Tired of 3D-printing guns? How about printing something that encourages life?

This birdhouse is the entry/donation from my daughter and me to the annual Birdhouse Display and Benefit Auction, May 24-June 2, 2013, at The Arboretum in Lexington, KY, http://www.ca.uky.edu/arboretum/. Some of you might recall https://www.instructables.com/id/How-to-make-the-bird-house/ from two years ago, a rather large wooden "bird house" that had entrances in the holes of the letters "b" and "d." Well, that was too wordy. This one looks like a road sign with pictographs for bird and house -- with the entrance in the house pictograph. We call it "A Sign." And it is a sign in another way too -- it is a sign that 3D printing has come of age, because this birdhouse is 3D-printed. Yes, the whole thing. Only a few folks have made 100% 3D-printed birdhouses, and this is probably the largest built thus far.

Now, you don't have to 3D print yours -- it isn't all that hard to make a good approximation to this with wood and paint, or simply to print the front decoration and glue that to a wooden birdhouse, and all those options are discussed -- but this is designed to take advantage of some of the things a cheap, environmentally-friendly PLA-extruding, 3D printer can do. It's huge as 3D prints go, and is a bit of a torture test for your printer's calibration, but the one shown here was printed in less than a day using no more than $15 worth of material. It was painted, rather than printed using the appropriate PLA colors, because we felt the paint would help protect and extend the life of the PLA material.

My daughter had the idea of making this year's birdhouse a sign, I created the design, it was printed in my lab at the University of Kentucky (http://aggregate.org), and my daughter and I finished it together. The basic sign shape and layout follow http://www.roadtrafficsigns.com/. The caricatured bird image was inspired by the wearable pendant design at http://www.thingiverse.com/thing:47032, and the house image is a lot like many found in WWW searches. It didn't take long for me to create the 2D decoration image using gimp. Inkscape was then used to vectorize the image. The 2D design was then extruded as a component of my 3D model of the sign-shaped birdhouse using OpenSCAD.

All the design files, including a customizer version of the OpenSCAD file, were originally posted at: http://www.thingiverse.com/thing:92431 ; in addition, as of July 14, 2013, there is an improved 3rd version posted at: http://www.thingiverse.com/thing:117929 .

Step 1: How Much 3D Printing Are You Willing to Do?

Before we jump into building "A Sign," it's worth noting there are several different ways to build variations on this birdhouse design. Which you should build depends mostly on the toys to which you have access:

Big-enough, well-calibrated, 3D printer: Go ahead -- you can print the whole thing. We made ours on a MakerGear M2, which is a very solid machine with a 8"x10"x8" build area, but about half the current crop of 3D printers have sufficient print volumes. The design can be scaled-down to fit a build plate as small as about 5"x5".
3D printer with issues: Print just the front decoration (see step 3) and glue it onto a conventionally-built birdhouse. This greatly reduces the 3D print volume and makes the print short enough so that printers with layer misalignment issues should still be ok.
No 3D printer: Conventionally build the birdhouse out of wood (see step 4). You can decorate it using cut vinyl, a stencil, or freehand painting. A programmable paper cutter makes cutting the vinyl or stencil easy.

Yes, you also could build it using laser cutter, a CNC mill, ceramic, or even Legos for that matter. I'll only detail the few construction methods described above. ;-)

The design files intended for 3D printing also can be used as dimensioned drawings to guide non-3D-printed construction of the birdhouse. You'll probably want to simplify things a bit; for example, changing the fancy vent slots into some drilled holes should be fine for a hand-built wooden version of the birdhouse, and the bottom clean-out can be replaced by making the back plate removable via screws.

Step 2: Fully 3D Printed Version

There are three separate parts to be printed. All three part designs are available from http://www.thingiverse.com/thing:92431. There is also an improved 3rd version posted at http://www.thingiverse.com/thing:117929 , which can be tweaked using the customizer, has a "ladder" to help bird egress, an improved plate design, and optionally the QR code for this Instructable on the back. The file names differ in the different postings, and the back/body and plate are not compatible between the 2nd and 3rd versions, but the parts serve the same purpose:

The back and body: back.stl. This uses slightly less of the build plate than the front part, but it is also fairly tall around the perimeter. Not only is bed leveling critical, but the height means that any drift over layers will accumulate. Our M2 is virtually perfect in layer-to-layer alignment, so we were able to build this part in about 6 hours with 0.3mm extrusion, just a single vertical shell, 5% fill (i.e., 95% of the volume inside a "solid" part is air), and 3 horizontal shells.
The bottom clean-out and mount plate: plate.stl. Really a relatively small part, but printed in the tall orientation to avoid having overhangs. You might want to build this with a brim around the bottom to ensure it sticks to the bed while printing, although we didn't have a problem with it. We also used a higher fill percentage just in case the house gets mounted by screwing directly into this part; of course, the right way to mount the house would be to build mounting structures directly into this part. This part simply slides into the bottom of the birdhouse, so it can be easily replaced if damaged.
The front: front.stl. This will pretty much fill your build plate, but is quite short and has no difficult-to-print features. Bed leveling is critical. The only part that sticks up is the inch-tall post for the bird, which our printer did not make very cylindrical. The perch got sliced as a solid, and that made it a bit squishy during the build. Our M2 printed the front in about 2.5 hours with 0.3mm extrusion, 3 shells, and 10% fill.

We used PLA (polylactic acid -- a polyester made from renewable materials) for these parts. PLA has many really great properties, and should be quite suitable for this application. However, PLA does start to soften at a fairly low temperature, and prolonged exposure to temperatures above 140º F, such as sitting inside a car in direct sunlight on a hot Summer's day, can cause parts to sag. The vents in the back and body, which are angled to keep rain from getting in, should help keep internal temperatures moderate -- the same goes for the paint we'll cover the outside with. The single-shell walls and 5% fill of the body also provide a good thermal break so that even if some portion does get hot enough to sag, the support structure behind it shouldn't -- at least that's the theory. Other plastics that have higher temperature tolerance could have been used, especially ABS or Nylon, but those materials are nowhere near as environmentally friendly as PLA... so for us the choice seemed very clear.

It's worth noting that our MakerGear M2 is capable of much finer print quality than these parts show. These are all 0.3mm extrusions and we've gotten accurate prints with 0.05mm. However, this is a birdhouse. Printing quickly was a priority and thicker extrusion also reduces the likelihood of filament fusion boundaries separating when exposed to harsh weather, etc. We also printed rather hot to strengthen fusion bonds, which, combined with the low fill factors, magnified the imperfections visible on horizontally printed surfaces by essentially creating unsupported, slightly saggy, spans between internal supports. Anyway, all that really does is give the birdhouse parts an interesting texture -- not at all inappropriate for a piece of artwork.

If you're sure you want to build the birdhouse 100% 3D printed, you can print these parts and jump to step 5....

Step 3: Just 3D-Printed Decoration

Rather than printing the entire birdhouse, in many ways it is much more practical to just print the front decoration and stick it on a traditionally-built birdhouse. To begin with, the decoration is relatively fast to print and uses only a tiny fraction of the filament needed for printing the complete birdhouse -- and you can easily print it using black filament so it doesn't need painting. With a little work, you can even segment the decoration into pieces printable on 3D printers with the smallest build areas.

The design is posted as decor.stl from http://www.thingiverse.com/thing:92431.

This should be a very easy print in either PLA or ABS, probably best with between 5-25% fill. If that's what you'll do, then print it, build the conventional birdhouse, and skip to step 5....

Step 4: The Wooden Box

You don't need to be fancy about woodworking. The body shape used in the 3D model is cooler, but you can literally just make a square box that gets mounted at a 45º angle. I don't really need to tell you how to do that, do I?

The decoration on the front should be as shown here. The pattern is full size at about 300 DPI, but you obviously can scale it to whatever size you need. There are basically three ways to get the pattern on the front of your otherwise-complete box:

Cut black vinyl. Vectorize the design and cut adhesive-backed vinyl according to this pattern -- this is easy if you have one of those programmable paper cutters (e.g., I have a sub-$200 Silhouette). Glue the cut design to the flat front of your otherwise complete and painted wooden-box birdhouse. If you have holes pre-drilled for a dowel perch and entry, use a sharp knife to slice the vinyl to open the holes -- that ensures alignment of vinyl and wood holes.
Make a stencil. Make simple cuts in the outside line and the bird's legs so that all portions of the stencil will be connected, then cut an appropriate stencil material using a programmable cutter or by hand. Use the stencil to paint the bulk of the design, connecting the straight parts of the outside line and bird's legs afterward.
Freehand paint it. This is really not as hard as it sounds, especially if you use some of that blue masking tape to help you keep the straight edges straight.

Any of the above should be pretty straightforward, but I didn't build this birdhouse this way because I have better toys.... ;-)

Step 5: Assembly -- Gluing

I'm not going to describe all the ways you can put a wooden box together... but bonding 3D-printed PLA parts is a little tricky.

Thermal welding, or welding induced by friction from (ultra)sonic vibration, works very well when bonding PLA to PLA. Unfortunately, it is difficult to get an even thermal bond over an area as large as the seam between the front and back parts of this birdhouse. A soldering iron can be used to spot weld parts together and then to melt a PLA rod (unextruded filament) to create something looking a lot like a metal weld. In fact, using a glue gun to run a bead of hot glue along seams appears to work very well, although hot glue is stable over a much smaller temperature range than PLA.

In general, glues do not bond well to glassy smooth PLA. Despite being made from plant matter as innocuous as corn, PLA plastic is remarkably immune to most chemicals. That's a problem for gluing because most plastic glues work by partially reacting with the plastic to "melt" it for welding. Cyanoacrylate (super glue) seems to work, as do some types of cement intended for welding PVC pipes together. If the PLA filaments offer a rough enough surface texture, various glues might work -- light sanding of the bonding surface can help, as does clamping while the glue is setting.

In summary, the two prototype 3D-printed birdhouses we've made have both been assembled using PVC pipe glue, and that seems to have worked very well, but test whatever glue you'll use on some scrap material first....

Step 6: Painting

We could have printed the birdhouse using black and yellow PLA, but we figured painting would extend the life of the PLA. Both our prototypes have been made of "natural," clear, PLA.

Just as it is difficult to find solvent glues that will bond with PLA, it can be difficult to find paints that will stick to a glassy-smooth PLA surface. Fortunately, the fine-grain surface texture left by 3D printing provides lots of binding surface, and with a little sanding, most paints adhere fairly well. However, fairly well isn't really good enough for a birdhouse.

Thus, after light sanding, we used Krylon Fusion for Plastic spray paint in the "Sunbeam" color to paint the entire outside. This paint is "formulated to provide a super bond to plastic without flaking off" and spray on a test piece of PLA certainly seemed to validate that claim. This paint is also fine on wood, if you happened to build the birdhouse as only partly printed. Feel free to use a different paint, but be sure you test it on PLA before painting your birdhouse. This paint actually covers well in one coat, although the inside of the birdhouse has a bit of a yellow glow in bright sunlight, indicating it isn't entirely opaque.

After one coat, a little plastic wood filler was used to fill the few now-visible gaps between filaments. You can get the wood filler to just fill the gaps in the PLA by using a damp paper towel to wipe-away the excess. After drying overnight and a light sanding, a second full coat of the yellow paint was applied.

After that dried, we began hand-painting the top of the raised decoration with a gloss black paint. That paint did not cover as well as the yellow spray paint, but 2-4 coats gave a solid glossy black finish.

If time had permitted, I probably would have put 3 coats of a clear polyurethane over everything to give a consistent gloss with a uniformly hard "one piece" finish. The clear polyurethane is great stuff, but the durable water resistance only comes after a week or more of drying, and we just didn't have that long before the Arboretum deadline. I have no doubt the finish will be quite durable without the clear coats, but the yellow isn't as glossy as the black.

Step 7: Mounting

There are thousands of ways to mount a birdhouse. However, we want this one to look like a road sign.

For the Arboretum's exhibition, we don't have much choice; they use a 4"x4" metal plate on top of a black, thin, square rod. That can work. Rather than screwing into the bottom of the birdhouse, we're providing heavy-duty two-sided tape to fix it to the mounting plate for the short duration of the exhibit. Screwing into the bottom would work, but would leave holes afterward that might detract from the value for the benefit auction at the end of the exhibition.

For normal use, a nearly perfect scaled-down match to a road sign post is a "green metal U-post" -- we don't need the heavier T-shaped version. These painted metal posts are intended to secure rolled fencing material, but they're actually quite versatile and generally cost between $2 and $6 depending on height. Be warned that there are a few variants with somewhat different cross-section shapes... the one shown here is from Lowe's.

If you built this birdhouse out of wood, you screw through one of the holes in the post into the birdhouse. Mounting the 3D-printed birdhouse on this type of post offers more options. In particular, you can 3D print a custom part to mount on this post. The part we made is fitted to slip over the top of the post we got from Lowe's; it can be printed separately and permanently glued to the bottom of the birdhouse. In case you're wondering, we made the part fit by photographing the top of the post and then processing that image into a 2D cross section and then the 3D part model.

The design of the part is mount.stl from http://www.thingiverse.com/thing:92431, although you also can use the customizer version there to design a mount with a different depth for the slot that takes the top of the U-post. The default depth is about 2 inches. We have discovered that this mount design is very specific to the particular post we used; to keep people from being disappointed when it doesn't fit their post, the 3rd version, http://www.thingiverse.com/thing:117929 , no longer includes the mount.

Step 8: A QR Sign for the Sign on a Sign

The sign on "A Sign" in the Arboretum just says "A Sign" -- it doesn't say anything about being 3D printed. So, I (with permission) stuck a 3D-printed QR code pointing at this Instructable on the sign about A Sign.

The QR code doesn't print cleanly at really tiny sizes, but this good-sized print took well under 30 minutes. In fact, it took longer to slice the asignqr.stl file than to print it. It was printed in clear PLA, which I left unpainted to emphasize the fact that the QR sign, added to the sign about A Sign, is 3D-printed. The top surface of the QR code was blackened using a permanent marker.

The 3rd version ( http://www.thingiverse.com/thing:117929 ) no longer has a separate QR code part, instead optionally embossing the QR code into the back of the birdhouse. Normal shadows should make it work on the back; alternatively, the embossed area could be painted black.

Signing off for now.... ;-)