Wednesday, July 30, 2014

3D Print a Minecraft Creeper: Wet Sanding and Finishing PLA

The other day I started learning how to sand and finish my PLA prints.  In the process I also learned how important it is to decide how your object is oriented for printing and how to create movement with joints!  In this post I will be focusing on finishing techniques but I will also give some tips for orienting your model correctly for printing.

I decided to print a character from the popular video game Minecraft and started by finding a model that I liked from  I could create this model from scratch but sometimes it is more efficient to modify an existing model, especially for practice.  At first I printed the Creeper without any moving parts, as is, from a model similar to this one:

3D rendering of basic starting model

When I printed this model, I did not change its orientation and printed it on its side as a test.  I knew that I would have to use supports for the face detail if I printed it this way, but the only other way would be to cut it into pieces to be able to print without supports.

Printing the character on its side with supports for face details.  If you look carefully you can see that the bottom of my print is slightly smooshed outwards because my Z-stop needs to be adjusted.

After printing and quickly spray painting this model, I was not happy with it.  The fact that the flattened bottom layer made him look so lopsided and the print layer lines being vertical really bugged me.  It was also annoying that the side of him that was printed against the bed had a radically different texture than the opposite side.  I realized that I would need to learn more about finishing to make an appealing creation.  Below are some more printing tests before I applied any finishes.

On the left you can see a model printed in one piece, but upright instead of on its side like the gold one.  It looked better than the earlier gold model, but the face still lacked consistent detail.  The middle creeper was printed in two separate parts but the head should have been printed in a different orientation.  The third model was a solid model I printed as a test, with 100% infill.  After these tests I decided that the best way to print the Creeper would be to edit the model and disconnect the head from the body so that I could put it on a joint and have a swiveled head!  This would allow me to print both pieces with a better orientation and less support material.  It also makes the print layers align horizontally and without the lopsided texture on one side of the model like the gold Creeper up above.

The best way to print the creeper model would be to print the body upright with just a little support in between his legs to hold up the body, and print the head separately with the face pointed up.  This gives both pieces the support they need while still providing enough detail in the most prominent places.

For this print I am using a Maker Gear M2 at a temperature of 224C, with a .25mm layer resolution and a non-heated bed.  If this was not a practice piece, I would recommend printing at a higher resolution closer to .05mm.  I'm working with PLA right now because when I work with ABS I have to close up my apartment to stop drafts to prevent cracking and it gets way too hot in the summer!

After I printed the model I did a process called wet sanding.  If you've ever tried sanding a PLA print before, then you know that it can splinter the layers, cause the surface to look rough and gets plastic melted into your sandpaper.  I learned recently that if you get a bowl of water and some fine sandpaper you can just keep your model and the sandpaper wet so there isn't so much heat from friction.  If you wet sand like this, your models suddenly transform into a smooth surface ready for priming!  The first time I did this I could hardly contain my excitement.  The material feels more like a toy and less like "cheap plastic".  Don't worry about getting any sort of special sandpaper, it does not need to be labeled as water proof.

Here is one of the creeper models after it was wet sanded and dried.  This is the solid model I printed, not the one with the swiveling head.  I started with a 220 grit sandpaper, and then did a pass with 400 grit before the next step.  The most important thing to consider when doing this initial sanding is just exposing any crevasses or dips that need to be filled, as shown in the photo above, including lines between layers.  In retrospect I maybe should have sanded slightly longer in this step.

I used "RUST-OLEUM Filler Primer - High Build Formulation" from Home Depot.  I've also heard of people preferring Dupli-Color, but they don't carry it at Home Depot.  After doing a basic wet sanding of your model, spray it with a thin but consistent layer of this sandable filler primer.  The primer will puff up just slightly upon spraying it onto your model so you don't need to use a lot.  Also be wary that you may need to clean the nozzle before spraying for the first time because the primer is so thick.  I didn't do this and my first model got sprayed with small rocky bits at first!  If this happens just use a can of air to clean out the nozzle.  After you are done spraying, wait about 10 minutes and you can do another wet sanding pass.  In this pass you will start with 220 grit until you see PLA starting to shine through.  After 220 grit move to 400 grit, and when you are happy the result that use 600 grit as the final finish, all wet sanding.

When you are happy with the smoothness of your model, you can begin to paint it.  I have a bunch of acrylic paint that I used, but I believe that enamel will work as well.  I chose to use matte/satin finish so that I could apply a clear gloss finish at the end.  Apply multiple thin coats or use spray paint as a base layer.  Have multiple brush sizes available for hard to reach spaces.

After a few layers of painting here is the result without the gloss finish.  It looks like I could have sanded a little better on the side, but over all it looks much better than anything I have ever 3D printed.  It looks even better in gloss!


I used a spray painted glossy finish for my last layer.  Obviously if you have a swivel head design, you will need to paint the pieces separately so they don't stick together.  The glossy layer will also help with any minor inconsistencies you missed during the sanding phase.  In the future I would like to try a sort of wet decal to apply exact textures to objects, rather than strictly painting them, but I am definitely super happy with how this turned out!

I hope this helped you or at least opens up possibilities for future projects!  Leave a comment or drop a line if you have any comments, questions, or suggestions!

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