Wednesday, March 09, 2005

PCB mounting

Here's a picture of the case!

I'm now worried I won't be able to get all the original switches to fit on the front panel.
I'm planning to make a mocked up front panel in MDF to see if it will all fit using the original switches.

So, now I have a case it's on to the mundane but vexed question of how I mount the PCBs in the case. I originally though about mount the PCBs vertically (along the long edges) as they were in the orignal case but the wiring terminals scattered around the edges make this difficult. So instead I'll stack the boards in horizontal layers. This still leaves one problem.

The case has a completely blank base (apart from an earthing point) so there's nowhere to fix anything to it without drilling through. If I drill though the base any nuts or bolts used to fasten into it will stand proud of the base and ultimately scrape the lid of whatever the case is resting on top of. As eth base is only 0.9 mm thick counter sunck screws won't pass muster here either.

I could drill holes and then fit bushes (AKA clinch nuts). These are nuts that are stamped into sheet metal and basically give you something to screew your bolts into. RS do bags of 50 for around £3.50 part number 827-625. Or they sell a 'nutsert' kit for abot £7.50 which has 100 pillars with threaded stubs which are also stamped into sheet metal like the bushes. You get a tool with kit too. This is a bit of scary option though and I'd rather not drill 30 or more holes into the base of my unit espescially when I'm a) not that experieced at metal work and b) new bases are expensive.

Fortunately the case already has bushes fitted on the inside of the side panels. There are two on each side about 1-2 cm above the base. You can just see the front two in the picture. I'm guessing that these are fitted for the purpose of mounting your own base plate and at present this is what intend to do. I can use a piece of MDF, around 5mm thick and then attach it to the side bushes with angle brackets. The MDF is easy and safe to drill and cut and I can fit counter sunk M3 bolts from the underside to fit M3 PCB pillars to on the top.

This is the next task then. I have to cut a piece of MDF to size and calculate how many nuts, bolts, washers, lock-washers, pcb-pillars I need and of what sizes. I also need to determine what size nuts the side bushes take and find suitable angle brakets to fix the MDF to the side bushes with.

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