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I would like to know how to secure the PCB into a watertight die cast aluminium enclosure that has no visible mounting posts. There are plenty of those on the Hammond website, and I don't understand how they are meant to be used.

It has to be IP65, and reasonably vibration resistant for mounting on top of a high tower, and resist about -10°C to 75°C inside.

An example is the Hammond 1590W Series.

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  • \$\begingroup\$ Elevator bolts glued with neutral cure silicon rubber to the box? Spot welding aluminium studs in the bottom? \$\endgroup\$ – nraynaud Jul 2 '16 at 0:10
  • \$\begingroup\$ Can your PCB be two layers with minimal vias? \$\endgroup\$ – scld Jul 2 '16 at 1:33
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    \$\begingroup\$ @nraynaud You sound like you are trying to do things (commendably) properly to meet real world variations. It would seem logical to choose an enclosure that does have manufacturer defined and toleranced mounting points that meet your need rather than trying to fit your requirements into a system with loose overall tolerances. However, if the wide range of "loose fit" enclosures make their use attractive you could consider a "tensioning jig" or similar which makes the overall assembly a good fit in an low tolerance housing. this could use eg springs or (agh!) installer adjustable spacing. \$\endgroup\$ – Russell McMahon Jul 6 '16 at 22:33
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This sort of housing assumes the pcb will mount perpendicular to the cover. That is, the card is just as wide or long as the inner dimension, and slides in between the ribs around the edge. These ribs, and their spacing, act as edge guides and supports. This means, of course, that your pcbs will be pretty small.

Alternatively, you can use a larger board which fits parallel to the cover. In this case, you drill holes in the back face, then mount standoffs which then connect to mounting holes in the pcb. If you do this, it's important to place elastic washers between the standoff and the back face to form a water-tight gasket for the screw hole. Generally, a metal washer between the standoff and the elastic washer is a good idea to spread the mechanical load on the gasket. Alternatively, if the back wall is thick enough, you can drill and tap for screws which will engage the standoffs.

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  • \$\begingroup\$ Die casting generally implies quite thin walls, you can't use risers like in gravity casting, and cycle time increases with wall thickness. \$\endgroup\$ – nraynaud Jul 1 '16 at 23:51
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Different Hammond's enclosures have got different ways of mounting PCB.

The 1590W series has got vertical PCB card guides on all 4 sides.

enter image description here

From datasheet from here.

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    \$\begingroup\$ I know we are not on a mechanics SO, but the fit will have to be quite loose to accommodate for manufacturing variations in both the enclosure and PCB and for thermal expansion. Loose fits and vibrations are not really a good mix. And the draft angles are going to be a pain to manage ; they are not big, someone will screw up somewhere in the PCB design (oops, I made a rectangle), manufacturing (that stuff is crooked, let's fix it) or assembly (- "dear customer, the PCB doesn't fit" - "have you tried the other way around?"). \$\endgroup\$ – nraynaud Jul 1 '16 at 23:44
  • \$\begingroup\$ I want to use these card guides, but they are so much thicker than my PCB (~1.6mm). Is there any way I can make my PCB pressure fit into the card guides ? \$\endgroup\$ – VanGo Aug 25 '17 at 13:00
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I normally do not answer questions here that are basically shopping questions that can be solved with Google searches. However in this instance I want to point out that there are die cast project boxes that have very nice PCB mounting provisions if you look for them. Camden Boss is one company that has the type of enclosure that you require in a variety of sizes.

Here is a picture of one of these boxes:

enter image description here

You can see the board mounting turret in the corner. A nice feature of this box is that it has more than just four cover screws so that you are assured of a better lid seal to the gasket.

Here is another picture showing that for this size box the mounting turrets are in all four corners. (Some of the smaller or narrow enclosures may only have two mount points on opposite corners).

enter image description here

Note: I have no affiliation with Camden Boss and have not used their products. Pictures borrowed from one of their freely downloadable PDF box data sheets. Showing the power of Google searches.

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    \$\begingroup\$ this is not a shopping question, I'm not asking for a different box, I wonder what the designer had in mind when they invented an entirely flat watertight industrial box. \$\endgroup\$ – nraynaud Jul 2 '16 at 9:32
  • \$\begingroup\$ seconding this comment; this doesn't address the question at all. it sounds like you're too eagerly invoking the "x/y problem" instead of addressing the question asker's legitimate curiosity! \$\endgroup\$ – dn3s Nov 9 '18 at 18:26
  • \$\begingroup\$ This is a legitimate answer.....i.e. change to a box that has the mounting facilities that you need. I am amazed that you even take the time to complain about how this is not an answer. Someone could ask how the can haul 5 cords of wood with their Mini Cooper but common sense says to rent or borrow a truck to haul the wood! \$\endgroup\$ – Michael Karas Nov 9 '18 at 18:38

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