I Made a Box Inside a Box!
About six months ago I wrote a blog post about an acrylic box I made as an enclosure for my small CNC milling machine. Well, yesterday I made another box, and this one has yet another box inside it!
As I’ve written about in a previous blog post, I’ve been using a stereolithography printer to make parts for the models I sell. A dirty (more like sticky) little secret of resin printing is that after the parts are formed, they need to be fully cured (polymerized) with additional exposure to 405nm (nearly UV) light. Straight out of the printer they are a bit sticky and just a bit soft. After curing they are rock hard and much stronger.
In the summer curing is easy: just set them out in the sun for about 15 minutes and they are good to go. But in the winter we don’t get much sun around here, so I needed a UV baking oven.
As usual, the ones you can buy off the shelf are very expensive, so I ordered a batch of 405nm LED light strips and wrapped them all around the inside of a box I made from sheet metal heating duct.
This worked in the sense that after about 45 minutes in the box, the parts were cured. But it didn’t work in the sense that after about 5 minutes the whole thing got so hot I was worried about the LEDs failing. I was able to use it by cycling the power on and off, but this was hugely inconvenient and it’s really not good for the LEDs to get hot at all.
So I ordered a batch of 24 really cheap computer fans and laser cut an acrylic meta-box to hold them around the metal box. Half of them blow in and the other half (on opposite sides) suck out. I was not confident that this would work, especially since there are no ribbed heat sinks, just the flat bare metal to which the LED strips are stuck. But it does work! Gloriously in fact: the box now remains cold to the touch indefinitely. As you can see, I had a backlog of parts waiting to be cured, so the box has been running non-stop for many hours. (These are stacks of, respectively, 104 corner brackets and 160 edge brackets for my Safe model, printed as dense blocks almost entirely filling the print area of my ANYCUBIC Photon S printer.)
Since this is basically an oven, it’s not surprising that I found myself wanting some oven racks (also known as kiln furniture in potting circles). I made this set using sheets of the same oddly soft FEP (fluorinated ethylene propylene) film used in the bottom of the resin vat of my printer. I could probably have used ordinary acrylic, but I’m just not entirely sure that acrylic is fully transparent to the wavelength of light needed to cure the resin. (Here you see a batch of camshafts from my Single Overhead Cam Internal Combustion Engine model.)
Well, sorry for what is probably not a very interesting blog post, but I am really enjoying my new vortex concentrator box. It looks very sci-fi, and the deep violet glow coming from inside really helps with the look.