Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Codesuidae <codesuidae@...> wrote:
>
> wbblair3 wrote:
> 
> > --- In Homebrew_PCBs@yahoogroups.com, Codesuidae <codesuidae@> wrote:
> >
> > > Did you try your switch to increase the temperature of the
laminator? 
> > > Any thoughts on how practical it is to get the temp on the
laminator up
> > > to where the oven would not be necessary?
> >
> > Frankly, as an afterthought, I didn't want to in any way endorse
> > modifications which might cause "problems," 
> 
> Fair enough.
> 
> Any idea how much pressure is required to get the toner to transfer?

I really have no hard figures for that although I'd suspect that the
laminator applies a considerable amount of pressure just from looking
at how it does its thing.  How's that for non-empirical?  Perhaps
someone with an adjustable-pressure laminator can give some figures if
there's some kind of scale on their pressure adjustment (beyond just
"light" or "heavy").
 
> Would it be reasonable to dispense with the laminator entirely and
> use the oven with either a heavy hand roller or spring-loaded crank
> roller (kind of like the old style washing machines)?
>
> Seems like the main problems would be with getting consistant
> pressure and with the temperature dropping off too quickly if 
> not using heated rollers.

We're really on the same wavelength here (i.e. keep it simple and
_cheap_)!  You've posed both the idea and some of the possible
problems with that idea that I considered before I even spent $30 on a
laminator.  The PCB material heats up and cools down _very_ quickly,
so the heated rollers of even a laminator that doesn't quite reach the
fusing temperature by itself _really_ helps to keep the board hot
enough for the transfer of toner.  Plus, while going through the
laminator's heated rollers, the board has no contact with effective
heat sinks of any kind.  Finally, the high-temp rubber(?) used for the
rollers probably ensures that the roller contact pressure is applied
fairly uniformly across the PCB.

I considered using the rubber platen from an old typewriter along with
a cheap rubber mousepad to set the hot PCB on to both cushion and
insulate it, but I didn't have access to a really cheap typewriter to
rip apart.  To make it worth the attempt to replace something that I
knew I could eventually get to work (the $30 laminator), I'd have to
get the typewriter for free or very close to it. Then there's the
question of how cylindrical IS an old typewriter platen and can it and
the rubber mosepad withstand the 390F heat?  I'd love to know.

Finally, I considered using a rubber pad to place the heated PCB on
and the back of a large metal spoon to press down on the transfer
paper in overlapping circular patterns.  However, that introduces a
potentially random factor related to technique which was a weakness of
the iron method I was trying to avoid.

I'd bet the laundry roller method that you mentioned just might work
as long as there was unform pressure across the rollers with no
variation caused through many years of wringing laundry.  However, I
don't have access to one of those to try it.

I'd welcome further experimentation on this.  It'd be neat to come up
with an oven method that would use _really_ cheap (near $0) hardware
to replace the laminator. 
 
Bill