Ernest Christley wrote in message m...




Draw your plane up in a CAD program, 3D CAD would be especially useful.
Your eventual distribution would be a lot cheaper, and there is
nothing like being able to drop an additional line to get a measurement
between point that you find particularly convenient but the original
builder didn't/couldn't include because of space limitations on paper.

When the original builder is using CAD, measuring dimensions as you
indicate above is very useful. The builder is doing Computer Assisted
DESIGN, as opposed to so many who merely do computer asisted drafting.

But a cardinal rule for fabrication is to not rely on a dimension that
was determined by scaling from the drawing. You never know when the
draughtsman may have departed from the scale either when executing the
original or during revision. In particular, it is not uncommon for
revisions to be made by editing the dimentions without changing the
drawing per se.

Complete plans will have all the dimensions needed for fabrication
explicitly called out in the drawing package. If a necessary dimension
is missing then you should calculate it from the dimension that are
called out. People making plans should keep this in mind and try
to provide all the dimension needed for fabrication and to also call
them out on the drawing in a way that is useful for the person
doing the fabrication.

However, I learned standard practices for drawing and fabrication in
the nuclear industry. I appreciate that when not building reactor
vessels a more relaxed approach is appropriate and most of the plans
I have seen for sale are a good value for the price even if they
are less than complete by ASTM boiler and pressure vessel standards.

If you have to scale something for yourself off a drawing (or within
a cad model) then my advice is to be cautious and plan for a little
hand-fitting to make it right.

--

FF