The difference between the original thickness of ~8.5mm and the new thickness of 13mm yields a dimensional difference along both axes of 9mm, which when converted to Imperial (0.35433071") is reasonably close to 3/8", so we adjust based on that to arrive at:
which has proportions of 1 (height) to 2.25 (depth) to 4.25 (width) — not the golden mean, but seems reasonably pleasing/workable (and certainly an improvement over the initial with its very small interior space) — this one would have an interior space of:
- height — 2" less 26mm is almost 1"
- depth — 4.5" less 26mm is almost 3.5"
- width — 8.5" less 26mm is almost 7.5" — about enough length for a full-length Mirado “Black Warrior” pencil
Re-working the joinery will involve a couple of tools, since the intent is to have a full miter at the ends, and to cut this in the simplest fashion possible. Necessary tools:
- a large diameter 90 degree V endmill such as:
- a narrow 90 degree V endmill such as:
-
a 90 degree square endmill which will match the diameter of the above tool (a #102 should be fine, though you may want to consider a downcut tool)
-
two roundover tools — one whose radius matches that of the above two tools such as:
- a second which would ideally have a radius which would add up to a diameter close to that of the thickness of the stock — I believe a 1/4" radius (6.35mm doubled to 12.7mm is reasonably close to 13mm for woodworking purposes — worst case, cut a bit deep and ease the beginning/end of the cut w/ a file or some sandpaper)
https://www.whitesiderouterbits.com/products/1572
for more on roundover tooling see: