Tech Inspection Question

[Christopher Crowe]

-- that kinda rhymes...

Here's my question. We're using .063 2024 T4 in certain areas of our car's floor pan. This is relatively light. So. Would anyone bitch about a patch of basalt or Kevlar ballistic fabric being epoxied to the upper top surface of the pan in the area just under the driver's bottom? This would be strictly for safety, not for structural gain.

The fabric patch would reside INSIDE the frame rails and not be riveted, just glued flat. Any opinions on the real-life acceptability of our doing this?

Thanks,

Chris

[starkejt]

Unless you post about it online, no one would ever notice, regardless of legality.

[Purple Frog]

My experience...ouch! The floor gets ripped off and one is skidding along on his nomex drivers suit. So, if the floor goes, so does your the Kevlar.

So... during my last rebuild (due to forementioned skid marks on driver's suit) I formed a second .062 tray to be riveted on top of the rails in the seat area, but bent it so it is touching the floor across the car. Gives me .122 of thickness for stopping intrusion, still .062 if the floor disappears.

YMMV

Tech wise, if you glue the Kevlar to the bottom of the foam seat insert it would probably provide the same protection and not be part of the car for inspection purposes. Just a thought.

[R. Pare]

Chris:

First off, .063, while the legal minimum, is really too thin for maximum performance. You should look at at least .083, bonded and riveted in the manner we have described before (with the 1" strips along the inside edges of all of the lower rails) - your body will thank you if you ever have a big wreck, never mind that when done correctly, the bond will last for years instead of 1/2 a season.

As to the kevlar - no problem legal-wise since it is (1) attached to the pan and not the frame, and (2) not the floorpan itself.

Won't be an issue at all.

[RobLav]

Weld in the 1" strips of steel to the inside of the lower frame rails - that Richard has been a proponent of - then use .083 (I used .090) aluminum properly bonded and riveted as the bellypan, then bend some .063 or .050 aluminum to sit on. This piece gets riveted to the top of the 1" steel strips and bent up and back behind the driver and riveted to the front of the fuel cell surround. This will keep you in the car if the bellypan ever decides to follow its own path.

This is an attempt to clarify what Richard and Mike have already stated.

[Christopher Crowe]

Thanks, you guys.

Chris

[Herman Pahls]

I appreciate this discussion since the only thing preventing an unwanted Hemrhoid Ectomy in my car is .063 aluminum and pop rivets.
Do the 1 inch strips get welded in only on the perimeter (4 sides) or some in the middle of the space to support the "back-up" floor?
Since my car is powder coated I would like to go with a non welded solution.
Since we all sit in a rectangle surrounded on four sides by tubing with the floor riveted to the bottom, what about bending aluminum so that it creates a upside down shoebox like lid that fits just inside of these 4 tubes with another 90 degree outward bent horizontal flange.
These 4 horizontal flanges would sit on top of the 4 tubes to support our weight in the event the floor pan gets ripped off and also allow vertical rivets from the top and bonding to hold in place.
I would appreciate your ideas.

Thanks Herman

[Jnovak]

I appreciate this discussion since the only thing preventing an unwanted Hemrhoid Ectomy in my car is .063 aluminum and pop rivets.
Do the 1 inch strips get welded in only on the perimeter (4 sides) or some in the middle of the space to support the "back-up" floor?
Since my car is powder coated I would like to go with a non welded solution.
Since we all sit in a rectangle surrounded on four sides by tubing with the floor riveted to the bottom, what about bending aluminum so that it creates a upside down shoebox like lid that fits just inside of these 4 tubes with another 90 degree outward bent horizontal flange.
These 4 horizontal flanges would sit on top of the 4 tubes to support our weight in the event the floor pan gets ripped off and also allow vertical rivets from the top and bonding to hold in place.
I would appreciate your ideas.

Thanks Herman

This works nicely Herman. Have done it on several cars. It does require some very carefull sheet metal work but that is about it.

Jay Novak

[R. Pare]

Herman:

That second skin will work in helping to keep your butt inside the car.

The strips are welded to the inside edges of all of the lower tube, effectively doubling the the bonding area. With this extra bonding, the pan itself can be stiffer (thicker), adding stiffness to the frame, without over-stressing the bonding.

The pan needs to be anodized before bonding, though, in all cases (strips or not) to eliminate the brittle aluminium corrosion that would otherwise form and thicken over time (which is where the bond always breaks).

Just make sure that the second layer does not run afoul of the 6" fastening rule, and no one will bat an eyelash about it.

[Christopher Crowe]

I would think that a structural aluminum L section 1" x .125" -- or even 1" x .063" --attached by rivet and epoxy to the inner vertical surfaces of the chassis' bottom tubes would achieve the same end. That's a LOT of surface area and the L sections are very light.

Herman, I hate touching a chassis that's flat and straight (and especially painted!) with tig-heat too.

Richard and Jay -- opinion?

[RobLav]

Your aluminum angle riveted and bonded to the rails will not work very well. As the chassis twists, you will put those rivets and bonds between the angle and the chassis rails in tension, and they will eventually pull. Rivets are not tension fasteners.

[R. Pare]

I would think that a structural aluminum L section 1" x .125" -- or even 1" x .063" --attached by rivet and epoxy to the inner vertical surfaces of the chassis' bottom tubes would achieve the same end.

Not even close. The strips have to be structurally part of the frame rails, or as Rob pointed out, they will just flex at the rivets. The bonding agent would also be put under tension, which most don't like - most are MUCH stronger in shear than tension or peel.

When welding in the strips, you stitch-weld to keep heat in any one area to a minimum. The biggest hassle is insuring that the strip and the bottom face of the tube line up nicely with each other, and then grinding out any protruding weld afterwards.

Go back in the building thread section and look up the pics of Brandons chassis while it was under construction 3 years ago.

[Christopher Crowe]

-- however, I don't know how in God's name that long bead isn't contorting things...

Also, I believe the really great pics that showed Brandon's riveting details have been removed. Those were fantastic how-to shots.

Again thanks for the help, Richard.

[RobLav]

Why not weld 1.5" width strips of steel corner to corner in an "X" pattern rather than all the way around the perimeter? This would triangulate the box as well as add bonding area.

[R. Pare]

Rob;

That would do zero for reducing the stresses at the main lower rails as the chassis is twisting, except maybe a bit at the corners.

Chris:

If you look closely at the discoloration, you can see that the welds are only a couple of inches long each - longer than I would have done it ( 1" long). What you do is weld on one strip for an inch, then go to another strip, weld it 1 inch, go to another , etc. This allows the strip and tube to cool properly between weld and will minimize distortion - trying to do it all at once is what gets you into trouble.

[Christopher Crowe]

-- that sucker looks like it's continuously welded!

Regardless, and as always, thanks for the info.

C

[R. Pare]

Chris:

Look at the heat discoloration on the strips - you can see how it spreads out wider at the middle of the weld length, then gets narrower where the "stitch" ends. The idea is to weld a short length - 1 inch or so - and then go weld somewhere else to let the first weld cool, then go back and weld in another area of the same strip, etc, until all of the strip joint is welded. If you tried to weld the full length of the strip in one go, it definitely would warp all over the place, but by only doing short sections at a time, the distortion is held to almost nothing.

When I would do long strips, I would tack it (1/8" to 1/4" lengths max) at the ends and every 4-6" or so, let it cool while I did another strip, and then go back and weld 1" at the ends and middle, go to another strip while that one colled, and repeat until all done.

[nulrich]

This photo shows what Richard is describing. The front section of the floor is being tacked into place, the rear section has been stitch welded along the entire perimeter. If done properly, there is no distortion of the frame.

Nathan

[rmstringham]

Also, I believe the really great pics that showed Brandon's riveting details have been removed. Those were fantastic how-to shots.

Here you go...