Following the dimensions provided in Le
Menuisier Ébéniste, I simplified the design somewhat,
leaving out some details such as the turned handles and the
decoration on the opening for the workpiece.
The bolt I used to make the tap has eight
threads per inch. For metal bolts that is a coarse pitch
(pitch measures the distance between the peaks of the
adjacent threads). For threaded parts that need to move a
lot and are in constant use, such as the screw of a bench
vise, a very coarse pitch is preferable (fewer threads per
inch). And with wooden screws another reason for a coarse
pitch is that thicker threads will hold up better.
Hard woods should be used for these parts,
as with softer woods the internal threads could wear away.
Woods such as Jatobá, Tauari, Peroba-de-campos, Ipę, and
Roxinho are excellent for making the screwbox. I used Jatobá
(Hymenaea courbaril), which is hard and very versatile.
The screwbox has two parts: a lid or guide
plate, which secures the cutter and guides the round stock
at the beginning of the cut, and the main body. After the
block is cut to dimensions the guide plate is cut away.
two parts are then put back together and secured with two
screws on diagonal corners (placing the screws in line with
the grain could split the wood). Then the hole in the lid is
bored, with a chip drill, auger, or Forstner bit, marking
the desired depth with a bit of masking tape. I used a 1”
The first cut should go through the lid, with
the tip or lead screw going into the main body to mark the
center. The bit is then changed to a smaller size, 7/8” in
this example, and the smaller hole is bored through the main
body. The difference in the diameter of the holes is exactly
the difference between the two bits – 1/8” in this case.
Once the hole has been bored the internal
threads are cut in the main body.