PEM nuts, or something like that for sheet metal

[ChazzC]

If only you knew a machinist that could make a few of those in the thread you need

Or buy appropriate metric ones, hold in a collet and drill & tap 6-32.

 

[foolishgrunt]

I did finally get through to someone at Trifast - they do not carry UNC versions standard, and would have to run a special production order with a 100k min order.

If only you knew a machinist that could make a few of those in the thread you need

Well then, a question for the machinists: how do you think Trifast (or their competitors, or whatever overseas supplier they might use) would likely produce these bushes? I assume they're die-cast, or something like it - meaning I'm afraid a machined sample would have marginally different physical properties.

Backstory of application: my company has used PEM (self-clinching) nuts for decades in sheet steel with no issues. Now we're running new products with aluminum sheet (16ga and 18ga), and the material is just soft enough that we've have a few PEM nuts strip out. We're hoping that rivet bushes could do for us exactly the same thing that PEM nuts have traditionally, but hold in aluminum more securely. So I'd hate to test and approve a new design based on a machined sample, only to find out later that the cast part was inferior and gives us the same issues as PEM nuts did.

 

[woodchucker]

I'm surprised that the PEMs won't work in AL. I wonder if it's the type of AL. is it a 2000 series AL? I'll assume when you say strip out, they are turning and chewing up the AL so they don't dig in?

No expert just trying to understand for my own knowledge.

 

[foolishgrunt]

I'm surprised that the PEMs won't work in AL. I wonder if it's the type of AL. is it a 2000 series AL? I'll assume when you say strip out, they are turning and chewing up the AL so they don't dig in?

No expert just trying to understand for my own knowledge.

It's 5052. I don't mean to suggest that they flat out *don't work* in AL, but we've had them fail just often enough that we're investigating how to improve.

In the 16ga sheet, most of the issues are the nuts popping out when pressing on the screw head while tightening - though in one case the nut did start turning and chewed up the hole, which is more concerning. In the 18ga sheet, the nuts turn noticeably more easily.

Anyway, I don't know why I didn't think of this before: I'm going to order a small quantity of metric thread rivet bushes to do our tests with. If they work out, then we'll discuss placing a bulk order for the 6-32 threads.