Homebrew PCBs

Markus Zingg wrote:

> I honestly don't fully understand this question. Again, the chemicals
> are from Bungard. It's the "entry chemicals set" for their "Compacta
> 30" throughplating machine (which is btw. in a completely different
> league than my machine - IMHO ~8000$). This set is reasonably priced
> and because the Compacta 30 operates with 15 and 30 litter tanks as
> oposed to my machine (2 and 5 liters) the chemicals obviousely last
> longer. Everythnig (chemical wise) is included in this set. I also
> ordered replacement Anodes for this same "Compacta 30" model cause
> they are well suited for my machine also. I can....

 From what I imagine, you have all the tanks close to each 
other and you dip the boards in the appropriate order in 
each bath. Obviously you must rinse between baths so that 
the subsequent baths do not become cross contaminated at any 
  appreciable rate. I'm wondering how you do the rinsing. Do 
you have the tanks near a water tap, and simply lift the 
board from the process tank, wait 20 seconds to finish 
dripping, move to the running water tap, rinse, wait another 
20 seconds to drip, then proceed to the next process tank?

I am thinking of building my own processing tanks, but 
wondering if its worth including the rinse tanks after each 
stage. Like you I have managed to weld 3 mm PVC plastic 
sheet (the gray stuff) and I bought a secondhand hot air 
welder for this job. I also built a plastic sheet bender 
using a hot element wire running a line in the middle of the 
piece of particle board. I found it impossible to get 
straight and neat right angle bends using only a hot air 
gun. The best way to construct a series of small narrow 
tanks is to divide a big tank into small ones by welding 
dividers inside. In this way 10 or 15 separate baths could 
easily be built with the least amount of welding and materials.

	A two stage counterflow rinse stage would consist of two 
tanks next to each other, the first tank (the tank you first 
dip) has about 1" higher liquid level than the second tank. 
The wall between the two tanks has a open hole so the first 
tank pours into the second tank when its liquid level goes 
above this hole. The second tank has an effluent hole about 
1" below this level. If you are a bit interested in 
counterflow rinsing then check out;
http://www.justoffbase-tools.co.uk/tools.asp?parent=1I2433P1056M0

Theoretically a 20cm x 20cm PCB will need 100 mL of fresh 
water added each rinse cycle to keep the concentration of 
the second rinse tank 1/1000 of the process tank in a two 
stage counterflow rinse system.
If 3 stage counterflow rinse is used the concentration of 
the final tank is reduced to 0.005% or 50 ppm. Ok its clear 
2 stage rinsing is more than enough for the job.

In your setup, is it possible to empty individual baths ? I 
was thinking of welding small block of plastic to the tank 
bottom and then tap a 3/4" BSP thread into this block for 
screwing in a drum tap. Something like shown 
http://www.justoffbase-tools.co.uk/tools.asp?parent=1I2433P1056M0

My aim is to have then entire PCB processing equipment in 
the one area so I can make a board without having to run 
around over the place. By including rinse tanks I think it 
will make the job easier to control. Would you agree ?