22 May 2013

Todays result: Carbon filter

I have created a filter to add to my printer. It helps by removing some of the bad plastic odours. The filter medium is activated carbon pellets purchased at an aquarium shop.

It is a box shape with a fan at both ends and a diagonal wall of carbon through the middle. The intent was to double the force moving the air through a large area of thin carbon. It was designed to mount on the side of my Mendel90 it fits neatly on the inside of the right stay. I directed the air flow downwards. When the printer is operating in enclosed box it will pull warm air back down from above.

The y length is 17cm, almost the full length of the printer bed. The z height is 70mm - the fan size, and the x width is fan size + 2 cm wall of carbon. The filter grill is spaced with 3mm gaps to hold the 3.6mm diameter pellets.  I used 70mm fans due to a surplus from a botched order and 2cm of carbon seamed a useable thickness. Each end has m3 nut traps to attach the fan, and a slide cover to hold the carbon. 

The very bottom layer is mostly missing. The second layer droops a little when printed and restores a flat bottom. All but a few mm around the perimeter of the bottom layer have been removed. This reduces the adhesion to the bed otherwise it would be very difficult to remove.  To avoid severe warping the bed needs to be heated. I used PLA, ABS is a different beast where a complete bottom layer would probably work better.

The top came out well; I have to admit I was surprised, but it is not air tight. Along the sides of the top there are gaps between strands of plastic. This is where the largest bridging was. I suspect in 1 or 2 more layers it would have completely sealed. Painting it should resolve this. The model has inbuilt support structures and does not need generated support when slicing. The supports for the top branch off the filter grill and walls. They snap away easily after printing allowing access to the nut traps. The nut traps are still fiddly to use as they face into the chamber.

This is my third filter attempt; the previous filters had too much carbon and almost no air flow. 

The model is available here, though I am not releasing the scad files due to objections to thingiverse. I may produce stl files for other configurations if you leave a request it in the blog comments (no promises!).

 Mounted filter box on Mendel90

Failed filter attempt #2, converted broken PC power supply box. 
Electrical tape covered the screw holes and a tissue was placed inside the box over the vents on the far side.

Failed filter #1, printed mesh tube ends, designed to hang off my spool holder rod.