Mounting stacks of PCBs in sheet metal+plastic case - Page 1
Forum section: electronics / projects

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 13, 2020, 03:51:12 pm
content: I have the enclosure depicted below, made from sheet metal. A magnet says: steel (well Iron to some extent anyway)From some Chinese seller on amazon, IIRC. Laying around for a while.Dimensions: 24 x 19 x 11 cm³, sheet metal is 0.75mm thick.Well not quite "metal case", because, as you can see, it is held together by bent metal sheets screwed to the front/back white plastic frames.The outer most ones have nuts, the center ones are self-tappers... (which could be corrected).Now I also have a bunch of same-type PCBs from china ebay (each with 8 relays, so some weight) with a M3 hole in each of its 4 corners, that, if I stack 4 of them on top of each other with maybe spacer tubes on long M3 screws, two such stacks next to each other, it will roughly take one half of the case interior, and the other half has space for PSU and control electronics (and a bit for front panel controls).(I feel the metal is too thin and space too low to put a AC mains PSU with its socket in there, given the forces of plug wiggling - so the mains part will be external)I'm just not sure how, and where / to which parts of the case exactly one would actually fasten this to.How would I get those stacks of PCBs in there - if it's at all advisable for this somewhat flimsy seeming case?Although I guess I could bolt a few strips of sheet metal in some places to make it a bit more bending-resistant. Especially where screws are going through.Say I have 4 vertical M3 screws stacking 4 PCBs: Do I just drill 4 corresponding holes in the bottom of the case, put some bigger reinforcement washers on both sides of the bottom sheet metal and fasten it with nuts?Or maybe strips of sheet metal from one hole to another as better reinforcement?I guess the 4 screws going through all PCBs of a stack could reach high up through the top sheet metal, and after closing, add nuts on top, which make it more stable, but it doesn't seem aesthetically favorable having screw ends stick upwards out of the box. Mounting this with screw heads on top would seem more difficult, especially with regards to connecting things when the case is... close and its contents inaccessible - unless *everything* is top-mounted, dangling in this flimsy, bent metal sheet, probably not fun to assemble.Any suggestions?Stack 4 of those suckers vertically, making two stacks then occupying the left half of the enclosure.

author: coppercone2
author_rank: Super Contributor
timestamp: June 13, 2020, 04:47:05 pm
content: to attach the PCB you can1) sand an area and glue something thick into place that you can drill holes in and tap threads into so you can thread standoffs into it and then put the PCB on standoffs2) drill holes and use chamfuered screws to attach the standoffs to the chassis then put the PCB on standoffs, or just use normal screws if you don't care for the protrusion because it should have feet but its not really nice looking.3) try to figure out cheap bullshit with clips etcThat chassis actually looks kind of nicehttps://www.amazon.com/ZYAMY-Standoff-Assortment-Mounting-Hardware/dp/B07CN3N8BS

author: phil from seattle
author_rank: Super Contributor
timestamp: June 13, 2020, 05:15:41 pm
content: I'd use aluminum angle or U channels to create a "ladder" to hold your relay boards. Make the bottom and top cross pieces wide enough so you could attach it to the top and bottom plastic brackets via screws. I'm not a fan of tapping plastic - would use those metal heat and press inserts they use in 3D printed stuff.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 13, 2020, 05:35:16 pm
content: Quote from: phil from seattle on June 13, 2020, 05:15:41 pmAh! Hadn't thought of "guiding rails" to slide them in, if I'm understanding it correctly.Those soldering inserts, I have seen them, good idea!Quote from: coppercone2 on June 13, 2020, 04:47:05 pmYeah, Chinese tend to make things that *look* the partMy good old mechanical 1:N VGA switch box has ratio of max dimension vs. thickness that instills much more confidence. But the price was ok for it, can't complain.It would be a lot nicer if all metal parts actually mechanically held each other together instead of critical plastic pieces in between, though.(Simpsons: Flanders' house community rebuild: "Nooo, this is a load bearing poster!!!")

author: phil from seattle
author_rank: Super Contributor
timestamp: June 13, 2020, 05:48:18 pm
content: Actually, used correctly, plastic makes for a reasonable rigid structure. Big problem is exactly what you pointed out - fasteners.I was thinking more like this. Wrong size circuit board, of course.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 13, 2020, 08:04:31 pm
content: Ah, a rack. I like it. Thanks for the pic.Neat. Because I have a couple meters of those 90° plastic things laying around, if the weather tomorrow is also bad, I know what I'll be doing

author: Lomax
author_rank: Frequent Contributor
timestamp: June 15, 2020, 01:14:29 pm
content: If you have access to any kind of press thenself-clinching standoffsare the bee's knees!