Cage question! - Lateral-g Forums

novanutcase · #1 12-31-2006, 01:09 PM

I am trying to figure out how I want to configure the cage in my build and had a design question. I want to run the rear downbar inside the C-pillar('66 Chevy II/Nova) but if I do this it will hit right off the top of the minitub. If I welded tubing that was bent to the same outside radius of the tub and ran it from the trunk to the inside rear floor then welded the C-pillar down bar to it would this be structurally OK? I could weld a crossbar between the two radiused tubes underneath the package tray for lateral stability!

ccracin · #2 12-31-2006, 01:42 PM

This is a reasonable solution, but I have a couple comments. If both ends of the curved tube have a direct path to the chassis than it would be OK. If you are only welding to the pan than this is not a good idea. Not just with what you are doing, but any cage should never be welded to just the pan. Also, the cross bar is a good idea. You may also want to try to triangulate this area under the tray. Right angles do not provide good lateral stability. JMO. Good luck with a great project.

novanutcase · #3 12-31-2006, 01:48 PM

THIS is the info I was looking for! Thank you Chad! The car will be full frame( Check out the build https://lateral-g.net/forums/showthread.php4?t=4432) and, yes, I plan on welding the curved tube to the new frame at both ends. Any other comments and/or questions would be greatly appreciated!

John

ccracin · #4 12-31-2006, 02:10 PM

John,

No problem, the build looks like it is moving along well. I have to agree with everyone else that car is on my list of "Want To Builds". I love talking about this stuff. I'm getting excited, we are hopefully going to be cutting steel for the chassis of our truck this coming week. I will post some pics once we get started. Later!

novanutcase · #5 12-31-2006, 02:29 PM

Yes...Please..Post away Brother!!

ccracin · #6 12-31-2006, 07:37 PM

John,

I was playing around with my new software and did the attached drawing. It is crude, but this is what I meant about the triangulation part of my comment.

novanutcase · #7 12-31-2006, 11:34 PM

That is very close to what I am thinking although what I am thinking is to take the bars that are curved and curve them to the radius of the tub and attach them to the frame in the trunk and the rear passenger foot wells! Thanks for taking the time to do that! Can you and I work on this more? I love the drawing you did. It really brings out the idea that I have. What program are you using to make this? The fabricator will be using DOM throughout instead of 2 x 4. It's stronger than 2 x 4.

ccracin · #8 01-01-2007, 07:34 AM

Quote:

Originally Posted by novanutcase

That is very close to what I am thinking although what I am thinking is to take the bars that are curved and curve them to the radius of the tub and attach them to the frame in the trunk and the rear passenger foot wells! Thanks for taking the time to do that! Can you and I work on this more? I love the drawing you did. It really brings out the idea that I have. What program are you using to make this? The fabricator will be using DOM throughout instead of 2 x 4. It's stronger than 2 x 4.

John,

I figured this wan't exact, I was just playing around. The software is Solidworks. I will do what I can for you, I'll be right in the middle of our project as well. I need to address your comment of DOM being stronger than 2x4. I assume you mean DOM round tube, if that is the case your statement is not completely true. First with regard to Drawn Over Mandrel tube vs. Standard Electric Weld for a given material grade. The only reason DOM is a bit stronger is due to the more consistent wall thickness and diameter due to the mfg. process. Now when you compare round tube to rectangular or square, the round tube is not stronger for a given equivalent size. It comes down to the moment of inertia of each tube when doing stress and deflection calculations. I don't know how much you like or use math but here is a simple calculation for deflection at the center of a member supported at both ends and with a load at it's center.

((load)x(length cubed))/((48x(Modulus)X(Moment of Inertia))

The modulus is the strength of the material the tube is made from. You can see that in the formula the moment of inertia in the denominator. The bigger this number the less deflection for a given load. Here are some moments of inertia for different sections:

2x4x.125 Rect. Tube: 4" direction-2.964 2" direction-.549
2x2x.125 Square Tube: .549
2"x.125 DOM Round Tube: .324
4"x.125 Round Tube: 2.854

You can see for one tube the 2x4 is the strongest. You would have to use 4" tube to come close with round. Now if your fabricator is going to use say 2 round tubes welded together to make a truss effect than it can definately be as strong or stronger than the rectangular. Much harder and more expensive to do, but it really looks cool. The calculations for that are more invloved.

My point is not to cause you any problems, I just think you should have the facts. For given size DOM is not stronger than rectangular tube. When you take into account a roll cage and such the need for rectangular or multi-round tube rails is not as great. Let me know if I confused you. Thus ends my rambling.

Talk to you later,

novanutcase · #9 01-01-2007, 03:31 PM

Chad,

Although some of the math is a bit confusing until you actually run through some if it please feel free to continue posting any and all information as this only makes me better and more informed as to what I can and need to do. Thank You!

I should have mentioned that he will, in fact, be using double DOM in an I-Beam configuration for the main frame much like he did on a truck he is now building. You should check it out! Pretty cool '57 truck build! Their site link is in the sig below!

Comments and Questions on the drawing:

In the area where the C-Pillar down bars connect to the half hoops that are resting on the frame rails, would it be doable and advisable to actually move the half hoops out almost against the rear quarter sheet metal and have them start from the frame in the trunk area and follow the radius of the tub to the outerrear corner behind the backseat where the tub ends? Of course they would attach at the frame again so as not to be using the sheetmetal as an attach point! This way I could run the C-Pillar down bars sandwiched between the outer sheetmetal and inner skeleton of the C-Pillar. The cross bracing would be as you illustrated! I will try and use my CAD program to give you a rough idea as to what it is I am talking about if I am not clear.

Again! A HUGE thanks for the time and effort you are putting into helping me on this!

John

**Sales@Dutchboys** · #10 01-01-2007, 03:37 PM

Those pictures on Steves nova site of that guys car were crazy.