An odd thing about CAD...

Robert Schieck wrote:

So fess up, what do you print your 56" rib out on ?

-----------------------------------------------------------------------------------

Regular typing paper :-)

Select a new LAYER called 'Grid' and draw a grid atop the finished
drawing. I used a 2" square and selected THIN pale blue lines, printed
the rib 1:1, which took 6 sheets, then glued them together aligned on
the blue lines.

If you don't have a light-table, attach a small weight to a length of
black thread and tape it to the OUTSIDE of a picture window or sliding
glass door. Gravity does its thang and the black line of the thread
becomes your vertical alignment guide, easily visible through the paper
when in contact with the INSIDE of the glass. The regular (ie, black)
lines of the drawing are clearly visible and each sheet is fairly easy
to align in the horizontal plane. But for maximum precision, you may
print TWO copies of the drawing and OVERLAP the sheets, using the blue
grid for both vertical and horizontal alignment.

Printing was done on a garden variety HP Deskjet 930c. Using an
optical comparitor, accuracy is better than .001" over 8". If you wish
to verify the trammeling of your paste-up, compare your 2" grid to a
steel tape as the paste-up progresses. To transfer that degree of
precision to the work-piece, use spray-glue to attach the pasted-up
pattern to a sheet of aluminum, use an optical center-punch to prick
the centers of your tooling holes and check that with a regular
trammel.

Crude as the method above may appear, the dimensional accuracy of such
a pattern will typically exceed the standard of precision available to
the typical home-builder. Although maybe not the first time they try
it :-) Parallax plays a role in the accuracy of your paste-up as does
paper quality in your printing. But on average, ribs are pretty easy
compared to a 4x4 paste-up for a firewall or bulkhead.

-R.S.Hoover

wrote:
Robert Schieck wrote:

So fess up, what do you print your 56" rib out on ?

use spray-glue to attach the pasted-up
pattern to a sheet of aluminum,
-R.S.Hoover


I'll add just one point. In my experience, spray glue won't work if
you're makeing steel pieces and have to grind it down to the line.
Cutting the metal gets it hot, and that melts the glue. I've used a
little paint instead. I have a couple little cans of Killz white primer
that I keep around. Spread a thin layer using some scrap paper or
whatever's handy. It will come off easier later if the metal still has
the shipping oil on it, but it will still stick plenty well enough to
make the part.

I've also used the Kinko's trick mentioned earlier, but they don't like
the CAD formats and only play nice with PDFs. And then they didn't like
the 8' airfoil of the Delta. Finally settled on printing it half size
and then blowing it up to full size using the blueprint copier they all
have.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."