Self Drilling/Tapping Screwstuds?

[Firestar1485]

This is NOT a "leather" question, but knowing many of you are also involved with other heavy materials and fabrication, I thought I'd ask ...

I'm sewing a canvas awning that utilizes snaps to attach to a steel framed roof rack on our expedition van.  Problem = I've tried several varieties of self-tapping "screwstuds" and none seem to do the trick!  The screwstud will start to bite into the steel but then it seizes and the head either strips or completely spins off.  Here's a link to screwstuds I'm using ... http://fasteners.fasnap.com/viewitems/screwstuds/self-drilling-screwstuds

Notes: 

1. I've used various types of self tapping screws in the past without this issue (i.e., sheet metal roofing screws).  Side by side these look identical to these screwstuds, other than they don't have a snap top. 
2. Just to rule out the strength of the steel frame, I tried some of my regular self tapping screws on the same metal and had no issue.
3. Also tried predrilling smaller diameter holes into the steel frame and then use the self-tapping screwstuds, still no luck.  They bite and then strip or break.
4. I tried a slightly larger drill bit size and the hole ends up too big to provide any grab for the screwstud threads.
5. I even tried "drilling" a hole with the standard self tapping screws that I have, backing out the standard and then screwing in the screwstud.  Same issue, either the hole is too large and no bite, or too small and the screwstud seizes. 
6. Also each of the above with lubrication (heavy cutting oil), no change.
7. I am using a basic cordless impact driver to set the screws, just like I always have.

This really has me stumped!

Pictures attached of the screwstuds I'm trying and my roof rack that I'm trying to attach them to.

Any thoughts, suggestions, tricks would be appreciated!!

 

[Thornton]

How thick is the metal on the roof rack?

[Elliot]

It looks to me that they are to be used in aluminum, or soft metal.

You need a sharper thread for steel.

[TinkerTailor]

Have you tried using a standard snap base with a screw instead of the rivet? Why buy the special ones when a standard snap is ready to go with the hole. Just choose a screw with a nice low profile. Since it is steel, you could tap the hole and use a machine screw. Aluminum may not have the strength to hold the tapped thread if the wall is thin.

[alpha2]

It is possible that the brand you are using is sub-standard. Pre-drilling with the appropriate bit will work fine with any quality brand, assuming it's sheet metal and not plate that you're trying to "drill" into. (Pre-drilling should NOT be needed for proper grade items and appropriate thickness sheet goods).
 

[Firestar1485]

Back to this project and I appreciate everyone's feedback.

1. I am drilling into 1/8" thick structural steel, not sheet metal.

2. Standard snap base with a machine screw?  I'm confused, I have not seen a standard snap base that would be big enough or deep enough to fit a screw head inside of it.  What am I missing here? 

3. The screw studs I am using are steel, not aluminum.  In fact they are stainless steel.

[Sonydaze]

Stainless steel screws are not nearly as strong as steel screws.  The stainless screws may be galling and seizing to the steel. Once they 'freeze', you usually can't get them in or out.  I would try drilling and tapping as well as using an anti-seize compound.  One other thing you may consider is pop riveting the snap studs on.

[Firestar1485]

I choose stainless because of the potential for rust in this application.  Yes, the problem I am having is that as soon as they start to bite, they seize and then cannot be backed out nor driven in fully.  I tried predrilling, but I have not tried an antiseize compound, nor tapping the holes first.  I am not sure pop-rivets would work, but I will check into that too.  Thanks.

 

[Sonydaze]

One other thing, putting screws in quickly generates a lot of heat.. which causes the galling.  Don't use power tools to screw them in, use a screw driver or ratchet and go slow.  

Pop rivets are easy if you can put them in from the opposite of the stud.

Lol I've done a lot of work on boats and I've learned this the hard way a couple too many times.  If you have silicone cauking on the threads it is even more prone to seizing up. 

[brmax]

As mentioned, the standard stainless screws are neat and prevent some corrosion but simply cannot hang when trying to use self tapping in plain ole steel, or actually most anything.  And really they will be eliminated when ya have to remove them when broke what a pita. So respectfully they should only be used in material thickness close to thread dimension, imo. With that pre drilling is the best method on any material usage, and that dimension seriously dependent on thickness and material.  To your support many self tapping steel screws no matter their makeup need pre drilling, And I sure like them but, the other ones that don't require pre drilling on general fastening to steel are a bit more expensive.

So being you have these already I suggest pre drilling ?if thin base steel with maybe a range of needed bits 7/64, 1/8, 9/64" as I don't know what size screws your using and the link has a zillion op's. What I keep here is typical size 8 and 10 screw these have a rough .030" on the #8screw between threads and for the #10 screw having about .040" between threads so on steel this is where thickness runs best generally in metallic stuff. Many times as ya know the aluminum will givway and offer you options. I also like or generally only use 3M fast cure 4000 sealant.

So closing I could glady go on and on but truthfully Thorntons at the Top question of how thick is the steel is the real primary to help you out, and do you have other option fasteners  avail nearby. Of course if this is your own project or something of a production, if the latter I would certainly use rivets if doing again and still use 3m 4000.

good day there

Floyd