HILTI Kwik-Flex 1/4-20 fastener through 3/8" thick material 1

[Ingenuity]

The ICC-ES report Link for the HILTI Kwik-Flex 1/4-20 fastener states that the maximum self-drill capacity is 0.5" thick.

I have an application where it has been specified that a aluminum handrail post (with patch plate), be attached to the 3/8" thick web of a mild steel channel and wanted to check how readily such a web thickness can be self-drilled with these fasteners.

I have never directly used these fastener types before and thought they were only used for cold formed steel but I guess they get specified for bi-metal applications too.

 

[MikeHalloran]

My travel trailer's frame comprises I-beams ~6-1/2" deep and ~2-3/8" wide made from 1/8" thick steel strip and welded together with a tiny bead for their entire ~25' length.

I've just had occasion to add some steel angle reinforcements (#14 gage) to the bottom of the frame, using 1/4-14 self-drilling screws that I got from Home Depot.

You know how the point of a new twist drill bit is sharp enough to draw blood?
Self-drilling screws are not that sharp.

Using my Craftsman Nextec 1/4" impact tool (wonderful tool), it took a couple of minutes to drive each screw through ~3/16" of steel. If I had to do more, I'd probably drill pilot holes. The impact tool had zero trouble driving the threaded portion of the screws in, but actually drilling the metal required that I push _really_ hard on the back of the tool to cause the screw's drill point to make chips.

If you expect someone else to put a self-drilling screw into 3/8" of steel, you really need to go drive a few for yourself, to understand what you are asking.

Have you settled on a thickness for the aluminum baseplate? I'm not seeing how you get full strength of the screw if the plate is more than 1/8" thick, and a plate that thin won't survive the high school cheerleaders, much less the football team.




Mike Halloran
Pembroke Pines, FL, USA

 

[BAretired]

Is there a corrosion problem with dissimilar metals coming in contact? Do you need some kind of separator between the aluminum and the steel?

BA

 

[Ingenuity]

MikeHalloran:
Thanks for your input.
The preprinted alum patch plate that is prewelded to the vertical handrail post is at least 1/4" thick.
I have drilled TEKS into 1/4" steel without any problems, but it did take a bit of pushing, as you indicated.
I too thought it would take about a minute per fastener, but according to a data sheet I found via Google that compares comparable fasteners Drill-Flex (same as Hilti Kwik-Flex) to TEKS they state the time is seconds.

We are going to get the contractor purchase a few of the fasteners and trial drill a few to check production. The original design (by others) calls for SS through bolts and the contractor wishes to substitute for the self-drill fasteners.

BAretired:
According to the tech sheet, these fasteners are designed for dissimilar metal use, and specifically alum and steel.

 

[XR250]

I had to install a bunch of #12TEk5's to install metal deck on a W10x33 I-beam (7/16" tf)
It was not too bad. Took about 30 to 45 seconds per screw IIRC.

 

[MikeHalloran]

I concur with a _tapping_ time of a few seconds.

To get a drilling time of seconds, you would need a power-feed drill press, or a very burly craftsman bearing his or her full weight on a big portable drill.

In my case, I was pushing up against the trailer frame, with my elbow bearing on the driveway beneath, so chip clearance was not a problem, but drilling force was limited by my wrist.

Separately, I witnessed the techs at the trailer dealer using somewhat larger (~5/16") self-drilling screws to install a 'load equalizing' hitch. (Trailer dealers must love self-drilling screws.) For every one of those screws, it took a minute or more to drill the hole, and seconds to tap the hole and seat the screw, using a hand-held impact tool, through ~1/4" of mild steel in the trailer tongue.

Maybe the TEKS or Hilti screws have sharper points than the ones I have used, or the ones the trailer dealers used, so I am curious to see the results of your contractor's test.




Mike Halloran
Pembroke Pines, FL, USA

 

[Ingenuity]

Thank you Mike and XR for your experiences.

It appears that the major manufacturers of these fastener types all state drill times that seem exceptionally optimistic. Stated values of 6 seconds to SELF DRILL a 1/4-20 in 3/8" thick steel seems awfully quick!

We are going to get the contractor do a few field trials and report back to us there findings.

Thank you for your help.

 

[berkshire]

Having thrown a few of these screws into steel beams in my lifetime, 15 to 20 seconds per screw is more realistic, and the minute the screw stops throwing chips out of the hole, scrap it and get another one, or they will burn up in the hole, and leave you with a hardened steel mess that the next screw will never get through. The other thing to watch is that the length of drill point is sufficient to enable the screw to drill through completely before the tapping starts, or the tapping portion will be burned off before it gets to do its job.
B.E.

You are judged not by what you know, but by what you can do.

 

[MikeHalloran]

Star for berkshire, for the last sentence.


Mike Halloran
Pembroke Pines, FL, USA

 

[XR250]

Maybe the TEKS or Hilti screws have sharper points than the ones I have used, or the ones the trailer dealers used, so I am curious to see the results of your contractor's test.

I imagine the screws from home depot are no match for the quality of screws designed for commercial work.
I have used the wood to metal screws from Home Depot to attach 2x4's to a 1/4" tube steel column. They definitely did not cut like the Buildex Tek5's

 

[Ron]

The dissimilar material issue also applies to the aluminum plate/steel interface, not just the fasteners. Make sure they are isolated.