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I recently acquired some PCBs for building a Divergence Meter as described on Tom Titor’s site. I’ve been meaning to build one of these for a long time.
I struggled for quite a while trying to figure out how to build the case. I didn’t like the idea of using glue as a structural element, and I thought it ought to be possible to source something other than hex standoffs to form the corner posts. I did manage to find a source for square standoffs – though not in small quantities, but that still left the problem of using glue. Ideally I wanted to use actual screws, but that would have meant tapping some small metal rods. I was getting nowhere, so I went to visit my local model shop and chatted with them about various options. I came away with some styrene sheet, some square plastruct rod and some plastruct angle. I figured I could prototype a case and see if anything came to me. I also bought some steel sheet and some aluminum sheet to see how good the glue approach was.
As I messed around with prototypes, I discovered that #4 screws (such as the screw part of the hex standoffs used on the perfboard) screw into the plastruct rod perfectly, so I went to my local hardware store and picked up the smallest self-tapping screws they had – some #2 – 1/4″ screws, drilled pilot holes in the plastruct rod and tried fixing them to some of the metal sheet I had bought. It gripped really well, so I decided that I would CAD up some parts for a case and get them made at Big Blue Saw.
I also decided that I would support the PCBs on plastic hex standoffs, they needed to be well fixed to the case. 11/16″ standoffs work for the main board, with 10mm standoffs between the main board and the display board. For the screws that screw into the bottom of the plastruct rod, I used #4-40X1/8. I have node idea where I bought them – I can’t find them in my ebay, DigiKey or Mouser orders. They need to be short to clear the self-tapping screws.
I have just finished putting together a case using the parts made by Big Blue Saw, and it works great. I had 10 sets made as each set is then a lot cheaper, so I have many left over I currently have two left that I would be willing to sell for $59 + shipping.
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The following pictures show the case in various stages of construction. This first one shows the plastruct rods and angles. The pilot holes in the rods are 1/16″, the holes in the angle are 7/64″, and not shown – but the holes for the hex standoffs in the perfboard are at least 1/8″.
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Big Blue Saw offer several finishes. The one below is raw. The edges are very rough, and there are marks left over from the water cutter, so I ordered the rest in basic finish instead.
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In the photograph below, I have yet to paint the plastruct angle – I was just checking that everything went together.
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The stencil that Tom provides is slightly different for this case. The holes for the hex standoffs are back where they were with his build #1. In the PDF below I also show cutouts for the tubes with a diameter of 14mm. This is a standard size for things like Forstner bits and it gives you some room for error in drilling these holes!
Perfboard Stencil