I really like the idea of a vacuum reservoir because it can also serve as a
"sucked solder catcher". Using something like an empty propane cylender
would probably take at least a half a lifetime to fill up (and I hope I
don't have that much longer to go ;-).

Norm

"Don Foreman" wrote in message
...
Good ideas from "Wild Bill." I'd add the following -- I'm thinking
about doing this myself, perhaps this winter.

I think I'd want a vacuum reservoir. I don't think it would take
much, maybe an old 14 -oz propane cylinder or two, or perhaps a piece
of 4" ABS pipe with caps. Scrounge or contrive a simple
vacuum-actuated switch: maybe a diaphragm and a microswitch. Find
some cheap surplus solenoid valves. They show up at my surplus store
every now and then for a couple of bucks each. I'd valve the air to
the venturi, but the line from vacuum tank to venturi would also have
to be valved. Then a third valve would pulse vacuum to the sucker
with a finger-operated or foot-operated switch. The "sucker" might
just be a bit of small-diameter stainless or teflon tubing. I think
I'd keep the sucking and heating functions separate: melt the solder
with a temperature-controlled soldering station I already have.

I've found that fluxed copper braid (Solda-Wick) works pretty well
with surfacemount stuff, but sucking out the bulk of the solder first
would speed that up some.

BTW, that HF vacuum venturi is dirt simple (I've taken one apart) ,
but for $9.95 it's hardly worth bothering to make one. They claim a
pretty good vacuum, something like 27 or 28". I don't have a gage
suitable for testing to verify or refute that claim. It is
definitely noisy, but so are inexpensive electric diaphragm pumps
that produce significantly less vacuum. With a good vacuum you'll
have more delta P (maybe 13 PSI) so I think we'll get more volume and
velocity thru a given vacuum nozzle, hence more vigorous
soldersucking.

The problems with the pushbutton soldersuckers like Solda-pult a
the nozzles are kinda bulky, they "kick" when released which sometimes
jerks the nozzle away from the site to be sucked, , and you only get
a pulse of vacuum that doesn't always do the job.

Keep us (or at least me) posted on your progress, please.

On Sun, 20 Jun 2004 15:38:46 -0400, "Wild Bill"
wrote:

For a desoldering iron application, I think you'll end up wanting
something
more effective than a Harbor Freight generator (not that I've tried them,
but I've used numerous different brands of commercial desoldering
stations).

The Air-Vac desoldering iron venturi generator is very effective for two
reasons.. it's designed very well (and provides instantaneous vacuum at
the
tip), and because it's located on the handpiece (being closer to the
tip).
The older irons are often on eBay and sometimes don't even get any bids.
These desoldering tools are the style with the glass collection chamber
above/alongside the heater-tip assy.

Many other systems use an electric pump with a reciprocating diaphram and
rubber-like reed valves. The glass collection chamber is inside the
handpiece (which is more compact), and the handpiece has a long piece of
flexible tubing between the handpiece and pump. This introduces a little
delay in the vacuum, but they work fairly well.
The electric pump is typically a 12V, 1 to 2 amp PM DC motor (about 2" x
3")
that's run intermittently with 24V.
The pump diaphram is about 1-1/4" diameter with about a 1/8" stroke.

Nearly all of the heater-tip assemblies of the more recent models are low
voltage heaters.. typically 24V. For a scratch-built improvised design,
you
wouldn't need closed loop temperature control, but a temperature
adjustment
will be a good idea (triac or variac), so you can turn the temp down for
more delicate, easily damaged circuit board work.
For circuit board work, you'll definitely want the tip to be earth
grounded.
The Pace heaters are short, and aren't as versatile as the longer heaters
are.

The glass vial is a nice sight glass feature, but a metal tubing chamber
works just as well. Silicone rubber seals are usually used at the ends of
the chamber.

Another feature you might want to include would be the versatility to
enable
you to use hot air coming out of the tip for surface mount components or
some other non-contact application (such as heat shrink tubing). You'll
probably want to implement a needle valve similar to a CFH gage, since
the
air flow needs to be low to maintain heat.

Fitting numerous features into a handpiece are a bit complicated, but you
can use a foot switch to energize the solenoid for the air source (that
way,
the iron heat is replenished/saturated when the vacuum is off), or on/off
for an electric pump.

For solder/flux vapor filters you can use a variety of materials, but you
should avoid steel wool if you're doing circuit board repairs.. a single
strand of wool can be hard to find if the circuit doesn't work (I found
that
out many years ago).
I've used roll-type bandage gauze for filters.. it's a convenient size to
roll up into the pellet shape.

WB
...............

"Norm Dresner" wrote in message
...
I'd like to build a desoldering station. Conventionally this is done
with
a
soldering iron and a vacuum source. In the best units the tip of the
iron
is hollow and the vacuum draws through it. But I don't want to
purchase a
vacuum pump for the same reason that I don't want to purchase a
commercial
soldering station: cost. I have a compressor. Since there are COTS
desoldering stations that work from a compressed air supply it's
possible,
using the Venturi effect, I believe. Are there any on-line tutorials
for
creating a vacuum from an air source?

TIA
Norm