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PostPosted: January 23, 2013, 10:43 pm 
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Location: Winter Park / Orlando
I've searched and read many links, but if there's a topic regarding FLOORING, I've missed it.

I'm going to pull my motor/tranny tomorrow and flip the car to do all the final welding that's hard or impossible to do right-side up. I figured this would also be the perfect time to install the floorboards. My questions are:
(1) what materials are other builders using, steel or aluminum, and why,
(2) what gauge material would other builders recommend and why,
(3) what rivet size/length are other builders using, and
(4) any suggestions, recommendations, tip or advice for builders new to this process!

THANK YOU!
-Gar

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viewtopic.php?f=35&t=14227


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PostPosted: January 24, 2013, 9:54 am 
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My plans are for 16 gauge steel sheet, welded to the frame. I then plan on installing some "drain plugs" that go on the floor boards of many factory cars, to let water out when I get rained on. And maybe some very small tubes hidden away.

Why?

Cause... uh... I'm not inclined to drill and rivet 10 million times? Cause I have my welder set up for 16 gauge steel?

And, cause I think that some of the lighter, thinner solutions might not have much protection for the time when I run over something. And this is NOT a race car (that might be the next one!) so a few pounds more won't be that much of a consideration -- I could probably do better by simply losing 30 "personal" pounds instead.

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PostPosted: January 24, 2013, 4:45 pm 
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I'm pretty much on the same page with Tim, 16 gauge steel stitch welded around the perimiter and plug welded to the interior tubes. You could get away with 18 gauge if you wrinkle it up a little. The weight is way down low so I don't mind.

I also like that the steel floor acts like a giant gusset, reinforcing some of my earliest welds, which I'm sure were fine but it was nice to have the opportunity to weld on them again.

IMO the main advantage of auminum, besides weight, is that it'll stay flat. Hard to weld a giant sheet of 16 gauge steel without getting a few bumps in it.


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PostPosted: January 24, 2013, 4:50 pm 
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Location: Coos Bay, Oregon
mine is stitch welded, 16ga. Cuz that's how i bought it. :D


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PostPosted: January 26, 2013, 2:30 pm 
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So steel floors are less expensive and stronger (if both are the same gauge)?
Welding is easier & quicker than drilling/riveting?
Steel floors need to be painted so they don't rust.
Any other thoughts?


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PostPosted: January 26, 2013, 2:37 pm 
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Keep in mind that the steel materials will rust where they face each other unless protected or sealed against oxygen.

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PostPosted: January 26, 2013, 3:09 pm 
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A few other comments:
-Steel weights 3x as much as aluminum so a 0.040" steel floor will weight as much as a 0.120" aluminum floor.
-Steel and aluminum can have similar strength properties depending on the alloy so a 0.120" aluminum floor will more like likely end up being stronger and more puncture resistant.
-The material's hardness is going to effect when something penetrates. A higher strength/less malleable alloy will be more likely to crack or fracture rather than deform.
-Stiffness and its ability to resist a perpendicular load varies by a power of 3 so going from 0.040" to 0.120" will significantly increase the floor's stiffness.
-The sides of the car are covered in 0.040"-0.063" aluminum; why everyone makes a huge deal about the bottom is beyond me if it is really *that* big of a deal. If you were to slide a car sideways into something sharp at just a few mph it could be lethal.
-I would be more afraid of that 2x4 coming over the hood and through the windshield than I would puncturing the floor.
-A ton of production cars have floors made of material no thicker than 0.040" and there is not much more ground clearance.

Do whatever is easiest.

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PostPosted: January 26, 2013, 3:57 pm 
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I went to my steel yard and they had a bunch of 20ga steel for super-duper cheap. Steel is weldable so that simplifies the attachment to the chassis. Also, it's easier to roll beads into thinner steel to stiffen up the panels. Like Andrew said: do whatever's easiest.


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PostPosted: January 27, 2013, 10:38 am 
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The 0.120" aluminum has a lot of appeal for me. If you do the semi-traditional treatment and use an adhesive between the aluminum and RHS of the chassis plus pop rivet and seal same, it would seem like you have all the bases covered. I actually read a good review of the HF pneumatic pop riveter, so you could get an affordable tool to do the job. Of course, you've still got to drill the holes.

My questions would be:

1) Cost of .120 aluminum versus steel sheet of 16 gauge;

2) Spacing and number of pop rivets when used in conjunction with adhesive;

3) Identifying and purchase cost of good aero-quality pop rivets for use with thick aluminum to steel.

I believe one can get into some trouble joining dissimilar materials with rivets depending on the rivet material and coatings (or lack of it really). I don't know that it would be a factor here unless you have the vehicle outside a lot and moisture can creep into the joints on a regular basis. Any members out there really up on galvanic action and corrosion?

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: January 27, 2013, 12:00 pm 
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Steel and aluminum can be pretty reactive when not isolated and road salt makes it even worse. I would put some sealant between the floor and the frame install the rivets wet with some sort of sealant and hope that keeps moisture out.

Regarding spacing, 4-6D is typical in the aircraft industry for structural joints to eliminate the concern for tear out (rivets too close and the sheet is perforated) and inter-rivet buckling (rivets too far apart and the sheet can buckle between fasteners). Going by standard rules of thumb a 1/8" rivet would be too small to secure a 1/8" thick aluminum plate since the rivet will shear before the hole in the floor elongates - the theory is that a failed rivet will carry no load while an elongated hole with a rivet still intact will carry as much load as it will take to elongate the hole and no more. Since the floor is 1/8" thick, you could go greater than 6D before buckling will occur however there will be fewer fasteners so less strength so it will be a trade off.

If you wanted to gain the most from riveting the floor, you would need to spend the money and buy aircraft blind rivets. The standard pop rivets have strength values anywhere from about 50 lbs to 220 lbs in single shear while something like an aluminum Cherry Max rivet will start at over 600 lbs and go up. These are also manufacturer single shear values; when they are tested in the real world the joint strength will be lower due to some bending in the fastener. Since the aerospace rivets have a higher clamping load by the nature of their design, the real world value will be a greater percent of the advertized strength compared to the hardware store variants.

My take has always been "I'm too lazy to drill all of those holes" and "I can attach a few weld nuts to the frame and use 1/4" bolts that are stronger than a much of 1/8" rivets" and "I have some diagonals in the floor to triangulate it so the aluminum isn't doing *that* much". In reality we are not building our cars to the same standard as the FARs require for airplanes so do whatever seems reasonable.

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PostPosted: January 27, 2013, 3:01 pm 
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i used 16 ga. anywhere i couls stand or put my feet, anywhere else i used 20 ga.

i also cut each piece to fit inside the tubework so that it fitted flush with the bottom of the frame and perifery welded it in with a continuose weld as i felt it would act like bracing for the frame rather than just stitching and plugging.

i also did this in the bottom of the frame in the front suspension area.

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PostPosted: January 27, 2013, 3:35 pm 
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What are the recommendations near the bell housing (clutch explosion)? What are the recommendations in the tunnel to protect in case of u-joint failure (drive shaft hoop)?

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PostPosted: January 27, 2013, 3:36 pm 
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a.moore wrote:
. . . <SNIP> . . .
Regarding spacing, 4-6D is typical in the aircraft industry for structural joints to eliminate the concern for tear out (rivets too close and the sheet is perforated) and inter-rivet buckling (rivets too far apart and the sheet can buckle between fasteners). Going by standard rules of thumb a 1/8" rivet would be too small to secure a 1/8" thick aluminum plate since the rivet will shear before the hole in the floor elongates - the theory is that a failed rivet will carry no load while an elongated hole with a rivet still intact will carry as much load as it will take to elongate the hole and no more. Since the floor is 1/8" thick, you could go greater than 6D before buckling will occur however there will be fewer fasteners so less strength so it will be a trade off.

If you wanted to gain the most from riveting the floor, you would need to spend the money and buy aircraft blind rivets. The standard pop rivets have strength values anywhere from about 50 lbs to 220 lbs in single shear while something like an aluminum Cherry Max rivet will start at over 600 lbs and go up. These are also manufacturer single shear values; when they are tested in the real world the joint strength will be lower due to some bending in the fastener. Since the aerospace rivets have a higher clamping load by the nature of their design, the real world value will be a greater percent of the advertized strength compared to the hardware store variants.

. . . <SNIP> . . .


Thanks for the info, Andrew. It is a big job doing the holes/rivets/adhesive approach, but you only have to do it once. I think it will be worth it to use aircraft quality rivets. Of course, I could get right to the moment of having to do it and get real lazy and say "shoot, I've got plenty of MIG wire, I'll just weld steel." I usually don't go that way, but I might. Besides, JD Kemp did the adhesive/rivets/aluminum approach (I've seen the pictures), so why can't I? :mrgreen:

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: January 27, 2013, 11:54 pm 
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Yo, Lonnie-
Yup, iffen I can do it, pretty much anybody can... :mrgreen:

But, if you go with the structural rivets, and I'd really recommend you do, then you'll be wanting an air riveter. Those Cherry rivets are no fun at all to do by hand. It's more like "do by hands" - plural- because it will take both of 'em. I think I did maybe two before saying I had to have a riveter. Maybe it wasn't that many... :mrgreen:
:cheers:
JDK

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PostPosted: January 28, 2013, 12:25 am 
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^ JD "My hands hurt from riveting" Kemp^


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