Use and purchase of PEM nuts

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rbraibish

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I have seen several build threads or construction videos (j Coker) That mention the use of PEM nuts. I have no experience with them and really don't know what I am shopping for. I have looked at McMaster-Carr and other hardware suppliers and found a variety of options, ones for soft metal and plastics, sheet metal etc. My first impulse was to go with the soft metal/plastics type but then saw that the sheet metal option had inserts with a deeper engagement.

If you have used PEM nuts with 4" fiberglass tube I am looking to learn what to buy (and what not to buy) So far my only exposure to these has been pictures on the net. If I had a bin of these to sift through, look at etc. I think I could make the decision easily but I don't.

Right now, I am inclined to go with this one for sheet metal (vs plastic), it has the deepest engagement. https://www.mcmaster.com/#95185a171/=13eb3xs

Any other advice or guidance on install etc. of these little do-dads would be nice... though I have a pretty good idea on how I plan to put them in I am always willing to listen to one who has done it.

Thanks
Robert
 

markkoelsch

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I use them. What you want are Pem broaching nuts. In a 4" rocket I am using 8x32 to hold AV bay. There is a particular size bit you will need for each size of Pem but. Generally, I drill the hole. Line up the Pem nut, and use a screw and washer to pull it into place. Then I usually throw an epoxy fillet around them for good measure.
 

Worsaer

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I have used them extensively. One of my key learnings was that the hole in fiberglass needs to be clean, and not out of round. If you use brad point drill bits, and back it with a rounded piece of wood (like 1" wooden pole), it will cut a relatively clean hole in fiberglass.

Here is the p/n of the ones I use...

https://www.mcmaster.com/#95117a444/=13ecto3
 

smapdiage9

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I've read a few accounts of people pressing Pem nuts into fiberglass tube only to have them separate after a few uses. I imagine they're designed to be pressed into a material that deforms rather than splinters.

My Ultimate Wildman uses 4-40 Pem broaching nuts to hold the payload tube to the avbay, which I held in place with a dab of five min epoxy. They've been rock solid for a few M flights so far...
 

jimzcatz

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I don't use them. To each their own. But I'm old skewl. My avbays are not removeable.
 

Tonimus

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I prefer plastic push rivets. I like that they are completely removable.
 

mpitfield

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I have seen several build threads or construction videos (j Coker) That mention the use of PEM nuts. I have no experience with them and really don't know what I am shopping for. I have looked at McMaster-Carr and other hardware suppliers and found a variety of options, ones for soft metal and plastics, sheet metal etc. My first impulse was to go with the soft metal/plastics type but then saw that the sheet metal option had inserts with a deeper engagement.

If you have used PEM nuts with 4" fiberglass tube I am looking to learn what to buy (and what not to buy) So far my only exposure to these has been pictures on the net. If I had a bin of these to sift through, look at etc. I think I could make the decision easily but I don't.

Right now, I am inclined to go with this one for sheet metal (vs plastic), it has the deepest engagement. https://www.mcmaster.com/#95185a171/=13eb3xs

Any other advice or guidance on install etc. of these little do-dads would be nice... though I have a pretty good idea on how I plan to put them in I am always willing to listen to one who has done it.

Thanks
Robert
The word PEM is a name brand by Penn Engineering. Add self-clinching to your search criteria.

I use 2-56 self-clinching nuts for this purpose and they have worked very well. I don't press fit them, as designed, right into the air-frame. I rough up the inside where the nut will be then I carefully apply epoxy around the knurled part of the nut and screw it in place with a temp metal screw that has another nut on it so I can tighten it right down. It likely does pull into the airframe somewhat as designed, but regardless it is strong and I have yet to have one fail, albeit I am sure if used enough it would.

Bottom line is this installation method and technology have been very reliable for us in both carbon fiber and FW/FG air-frames.

View attachment 297653View attachment 297654View attachment 297655
 

cvanc

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I've used these on several birds with no problems https://www.mcmaster.com/#94648A320

They're very similar to the ones Worsaer mentioned. As others have discussed, having the exact right size drill bit and a nice clean hole is critical. To install I just tighten a screw into them as hard as I can and then back out and discard the screw (being only 4-40 you can feel the screw 'stretch' as you tighten it hard - that means it's become a one-use device LOL).

I have never epoxied them in and I have never had one come loose. YMMV!

Good luck,
 
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