X Member Design and Frame Bracing- '66 C10

[theastronaut]

I've decided to box the frame on my '66 C10 and while I'm at it I want to add an X member to limit how much the frame is able to twist. I've already started making patterns for the boxing plates but need some help on the X member. I've been looking over a few different frame builders' pics and came across Fatman Fabrication's Tri-Five frame, and really like their X member design.

http://www.fatmanfab.com/55_57chevy.php

It's got a full tube center section instead of an open square tube design. Round tube is really strong against torsional twisting so I think that would be a good idea to integrate into my X member.





I'm starting from scratch and have the ability to build it myself. I also have a tubing roller so I can make arches. Would the arched tubing have any strength benefits over straight tubing? And what about round tubing vs square tubing? I'd like for it to be able to accomodate dual 3" exhaust, and keep in mind that a '66 has trailing arms instead of leaf springs.

As you can see in the pic below, with only one of the rear bags inflated there's quite a bit of frame flex. I'll be boxing the frame from the C notches up to the steering box, and welding around the rivet heads that hold the crossmembers in place.


Any ideas/comments/input would be greatly appreciated!

[Alan's Classic]

Tuned in.
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[65Custom]

Me too!! Since I boxed mine in I might learn sumtin!

[andrewmp6]

Or you could make something like this http://www.speedwaymotors.com/Deluxe...-Kit,6815.html

[aggie91]

This sounds like a good idea. I remember something in the past like this. I think it was Porterbuilt that did a tube structure. Not sure.

Can't wait to see what you come up with.

[oldspowered67C10]

I'm trying to accomplish the same thing on mine as you are on yours. I made somewhat of a x-member set-up but did it in a simpler way. Heres a link to a thread I started when I installed my rear sway bar but has some pics of the frame.http://67-72chevytrucks.com/vboard/s...d.php?t=350913

[theastronaut]

Originally Posted by andrewmp6

Or you could make something like this http://www.speedwaymotors.com/Deluxe...-Kit,6815.html

I found Speedway's kits doing a google search. Looks pretty decent, but I think the four straight center connectors would still allow some flex compared to Fatman's center tube design? It would still be better than not having any bracing at all.

Originally Posted by aggie91

This sounds like a good idea. I remember something in the past like this. I think it was Porterbuilt that did a tube structure. Not sure.

Can't wait to see what you come up with.

I did search the site here and didn't find a whole lot. I did find some of "oldspowered67C10"s frame pics.

Originally Posted by oldspowered67C10

I'm trying to accomplish the same thing on mine as you are on yours. I made somewhat of a x-member set-up but did it in a simpler way. Heres a link to a thread I started when I installed my rear sway bar but has some pics of the frame.http://67-72chevytrucks.com/vboard/s...d.php?t=350913

I found some of those pics when searching earlier, thanks for those links! It looks like you've got a good bit done to minimize twisting!



Keep the ideas coming guys!!

[vin63]

I boxed my frame pretty much the same way you plan to. I thought about doing a tubular X-member, but decided against it after plotting it and realizing that it interfered with too many things I was planning, in particular the 4L80. To stiffen the front a little, I did down tubes from the firewall to the frame and a front motorplate to complement the existing inner fender structure.

[theastronaut]

Keith, I don't disagree with anything you posted but I wonder how much of it is applicable? You're talking about big trucks made to carry large amounts of weight. Also, were the frames on the old Chevy trucks heat treated, or just stamped from plain steel? The rails sure do drill through easily enough, I can't imagine them being hardened in any way. I'm after bracing the frame to resist torsional twisting, not to handle high towing weight. I would think that different types of bracing are needed for the two different applications? Again, not disagreeing with anything you posted, just wondering how much of that works to resist torsional flexing.
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[vin63]

I didn't box my frame for vertical load bearing, but to resist some torsional flex/movement. I transferred my plate patterns to a water jet mill and cutting the patterns from 0.1875 1018 steel plate. The plates fit snuggly inside the C-channel frame (which is not heat treated) and I TIG welded them in an inch at a time rotating locations (both front to back and top and bottom). This, in addition to the strength of the OE sheetmetal structures helped to reduce some of the torsional flex in my case without having to go the full roll cage route.

[aggie91]

I agree with Kieth also. His #5 above is what we are trying to improve by boxing the frame. A boxed frame is now a rectangle in cross section as opposed to a C shape for an unboxed frame. A rectagle tube has a better section modulus than the C for a give material. For the welding reducing the yeild strength of the material, that is true, but if you reduce the yeild from 55,000 psi to say 40,000 psi, than your RBM for "new" box is now = 680,000 for example 5b above, still an improvement over the stock number of 605,000.

Now for a frame on a '66 that is not heat treated, the improvement would be a larger precentage. In example 5a 6+2.5+2.5x30,000(mild steel yeild strength) = 330,000. The boxed version (5b) would be = 510,000. That is a 54.5454% improvement in RBM.

[theastronaut]

Like I posted earlier, I agree with Keith, but again, we're talking about two different types of forces acting on the frame. He's talking about vertical loading- heavy weight pushing straight down on the frame, and strengthening a frame to resist downward pressure from high towing weights. I'm trying to reduce the twisting motion of the frame, not keep the frame from bending downward when I've got the bed loaded down.

This pic represents a frame rail under torsional strain. It's twisted down it's length, much like a torsion bar would be under a load. Much different type of load applied to the frame rails than vertical loading.





This is a vertical load bending a frame rail (left side of pic, ignore the right side). It bends downward. I'm not trying to prevent this from happening because I'm not planning on towing a gajillion pounds of weight with the truck.





Now look at this picture, notice that the front crossmember is level. Which of the two pics above does this match? Only one of the rear bags are pumped up. This is a torsional load being applied to the frame, and the frame is absorbing the load instead of resisting it. If it was resisting the load the frame would be straight- the front crossmember would be sitting at the same angle as the rear of the frame, and the front suspension would be absorbing the load instead.

[jmlcolorado]

Originally Posted by theastronaut

Like I posted earlier, I agree with Keith, but again, we're talking about two different types of forces acting on the frame. He's talking about vertical loading- heavy weight pushing straight down on the frame, and strengthening a frame to resist downward pressure from high towing weights. I'm trying to reduce the twisting motion of the frame, not keep the frame from bending downward when I've got the bed loaded down.

This pic represents a frame rail under torsional strain. It's twisted down it's length, much like a torsion bar would be under a load. Much different type of load applied to the frame rails than vertical loading.




Very interesting topic, I must subscribe


This is a vertical load bending a frame rail (left side of pic, ignore the right side). It bends downward. I'm not trying to prevent this from happening because I'm not planning on towing a gajillion pounds of weight with the truck.





Now look at this picture, notice that the front crossmember is level. Which of the two pics above does this match? Only one of the rear bags are pumped up. This is a torsional load being applied to the frame, and the frame is absorbing the load instead of resisting it. If it was resisting the load the frame would be straight- the front crossmember would be sitting at the same angle as the rear of the frame, and the front suspension would be absorbing the load instead.

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[theastronaut]

I posted this over in the "Make it handle" thread, but I'll post it here too to keep everyone up to date.

The distance between the upper and lower sections of the frame C channels changes as the frame twist. An upper and lower X member will tie the top and bottom flanges of the C channel together and won't let the distance between them change. If I just made a single layer X member and welded it in the frame rails, it wouldn't hold the frame rails from spreading top-to-bottom.


I made this drawing in paint to show how the distance between the frame rails change as they twist. Notice how distance "A" is shorter than distance "B". Just one brace in the center would still allow the frame to pivot around that one brace, no matter how strong the brace is. Upper and lower X members with triangulated vertical bracing in between should lock down the distance of the rails, keeping them from twisting.




This is sort of what I'm planning on building, just not in such bright colors.

[jmlcolorado]

Originally Posted by theastronaut

I posted this over in the "Make it handle" thread, but I'll post it here too to keep everyone up to date.

The distance between the upper and lower sections of the frame C channels changes as the frame twist. An upper and lower X member will tie the top and bottom flanges of the C channel together and won't let the distance between them change. If I just made a single layer X member and welded it in the frame rails, it wouldn't hold the frame rails from spreading top-to-bottom.


I made this drawing in paint to show how the distance between the frame rails change as they twist. Notice how distance "A" is shorter than distance "B". Just one brace in the center would still allow the frame to pivot around that one brace, no matter how strong the brace is. Upper and lower X members with triangulated vertical bracing in between should lock down the distance of the rails, keeping them from twisting.




This is sort of what I'm planning on building, just not in such bright colors.

Are you worried at all that the forces the frame eats during hard driving will be transferred to the rear and forward diagonal joints causing the frame to crack at the joint?

That setup will make your frame very rigid and the forces have to go somewhere. I guess that's where over engineering come into play you engineer it strong enough that you won't be able to creat enough force to break anything

Your drive train will take it all. Motor mounts and the trans might suffer.

Just a reminder, I have no clue what I'm talking about, just
Tossing it out there
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[theastronaut]

Originally Posted by jmlcolorado

Are you worried at all that the forces the frame eats during hard driving will be transferred to the rear and forward diagonal joints causing the frame to crack at the joint?

That setup will make your frame very rigid and the forces have to go somewhere. I guess that's where over engineering come into play you engineer it strong enough that you won't be able to creat enough force to break anything

Your drive train will take it all. Motor mounts and the trans might suffer.

Just a reminder, I have no clue what I'm talking about, just
Tossing it out there
Posted via Mobile Device

Instead of the forces being absorbed by the frame (twisting), the frame will be more solid and transfer the forces into the suspension instead. Boxing the frame should spread out the forces being transferred through the frame over a larger area. I would think that the engine/trans/body mounts would be less stressed since the frame won't be twisting as much; the mounts wouldn't see as much movement.

I don't know much about any of this myself; I'm completly new to ladder type frames. I've always worked on unibody cars (VW Bugs) so this is all new to me. I got the itch a few weeks ago to brace the frame of my truck while the body was off and I've been trying to figure all of this out since then. I'd like to get it where it handles decent for now, not trying to build something that would even be halfway competitive at an autocross event, but I do want a good base to start with if I ever decide to do more serious suspension upgrades in the future.

[vin63]

Originally Posted by theastronaut

..Instead of the forces being absorbed by the frame (twisting), the frame will be more solid and transfer the forces into the suspension instead. Boxing the frame should spread out the forces being transferred through the frame over a larger area. I would think that the engine/trans/body mounts would be less stressed since the frame won't be twisting as much; the mounts wouldn't see as much movement....

This is the same principle that allows the use of solid trans and motor mounts in full-chassis drag cars. As an example, when I raced my '63 Chevy II in bracket classes with only subframe connectors many, many years ago, I would occasionally crack my trans case. I built a full chassis with a 14-pt roll cage, solidly mounted my trans and engine with more than twice the horsepower, and have yet to crack a trans case in 20 years of Super Gas racing. These days, I build double frame rail chassises for really high HP applications, like my funny car where everything is solidly mounted to the frame.

[kieth]

I understand that we are not hauling a lot of weight per se, but if the frame is more rigid then it will have less flex to begin with, The cross bracing will work better if the outer beams of the frame are stronger, of course the additional x bracing will add rigidity but so will doubling the frame. ps no matter what they say I still do not like welding a frame.

I think our frames are made out of mild steel (55,000 psi yield strength) Newer big truck frames are made from 110,000 psi yield strength material, one could add full U or L channels made of this harder material and bolt it in place and have a really strong frame.

Since I want to add full C channels just like the std frame the picture that you show of the twisting of the frame would be different since the flanges help it to resist twist (some work on the way our crossmembers are attached or adding more crossmembers would also help in this torsional rigidity.) The X bracing sure will help also.

Want you guys to understand I was not trying to pick a fight just get more information out there and make us all think a little bit before we dive off and do things in a way that mght do more harm than good. i.e. welding to the frame, adding bracing in certain areas can lead to a frame failure right where the reinforcing stops.....due to the weld. We always try to spread out the loads on the frame by adding more material all the way to a area that has more reinforcing above the rear axle or to the center above the axle . by doing this we keep the loads in areas that see the least twist.....

If you double frame a truck and stop the reinforcing material right behind the cab of the truck, that is where the frame will fail......if you take it forward to where the frame sees less loading (twist) it will not have that problem...

bolting it together is stronger than welding it. If you do weld an area of frame together, then add a diamond patch, it is still better to do a bolted in longer u section to the front and rear of the weld. This is done so the weld does not see loading where the heat treat has been removed. Bolting the frame together spreads the loads out to the web of the frame instead of to the flange.

[tubbedII]

Is the goal you are trying to reach just to improve the flex with just crossmembers? I only ask because wouldn't a roll cage stop this type of flex much more?

[SCOTI]

Originally Posted by tubbedII

Is the goal you are trying to reach just to improve the flex with just crossmembers? I only ask because wouldn't a roll cage stop this type of flex much more?

My thoughts are boxing the frame or strategic x-bracing below the sheet-metal would be preferred because even though a roll cage could help limit frame flex, it would do so @ the cost of reduced interior space.

Roll cages can also be a hazard in a mild crash if they're not properly built & occupants are not properly secured in place.

[vin63]

Originally Posted by vin63

I didn't box my frame for vertical load bearing, but to resist some torsional flex/movement. I transferred my plate patterns to a water jet mill and cutting the patterns from 0.1875 1018 steel plate. The plates fit snuggly inside the C-channel frame (which is not heat treated) and I TIG welded them in an inch at a time rotating locations (both front to back and top and bottom). This, in addition to the strength of the OE sheetmetal structures helped to reduce some of the torsional flex in my case without having to go the full roll cage route.

Originally Posted by tubbedII

Is the goal you are trying to reach just to improve the flex with just crossmembers? I only ask because wouldn't a roll cage stop this type of flex much more?

Yep, previous post above...since these will be street driven, a roll cage is not a good option.

[kieth]

Thanks a lot for the information and I feel like I have learned a lot by participating in the discussion. Lots of really good information on this site and there are a lot of knowledgeable people as well. That is why I come here to lurk, learn, and discuss. Great ideas on how to increase the strenth of the frame and the X brace design is great........Kieth

[65Custom]

Originally Posted by kieth

Thanks a lot for the information and I feel like I have learned a lot by participating in the discussion. Lots of really good information on this site and there are a lot of knowledgeable people as well. That is why I come here to lurk, learn, and discuss. Great ideas on how to increase the strenth of the frame and the X brace design is great........Kieth

I second this

[theastronaut]

I have this week off so I was able to start making some progress. I decided to use 1"x2" 14g rectangle tubing for the X members, and it should be here tomorrow. I got the frame stripped down and temporary braces welded in, then flipped the trailing arm crossmember and temporarily reinstalled it and the the trailing arms/axle. I laid out the rear X member with string to check for trailing arm and driveshaft clearance at full drop and lift. I've decided to use a T56 trans and have a friend that's going to let me borrow his to mock up the engine/trans so I can build the front X member around it. Here's the pics of the rear, let me know what you think before I start welding in tubing!


Flipped T/A crossmember.




Full drop, string represents bed floor.




Upper and lower X's, will have triangulated braces tying the top and bottom together.








Bottom tubes will be bent for trailing arm/driveshaft clearance. I have a tubing roller to do this with.

[theastronaut]

A cage would make the frame much stiffer but it's just going to be a driver and not an all out track car. I'd like to eventually upgrade the suspension and occasionally autocross it but that'll be later down the road. I want to do the frame mods while the body is off now, so the later upgrades will have a good foundation.