Wednesday, June 7, 2017

PLA Heat Resistance: Confirming What I Already Knew

Making 3Dprinted pinhole cameras requires opaque materials. I have had difficulties finding and maintaining a supply of suitably opaque PLA filament for my designs and customers. This unusual situation has been blog-flogged HERE. A side effect of this is a stockpile of filament for non-photographic applications and the occasional translucent camera.

I recently designed a 6x9 version of my OSKAR Tuxedo camera, and printed it in Matterhackers Gun Metal Gray (now called Jet Grey). Only afterwards did I discover that the filament (and the resulting camera) was not longer opaque.  I have received excellent customer support from Matterhackers. This is not an indictment of them in any way - They were apparently mortified that their product had changed without their knowledge. I have since received replacement spools, which I have yet to test.

However, I found myself in possession of a useless camera. So, I found a use.

I have long cautioned people to treat their 3Dprinted camera with the same respect they would afford the film inside it. I specifically caution people not to leave their camera in a car on a hot day because the melting point of PLA is lower than other thermoplastics. Today, I tested this assertion.

I donned my Schlab coat, eye protection, oven mitts and tossed the big OSKAR onto the dashboard of my Prius. The dash is dark grey, the outside temperature is in the mid-seventies (a little more than 20 degrees Celsius).  In a dutiful nod to my all my chemistry teachers, at close to sea level, I effectively tested this at STP (Standard Temperature and Pressure).

terraPin OSKAR 6x9 tuxedo body on Prius Dashboard

I ran to the grocery store for some soup ingredients (I'm making a mushroom-bean chili; I am very excited about it).  The camera was left on the dashboard for approximately thirty minutes.  During the short drive, the air conditioning was turned off and windows rolled up. In the interest of parking efficacy, I parked the car pointing toward the north, and not facing the noonday southerly sun. I did not measure the temperature on the dashboard, preferring to relate a cautionary tale based on qualitative findings. 

When I was done shopping, I hopped in the car to observe a very slight drooping of the unsupported front wall of the camera. It yielded without much resistance when I pushed on it. I assessed its rigidity by twisting it. The thicker structure in the bottom of the camera wasn't soft enough yet to twist out of shape, but I easily pulled the camera body apart, stretching and deforming the softened PLA. 

Manual deformation of softened PLA camera body I

I can easily imagine someone ruining their camera in a similar situation, solely through indifferent handling. Based on this experiment, I would suggest that 30 minutes is a general threshold for exposure to the high temperatures found in the sunny day dashboard environment. An assembled camera, with the caps in place, could possibly withstand this temperature extreme if handled very cautiously and deliberately while hot. Any deformation of the front of the camera could easily compromise the shutter's ability to move and/or keep light from the film inside the camera. 

A lengthy hours-long interlude on the dashboard, in similar circumstances, could conceivably reduce your camera to a pile of slag. I may test this next - I have an identical camera body from the same batch of filament. 

Manual deformation of softened PLA camera body II

I repeat: Treat your terraPin 3Dprinted pinhole camera as you would the film inside of it. 

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Thanks for the input!