Page 133 of 339

HOW TO DIGITALLY DIAL IN JOINERY FIT
HOW TO DIGITALLY DIAL IN
JOINERY FIT
The key part of digital craftsmanship is match-
ing your digital CAD file to your physical mate-
rial. Now that we’ve explained the inherent
dimensional variation of actual sheet materials,
let’s shift our focus to the virtual side of the
process.
DESIGNED FOR 19MM PLYWOOD
Designers model a project using a virtual mate-
rial thickness that is approximate to real sheet
material stock. Since it is a general approxima-
tion, material dimensions in a digital CAD file
will likely differ from real materials, because of
the variability we explain earlier. Nominal thick-
ness in design files, or TNOM, is an assumption,
not an exact measurement. To model the two-
seater bench in Chapter 4, you had to assume a
sheet material thickness of 19mm. Each AtFAB
project in this book was modeled with sheet
material in these assumed thicknesses. The
interconnected joinery in the cut files derived
from those 3D models will only fit together if
machined from plywood with an identical thick-
ness.
Dialing in your joinery fit requires a few
methodical steps, so the nominal material in a
CAD file matches the actual material you have
on hand.
Because of plywood’s uncertain actual thick-
ness, it’s critical to thoroughly measure your
material. Once you know your material’s physi-
cal properties, you can then calculate the differ-
ence between the actual and virtual material
thickness, and adjust the CAD file to match the
actual material.
TNOM IN CAD
Nominal thickness is an assumption made by a
designer; it’s the thickness of the material used to
model a CAD design. For most of the AtFAB CAD
files and the projects in this book, TNOM is equal to
19mm (or 0.748031”).
There are a small number of projects that use thin-
ner materials. The Cellular Screen (Chapter 16) is
made from nominal 12.7mm, or ½″ material. The
Open Storage Cabinet (Chapter 14) incorporates
12.7mm (½″) and 5mm (roughly ¼″ or 0.19685”)
thick material for its shelves and dividers. While the
Poke Credenza (Chapter 15), employs 5mm
(roughly ¼″ or 0.19685) for its sliding doors.
You might recall in Chapter 2, AtFAB designs
use sniglets that are 110% of the actual end-
mill diameter size to accommodate downward
file scaling. This additional percentage ensures
your sniglets won’t be too small for the end-
mill, if you reduce the file’s scale to match
material that’s thinner than TNOM.
The following pages walk you through the steps
of measuring, calculating, and scaling.
05/PRECISION-FIT PLYWOOD JOINERY
131
    "