SuckWell

Projects
Participants	Ultratux
Skills	Soldering, pneumatics, mechanics
Status	Active
Niche	Mechanics
Purpose	Fun

SuckWell...er...

Two decades ago I purchased a Weller® desoldering contraption that is compatible with the venerable WTCP-S soldering stations. It consists of a heated suction tip leading to a rubber 'bellow' that you're meant to squeeze & hold and release it at the right moment when the solder you want to suck away is liquefied. For various reasons I never had any success using it. Probably partly because the suction it creates is much too small and acts too slowly, especially compared to your standard desoldering tools which are spring-loaded. And in other part possibly because the act of suddenly releasing the bellow is not entirely compatible with keeping the desoldering tip steady and motionless at exactly the right spot. So it ended up in a box in the attic.

Now with the Chinese offering various nice and cheap parts I decided it was worth a shot to electrify it; a small vacuum pump, a solenoid valve, some buffer vessel and some tubing ought to be all that's required. The hacked soldering station I built has plenty of extra power available, both 12V and 24V (100W ring transformer). It just needs a rectifier for the vacuum pump and valve.

Having finally received the pump and valve this weekend I set out to acquire fitting tubing and make a quick 'n dirty prototype setup, as pictured.

Testing it, this vessel (a small soda bottle) builds up sufficient vacuum to have the tip suck air for over 5 seconds so that ought to be largely enough. But maybe the nozzle is simply too small. I think I have different sizes nozzles in that box in the attic, so I ought to try real-life desoldering to get proper test results.

I haven't yet tried it heated up. But I researched the tube I'm using. It's rated up to 60℃ and made of PVC(!) Especially that latter thing made me uneasy... PVC gives off really toxic fumes when too hot. Coupled to that the fact that the tube might, over time, get clogged with solder, I'm now pondering on how to insert a small container in between the end of the solder part and the tube, preferably something that can open easily to evacuate the solder gathered there... But it needs to be small & light enough to not be a hindrance when using it. I'm still thinking about suitable materials and whether I might have anything in the attic... An alternative might be simply to buy a different kind of tube for the first 10cm or so. I'm not up to speed on what's available but I'm sure some type exists that is airtight and safe up to >>100℃. Like steam tube... but that is extremely expensive and thicker than I'd like: [[1]]

A short while later I've decided what to go for; a tiny glass bottle (think perfume/medicine size) with two metal conduits entering from front side. That ascertains hot solder can never get sucked in to the tube (unless it learns to do a mid-flight U-turn) and thermally insulates the PVC tube enough from the hot tip. I used a piece of aluminium 6mm OD pipe that I managed to fold as a U-turn using a pulley wheel as 'bed' to help avoid it kinking or breaking. (You gotta get a little inventive when your pipe bender is only suited for 12mm and 15mm...) Lacking a suitable cork I figured to glue both pipe ends into the bottle using two-component adhesive. It will likely be years, if not decades, before the bottle fills up with solder, so it's a design compromise I dared to make. I have to wait some 24 hours for the glue to cure completely now before I can test whether my design holds up to scrutiny... one aspect is physical strength... the whole assembly is not supposed to be attached to the iron except by the heating element. That way you can still replace this thing with a regular solder tip. But that then means that the glass bottle neck combined with the glue has to withhold all the stresses that the movement and weight of the tube excert on it... that's interesting.

Parts list (so far):

small 12V vacuum pump, aliexpress, $ 8.85
solenoid air valve, aliexpress, $ 4.97
Weller desoldering thing, $ unknown (*)
Various tubing, found in attic and elsewhere
bridge rectifier
momentary switch to mount on soldering iron
desolder section on/off switch 
12V relay (could be needed to drive the solenoid)
wiring
aluminium tube 6mm OD
small old bottle from medicine cabinet or similar
...
possibly an arduino and a pressure sensor to tell the pump when it should engage

(*) Not exactly advocating to purchase it, but Reichelt still sells it [[2]]