Bolting to steel tubing

[flynntuna]

Has anyone used " box bolt" type expansion bolts for attaching parts where high strength is needed?
https://www.beamclamp.com/connection-solutions/detail/boxbolt-cavity-solutions#cat3
https://www.mcmaster.com/expansion-bolts

[GoDadGo]

Tuna,

Thanks For Posting Because These Really Could Be Of Great Use To Many Of The Gang On The Forum!

Steve

[shark92651]

Interesting, looks like a drywall anchor for steel. The sleeve looks to be too long to work in the 3/4" tubing and the larger tubing on the frame is usually thick enough to tap. I would probably just stick with rivnuts for blind applications or through-bolt it if you need maximum strength. At least I know rivnuts are easy to drill out if you spin one (which I may have done once or twice in my build).

[mike223]

I prefer jacknuts.

123321

[flynntuna]

Jack nuts are useful but are they grade 8? I only asked because I'm looking for some way to attach steel plate to the frame so that I can attach my seat and seatbelts to. These box bolts are used in building construction. If they're used to attach balconies to the side of buildings, they should be good enough for my application. They are expensive though, starting at $5 each for the smallest size.

[fletch]

Hmmm. Are those one-time use? Is the cone-shaped mandrel/nut captive so you can remove the bolt without losing the female threaded part inside the steel tubing? Seems like it must be captive, but the pictures sure don't look that way to me.

[flynntuna]

Hmmm. Are those one-time use? Is the cone-shaped mandrel/nut captive so you can remove the bolt without losing the female threaded part inside the steel tubing? Seems like it must be captive, but the pictures sure don't look that way to me.

Yea they are one time use. They would have to be drilled out to replace, but I was looking for an alternative to welding.

[lance corsi]

There’s really no substitute for welding. It opened up a whole new world for me when I decided to learn it. There are some places where a threaded fastener just won’t do. Anchoring a seat isn’t hard but I wouldn’t use any type of similar fastener as the rivnut for such. I mortised some flat 1/4 x 1” into the existing x-bracing. I then drilled & tapped those inlaid bars for my seat mount. Seat belts should also be attached in such a way that a nut & washer can be installed from the back side.

[mike223]

Jack nuts are useful but are they grade 8? I only asked because I'm looking for some way to attach steel plate to the frame so that I can attach my seat and seatbelts to. These box bolts are used in building construction. If they're used to attach balconies to the side of buildings, they should be good enough for my application. They are expensive though, starting at $5 each for the smallest size.

Jack nuts are not grade 8.

Where specifically are you going with them?

The thinnest "material thickness" specified for the expansion bolts is 1/4" - I do not think there is 1/4" thick material anywhere in the frame.

I think the 4" round frame tubes are .120" wall thickness (if that's where you're going?).

Additionally the smallest (8mm) expansion bolts require a 9/16" hole. 1/4" jack nuts go in a 3/8" hole, 5/16" jack nuts in a 1/2" hole - I used 1/4" jack nuts in the 4" tubing to anchor the inside bottom seat mounts

I think either (or any?) fastener "properly installed" - the .120 wall of the 4" tubing is going to deflect and and allow the fastener to pull through before either "fastener" actually "fails".

But it's going to be easier to (tear out and) pull through a bigger hole, especially when the wall thickness is under the minimum specification (for the expansion bolts).


Jack nuts are $9 - $10 for 25.

And they're designed for the right wall thickness (if you buy the right ones).

And they fit in a smaller hole.


Perfect or best answer? - maybe not, but probably good enough to anchor the 4" tubing side of your seats (or seat mounts).

The best answer I've found so far for that particular application.

[flynntuna]

[QUOTE=lance corsi;401097]There’s really no substitute for welding. It opened up a whole new world for me when I decided to learn it. There are some places where a threaded fastener just won’t do. Anchoring a seat isn’t hard but I wouldn’t use any type of similar fastener as the rivnut for such. I mortised some flat 1/4 x 1” into the existing x-bracing. I then drilled & tapped those inlaid bars for my seat mount. Seat belts should also be attached in such a way that a nut & washer can be installed from the back side.[/QUOTE

I also thought about making a mortise on the back side of the tube like you discribe. How big of an opening did you make?
The box bolts I thought could be an option but tear out is a concern.

[SSNK4US]

I would DEFINITELY NOT use jack nuts on seat belts or any part of that equation! NOT NOT NOT!

Just my 2¢

Kurt

[mike223]

I would DEFINITELY NOT use jack nuts on seat belts or any part of that equation! NOT NOT NOT!

Just my 2¢

Kurt



All good.

Now, what pulls out first?

Jack nuts through .120" steel?

Or thick hardened fender washers through .100" aluminum? (kirkey race seats - as good as it gets).


My answer: Anyone who ends up in a situation to put that seat or mount under that much stress in a Mk4 roadster....


Doesn't get to make another mistake.



Feel free to disagree.

[SSNK4US]

I was referring to seat belts. He mentioned mounting his seat AND belts mounted to a plate attached with jack nuts. Sure a Kirkey seat is as good as it gets but I sure wouldn’t mount belts to one. Or a plate mounted with jack nuts? A seat mount doesn’t even come close to the stress of a belt mount in an impact.

And your right Mike, do it wrong and you don’t get to do it again.... but.....

At 6:20 he did have that much stress.... he did it right.

https://youtu.be/CQkqkOwuqac

I’m sure most of us have seen that and say I’m never gonna track the car. Freak accidents happen, sometimes I feel safer on a track. Broke my neck on the street....

123585


Kurt

[mike223]

I was referring to seat belts. He mentioned mounting his seat AND belts mounted to a plate attached with jack nuts. Sure a Kirkey seat is as good as it gets but I sure wouldn’t mount belts to one. Or a plate mounted with jack nuts? A seat mount doesn’t even come close to the stress of a belt mount in an impact.

And your right Mike, do it wrong and you don’t get to do it again.... but.....

At 6:20 he did have that much stress.... he did it right.

https://youtu.be/CQkqkOwuqac

I’m sure most of us have seen that and say I’m never gonna track the car. Freak accidents happen, sometimes I feel safer on a track. Broke my neck on the street....

123585


Kurt


Actually, my mistake - I missed the seat belt reference (or only glanced over it).


Seats need to mount to the frame - seat belts also need to mount to the frame (separately).

Every FFR design I've seen (not that I've seen them all in great detail - I can only speak directly to the Mk4 roadster) provides "exceptional" welded in seat belt mounts (frame). And those should be used.


Regarding possible inner mounting sites (transmission side) for race seats (in a Mk4) - It looks to me like "choose your poison" - you can mount in the provided x-frame or plate (too far from inside edge of seat for me), or anchor by some method to the 4" frame rails, or fabricate + weld something of your own design in.


My comments were simply related to considering what it is that you're trying to keep in place - .100" aluminum sheet metal seat in my case - there's no point in making 1/2 of the equation "completely bullet proof" when the other side of the equation is "what does it take to pull a fender washer (or 2 or 3) through .100" aluminum sheet".

[mike223]

To further the conversation - I'm satisfied with the bottom mounting of my Kirkey race seats (4 points).


What I'm currently trying to improve on is additional bracing (mounting) in the region around my shoulder blades - the higher the better.


I'd like to work in something like a Kirkey 99201 brace on the back of the seats, but have yet to come up with anything satisfactory.

If anyone has worked something like that into a Mk4 roadster - I'd love to see pictures to cheat off of / maybe even improve on.


Just food for thought / discussion...