This past week saw a few major steps in the chill box. This post describes building the acrylic container holds the parts and the plantings..
Cole came over to my (Jerry) home on Friday to work on the container. I had a couple long (8×2′) sheets of 1/4″ acrylic. We picked one and then cut it in half with a jig saw. The cut was pretty rough but it allowed us to put the resulting panels into the open door of the laser cutter. We cut them down to three 24″ x 9″ and some 9″ x 9″ panels. The long ones are for bottom and sides, small are for ends and dividers.[slickr-flickr tag="ChillBoxAcrylic" descriptions="on" flickr_link="on" sort="title" ]
To make assembly easier, we etched 1/4″ grooves around the edges of bottom and across side panels for the other panels to sit in. This worked fairly well, except for some alignment errors that resulted in a ridge along the edge of bottom panel. Also the Corel Draw document used distinct overlapping lines. When etched, each line was rasterized and drawn in total – where they overlap was etched twice each pass, making a pocket. Learning Experience! Also, these wide grooves were rendered as rasters and when doing the short cross grooves, there was a LONG time spent moving between them…. Etch 1/4″, move 14″, etch 1/4, move 12, etch 1/4″… on each raster line. To speed things up, I split the three cross pieces up into three separate jobs. The result was faster total time… although this may have contributed to creating the pockets.
Next we figured we need to etch some things into the side panels and cut some ventilation slats in the chiller area. I spent some (too much) time updating the Maui Maker logo and placed it along with “Chill Box” text in the planter area. I figured we would etch these into the inside for better effect so I mirrored the image horizontally so the text would be readable. Then I mirrored vertically so I could etch in one pass. It wasnt until everything was complete that I realized the 2nd mirror had reversed the text again. When viewed from outside that one side’s text is backwards.. Learning Experience!
For the ventilation slats, we could have gone with a big hole or simple cutouts, but thats too easy and simple. I opted to get artistic. On one side I created a set of sine waves of different frequencies. This took a fair bit of time as I learned how to make such lines in Corel Draw, offset them and then join the lines to make a cut out area. Learning Experience! To increase the open area, I added some circles. Unfortunately I did not check the results closely. When the waves were cut, a couple points were very close together, and effectively broke through where they shouldnt have. Learning Experience!!
For the other side, I thought, hmmm, Garrett’s E8 diagrams are pretty cool and would result in a lot of holes for wind to blow through (no reflection on his Theory of Everything). I popped over to the really cool E8 Elementary Particle Explorer site and came up with something half decent. I emailed the image to Garrett with background, just to get a sanity check. He quickly returned my email with an even better diagram, specifically with axis, labels, etc removed. I dropped this into the Corel Draw and ZAP! we had a mix of Agriculture and Theoretical Physics.. Fitting for our rather diverse maker group.
Laser settings for etching and cutting the 1/4″ acrylic:
- Raster: 400dpi, Speed 20%, Power 100%; Required 2 passes to get good depth
- Vector: Speed 5%, Power 100%, 5000Hz; Required 3 passes to completely cut
After all the etching and cutting was done, I setup my Festool table for assembling the box. Actually, I had it setup after we cut the pieces and was checking fit, measurements, etc at stages all along. The table is rather nice with large holes into which special clamps are inserted. These hold the work pieces securely in place. I put a couple scrap pieces of wood between the clamps and acrylic so as to get a good straight edge and distribute the compression forces. When all the pieces were cut, etched and test fitted, I squeezed a bead of Weld-on #16 acrylic cement into the grooves on bottom and side panels and assembled. (Note for next time – Have someone else around to help hold pieces in place.) The I put clamps on the top edges near or on the end/center panels, padding the metal clamps with some scrap cardboard. I left the whole thing dry in the clamps for 24hours. The end result was pretty nice looking – although there were a few places where the glue squeezed out and got some of the paper stuck. These can be touched up somewhat afterwards, but the larger one will leave a permanent blemish.
- Acrylic stinks when etched/cut. We need a ventilator that scrubs the exhaust. Commercial ones are expensive but perhaps necessary. Perhaps we can make one using simple water tower-in-a-bucket?
- Acrylic should be lasered with protective paper still on. Our piece had paper removed before we got it, but it scratched in handling. Also the vaporized acrylic can deposit on the non-etched surface. This can be cleaned using a soft scrub designed for light scratch removal.
- Check cuts and etches using cardboard standins.
- Always watch the cut – especially with cardboard. The burnt edges may have embers that continue to smolder, or burn outright.
- Laser jobs always take longer than expected. Most of the work is in the setup, eg CAD work.
- Laser rasters take a long time to run, plan the burn portions for efficiency, and have other productive work you can do while watching over the etch.
- When assembling lots of pieces, more hands can be very helpful.