Here's a silly question regarding plans

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

Fred the Red Shirt wrote:

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.


I was referring more to crosscheck measurements. You ever measure
something, maybe even two or three time, and just 'see' the measurement
you expect instead of what's actually there? With CAD, you can drop a
couple of extra measuments. Seeing a second measurement wrong is more
difficult. You have to be trying to screw up the third one. I like to
pull any important measurements from three points when I can. If
they're not all in agreement then I stop to figure out what's wrong.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

Always better to measure twice and cut once.

Peter

Ernest Christley wrote in message m...
Fred the Red Shirt wrote:

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.


I was referring more to crosscheck measurements. You ever measure
something, maybe even two or three time, and just 'see' the measurement
you expect instead of what's actually there? With CAD, you can drop a
couple of extra measuments. Seeing a second measurement wrong is more
difficult. You have to be trying to screw up the third one. I like to
pull any important measurements from three points when I can. If
they're not all in agreement then I stop to figure out what's wrong.

Again, ideally when fabricating you do not measure from the drawing and
apply the scale factor, and that is without regrad to whether you measure
with a ruler on a piece of paper or digitally within a software package.

You should use the dimensions called out on the drawing to calculate that
crosscheck measurement.

If you like, calculate it three ways and then average the answers.

;-)

--

FF

Fred the Red Shirt wrote:
Ernest Christley wrote in message m...

Fred the Red Shirt wrote:


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.


I was referring more to crosscheck measurements. You ever measure
something, maybe even two or three time, and just 'see' the measurement
you expect instead of what's actually there? With CAD, you can drop a
couple of extra measuments. Seeing a second measurement wrong is more
difficult. You have to be trying to screw up the third one. I like to
pull any important measurements from three points when I can. If
they're not all in agreement then I stop to figure out what's wrong.


Again, ideally when fabricating you do not measure from the drawing and
apply the scale factor, and that is without regrad to whether you measure
with a ruler on a piece of paper or digitally within a software package.

You should use the dimensions called out on the drawing to calculate that
crosscheck measurement.

If you like, calculate it three ways and then average the answers.

;-)


Or draw it up in CAD using all the dimensions that the designer gave,
then pull a line from the two points in question. You'll get
measurement accuracy down to nano-inches in a few seconds, vs the hours
it'll take to do 3-dimensional trig through rounded curves.

Personally, I'd never drop a ruler on the plans and then attempt to
scale up by a factor of 8 or 16. The thickness of the lines are enough
to throw you way off at those scale factors.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber