Can A Solar Oven Melt Failed Prints?

A few posts in 3d printing Facebook groups have shown flat masses made by melting shredded failed prints and filament scraps. I do not want to melt PLA in my oven due to the fumes that would be generated, so I never tried, despite wanting to recycle prints instead of throwing them away. Having large, flat masses of filament would save me the trouble of printing shelves for the cabinets I plan to make. After a recent slew of failed prints for a coffee table project, my desire to convert them into shelving pieces increased.

Photo by Giovanni Calia on Pexels.com

When I saw videos about a DIY solar oven, I thought it would be great if I could melt the prints in one. The components for the oven were easy to get and it looked to be simple to make. I just had to try it myself. Ideally, I wanted to place a large print in the oven and melt it into a viscous liquid that would spread across a cookie sheet like cake batter does. A shredder costs around $573.00; an investment I would only like to make if there is no other reasonable way to recycle prints.

I set about making a solar oven, mostly following a video by Hillsborough County, One thing I did not do that was suggested in the video was spraying the bottom of the oven with black paint. Another thing I skipped was using black heating utensils. I did not want to wait for them to be shipped and I did not feel they were absolutely necessary.

Trials

1  August 2, 2022 – Setup was styrofoam cooler lined with heavy duty aluminum foil. The prints were placed on a cookie sheet lined with parchment paper. The top was sealed with saran plastic wrap and tape. I did not measure temperatures. Solid prints felt a little squishy after approximately 1 hour at the lakeside. I moved the box to rooftop of my apartment building. The styrofoam top was used as a reflector at lakeside and for tilting the box towards the sun on the rooftop. The prints felt warm after about 2 hours on the rooftop.


2   August 10 2022 – I cut the sides of the styrofoam cooler, according to video instructions. I put rocks on the bottom of the cooler and reflector panes on all sides.The top was sealed with saran plastic wrap and tape. The setup was placed on my apartment rooftop at around 12:30 PM. I stopped the experiment at about 1:45 PM. The temperature of the oven per a meat thermometer was 165° Fahrenheit. The prints did not feel squishy. There was a strong melted filament smell coming from the oven when the plastic was lifted.


3   August 16, 2022 – Setup was the same as August 10 except the borosilicate glass plate from my CR10 Mini was used to cover the top. Plastic wrap was placed on the sides of the glass. The setup was placed on my apartment rooftop at 12:21 PM. The oven was out of direct sun when I returned at approximately 5 PM. The temperature of the oven per a meat thermometer was 130° Fahrenheit. After placing the setup in direct sun, the temperature increased to 140° Fahrenheit.


4   August 17, 2022 – Setup consisted of scrap pieces of plywood taped together to form a box. The box was lower in the front than the back. One reflector was placed on the back side. Rocks were at the bottom of the box with a cookie sheet lined with parchment paper on top. The box was sealed with saran plastic wrap and tape. The box was left in the sun for approximately 3 hours. The temperature of the box was photographed after 10 minutes from the start (125° Fahrenheit) and shortly before the box was removed (141° Fahrenheit).


5   August 18, 2022 – The top portion of the styrofoam cooler that was cut cut in the second trial was taped to the bottom cooler portion. Rocks were placed in the bottom and sprayed with water. The top was sealed with saran plastic wrap and tape. The box was left in the sun for approximately 3.5 hours. Upon returning, the sunlight was covered by clouds. When sunlight returned, the temperature was taken after waiting 10 minutes (140° Fahrenheit).


Conclusions

A deep chamber was best.

Coffee Table made with Ziro translucent filament

I reattached the top that was cut off in the first trial when I surmised that the oven was at its highest temperature then. Even though I did not take a temperature reading, the prints were more supple in this trial than in the later trials. If I had been able to remain lakeside for another hour, I think I would have been able to crush the print flat.

Translucent PLA prints win the full sun, outdoor environment debate.

I was trying to melt prints made with Ziro translucent filament. The interior of the print, which was printed at 20% infill, began to collapse after being squished, but the exterior walls did not show signs of melting or collapsing. At one point during the trials, I tried sawing one 3d print, but gave up quickly as it was more difficult than sawing wood. Perhaps, I will try it again using a metal cutting blade.

One long reflector attached to the back edge was best.

I think the reflector attached to the back did the best job of directing sunlight into the chamber. I am curious about whether the foil should be replaced by more reflective material. Glass comes to mind; however, I have seen videos and read news about what happens when sunlight passes through certain glass shapes.

Borosilicate glass was not better than plastic wrap.

Borosilicate glass did a poor job of retaining heat. I was really surprised.

Next Steps

My first goal is to repeat the success of the first trial. If the oven reaches temperatures above 200, I will work on increasing the temperature using the styrofoam cooler. If it does not, I will search for different material types and other methods of melting prints outdoors.

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