Introduction: PLA 3D Prints Smoothing Research Project

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About: Master student in Computer Science & Information Engineering, one of the developer of ArOZ Online Project. I love making something no one has thought of. If you like making things that seems not possible, send…

Recently, I am working on a project that requires some small 3D printed parts for prototyping. However, with PLA, I cannot put it into acetone for surface smoothing and the chemical solution that can dissolve PLA is really toxic that I don't want to use it. So I have done a simple research to find out what is the best way to smooth PLA with household chemical in which you can easily find at home or supermarket nearby. The testing has been done for more than two months and here are the results of ALL TESTS.

As the rest of the instructable will be quite academic and with many "seems like professional" words, you can skip to the ending of the instructable if you are only interested in the best methods of smoothing PLA with ASNOO methods. :)

Step 1: First Test With Glues on PLA Prints

Samples for testing

1. 407 Silicon based Heat Resistant Silicone Adhesive Sealant (407 sealant)

2. Modified Acrylic Adhesive / Epoxy (MAA)

3. Ethylene-vinyl acetate (EVA)

Application Methods for testing

1. None (Direct coloring onto PLA plastic)

2. Single layer 407 sealant

3. Single Layer MAA

4. Double Layer of MAA

5. One layer of MAA, One layer of EVA

Results as shown in the image above.

Step 2: Results of Glue on 3D Printed Parts

The sequence of the image above shows the following results:

None
With direct application of paint onto raw PLA 3D prints, layer lines are clearly shown on the surface of the paint with some of the place are unpainted due to its position.

Single Layer 407 Sealant
407 Sealant originally was used to seal electronic circuits. Due to there is no need for good surface, 407 contains small chunks of non-dissolvable silicon based solid residue. 407 can hide most of the layer line but the residue created an non smooth surface for painting. Lead to non-smooth finished surface.

Single Layer of MAA
Single layer of MAA can hide some of the layer lines. However, due to MAA’s properties, after mixing the coagulant with the glue, its viscosity started to increase. Leads to shiny but non-smooth surface.

Double Layer MAA
Double Layer of MAA configuration can solve part of the problem occurred in the single layer MAA. The 1st layer MAA has the viscosity same as the test in the Single Layer MAA, with the 2nd layer, the amount coagulant was reduced to reduce the mixture viscosity. As a result, it created a smooth and shiny surface with no layer lines was shown in the center of the dual layer MAA application sample. With the cheap price of MAA, this method is suitable for color application and surface smoothing for 3D prints with large surface area.

Single Layer MAA and Single Layer of EVA
This method can hide most of the layer lines with an extremely thin layer of glue. The only disadvantage of this method is the price of EVA glue are relatively expensive. (1.6HKD per gram of EVA compare to 0.088 HKD per gram of 407). Suitable for small surface application.

Conclusion
This research report suggested that the methods of smoothing PLA 3D prints and applying color are listed below. Methods Conditions Dual Layer MAA Application

Large Surface Area / Thickness change < 1mm / Well Ventilated Environment

Single Layer MAA with Single Layer of EVA on top

Small Surface Area / Thickness change < 0.3mm

Step 3: Advanced Smoothing Experiment With PLA and Nail Paint

This experiment provide further research over 3D printed PLA parts and its smoothing effect with oil based nail paint.

From left to right:

- Dual Layer Black nail Paint (DLBP)

- Black oil based paint (PAINT Marker) with single layer transparent nail paint (SOTO, Single-layer oil-based paint with transparent nail paint overlay)

- Single layer oil base black paint (PAINT Marker) (Control)

Step 4: Results of Nail Paints on PLA Prints

The sequence of the image above shows the following results:

DLBP
Dual layer of black nail paint cannot cover the layer line of PLA prints as its viscosity is not high enough.

SOTO
SOTO created a smooth surface better than all the results before. However, as the nail paint layer is transparent and the layer lines cannot be covered by the PAINT Marker, the layer lines can still be seen on top.

Controls
Here is a reference image for the control group.

Conclusion
Nail paint cannot be the main factor to cover layer lines on PLA prints. However, Transparent Nail Paint may provide an alternative solution to the more expensive “Single Layer MAA with Single Layer of EVA on top” method.

Step 5: Printer Setting and Sanding Based Smoothing Experiment

This experiment provide references to manual sanding methods

(The traditional and only way of smoothing PLA prints excluding primer application method).

This method used a 1cm ^3 cube printed with 0.1mm layer height (Minimum layer height can be achieved by Reprap Delta 3D printer) to perform the advanced sanding experiment. The smoothing compare 4 sides of the cube with the following treatments:

1. Direct color application (DCA)

2. Basic Smoothing Process (BSP)

3. Advanced Smoothing Process (ASP)

4. Advanced Smoothing Process with Nail Paint chemical treatment and oil based paint overlay (ASNOO)

Step 6: Results of Sanding Based Smoothing Experiment

Images are wrapped due to the focus lens adjustment and magnification lens light diffraction.

The sequence of the image above shows the following results:

DCA (Control)
The oil based paint directly applied on the 0.1mm layer height 1cm ^ 3 cube.

BSP
This side of the cube only performed simple sanding process with sand paper.

ASP
Advanced Sanding process has been performed on this side of the cube. Included electric sanding with sanding tools and basic polishing.

ASNOO
Advanced sanding process has been performed on this side of the cube. Followed by 1 layer of transparent nail paint process mentioned in the previous experiment and UV light treatment for 15 minutes. After the above process, oil based paint (PAINT maker) was put on top to overlay all layer lines. This shows the best result of all the experiment mentioned previously.

Conclusion
The “ASNOO” methods provided the best way to color a 3D printed object. This method can cover the majority of layer lines and create the best looking 3D printed object that has similar quality to mold injection objects.

Step 7: PDF Download

You can download this pdf for further research on this topic. However, I won't be continue this research as I have already purchased an DLP printer :)

If you have any comments, feel free to leave them in the comment section below. I will try my best to reply your comments or question as soon as possible.

Thank you for reading this instructable and have a nice day.

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