I made a basic Lego sifter (a la Lego sorting head/ BoxForBlox) out of some spare timber and nylon fishing line.
First I did a quick test using a tennis racquet and it seemed to work so I went ahead and made the first one using a 20mm grid because that was the biggest I thought I'd want and hence the fastest to assemble. That worked. Then I had to think about grid sizes. I build mostly Technic so I really wanted the finest grid I could so all the little pin/connector parts would fall through but ideally liftarms and bricks would not. Preferably plates and tiles too. Which meant about 5-6mm spacing. But that's a lot of holes so instead I got a smaller grid on one by running the string diagonally for the finest grid.
1/8" holes at 12mm intervals. Go! I started marking 12mm intervals on a line and gave up. Instead I made a "pointer" by clamping a bit of wire to the drill vise and bent it to be 12mm from the drill bit (thanks for the idea Stefan). That way I could just line the pointer up with the previous hole, push the wood against the fixed jaw of the vise, drill the hole then move along.
Also, I got carried away and pulled the string too tight, hence the bend in the cheap softwood you can see in one photo. Don't bother doing that, the 12mm grid one is much looser and works just as well - the weaving holds the string at pretty even gaps. With the diagonal string it would have been better if I'd paid attention to the gaps in the corners, I really should have had an extra hole right in the corner. Fixed with cotton tied to the nylon.
It works brilliantly. I bought three of the 1600 piece XXL boxes in the end of financial year sales, and those were full of road train bits that need to be sorted. I'm about half way now. It's much faster with the presorting/sifting stage.
Total build time probably about four hours, because threading the line is very slow.
I used very rough monofilament knots based partly on my memory of what tennis racquet knots look like. Anyway, they haven't fallen apart yet. Several per sifter because there's a lot of string to pull through and I couldn't be bothered. It's easier (and just as effective) to start with 5-6m and go until that runs out, then tie off and start a new length. It's easier if you do the short side first, because the second direction involves threading under and over and it's slightly easier to do that along the long side. My main tip there is use your fingertips, one hand above, one below, and kind of wiggle the tip of the line through with your fingertips. That's faster than trying to "sew" it fully through each way.
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