Steel-to-Steel Fastening with total thickness greater than 1/2"

[Hunter90]

Hello all,

When you are using screws to fasten for example a 3/8" STL. PL. to a 1/2" STL.PL. for example, what are the best methods?

When it comes to self-drilling screws, I understand that this is too thick for that application.
Through bolts I know is an alternative.

Can these be an alternative?

1. Predrill and use a 1/4" SDS or 1/4" Self-Tapping
2. Predrill and use 1/2" DIA. threaded Bolt

What are some common methods to attach these kinds of steel plates?

Thank you,
Hunter

 

[XR250]

I would be using through bolts for this if it is an option - not screws. Whatever size meets the demand.

 

[dvd]

If you could pre-punch / pre-drill one of the sheets and then use a self-drilling screw you could get a #5 drill point to work.

 

[XR250]

In theory this works, but it sucks in my experience. Screws break, drill points burn up. I suppose if he needs blind fastening, this is an option though.

 

[gte447f]

Standard procedure would be bolting or welding for structural steel applications.

 

[Tomfh]

For that size plate bolt or weld

 

[Ron247]

Are you dealing with shear, tension or both?
Which thickness plate is the first one the fastener goes through?
Are the 2 plate sizes you note really an "example" or are they real sizes you are considering? Different plate sizes may get you different responses.

 

[jjl317]

I have on occasion used the Tapflex from Dewalt (originally an Elco product) - basically a larger diameter bolt/screw, (3/8" to 5/8" diameter) where the installer pre-drills a smaller clear hole, and the fastener creates the threads in the base material (up to 5/8" thickness). Similar to drill and tap, but easier to install.

And as mentioned above, some self drilling self tapping screws (1/4"-20 #5) are listed for use into material thicknesses up to 1/2" - Thought I would make sure you considering specifying a better quality, "name brand" version (ITW Tek Select or Dewalt Dril-Flex) - cheap ones can be more likely to break during install.

 

[Ron247]

cheap ones can be more likely to break during install.

Someone wanting to use cheap and generally untested fasteners is still something that really bothers me when they propose it. I have never seen the requested substitution pan out unless the alternative is also a premium fastener.

I call them "Carnival Bolts". Go to the carnival, pay someone $1 to guess your weight. If they get it wrong, you win a prize worth far less than a $1. The prize is the suggested fastener substitution.

 

[jjl317]

I agree completely - and especially seems prevalent with "TEK" type screws

 

[David3399]

Oh, please do not use screws.