Give it the board width and the tail width you want, and it works out how many tails and
pins fit and what the real tail width has to be so the spacing divides exactly across the board — the
arithmetic nobody wants to do at the bench. You get the position of every knife line from the reference
edge, the baseline depth for both boards, and a full-size 1:1 template you can print, cut out and stick
straight onto the work. Everything runs in your browser; it works with no connection.
Joint
Standard for dovetails: the joint starts and ends with a half pin.
Tick only if you measure the second board from the opposite edge.
Wider layouts are split into tiles you tape together.
Notes
How do I know my printer hasn't shrunk the template?
Every printout carries a 100 mm control ruler next to the drawing. Print it, put a steel rule on
that bar, and it must read exactly 100 mm. If it reads 97 mm your printer is scaling — turn off
"fit to page" / "shrink oversized pages" and set the scale to 100 %, then print again. Do not use a
template that fails this check; a 3 % error over a 150 mm board is 4.5 mm of accumulated drift.
Why is the tail width not the number I typed?
Because a whole number of tails almost never lands exactly on your board width. You give a target,
the tool picks the count that comes closest and then adjusts the tail width so the last half pin ends
precisely on the far edge. The pin width is held at what you asked for — pins are sized by your chisel
and by how the joint should look, tails are the elastic part. The summary tells you how far the actual
width drifted from your target.
Do I still need to transfer the tails to the pin board?
Yes. Cut the tails first, then scribe them onto the pin board with a knife. The pin board layout
here is a check and a guide for chopping, not a substitute for scribing: it assumes your tail saw cuts
are perfectly on the line, and they will not be. Use the printed pin layout to see where the waste is
and to set the socket depth, then trust the scribe marks for the actual cut.
What this tool does not do
It handles through dovetails and through box joints only — no half-blind, no secret mitred, no
sliding dovetails. It adds no fit allowance: the geometry is nominal, and the shaving of fit is yours.
It knows nothing about your saw kerf, so on a router-table or table-saw box joint jig you cannot cut an
arbitrary finger width — a jig with a fixed key can only produce multiples of the key, so use the
calculated width to choose your cutter and board width, not to reset the jig. It also assumes the board
is exactly the width you typed and the ends are square; plane and shoot the stock first, then measure,
then print.