Homebrew PCBs

I agree completely about the two primary points - 

1) Rubber or some other material that gives to compensate for board 
thickness variations

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.  

My brother in-law is a garage sale junkie.  I will describe to him 
what I am looking for and he will find one for a couple of bucks 
somewhere - that's worth a try :-) 

Chris





--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@g...> wrote:
>
> On Thu, 20 Oct 2005 21:58:52 +0200, lcdpublishing  
> <lcdpublishing@y...> wrote:
> 
> > Hmm, this is a good point so it bears checking on.  I currently 
use
> > a clothes iron and press it by hand and use about 5 inches 
square of
> > the sole plate at any one time.  I weigh about 225 pounds these 
days
> > and am pushing down on the iron with a fair amount of force - 
lets
> > say half my weight 112 pounds - which I am sure is more than I am
> > pushing down.
> > 5 x 5 = 25 sqaure inches of surface area
> > 112 / 25 = 4.48 pounds per square inch
> > This has worked very good for me so far (although I suspect I 
have
> > beginners luck).  So, a 12" x 12" board would require
> > 12 x 12 = 144 square inches x 4.48 pounds per square inch = 645
> > pounds of presure on that plate for a large circuit board.  This
> > would be pretty hard to achieve without some form of mechanical
> > advantage (unless I keep putting on weight since I quit smoking!)
> > Chris
> 
> 
> My worry was not so much about the magnitude of pressure in 
general, but  
> how to adjust if from board size to board size.
> With the fuser i can choose to let the wide or the narrow side 
run  
> through, thus i can keep the "length" in the fuser similar with 
all the  
> different boards i make. I have not found variations of a factor 2 
or even  
> 3 a problem. The rubber roller is doing a pretty good job at 
keeping  
> things in contact.
> 
> 
> If a press should work, i think it must have a rubber plate below 
the  
> board, a rigid material both sides will probably cause trouble. 
Also, i  
> would be afraid of temperature patterns, they can be quite extreme 
with  
> heating elements that are concentrated in one area. A pressure 
gauge could  
> be made easily, just take the bathroom scale and put it between 
the press  
> plate and the screw/lever you use to tighten it.
> 
> At this point, i'm just not seeing the advantages.
> But you know - never listen to the nay sayers. Look at the 
arguments why  
> it mightn't work, fix them, and do it.
> 
> ST
>