Make a custom plastic box for your project without 3D skills or a 3D printer
If you are a tinkerer like me (and I know you are if you are reading this), you often find yourself in need of a custom plastic box to fit your not-so-common projects. When this happens, a few options come to mind:
1) design a 3D shape and print it on a 3D printer or have it printed and shipped to you;
2) design a set of cut-outs and run them through a CNC or laser-cutter;
3) more of the same…
While these are all viable solutions, they often have a few disadvantages:
1) It is somewhat costly;
2) It can run into delays that are out of your control;
3) It requires 3D design skills and 3D printing knowledge that is not accessible to everyone;
4) It can produce a lot of plastic mistakes that goes to garbage and is not very ecological;
5) It can be restrictive in its implementation.
In my years of tinkering, I have run into the same issues and met plenty of talented people who just did not have the know-how or the budget to handle this. The solution I propose today is simple, economical (a custom project box will cost you pennies), ecological (it is plastic but can use up to 80% of recyclable material), practical and extremely simple (children welcome). The trade-offs are that it takes some time to dry, which can be less of an issue if you plan in advance and also that it is not as precise as a micron-level 3D automated instrument, something that I personally find attractive as it often gives a much more organic feeling to the custom boxes I build. Finally, it has the advantage of controlling the rigidity of your custom box depending of the type of cloth you use, which can make it rubbery (normal cloth) or hard (fiber from hard-mesh) and contributes to waste reduction by reusing material that would otherwise go to the dumpster.
While this method is fairly safe, it has not been used or tested in an industrial fashion and cannot provide assurance that it can manage a continuous protection for a heat-sensitive device. However, I have tested it with many common off-the-shelf microcontroller PCBs and it seems to handle heat well for normal every day use, provided that it can be turned off at night. Experiment thoroughly before using without supervision.
In addition, the type of plastic generated is based on PVA (polyvinyl acetate) which is non-conductive dry but will conduct electricity when still wet. Make sure that you let your builds dry well before mounting anything electric on it.
Step 1: Materials and Tools
Common household tools are the only required parts for this build. In fact, you may find this build to be a very interesting school project as it is so simple to achieve. You will need:
-PVA glue (standard school grade white glue, I got a liter of the stuff for 10$ Canadian);
-some rope (length dependent on the size and depth of your custom box);
-8 to 10 nails at least 2-3 cm longer than the required height of the box (more if the shape is not rectangular);
-hammer (because hitting nails with your fist will hurt);
-some cloth of fiber-type material to absorb the glue;
-a wooden stick to apply the glue;
-a marker to write on the cloth and the box for cutting measurements;
-a wooden board to nail to (can be discarded later or kept for other projects);
-knife of blade to cut the box and create holes;
-screws to attach your PCB;
-scissors to cut the cloth, rope and fix some minor details on the box.
Optionally, to make your project look spiffy:
-sand paper or sanding block to remove rough edges;
-spray paint to give it a nice finish;
-screw spacers to act as feet.
Step 2: Build the Custom Shape of the Enclosure
First off, take out the part that you wish to enclose within the box and draw the approximate peripheral shape on the wooden board to define the contour. Once done, nail one nail in each corner approximately 2 to 3 mm further than the shape itself in order to accommodate the plastic coating and and shrinking while drying. Add nails at each turn (4 in total if this is a rectangular shape). Should you need to turn corners towards the inside, make sure to account for the thickness of the rope as well as it may add considerable space to the form.
Next, nail one end of the rope to the wooden board to keep it in place and start circling the shape with the rope, adding one layer at a time until you reach about 1-2 cm more than the height you need for your project. Nail the end of the rope in the same manner. If you plan to use spacers between the bottom of the box and the PCB, do not forget to account for this as well.
Before going any further, validate the shape by dropping your PCB or other component required to fit in to carefully gauge the fit. As mentioned, you should have at least 2-3 mm of clearance everywhere.
Once done, take out the PCB and start applying the glue on all the walls of rope, both in the exterior and interior. The glue is your run-of-the-mill white school glue which is in fact a liquid form of vinyl polymer that is not toxic, hence liquid plastic. Let dry thoroughly and apply one more coat or as many as it takes to make the walls rigid and behave as one single part – you can test its rigidity by moving slightly the wall to see if the rest moves with it along one of the nails. If sufficiently hard, you can remove the nails attached to the ends of the rope and cut the excess with your scissors.
As it hardens, you may want to add more coats on the exterior. For this, I suggest to simply carefully remove the nails to free the shape and let it rest on one side while applying more glue to the exposed side; repeat on the other side once dried.
Step 3: Add the Top and Bottom
To build the bottom of the case, simply stretch the cloth to recycle on the wooden board to eliminate wrinkles and nail it to the wooden board. Center the shape you built with the rope on your stretched cloth and hold it in place by putting nails on the exterior to keep it from moving. Do not hesitate to test often if your PCB or any other component destined to fit in still has appropriate clearance. Once validated and stabilized, apply glue to the entire bottom only on the inside, making sure that you apply it also in the corners and joints. The glue should be “painted” up to the beginning of the bottom of the wall, to ensure that it attaches to the previous part. Let dry completely and reapply a second time. Once you feel that moving a side of the wall actually pulls the bottom with it, you can release the structure by removing the nails and let it dry upside down to make the glue trapped between the wooden board and bottom fully set.
Once this is done and you feel comfortable with its strength (you can always apply a few more coats but carefully judge the thickness with your content), cut the excess cloth with your scissors and start applying the glue on the underneath of the bottom, turned on its head for the occasion. To harden and make sure that it does not cave, you can do one side at a time, turned on its ledge to keep the bottom aligned with the wall. As the glue hardens, you will likely want to fix a few rough shapes appearing on the sides so make those scissors work.
With the bottom and wall structurally sound, it’s time to attack the top. For the top, proceed as you did earlier with the bottom by stretching a piece of cloth and nailing it to the wooden board. Next, instead of locking in the unfinished box on it, you will instead draw the contour on the cloth and apply glue to the inside only, going over the line of the contour but no more than that. You can choose to apply the glue to the entire bottom as well but it depends on the material you choose to get a different hardening; your mileage may vary.
Since you can only apply one coat for this part until you can make it more resilient by gluing the other side, I suggest being fairly generous for this coat. For this demonstration, I chose to use an old towel that was ruined knowing that it would end up being very bumpy and thus much more organic, something that is harder to achieve with 3D design tools. As it dries, check to see if the strength is sufficient to pull it up. Once it becomes strong enough to move together, gently remove it from the cloth by pulling the nails and carefully cut the excess. This is the riskiest part so be gentle and take your time.
Once cleared and cut, simply add another coat of glue on the top right-side up by only applying to the contour and making sure to “paint” the glue to go over the exterior walls to attach to it. You do not want to apply in the middle at this point as it is likely still not completely dry and will indeed cave in if you wet it with more glue before the sides are strong enough.
Once dried and the structure seems solid, it’s time to cut the box along the line that will separate the top from the bottom. If you own a blade, simply slowly cut between two rope lines and it will easily separate in two halves. I suggest cutting only three of the four sides and cut halfway the fourth, leaving the middle uncut to act as a hinge. If you have some other form of attachment, you can of course separate them completely. After this step, apply more glue inside the top turned on its head and use the wooden stick to keep the box opened and exposed to the air to set the glue. If satisfied with the stiffness, simply put back the box right-side up and apply more glue on top. Let it dry and clean any rough edges to make this look the way you want. You can make it even more comfortable by sanding it to give it a polish finish.
Congratulations, it’s a healthy baby box.
Step 4: Cut Holes, Trim and Cleanup
I cannot stress enough the fact that you need to validate how your PCB fits inside the newly crafted box. Take measurements with your PCB or other component inside, tracing the holes that will be needed to mount it. Should you wish to add spacers between the PCB and the bottom of the box, make sure that you account for this extra space as well.
Once done, go ahead and make the cuts to punch out the holes you need in your box. Remember the old saying: measure twice and cut once. If you feel that some of the borders of your cut still have an old “fiberish” feeling to them, do not be shy to add some glue to the sides. Sometimes, PVA glue does not penetrate fully and you should not expose cloth to heat or electricity. Also, it is a good time to punch any holes for heat dissipation if you worry about components overheating.
Step 5: Embellish and Serve!
I happened to have old pegs/spacers from a previously built PC lying around and some old purple spray paint which I used rarely so I painted the box and mounted the PCB with the spacers and screws. In this case, I used the spacers on the bottom to act as four feet for the box but you can use what you want.
The result is interesting and definitely a conversation piece. I chose for this demo a rectangular form to fit my uncommon original PINE64 board that does not fit standard Raspberry PI enclosures. However, your imagination is the limit, 3D skills optional.