Studs in 5 mm steel plate enclosure

Sep 17, 2005 8 Replies
C

Hi all,



This autumn I'm going to build an enclosure to house capacitors, contactors and thermal circuit breakers as part of my phase convertor. As I mentioned in a previous post, it needs to be strong because the transformer will be mounted on the side, so I'm going to use 5 mm plate and weld it together (a bit like a pole pig tank). I might make the back plate where the transformer hangs a bit thicker. The top of the enclosure will be removable, with a flange around the edge and a sealing gasket underneath. I want to secure the top with stainless domed nuts, because they look good. So I need a way of attaching studs to the enclosure. Two problems: I don't know where I can buy studs (although I can buy all-thread) and I'm a bit doubtful about only having a 5 mm length of M8 or M10 thread. I do need to screw these nuts down reasonably tight in order to seal the enclosure, and I had also wondered about replacing two domed nuts with eye nuts for lifting, so they need to be strong. One idea I had was to thread the holes and screw a bolt in from underneath, so that the threaded section sticks up, then tighten the bolt against the plate like a locknut. I know this might seem like an academic discussion, but I want to do a good job. I'm interested to know how you guys would do it.



Best wishes,



Chris



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J

5 mm thick plate should be ample unless the transformer is very heavy. And the rule of thumb on threads is that you must engage at least four threads for maximum strength. The first and last bit of thread, of course, is a little questionable. But a coarse thread M6 or a fine thread M8 (1.0 thread pitch) should engage more than four full threads in a 5 mm. plate. A coarse thread M8 or a fine thread M10 (1.25 thread pitch) would be right on the boarderline. This doesn't mean that the threads would necessarily let go, simply that the threads will fail before the fastener...

Jerry

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C

Thanks for the information. That's pretty much what I thought - 5 mm is borderline. When designing things in the past I've aimed to make the length of the thread at least the same as the bolt diameter.

Chris

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E

Greetings Chris, Some auto parts stores and some good hardware stores sell heat treated studs. Some studs will have a fine thread on one end and coarse on the other. With 5mm thick plate and 8 or 10 mm threads I'd use a bolt going through the plate. If you do not want the head of a screw protruding inside the enclosure then a flat head screw will work. Tap and c'sink the plate and Loctite the screws into the plate. ERS

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C

Press in PEM-type studs then use your cap nuts. Where to buy them depends on where you live. In Maryland, USA,

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is a good source for us - I'm sure you can find them local to you.

-- Regards, Carl Ijames carl.ijames at verizon.net

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B

Just buy a NEMA enclosure. hey will hold heavy transformers. I see them on Ebay and of course they are available in Home Depot and the like. Bob AZ

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C

Thanks for all the suggestions. If I can't find any studs easily, I reckon I'll tap the holes, screw in bolts from the underside and tighten them against the plate. The heads don't matter, and I can't really countersink the holes as I'm going to drill them after the box had been assembled. My only slight concern was that the bolts might come undone as I tighten the nuts, but I think this is pretty unlikely, right?

Best wishes,

Chris

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C

Eric R Snow wrote: > On Sat, 17 Sep 2005 22:01:37 +0000 (UTC), Christopher Tidy > wrote: >

Thanks for all the suggestions. If I can't find any studs easily, I reckon I'll tap the holes, screw in bolts from the underside and tighten them against the plate. The heads don't matter, and I can't really countersink the holes as I'm going to drill them after the box had been assembled. My only slight concern was that the bolts might come undone as I tighten the nuts, but I think this is pretty unlikely, right?

Best wishes,

Chris

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E

If the bolts are tight against the plate they most likely will not back out. If loctite is used the chance for them to backout is miniscule. ERS

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