Robert,
You have too big holes, too few holes, and perhaps too much air.
I had the "currents" too in the past.
Now that i use a aquarium bubbler hose there are many many tiny bubbles
that do not create that forceful circulation.
Also, because the hose is over the whole length it lifts the water evenly,
and there are not big circular currents possible.
It s still mixing the etchant well.
For a etchant pump, aquarium centrifugal pumps are available with
no-metal, even cheap ones. But i don't think that is a good idea.
As for a holder, i have devised the following:
You need two plastic plates about 5cmx6cm. mount one at right angles to
your lid, in the center. then mount a little sqare plastic stick (as
spacer) along it to the lid (10mm wide). the second plate is now set
against the first plate, the spacer keeps it apart at the lid and it forms
sort of tongs. Cut a 5cm bicycle hose piece and slip it over the two
pieces to spring-hold them together.
Now drill a hole in the lid, through the 10mm spacer (ideally you do this
first). if you insert a round plastic stick here and press it down it
forces the two plates (tongs) to open. You can spring-load the stick so it
comes up on itself, then the holder is single-hand operation, and no
touching of immersed parts. (The lid also needs a handle of course).
For better grip put a 1cm wide piece of bicycle hose over the end of the
fixed plate (maybe glue). and cut the pivoting plate 2mm shorter so
inserted PCBs are pressed straight against the fixed plate, which is at
right angles.
A variation is possible to the round rod that opens the holder, if you
make a paddel at the end inside the clamp it can be opened by rotating
this stick. make a lever on the top, so that you can easily pull it
parallel with the handle. Both versions seem to work well, but with the
lever you can open several clamps with one hand, e.g. for allowing several
small or one big pcb in your tank at once.
ST
On Mon, 23 May 2005 19:05:45 -0400, Robert Hedan
<
robert.hedan@...> wrote:
> The 1st problem with pumping etchant is the metal parts in the system;
> corrosion will rapidly become an issue.
> I'm fabricating an etching bath myself. I'll post results as soon as my
> finger heals, a little slip while fixing the clothes dryer. I'm
> staying
> away from chemicals until the skin heals even if I wear gloves.
> At 1st I thought that making air bubbles in the etchant was going to be a
> breeze, yeah right. I quickly realized that air pressure, size and
> number
> of holes, and adequate 'return' circulation had to be balanced; the
> stronger
> the air bubbles going up, the more flow is generated upwards, so you need
> more space for the flow to return to the bottom to complete the cycle.
> My
> 1st attempt using water resulted in a nice volcano effect and my wife
> yelling at me for messing up the place.
> I blocked the holes at both ends of the tubing grid and reduced the
> number
> of holes along the middle area. I found a nice balance where I get
> decent
> bubbles, limitted splashing (a cover will still be essential), and a good
> return flow down both ends of the vertical bath. I have a plan for 2
> large
> PVC pipes to return the flow back to the bottom. This will maximize the
> use
> of the chamber for PCBs, as it stands, 2-3 inches at both ends lack
> bubbles.
> I have yet to fabricate the holder to dip the PCBs in the solution,
> that's
> my last TO-DO item. I use a shop compressor, mated a quick release air
> fixture onto the PVC piping, Gardena quick release garden hose fixtures
> mated onto the PVC piping so I can easily remove the tubing grid from the
> chamber for cleaning. I use an ordinary valve to limit the air flow into
> the system, and I also bleed additionnal air leak at the compressor.
> I've
> found that small pumps were just a tad weak, I prefer to use a stronger
> source and limit the output.
> As soon as I've burned some boards I'll post pics of the assembly.
> Robert