent marker. I can easily build a lightweight circle-drawing jig. If it goes bad I can simply wipe off the ink with a solvent. I ran some trials and got some good data.

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The marker I used.

I had gone through five varnish -> light sand cycles to this piece of scrap ply before drawing on it with the marker. I drew some straight-ish lines, a black patch and a big squiggle then let the ink dry for half an hour. I then drew some fresh lines as a comparison a few minutes before varnishing. I noticed that some of the ink had wicked out slightly from the lines. I suspect this would be wicking along the scratch lines from the sanding.

The ink did not streak or bleed during or after the varnishing! Great success!

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After that coat of varnish had dried I gave it a light sand in preparation for another coat. I think I sanded a bit too hard because I broke through the previous layer of varnish and erased some of my lines, though many were unaffected.

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These photos show two coats of varnish atop the ink.

I think my solution to this will be ensuring my varnish sandings are sufficiently gentle, and perhaps re-marking lines if they start to fade during the subsequent varnish layers. Overall I think this technique looks great and it's likely the one I'll be using on the final board.


====== What I want to accomplish next time ======

  * Cut out the top,
  * Glue the offcuts and cut out the base,
  * Drill the hole in the centre of the top,
  * Attach the bands to the base.
[<6>]