Homebrew PCBs

Tim, smack on the nose. 

Alan, when you see a sign on the side of a vehicle, if it isn't
painted then there is a 99.99% chance that it is sign vinyl. It
comes in various thicknesses on a pretty thick backing paper.

The cutter for it is a tiny Xacto-like blade that swivels in very
small ball bearings. The vinyl cutter works just like a plotter, in
fact many also take pens, at least the older ones.

However, think about how a swivel wheel on a TV cart works- if you
move the leg of the cart straight, then make a 90 degree change in
direction, the path left in the carpet is a rounded off corner
because the swivel has to catch up with the direction of motion.

You can compensate for this by pulling the leg past the corner
until the center of the wheel (or point of the blade) is where the
corner must turn, then you have to arc the leg around that axis
until it is in a line with the next direction of motion, then
continue on.

So it ain't so easy. For a vinyl cutter, it depends on how far off
from center the point of the blade is, and how sharp an angle the
blade is. And of course you can't turn on a dime. IE, it must allow
some curve to the corners to allow the blade to continue traveling
at all times and not just swivel in place.

Some sign vinyl cutters (most, I think) do this compensation in the
electronics. My old Graphtec does this, and of course it is
adjustable as it varies according to the blade and the thickness of
the vinyl. You can buy sign cutting software that will perform this
compensation so that you can use a regular plotter with add-on
swivel cutting blades, but the few pieces of software that will do
this typically run in the thousands of dollars. Cheaper just to buy
a new 12" sign cutter than buy that software.

Oh, and the way it cuts just the right thickness- on my Graphtec it
has a thickwalled brass tube the blade sticks out of, the brass
rides on the vinyl and you adjust how far the blade sticks out so
that it just barely scores the backing paper through the vinyl.

Then "weeding" means to remove all the vinyl you don't want
transfered. A transfer tape is then applied to the surface of the
vinyl. Transfer tape is sort of like a weak masking tape, only
really wide (up to 4 feet). The idea is that it sticks to the vinyl
better than the vinyl sticks to it's backing, but not as well as
the vinyl sticks to anything else. Anyway, then you lay down the
transfer tape with the vinyl on it onto the surface, burnish it
down, then carefully remove the transfer tape, leaving the vinyl
behind.

I have a huge roll of black sign vinyl that is very old, so I use
it for temporary purposes. It wrinkles up and peels away after a
few weeks of weather. So it works great for PCBs. Unfortunately
it's age means it is a big pain to weed when cutting very fine
shapes like PCB traces. Newer vinyl works much better.

Does that explain it?

Steve Greenfield


--- Tim Goldstein <timg@...> wrote:
> I would guess that he is referring to sign vinyl. It is the
> plastic film
> material that is cut then attached to a backing to make signs and
> banners. The stuff I have played with was about .005" thick with
> a self
> adhesive on the back.
> 
> Tim
> [Denver CO]


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