On Sun, 22 Feb 2009 15:30:57 -0000, you wrote:
>As a followup to my recent introduction and questions, I've got two
>more questions (well, two more for now ... !)
>
>1) How many of you fabricate your own boxes in which to mount your
>projects? For the latest board, I fabricated a box out of some thin
>sheet steel, snipped to shape with tin snips, bent with a vise and
>hammer, and tack welded the seams. It is workable, but crude. I'm sure
>there's a better way?
I tend to use aluminum, and since I don't weld, resort to tapped holes
and screws. The latest project has a case about 8 inches wide, 2 1/2
inches deep, and about 13 inches long. It's made of 1/8 thick
aluminum angle as a frame, with side panels that bolt on (for
shielding). Outside is thick plastic for looks and protection. Case
is yet to be completely done. Otherwise, I use plastic cases or
aluminum (purchased or salvaged) boxes as needed.
>
>2) Both of my recent efforts with TT have been double-sided layouts.
>The first time, I tried to align using the edges of the board; the
>second time, I thought I had gotten smart (based on something I read
>here or elsewhere), and I lined up the two prints using a bright
>backlight, then stapled them together to make a "pocket" into which I
>inserted the board. Both methods gave me boards that were usable, but
>not as closely aligned as I had hoped -- the second was marginally
>better, but still off in some places by maybe .010" - .020". What's
>the secret to getting a perfectly aligned double-sided board?
>
I haven't managed to do that yet, the perfect part, though.
Several methods. The nicest one is to etch in two steps. On the PC
board pattern, place symmetric vias at the corners, smaller than your
normal vias. Hole size roughly that of a straight (map) pin. Place
another via off center. Make no connections to these vias, they're
for alignment.
Place the pattern on the board, transfer, and etch one side. Self
stick shelf liner will protect the other side of the board. (do not
run the shelf liner through a laminator...).
Drill out the vias used for alignment. With a straight pin, punch
alignment holes in the remaining pattern (you can also do something
similar with the silk screen layer, but vias aren't there on that
layer). Align the board using the pins, tape, and transfer the toner.
Etch, with the previously etched side of the board protected.
Otherwise, you can try the same thing with aligning the top and bottom
to already drilled holes. May not be as accurate, though.
Sources of error:
1) paper slipping while laminating. I feed through in one direction,
reverse, feed through in 180 degrees, etc...
2) always feed the paper in the printer the same way, do not reverse.
This tends to minimize distortion across the width of the paper.
I can get pretty close with this.
Harvey