Drilling from 1/4" plate to gauge steel 2

[canwesteng]

I'm in a bit of a strange situation. I'm trying to fasten an angle to the outside of some existing ducting to stabilize it. Now I know that self tapping screws will go through gauge steel into structural, but can I do the inverse? Or does anyone have any other ideas?

 

[3DDave]

Drill clearance holes in the angle. The threads in the angle won't help hold it in place; only the engagement in the base material will.

 

[canwesteng]

Clearance holes is what I was hoping to avoid, but it can be done in the shop so it's not too bad.

 

[bob33]

Pop rivets are another option.

 

[jayrod12]

As far as I'm aware, most of the screws specify that the screw head must bear against the thinner material. However, I don't see how you can't just ignore pull over capacity and only use the pull-out capacity.

 

[GC_Hopi]

You can look into strapping or welding as other options.

 

[oldestguy]

Can you fit some 1/8" sheet in back to take the screw threads?

 

[canwesteng]

Don't really want to weld to gauge steel. Also don't have access behind the duct wall as the duct is already existing. Pop rivets are a great idea for this application though. Good feedback all around though, thanks all.

 

[jjl317]

There are a number of blind fasteners that might be an option (i.e. Elco Fab-Lock, Riv-nut).

 

[XR250]

I second clearance holes. With a sharp bit, it will likely drill as fast or faster than the self-drilling screws.

 

[dhengr]

Canwesteng:
Pop rivets may well be the answer, but they still have to predrill the angle and then predrill the light gage duct work too. Not much labor saving there. The problem with using a self-tapping screw to drill through the .25” angle and then the light gage mat’l. is that you have likely used up the self-tapping capability of the screw in the struct. mat’l. and since you are tapped (threaded) into the angle you have no feel for actually tapping into the lt. ga. mat’l. or when you are starting to strip the threads in the lt. ga. mat’l. Obviously, all you have for strength is the thread pull out in the lt. ga. mat’l., so any stripping would be detrimental. I think most screw manf’ers. have a foot note that limits the thickness of struct. stl. which can be drilled, and high str. stl. is tougher and harder, because the hardened tip on the screw gets warn off in the struct. stl. Then, you have no backing force on the lt. ga. mat’l. either, so you may not even penetrate it.

 

[12345abc6ttyui67]

We did this with pre-drilled angles and pop-rivets.

 

[BridgeSmith]

dhengr is right; the self-drilling screws will thread into the angle and lock up. You would have to strip the threads in the angle to pull the duct tight to it. In a 1/4" angle, more likely that the screw breaks than the threads actually strip out. Even if you do get it to spin in the angle, it's nearly impossible to be able to feel the screw tighten up in the light gauge duct; they'll likely strip it the threads in the duct metal without even realizing it.