Divergence Meter Project
Case Version 2
The version of the case I made for my B5441A tube Divergence Meter used hex posts as the corner pieces of the case (instead of the hardwood corner posts used in the first case). The reason I didn't use the hex posts for the corners of the first case was that I couldn't find the 3/16" hex posts in the needed length of 1.25". What I did for this case was use two shorter pieces of hex post and male/female hex post to make a total length of 1.25". The advantage of using these hex posts for the corner posts of the case is that they already have threaded holes in the ends (whereas I needed to drill holes and then tap threads into the hardwood corner posts).
This case uses the same parts as the first version, except that the hardwood corner posts are replaced by:
| Quantity | Description | Part Number | Source |
|---|---|---|---|
| 4 | Female Hex Standoff, 3/4" Length, 4-40 | 761-2061-440-AL-7 | Mouser.com $0.33 each |
| 4 | Male/Female Hex Standoff, 1/2" Length, 4-40 | 761-4505-440-AL-7 | Mouser.com $0.42 each |
The 3/4" and 1/2" lengths of the hex standoffs were threaded together so that their hex faces aligned (I tried matching the parts in various ways to find the best combinations that came closest to having the faces align after tightening).
The aluminum plates (which I had cut by a metal shop -- and which I have extras of if you want to buy some) were prepared by sanding the interior end surfaces with course sandpaper to give the adhesive a better surface to stick to. The surfaces of the hex posts were also roughened with sandpaper where glue would be applied. See below:
The next step is the gluing of the hex posts to the end plates. Below you can see the hex posts lined up with the edges of the end plates (not yet glued). I used JP Kwik adhesive for this step, and I mixed only small quantities of the adhesive at a time so that I could carefully align the hex posts with the edges of the end plates (using a square block) before the adhesive set. The "point" edges of the hex posts should line up with the edge of the plates. After the posts were glued to the plates, I added some extra JB Kwik to fill in the gaps between the edge of the plates and the hex posts, and a fillet along the inner edges of the hex posts.
I then glued the end plates to one of the side plates, and then glued on the other side plate. To make sure that everything was in place and square, I aligned the parts on top of a full-size pattern of the case layout as the adhesive set. Below is the pattern used (the holes have 0.1" spacing...check that yo have printed it out at the correct size). Click for larger image. NOTE! The holes for the hex nuts that are drilled through the top perf board and the bottom piece of the case must be slightly further inward from the corners than the holes indicated for case method #1 (with case #1, I drilled through the perf board hole locations).
Below is the case glued together. After the initial glue joints set, I added fillets of JB Kwik along the edges of the hex posts (but not such large fillets that they extended far beyond the hex posts in the directions along the long sides, because I didn't want the fillets to interfere with the placement of the pc boards). Also note the 1/4" x 1/4" x 3/8" blocks of wood that have been glued to the sides of the case to hold the main circuit board in place (keeps the circuit board from slipping downward). These blocks were glued in place with thick CA adhesive, and this was only done after the top of the case with the pc boards had been fitted into the case so that I knew where to place the blocks. Also, the exterior styrene corner angle pieces (painted silver except on the gluing surfaces) were glued in place with thick CA before this photo was taken.
The top view below shows where the main circuit board support blocks were placed. Note that one is not placed in the lower-right corner because it would interfere with the 9-volt battery placement there.
Below is the pattern that I used to drill the holes in the rear plate. NOTE! You should check that the positions of the openings will actually match the positions of your board components before drilling, because there may be small variations. The rectangular hole for the slide switch was made by drilling two 3/16" diameter holes there, and then using a small diamond file to shape the opening to the rectangular shape.
Below is the back of the finished case. Note the small 0-80 screw heads have been added to the corners. These screws were cut to a very short length (about 1/16") and glued with thick CA into holes that are drilled through the plastic corners and aluminum plates (but not drilled into the hex posts). These screw heads are decorative, not structural.
The bottom piece of the case was made as before.
NOTE! The holes for the hex nuts that are drilled through the top perf board and the bottom piece of the case must be slightly further inward from the corners than the holes indicated for case method #1 (with case #1, I drilled through the perf board hole locations). See the pattern above for the hole positions.
If you have questions, send me email:
--"Tom Titor" of /a/
tomtitor@mindspring.com