--- In
Homebrew_PCBs@yahoogroups.com, "lcdpublishing"
<lcdpublishing@y...> wrote:
>
> I agree completely about the two primary points -
>
> 1) Rubber or some other material that gives to compensate for board
> thickness variations
A Tshirt press has exactly this. They use a silicone rubber foam. And
it is possible to buy sheets of it if you are making your own press.
> 2) un-even heat from the element - this would be the biggest problem
> to correct I believe. The only thing that comes to mind is to have
> a thick metal plate on the heating element side of the press. Then,
> to use it, turn it on and let it get good and hot prior to use.
> Even then, I still think there is going to be some problems with
> some areas being hotter than others.
Growing up, Sunday morning breakfast was usually cooked on an electric
griddle with a simple 3/4 circle of heating element on the bottom. You
could clearly see on the bottom of pancakes where it was hotter.
However, my commercial Tshirt press, to my great surprise, had
essentially the same pattern for the element. Yet it holds very good
temp across the whole thing.
The differences:
1. Bottom of the griddle is open to the air, the top of the Tshirt
press platen is well insulated with fiberglass under a thin metal top.
2. A water filled pancake has a fairly high heat capacity.
3. The griddle is very thin, whereas the Tshirt press platen is very
thick.
BTW, common practice in the past was to paint/anodize them black on
the theory of increased heat transfer, when in fact that only helps it
-radiate- heat. Now many heat presses are anodized natural aluminum,
or painted white.
Keep in mind this prevents a pyrometer from getting an accurate temp
reading. However, it makes it -much- more comfortable to work in front
of it! I picked up some white porcelain 1200F engine paint to repaint
my Tshirt press.
Steve Greenfield