3d Printed Lego Guy / Finishing PLA




Introduction: 3d Printed Lego Guy / Finishing PLA

I have always loved Legos since I was a kid. I use them in my classroom and I love the NXT robotics products that they produce. I also love 3d modeling and 3d printing. I have always wanted to challenge myself to make a large scale Lego version of myself.

This Instructable will highlight the components that I created using AutoCAD, but will mainly discuss the challengs I faced of smoothing PLA 3d printing material.

I will upload the .stl files for the figure shortly. I am working on modifying the arms at the moment.

Step 1:

Below I have included the .stl files that I used to make the figure.

Step 2: Getting Started

I honestly started off by examining a Lego figure. I pulled out a ruler and took accurate measurements of the various parts and attempted to recreate them in AutoCAD the best I could.

I used the original dimensions because it allows me to create a scale object that has the properties necessary to function like the real thing.

Having created a 3d model of all the parts, this would allow me to create whatever sized man that I wanted. I increased the scale of the original parts by 300%, but could have gone as large as 600%.

Step 3: Finishing PLA

Finishing the PLA is probably the make or break part of this project. I really didn't want to create a figure that had the lines and seems that are created when 3d printing any object whether its PLA or ABS.

I scoured the internet for possible solutions and honestly there aren't many when printing with PLA. Acetone doesn't work, it just melts the PLA and not in a pretty way. I am no willing to get to crazy with some of the more toxic chemicals that I have read other 3d printers have been using since I use my printer with my students in the classroom.

Honestly, most of the research stated to either get a rock tumbler and use some polishing compound in it, or sand the parts by hand using high grit sandpaper.

Step 1 - Sanding with High Grit Sandpaper

I started off by using high grit 300 - 450 grit sand paper. You have to be careful when sanding PLA because it will melt very easily when exposed to heat. That also includes the heat created by friction. You cant use a sander or anything that will provide too much friction. You also have to make sure that you are using a much finer grit sand paper unless when printing you drastically increase your shell thickness.

I sanded all of the parts with 300- 450 sand paper until everything was roughly sanded the finish I wanted. I then upgraded to 600 grit sandpaper and sanded all of the parts again.

Step 2 - Filler / Primer

I next went to Home Depot and purchased a can of Automotive Filler / Primer made by Rust-oleum. This helps to better prepare the surface for spray paint, but more importantly it helps to fill any remaining gaps or textures left by the 3d printing process. Allow this to dry for at least 24 hours for best effect.

Step 3 - Sanding with Steel Wool

When the filler / primer has dried, I completed the sanding process by using Steel Wool to essentially polish the surface of all the parts to maximize the smoothness of the parts.

Step 4 - Spray Painting

I used a high gloss yellow spray paint for the hands and head, while selecting the colors I wanted for the arms, torso, and legs. I happened to use Rust-oleum paint/primer Oregano and Fossil colors for my figure.

Step 5 - Printing the Face and Shirt Details

I searched Google to find high resolution Lego faces and there are tons of them out there for you to use and modify. I modified a couple using Adobe Photoshop and combined them to create the likeness I was going for. I ultimately ended up printing them on a white address label on a yellow background that matched my yellow spray paint for the head.

I could have ordered an transparent adhesive sheet that I have seen on amazon and other websites online that ar used for developing your own stickers.

Step 4: Conclusion

This was a fun project that I used to further practice my 3d modeling techniques along with exploring ways to finish my 3d modeling projects using PLA.

Again, I have not posted the .stl files yet, but will do so in the near future.

I am also currently re-tooling the arm models having found a more efficient way of modeling them.

Please, feel free to critique what I have done. I am always looking to explore new options and ideas!



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    19 Discussions

    you could consider using heat to smooth the PLA , if done right you would end up with a smooth glossy finish similar to the finish of the PLA on the spool , but that would require that you melt only the outer/surface PLA.

    3 replies

    I read about that online too. I have heard that some people have baked things in an oven or used a heat gun. I have a heat gun at work and will have to try that.

    In theory it sounds good, but I've tried this and it just gets soft and starts to deform. What is the technique? As has been mentioned already, you may need thicker shells to avoid deforming. But I'd be interested in the proper way to heat-smooth the pla surface.

    I think that what you need to do is heat the surface of the model until the PLA melts (so that it can flow freely and create a smooth finish ) but you want to do that without melting the inside of the model. Because PLA conducts heat to a certain extent I am assuming you would want to heat up the PLA as fast as possible, and cool it down as quickly afterwards (not sure how a sudden change in temperature would impact the plastic ?), but in effect it comes down to keeping the temperature of the surface of the model above melting point for as short as possible. Perhaps a computer controlled heat gun/Laser would work ( I think that would require a 5+ axis positioning machine ) but it sounds like to much effort for such a simple job. I think that maybe a hot air soldering iron could work (because of the reduced area that is heated compared to a heat gun the structure might stay in place ?) anyone who could give that a shot ?(with a temperature of 100-200 degrees Celsius ?). And also If the model is printed solid it would be able to withstand more heat before it deforms. Maybe cooling down the model before heating it would also help and also having an ice bath ready to dump the model in after it has been heated could help ?

    Ive also been looking into finishing pla. Someone on here did some sandblasting that came out well. Ill be trying something like this soon, but i only have plastic primer, should i get filler primer instead?

    2 replies

    I do feel using the primer/filler adds more material to allow for sanding to create smoother surfaces compared to regular primer which just comes off.

    Honestly I am not sure how much of a difference it made. I do a lot of wood working, especially with a lathe and you get great results with gradually increasing sanding grti (rougher - smoother). When I really used the steel wool us when I felt the finish I wanted. Another thing I might do in the future is when printing, increasing shell thickness so I have more pla to sand before hitting substructure.

    I think that sales Lego will sharply decline)

    Lol, great question! I took the screen shot on my computer at the school I work for. I use Google Chrome at home but sadly I am reduced to Internet Explorer at my work place.

    actually yes, the pencil fits but is loose. might hold mechanical better

    I thought about it. Doubling the current size would take like 11 hours to print just the torso, no arms

    Cool Ible ..