Complete Circuit Board Lab & POV Business Card

Step 2 Build the Etch Tank

The hardest part of building this thing is just finding the finding the parts. It seems like my entire life is just an endless quest for the parts I need. The most difficult part to find was a pair of bulkhead fittings that were small enough for the tank.

Small fittings are not common locally, as everything is plumbing sized, and online, the lab grade small fittings are only orderable in bulk. Some of these parts are scrounged, most of them I had to order special, and most of them took several rounds of searching and receiving of parts that didn't fit together. US Plastics Corporation is the source of pretty much all of it; they are like the Digi Key of tubes and lab fittings, as far as I'm concerned. Sources listed where available.

Construction
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As far as the tank is concerned, the first step is getting it together. The standard for watertight acrylic bonding is Methylene Chloride, which is very nasty stuff, and cancerous, so do it outside. Just leaving a window open is definitely not sufficient. Accordingly, it is pretty hard to find given the recent regulation, so you may have to order a methylene chloride based glue online, such as IPS Weld-On 4, which is water thin as well. I got a tiny little bottle from a friend who does acrylic fabrication professionally.

To be sure, you could probably get by with just the right kind of epoxy, but ideally the parts should be chemically bonded to each other, instead of a mysterious foreign agent. If you want to play it safe, just use Weld-on 16 and be done with it. It is a more viscous solvent that can be treated as a glue, and will seal up any gaps. I had to use Methylene chloride for lack of the alternative.

When bonding parts with Methylene Chloride, you are after as tight a fit as possible. Laser cut edges need special attention, as they are melted and rounded off. I spent about an hour with a file and sandpaper cleaning up the parts for a good fit.. Even for parts that fit together perfectly from the start, especially the uncut face of the acrylic, it is important to roughen the abutting faces with sandpaper or there is no grab.

Once the parts fit together well, hold the parts  together and run the needle of a syringe or modified squeeze bottle full of the solvent along the crack; capillary action will draw it in. Within about 60 seconds the part will be secure enough to leave alone. It only takes about 30 minutes, for it to set up, sometimes a lot less. I left it overnight just to be sure, but it's actually waterproof after about an hour.

After that, you need to make a lid. I cut a self adhesive gasket for both the lid and the lip of the tank to fill the gap, and to seal it up I mounted a pair of wings to either side of the tank with magnets to pull it down and hold it in place. What happens is the lid tends to line itself up, and because the two sides are reversed in polarity, it is impossible to put the lid on backwards. I still feel clever about that one. The only caveat being that the magnets need to be sealed in heatshrink tubing to resist corrosion.

The bulkhead fittings I wanted only came in straight, not 90 degree, so I needed to cut down the one side and weld on an angled fitting. It works surprisingly well with polypropylene, which has melting point low enough that you can fuse parts with just a hot air gun.

References

1. How to Glue Acrylic

Parts

• 1/4 inch acrylic or polycarbonate sheet
•  EPDM or Viton self adhesive gasket
• 1/4" ID Tygon chemical resistant tubing, or high purity PVC
• 1 air pump
• 1/4" hose barb Polypropylene wye fitting
• 1/4" hose barb Polypropylene barbed bulkhead fitting x 2 (GVC Product Code: 119-116746 )
• 1/4" hose barb elbow
• 1/4" NPT nut (I cut down a steel hex bushing)
• 1/4" hose barb Polypropylene check valve
• 1/4" hose barb  3/8" NPT HDPE (3/8" fits the bubble wand perfectly)
• 3/8" NPT plug (for the end of the bubble wand)
• 1/4" to 1/8" hose barb reducer
• Rubber end plugs for bubble wand
• bubble wand
• 4 x neodymium bar magnets
• plastic handle, with screws
• Plastic epoxy, to fill any gaps
• Plastic Slide bar clip, from report cover (office max # 21936700)

Tools & Supplies

• Methylene Chloride or IPS Weld-on 16
• heatshrink tubing
• Dremel or other rotary tool w/ cut off wheel
• Hot air gun
• Rubber gloves
• Hot glue gun
• Cyanoacrylate Superglue
• Clamps
• Hacksaw
• Powerdrill
• Hobby knife
• Straightedge

Comments

[maxseeley]

The acrylic fabrication technique outlined is incorrect and needs to be modified. You do not tightly clamp pieces together went gluing with Methylene Chloride. The method you outlined will produce an extremely weak bond. When gluing acrylic using methylene chloride the first step is to consider what formulation to use. The three major formulas from weld-on that are used are 3, 4, and 16. For a beginner, 16 is probably the best and can be used like regular glue. Put a little alone the edges to be glue and press the pieces together. Even with this method it would not be recommend to tightly clamp the two pieces together because you might push out to much of the weldon 16 which is a solvent and gets a large part of its bond strength from melting the acrylic it is gluing. The other two choices - 3,4 are both water thin the following method should be used to glue acrylic or any other plastic that is going to serve as a liquid container - especially an acid. This is a good instructatble on how to glue acrylic.

[sponges]

Thanks, that's good advice. I will append my instructions accordingly.

Incidentally, that would explain why I did not get the bond I wanted. I had intended to use Weld-on 16 but wasn't able to get any in time, and had to use some pure methylene chloride.

[maxseeley]

Forgot the link:
http://www.instructables.com/id/How-to-glue-Acrylic/

[n0ukf]

"...swap it out with a switch one with a higher temperature rating. It's pretty simple; the switch closes when the rollers are too hot and opens when it's too cold."

I'm pretty sure you got that backwards. Now, if it were a refrigeration unit, then it would be right.

[sponges]

Your right! Thanks :)