28 replies to this topic

[dstevens]

How much you wanna bet that a combination of stitch welding and plug welding is stronger still? Can you test that while you are at it?

Where's the plug weld? An inch or so into the plate and at what spacing? It's an interesting idea. Punch through in a big enough shut is always a potential issue in a unibody where you're connecting to 22-20 ga sheet. You need to find a way to get it onto a larger structural member. Hard to do in the chick car.

@Mark O, I use Autocad Mechanical, Alibre and Bendtech Pro and Sheetmetal for fab instructions. I get a lot of my engineering data from Machinery's Handbook. Though even having those resources at my disposal, I look to see what the big time guys are doing. Leavitt, Blaine, Bloomquist and the like. I know I'm not an expert at this by any stretch of the imagination.

[KentCarter]

I imagine this is the strongest way to attach a tube to the sheet metal of a floor pan:

http://flic.kr/p/ckQ8D7

[Jim Boemler]

Doesn't the GCR require a continuous bead regardless?

[KentCarter]

Doesn't the GCR require a continuous bead regardless?

Best I can tell, only for tubes.

"It is recommended that all joints of the roll cage be welded. All welding must include full penetration, no cold lap, no surface
porosity, no crater porosity, no cracks, no whiskers, and so forth. Welds shall be continuous around the entire tubular
structure. Procedures for welding alloy steel shall be in accordance with accepted industry practice. It is recommended that
a certified AWS D1.1 welder do all welding."

[Jim Boemler]

Interesting. BTW, I really do appreciate you being my GCR reader, Kent!

Has anybody ever had a car tech'd with non-continuous welds around the plates? Just curious if the scrutineers are prepared for this.

[KentCarter]

I talked with the head of tech for the Houston Region. I think he gets it. He mentioned that the tubing had to have circumferential welds without gaps per the GCR. He understood that interrupted welds on sheet metal were likely to be stronger than a continuous bead. We were discussing the idea that crack propagation in thin metal was scary and how stitch welding was less likely to see that occur. He also understood the value of plug welding.

Whether that translates to all SCCA tech people, I don't know.

[KentCarter]

Interesting. BTW, I really do appreciate you being my GCR reader, Kent!

Expect a bill in the mail.

[exninja]

The Solid works wont give any valid data for the floor rip out values. Does anyone have any known good values? I ran a bunch of real world testing for the floor crush boxes, showed that 360* welding of flat floor plates is very weak. 1in stich welding is much better. How do I get a valid , typical floor plate rip out value? The rear bars should be less than 42*, any more and they spread the hoop. Not all bad actually. All of the cage builders that I have approached just use the common method without any engineering programs. Please speak up if you actually have a program !! Last , does anyone have any data for the shelf mounted hoop? I want to mount the next cage on the shelf for the driver side. Thanks,MM

You won't find an FEA "program" that will do this. You'll have to find the loads then pull out your machine design book and your calculator.

Hopefully you're using beam elements for your tubes. You can get good loads and stresses in your members, but you can't analyze the joints in the program.

[Protech Racing]

" Inex? " My Son uses this with his space intern deal, but still have to add up the values. I thought that we could use the solidworks but he says the same, cant add up the pieces.
I will model with no front tube tension values. I figure that they wil be the same and thus can be deleted. If i get the scale right I should be able to use my HD valve spring checker for percentage change.

RE" plug "sill welds. Anytime that the tin weld can be non linear, it will pull better numbers. I service many SCCA cars and am amazed at the floor plates that have log book numbers. Just welded in ,bolt in cages, on a 2x4 plate. way weak in compression/tension. The cage would work better mounted on floor mats/carpet.

My "crush boxes" have never been questioned by SCCA techs. " Hop scotched" welded( non linear) except at the sill top.
The Chumpcars are sill plated, tabbed to the pillars, etc. multi struted to the floor areas. lots of square inches of involvement.
Anti punch through seat bar. I hate punch through, killed a guy driving the car I wanted( Dart) when I started racing.1982.
I had a Buick .. still won most of the races, Spencer Speedway , NY.

MM