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Frame boxing alternative

Ned Kelly said:
Instead of boxing a frame, does this seem like a viable alternative to add some strength?
I can't recall if his build is on CK5 also. See post #21 and 22 for pics and explanation.
http://www.pirate4x4.com/forum/chevy/1431410-78-k30-brushtruck-build-general-purpose-rig.html
Click to expand...


Seems like a great way to add a lot of weight, but not much else.

What type of "strength" are you looking for? Load bearing or torsional?

I suppose that enormously heavy structure may increase it's ability to support more weight on top of it, but torsionally it adds almost nothing. (For that matter, neither does fully boxing the frame....)

To prevent torsion, you need a vertical component that allows you to triangulate and resist twisting forces. That is why you see rollcages tied-in to frames and firewall bulkhead areas.


There is a great set of diagrams in the Herb Adams book "Chassis Engineering" (Chapter 12 - Frame Design) that clearly show how torsion affects different frame designs, and how absolutely ineffective most "solutions" are at combating it.... until you really start to add vertical triangulation into the design.

Example:




The book is a pretty easy read, and it's cheap. :waytogo:

https://www.amazon.com/Chassis-Engi...490708336&sr=8-1&keywords=chassis+engineering


-G
 
We have a 1/2 Suburban frame with 1 ton drivetrain. Would be running a 38-40" tire.
Wanting to swap a 1950's Dodge M37 body on to it.
We were thinking the 1/2 frame may need some strengthening?

Greg..thanks for adding that pic. Ok, I see your point.
 
I remember looking at that build and questioning if it was really worth the effort.

The crossmembers are great addition to these frames though. I was amazed how much the noodle frame stiffened up with them.
 
While we're all here... I've seen a few frames that the rivets have gone all loose. I know replacing them w/ good gr8's will help in that case. Has anyone welded the crossmembers in and done any testing?
 
I have seen a few crossmembers welded, and I always found one end broken. My '72 K5 has one that way now. I believe that this style of frame flexes too much for that. Or maybe there is a welding technique to prove me wrong??
 
JoshHefnerX said:
While we're all here... I've seen a few frames that the rivets have gone all loose. I know replacing them w/ good gr8's will help in that case. Has anyone welded the crossmembers in and done any testing?
Click to expand...

I've welded everything to my frame in anticipation for boxing it. Adding a tube or two across at either end of the frame, and "boxing" the engine crossmember.

Definitely not going to be as strong as if caged, but if it helps keep at least some of the twisting confined to the springs, I'll be happy. I just want it to be solid enough so as to not flex the body so much things crack, warp, and doors don't open right when twisted up a bit.
 
Cage all things!

iwpzjy3ggdpapoagr8av.jpg
 
6872xtc said:
I have seen a few crossmembers welded, and I always found one end broken. My '72 K5 has one that way now. I believe that this style of frame flexes too much for that. Or maybe there is a welding technique to prove me wrong??
Click to expand...

That doesn't surprise me a bit.

Try to imagine that the orignal 14-foot long framerail is subjected to torsion.... along each inch of that frame, a TINY amount of deflection occurs but it is pretty consistent across the entire length of the rail.

When you weld a crossmember in, you create a MUCH stiffer spot in the frame and at the point where "soft" meets "stiff" during torsion... you are going to see tearing of the metal.


This is the most difficult part of trying to "retrofit" a stiffener to the factory frame. You are going to create "zones" in the frame where things are stiff, and unsupported zones where things are just as loose as they were from the factory. At every one of those intersections, you are introducing a failure point in the metal. SO.... (in my opinion) you need to think the whole thing through much more carefully and identify where the torsional forces are being introduced into the frame (ie. leaf spring mounts) and try to imagine how those can be dissipated more gently into the soft parts of the frame... OR..... how to aggressively lock everything together in a new way, so that the torsion is effectively eliminated.

-G
 
3D will always outperform a 2D frame.
I would love to run a small cage in my C10, maybe 5-6" above the frame. Go up though the bed, keep it low and to the sides, enter the cab and stay low, maybe do a small B hoop behind the seats but below the window, small door bar out of the way, enter firewall and tie into near the front cross member. Have welded tie-ins along the frame as it goes. Keep the cage unobtrusive and out of the way, but seems any "height" and triangulation you can add to the frame/cage the better.
 
@Greg72
yep, Bender's cage tie in at the frame near all the suspension points, which should help eliminate twist. Only spot I worry about is the front leaf spring hangers, the cage only goes to my shock hoops which are almost as far as the hangers.
 
Well I guess I should get that book and read up on chapter 12 as suggested.
As people are indicating, perhaps some caging options should be considered rather than boxing or reinforcement.
 
Ned Kelly said:
Well I guess I should get that book and read up on chapter 12 as suggested.
As people are indicating, perhaps some caging options should be considered rather than boxing or reinforcement.
Click to expand...


If you just want a stronger frame to support the weight of a heavier (?) body on top, then maybe boxing does what you want.

But if you are trying to increase torsional stiffness (for offroading, etc) then you kind of need the cage anyway, right?

OR (Door #3).... just let it be as floppy as the factory designed it and let the body be floppy too! Reinforce around the steering box to prevent issues there but you could just let the frame act like a "secondary suspension" and give you more wheel/tire articulation than you might otherwise get with a stiff frame!!! :waytogo:



-G
 
The only way a crossmember could ever replication what boxing does is if the crossmember vertically X'd the top and bottom of the opposing frame sides together. And even then thats a huge waste of time, just box it.
 
Stomis said:
The only way a crossmember could ever replication what boxing does is if the crossmember vertically X'd the top and bottom of the opposing frame sides together. And even then thats a huge waste of time, just box it.
Click to expand...
just like floor joist....(not mine)

Floor_Joist_Cross_Bracing.jpg
 
Never seen anything like that before.. lot of work for a bodylift.. I see what he may have thought he was going to accomplish.. I'm probably the minority here but just caging my K5 has significantly increased the stiffness. To the point now the frame does not deflect from the body if I lift a single corner up. I tied mine into the suspension mounts and engine cage. In the scheme it isn't a lot of material, it's just in the right places.
 
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