Making an Advent Calendar Using Small Houses

Every year, for Christmas, we try to create a warm ambiance in the house. It is generally the time to try new cake recipes and to find new ways to decorate the house. This year, my wife and I decided to make a new Advent Calendar. While surfing on Pinterest, we were inspired by some small DIY houses and we thought about combining 24 small houses on our coffee table in which we would find the family daily gifts. It is supposed to be candies for my wife, chocolates for my daughters, and electronics components for me.

In this Instructable, I will share the process of creating the calendar from the idea to the realization.

I made everything using my 3d printer, a Prusa i3 mk3, but any 3d printer will do the job.

A lot of materials were required for the post-processing of the 3d printed pieces:

• some fillers, as I didn't have any 2in1 filler primer spray, I used a polyester filler paste
• a set of filler knives, I used ice cream sticks and a very small plastic spatula to apply the filler
• a lot of sanding papers, sanding sticks, and sanding sponges
• a bit of epoxy resin or some superglue
• a few brushes of different size
• some acrylic paints (white and gold)
• a transparent primer spray
• two colours of spray paint
• a set of protections gear: a pair of glasses, some gloves, and a respirator mask

I only used Galaxy Black PLA from Prusa Research for all models.

I also used some electronics components to light the houses:

• a 12V power supply transformer (2A is enough for our use case)
• 12V light bulbs
• a few meters of wires

We had a rough idea of how the houses were supposed to be. We wanted two different models for the ordinary days and a bigger model for the 24th. A house should have a facade, a base, and a little bit of place to put objects in it because, you know, it's supposed to be an Advent Calendar.

I used Tinkercad to model the houses. It was my first time assembling a model composed of multiple 3d printed parts so my first try was naturally a failure. I managed to print a roof, a base, and a facade but assembling everything together proved to be a challenge. Furthermore, printing the roof as it was was rather risky considering the small surface resting on the printing bed. Thus I decided to add some guides to help the assembly. The guides also helped reinforce the roof.

You can find my first attempt here: https://www.tinkercad.com/things/dyDCwBIKtDU-advent-calendar-2018-house-1 Just don't use it for your houses!

You can find all the models on Tinkercad:

• medium house: https://www.tinkercad.com/things/dQXSZ2lIcOY-adve...
• small house: https://www.tinkercad.com/things/j5zEGQoORGx-adve...
• big house: https://www.tinkercad.com/things/aW20UFfQLac-advent-calendar-2018-house-3-v2

For decoration purpose I also printed some snowflakes using: https://www.tinkercad.com/things/3s42krccw6k-snowflake. It is basically a SVG image imported into Tinkercad. It will automatically create a 3d model that you can resize at will. I picked a free snowflake that I found with Google Image and converted it in SVG using an online tool like this one: https://image.online-convert.com/convert-to-svg

To print them using PLA, you don't need support or even brim, just ensure the infill is at least 20% as we will sand the surfaces later. I used Slic3r to create my gcode. Once the models are tested, it is recommended to batch the prints as we will need to print 24 houses for the Advent Calendar.

In term of cost, the big house costed about $ 1.86 of filament and the smaller one about $ 1.28 each for a total of roughly $ 32. You will probably need two PLA spools for all the houses.

After assembling the houses, I found some gaps that needed to be filled. Also a raw model, just out of the 3d printer, due to how FDM printers work, has a very rugged appearance. Applying paint at this step will produce very poor results.

Right now, what we need to do is to glue the facade, the base, and the roof together for each houses. A safe bet is to use superglue for the job. In my case, I used an old epoxy syringe. Apply some glue to the guide and put everything in place. You can use rubber bands to ensure the pieces are tightly fit together. I use my hands as clamps. I also applied some glue at the back to close some gaps. Once everything is glued, begin the hellish cycle of sanding.

First, we need to sand the houses to remove glue excess, artifacts, and to smooth everything up. You can stop when the model become white-ish. I am using PLA so I need to pay extra attention to the sanding process. If I am impatient and apply to much force, I can very likely melt the plastic. Either be patient or use some water during the sanding. I started with a grit of 120.

Once the houses are smooth-ish, it is time to apply some fillers. This step is crucial if one want to have a very good finish. I only had filler paste so I went with it. If you can find a 2in1 filler and primer, then by all means, use this. The filler paste is very useful when the gaps we want to fill are large. As you can see on the pictures, it is my first time applying filler. The more filler you apply the more work you have afterwards. After applying the filler, I waited for 30 minutes (following the maker's instructions) before sanding the house. I started with a grit of 180 and went done to a grid of 400. I used some sanding sticks for the windows and the chimneys, they are extremely handy.

The result is a very smooth piece of plastic without any gaps. You can add another layer of filler and do another sanding pass to further improve the results.

I used sanding sponges to prepare the snowflakes. I don't really care about their rugged appearance as they are supposed to be "imperfect".

Here is the fun part, painting!

To paint the model, I reused an old package and a piece of wood that acts as a stand. Don't forget to wear gloves and a respirator for this part.

I painted the houses with acrylic sprays and the snowflakes with brushes. I started with some layers of primer to ensure the paint will stick to the plastic then I sprayed many layers of acrylic paint following the instructions. The darker houses is actually dark blue or prussian blue and it reveals lot of flaws in the models especially around the junctions between the facade, the base, and the roof.

I should have applied another layer of filler for the bigger one but I am very happy with the result. I tried to paint on a raw 3d print before and the result was just disgusting even after printing at very low resolution (0.05mm).

I wanted to paint the houses' numbers with a gold paint using some stencils and I am quite frustrated when I see the result. The cheap stencils I found on Amazon (the only one I could find actually) produce some bleedings. The ideal would be to create our own stencils that stick to the model... I definitely need to invest into a home cutter.

After many layer of white paint on the snowflakes, the result is very good. The filament layers add a snowy touch to the piece.

To light up the houses I reused very old 12V light bulbs – I have those since I'm twelve... – and a 12V power supply. I also used a tracing paper sheet behind the windows to act as a diffuser. Every light bulbs are directly connected to the power supply in parallel with the help of Wago connectors.

It will be messy to have all the houses connected that way. You can either organize the houses in clusters or use a frame that will support all the houses and ensure everything is connected together. I will probably use the frame approach as I want to add some circuitry to only light up specific houses. You can even choose not to add lights which is perfectly fine.

If you want to use candles, you will need to enlarge the base to ensure the flame won't go near the roof. Otherwise, the PLA will quickly melt. If you decide to go that road, at least use PETG filament that can handle more heat.

It is a hell of a work to post-process that many 3d printed parts!

I can think of some ways to ease this work for the remaining 21 houses:

• redesign the facade to hide the junction between all the pieces
• use a filler spray, sadly I cannot find any 2in1 filler primer in France
• use smaller filling knives and learn how to apply filler...
• choose forgiving paints as the darker one tend to show many defects
• create my own stencils with a home cutter

There are also some things that I want to improve on the other houses:

• add cotton or felt pads into the hole
• add some sort of a guide for the light bulbs
• only light up the houses of the past days

All in all, it was an amazing experience. I learned a lot about designing for 3d printing, about post-processing, and painting. Hopefully by the time I build the last house I will be able to properly apply fillers...