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Cutting frame for prototype 3

September 25, 2019 — BarryK

Continuing the build of solar water distiller prototype #3. Here are earlier posts:

I purchased glass from Casey at Glass Perth:

I ordered three pieces, two are 572x672mm, and one piece is 572x630mm. I asked for "normal window glass, 3mm", however, it seems that the glazier's idea of "normal window glass" is 4mm thick, that's what I got. I checked, the previous order was also 4mm supplied. I don't have calibrated calipers to measure the thickness precisely, but just from using a measuring tape it looks like 4mm.

No problem with 4mm, probably better anyway from the strength viewpoint. However, I had cut the grooves in the wood with a 3mm router bit. So, a quick trip to Bunnings and purchased a 4mm straight single-flute router bit:

Went through the grooves again with the slightly larger router bit. The grooves are now 4mm wide, 5mm from the edge, and 6mm deep -- I had intended the depth to be 5mm, but the second router bit dug a bit deeper. That's OK. An end-on photo:


The width is spot-on. The glass is a snug fit, but not too tight. I don't want the wood to be stressed when inserting the glass.

Prototype #3 is small. Mostly, I want to verify the principle of this design, that it is significantly more efficient than #2. That remains to be seen. It doesn't have to be big, I think, for a valid efficiency test. Another reason that I want it small is to be able to slide it vertically into the rear of a small hatchback car.

What I have at this point is a 3m length of pine, with two grooves going the entire length. The pine has now to be cut for the four sides. To do this accurately, I cut the pine into two equal-length pieces, and inserted both pieces onto the glass. Firstly, onto the long sides, so as to measure the inside distance:


...that was 560mm, and I added 2mm onto that. Secondly, onto the short sides, so as to measure the required length of the two longer vertical pieces:


...that was 698mm, and I added 2mm onto that. Thus the two short pieces will be 562mm long and the two long pieces 700mm long. That extra 2mm could be a tad smaller -- it is to give a bit of slack so that the glass edge is not pressed hard against the frame when the frame is screwed together later (though I won't actually be using screws).

The pieces were cut in a mitre-box, using a tenon saw. There is a bit of sloppiness when the tenon saw is inserted in the mitre box, which can cause a slight inaccuracy when cutting, maybe 0.5mm or thereabouts. I found that a good way to grind a slightly-longer piece to the same length as the other, is to move it over coarse sandpaper, like so:


...I turn the wood around, to ensure that the grinding is not cutting more on one side than the other. One thing that I learned, do not use a hand file to grind the end, it will end up very uneven (that discovery was made when building prototype #1).  

Here is the result assembled:


...yes, fits together nicely! Only one piece of glass in the photo. In the final assembly, there will be three pieces of glass inserted, top, bottom, and in the middle.

The next step, planned for tomorrow, is to drill round holes for the pipes, and a groove on each of the long pieces, into which the smaller piece of glass will be inserted. 

Tags: nomad