Metal Screw to Attach 3/8" Steel Plate to 3" Wood Tread 2

[TXEng-USA]

I am designing a "floating" staircase which utilizes a 3" solid wood tread on top of a 3/8" steel plate. The client would like to use a flat head self-drilling or self-piercing metal screw that they would attach from the bottom.

I have only been able to find screws that are certified for attachment of wood to steel when the head of the screw is in contact with the wood.

Is anyone familiar with a screw that is certified for the condition noted above?

 

[TXEng-USA]

See the attachment for a snapshot of the detail.

 

[jayrod12]

Why not just use wood screws in pre-drilled holes in the plate.

 

[TXEng-USA]

That was my suggestion but they wanted to see if it was possible without pre-drilled holes.

 

[jdgengineer]

Seems like predrilling would be a lot easier/faster to install. On a side note, how are you guys defending 3/8" steel plates? With a central stringer we have always used 1/2" min at treads and 3/4" at landings.

 

[hokie66]

I would tell the client that his idea is silly...maybe not in those words. You need a wood screw, and that won't drill through 3/8" steel.

 

[dik]

Tek5 is the only self drilling fastener for 3/8" that I know of, but I know of no load capacities in wood. They are likely more than than adequate; just use a aimilar sized screw for load capacities. It's silly not to pre-drill the holes.

Dik

 

[hokie66]

jdengineer,
You don't need a plate that thick. The wood will carry the load.

 

[XR250]

Can't think of anything but a sarcastic remark so I am out.

 

[dik]

for an 1/8" plate use Tek3's... but, still not a good solution.

Dik

 

[XR250]

for an 1/8" plate use Tek3's... but, still not a good solution.

Teks don't work well going into wood. I think the debris coming off the drill point fouls ups the threads.
I have tried it personally on a project.

 

[dik]

XR... as I noted in the Tek5 comment... I have no idea of what the capacity is in wood... they're not meant for it... but, they are the only fasteners that I know of that will self drill thick material... as I noted... silly idea... right out of Monty Python Tech...

Dik

 

[dhengr]

Dik:
Silly ideas and details (dare say, stupid ideas and details) haven’t stopped a lot of Archs., clients, owners, and many engineers too, from doing really dumb things. Remember, most of the former aren’t engineers and too many of the latter aren’t either. They have a computer program, and that’s about all, and that hardly makes them thinking or knowledgeable engineers on any given problem. The client probably got suckered into buying a box of those screws, they didn’t work too good for the first project, so now he wants to use them up. Flat headed screws? Are they self counter sinking too? Drill and countersink the damn plates. A fab shop/machine shop will drill and countersink the holes faster than the time wasted debating here. Then use real wood screws that you can count on. It will cost the client something but nowhere near the time wasted farting around with his original idea, on the job site.

 

[TXEng-USA]

Thanks for the input, I will insist on pre-drilled holes.

 

[hokie66]

I wouldn't bother with countersinking the screws into the steel. Flat head screws will be under the tread, so why would they be objectionable?

 

[Compositepro]

The main issue is that if the screw is threaded into the steel and the wood, it cannot pull the two together.

 

[OldBldgGuy]

Try SFS Intec (I have no connection to them, but they have and make connections). Self-drilling screws for wood-steel connections.

 

[hokie66]

I think anyone who tries to use self drilling, self tapping screws in 3/8" steel will soon realize why it isn't a great idea.

 

[dik]

Hokie... it may even be considered a 'dumb' idea...

Dik

 

[hokie66]

Yes, Dik. I did already say it was silly.