anyone ever......

[71wrenchhead]

make their own frame?
like, get some 2 x 4 tubing, 12 gauge
and just weld up a frame that replaces the original frame rails and also works as a sort of subframe connector

just wondering, i was thinking about possibly doing this and also building in a custom engine mount and tranny mount out of the same stuff

ideas? pros? cons?

[Cooter]

Back-halved a bunch of cars...Even made a frame for a "Rat-Rod" once. Never tried anything for a whole car.

Not a bad idea if you have MASSIVE amounts of time and a jig. Otherwise, you will be having alignment problems.

[71wrenchhead]

thats where i got the idea is from rat rods (i want one of those too      )
anyway, i figure i would set up a jig using just some 2 x 4 first, make measurments and set it up with some metal posts welded to a flat base

i have pretty much all the time in the world, barring death, i dont really have any plans for the car except to have fun working on it

my question is, how accurate does the whole thing really have to be, like, are we talking millimeters accurate or like, 16ths of an inch accurate?

i never did anything like this except for a gokart i made for my lil brother, that came out just fine, but i never spent a lot of time measuring everything to be absolutely perfect

[Chryco Psycho]

Used to build full tube frame race cars , the more accurate the better obviously , there were always tricks like staggering the front wheels slightly to get more roll out . You can move the engine around as well such as moving it back a few inches for better weight distribution . Steering brakes & suspension an all be improved

[HPP]

Sure, it can be done. Pros- its hella cheaper than buying prefab frame rails. Cons- you have to be accurate or your suspension position or it can be off, which can cause all sorts of issue. It also wrecks the value for any collectibility to the restoration crowd.

Here is a Cuda getting tube steel frame rails: http://www.cuda-challenger.com/cc/index.php?topic=82472.0

[Mike DC]

 
It's not really more difficult than doing a separate front or rear clip, but it's a lot more involved in general.  Much more consuming of man-hours and shop space.

If you're doing it to save costs on a basically stock resto then it's not worth it.  But if you would have been heavily altering the car anyway (even if you had started with a non-rusty unibody) for higher performance, then go for it. 

[71wrenchhead]

no, im all for altering it, not just for more power, but for a better ride in general
i dont plan to resell it ever, i love this car and i dont feel to bad because it was just a vanilla charger with a 318, not much as far as the demand goes on those

thank you all for the help, especially the link, i will post pics as soon as i get back stateside with the progress

[71wrenchhead]

ok so im still stuck overseas, not a huge deal, i already found a supply for any sort of tubing that i could honestly ask for.

so here's my idea, please feel free to correct, or give me some advice on things

im thinking 2x4 mild cold roll probably 1/8th in thick (sound right?)

and as far as the design goes, i think that following the existing frame rails and where subframe connectors would go is the best route.

a couple things that i wanted to ask about though
does anyone know why exactly the front frame rails splay out away from each other as they get towards the transmission crossmember/mount?
looking at it from a design perspective, the only thing i can come up with is rigidity as far as side to side forces go, and possibly crumble factor when crashing.

otherwise, i was thinking about running a boxed design and instead of following the subframe connectors route, angle towards the exterior of the car and running along the rockers and then connecting back up to the rear frame rails positions.

please forgive the horrible representation that follows

the issue i see with this version is that the tubing that runs between the tranny mount and the rear crossmember will cut straight through my floor, now thats not horrible, but i would like to avoid ruining the interior look as much as possible.
                             
                         / |---------------|------------
               -------  |                     |                
acft fwd                 |                     |                 acft aft
               -------  |                     |                        
                         \ |---------------|------------

so instead i was thinking about running something along these lines (again forgive the horrible design)

                              /------------\
                         / |                     |------------
               -------  |                     |                
acft fwd                 |                     |                 acft aft
               -------  |                     |                        
                         \ |                     |------------
                              \------------/

i hope that makes sense to everyone

PS im also eliminating the whole k frame deal and simply installing a crossmember to put engine mounts on at the desired place, as well as eliminating the whoel torsion bar deal, i have not decided whether or not to put some tubing in place of the torsion bars or just leave it open, on account of everythign being welded together with some gussets as well

[HPP]

.125 wall seems like overkill if you're integrating it like a uni-body. If you're building a rolling frame that you are simply setting the body on, then it would be okay.

Before you get too deep in design, read through this; http://sn65.com/Chassis%20Design%20101.htm

Also check this out; http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.41.1562&rep=rep1&type=pdf

And this one: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.30.6272&rep=rep1&type=pdf

[Mike DC]

        
I think the factory subframe rails are no more than .070" thick, tops.  Rectangular tubing that's integrated into the rest of the unibody could probably be .095" or even .083" and you'd be doing fine.

Whatever you do, don't use tubing much smaller in shape than the factory rails even if it's a bit thicker.  (The factory subframe rails aren't 2x4".  They are more like 2.5-3" wide and 3.5-4.5" tall depending on where you measure them.)  I wouldn't go down to 2x3" rails anywhere inside the wheelbase unless the car was also getting a full rollcage chassis to finish the job of stiffening it.  

Basic engineering crap:
Thickening the wall of the tubing will strengthen the frame quite a bit for crashing purposes, but it will do virtually zilch to stiffen the frame for handling purposes.  Stiffness is almost entirely a product of the outer size of the tubing (and of course the placement of the tubes).  You just need enough wall thickness to keep the walls of the tubing from buckling & wrinkling up too easily in a wreck or from hard driving.  You won't gain anything by making the walls any thicker beyond that point.

--------------

When it comes to stand-alone perimeter frames, it seems like they're never much thinner than about .010" wall regardless of the application.  Something thinner might work for that application if the diameter/size of the frame tubes was a lot bigger than stock though.  (Notice that the large hollow factory rocker boxes are pretty thin sheetmetal.)

--------------

As for the factory front subframe rails kicking outwards back near the tranny crossmember . . . they didn't do that in the early/mid 1960s, only the later 60s stuff.  It was probably for lateral stiffening & crash help.  

Unibody, rollcage, or perimeter frame . . . either way, suppose you have the front subframe rails sticking out and there's no attached upper support for them, and you don't have the sub-rails stretching backwards past the firewall to attach to the tranny crossmember.  If you do this, then you need to make that "corner" area of the frame where the sub-rails mount (under the rear part of the front fenders) pretty large in shape to keep any acceptable stiffness on the front end.  Ford called it "torque boxes".    

[HOTROD]

I have seen hack jobs on ebay , but it has to be better than Capping it !!!

[Larry523]

If you've got big bucks (or if you just want an idea of what's possible), check out: http://artmorrison.com. They do front clips, rear clips, and custom full-frame setups with C6 Vette front suspensions, a variety of 4-bar and 4-link rear suspensions, etc. Full-frame setups run from around $8k and up, depending on options. It's pretty impressive! Now if I could just win the lottery! Of course, that could be difficult, since Hawaii is one of the only two states that don't have a lottery...

[71wrenchhead]

right, so to answer some misconceptions
im building it as an integrated unibody, not a stand alone perimeter frame
after reading the links and responses and talking with a buddy of mine that builds rat rod frames and things like that this is what i have come up with

3x4.5 tubing throughout im still going to stick with the .125 thickness just for stability and also im not concerned with weight or any such thing, its not a racecar, i just want it to be solid

also im going to follow the original frame design as far as where the new frame will be welded in, but instead of putting tubing where subframe connectors would go i am told that it would be better to run tubing along the rockers, just on the inside of them.
im also told that anywhere i have joint to gusset where i can just for extra rigidity

as far as any crossmembers are concerned, im told to remove the original and utilize tubing where i can, which is going to be tricky when it comes to the transmission mount, but i should be able to fab up something that will work and be as solid as i want it.

i dont plan on caging it at all, like i said, im not making a drag car, i just want something that i know i know is solid.

thank you all for the help, if any of this sounds wrong, please let me know, im new at this but i have the skill set and patience to do it

[RallyeMike]

This seems like a heck of a lot of work for little gain (since you are not building a race car). I you just want something solid as stated, you can get there reinforcing the original frame and still build your custom motor/engine/suspension mounts from tube.

I've done this without a jig, just using a flat concrete slab, levels, and plumb-bobs and scribing everything on the concrete. It turned out great - you just need to measure, measure, measure and re-measure.

[HPP]

I agree. With torque boxes, subframe connectors, and some bracing in the front third of the car, you can create a very capable and solid car. For the benefits of a seperate perimeter frame without the weight penalty, stitch welding all the body seams will have a similar impact for less effort, significantly less cost, and without the associated risk of potentially botching suspension geometry.

If you read through the SN65 project link I gave you, you would have noticed that by seam welding, rocker reinforcement, and floor pan mods, they increased torsional rigidity in that project significantly without even adding sub-frame connetors or a roll cage. While I don't think they call it out in that article, I followed the build up on protouring.com and they claimed a 65% increase in torsional rigidity using those methods alone. Meauserents were done using a lever rod and dial indicator to measure actual deflection during the build.

[Mike DC]

                             
If you duped the whole factory subframe rail & rocker structure out of 0.125" steel then it would probably add 100-200 lbs to the car.  I don't see much reason to do it.  
         
                   
It's not because I haven't thought about it before; In fact I have spent hours thinking about this very idea in the past.  But I came to the conclusion that the extra structure isn't gonna make it much stiffer than beefing up the stock frame, and the crashing benefits are debatable at best.  If the only reason is to thicken the walls of the existing frame's shape then I really don't see the point.

Throw in the fact that the new frame has to be hand-fabbed.  The factory floorpans won't fit to it.  Each & every place where the subframe rail changes shape/direction becomes another big welded joint that you have to trust . . . very big project, lots of issues to deal with, and very small gains IMHO.  

I would still consider doing the idea, but I would need a better reason than just "getting a solid car."  Just my opinion.  Like I said a few posts back, there are decent reasons to do this sort of thing if you're gonna change the frame in a bunch of places.  And the tubing doesn't have to be .125" thick just to be solid & safe.

---------------------------

                     
Also, you might wanna consider not hacking up a decent solid unibody to start with.  The countryside is littered with rusted-out $500 Charger shells that have the upper 2/3rds of the unibody structure still intact.  That is all you're really gonna keep from the original car by the time you're done.  

                     

[71wrenchhead]

stock frame is garbage, as in, it has to come out regardless of what i want to put back in there
and i can get tubing for way less cost than new rails, torq boxes subframe connectors and what not will cost
im also eliminating the kframe entirely as well as putting in a 4 link rear suspension and tubular front suspension.
i understand that it seems like entirely too much for my purposes, but i want options to be open down the road, like when i decide i need 2000 hp nelson racing engine, not saying thats what im going to do, but if i decide thats what i want, then i wont have all that much to do, and the frame will be there to add a cage to if need be.

[Mike DC]

Well, whatever you do next, start by get an idea about what kind of performance you really have in mind.  Drag racing, cornering, smooth cruising, etc.  No setup is best at everything, it's all a bunch of compromises.  Different parts draw those lines in different places.

[71wrenchhead]

isnt the main components behind the choice of driving i wish to do mainly suspension setup?
before i go any further, i want to say that im not trying to be difficult, or an a$$, i do take everythign said into consideration and do research on it, so please forgive me if anyone feels like im being bullheaded.
im basing this whole thing on general chassis design properties, for instance
unibody frames were created essentially for tehir low cost and low weight, now, low weight is fine, i get that, but i dont think that skimping on the chassis of a car is a good idea to even consider, and i understand that the design isnt made by completely moronic people, i also understand that purely by adding a few things such as subframe connectors and tower strut bars and whatnot to it, it can be just as good.
to put it in a metaphor, the current frame design is a 9mm, which is fine, and it can always get bigger ie. more powder, hollow points, and whatnot.
but a 45 will never get smaller
this is the basis of my thinking.
a solid, tubular frame custom made to be as structurally rigid as a ladder or perimeter frame, welded to the body will give me the availability to do what i wish to do without having to go back and remove, replace, or install a whole new frame.
as well ass keep me from having to alter the structure of the body extravagantly such as would be needed if i was attempting to convert the car into a body on frame design.
now i do understand that .125 is a lot for the frame, and i have taken this into consideration, as it was said that .090 was fine or even .083 i believe.
and that is something i believe i will end up following.
as well as the info that 2x4 tubing isnt the correct size of the actual rails, and that i should most likely use something along the lines of 3x5, and that makes perfect sense.
i understand that purely by beefing up the stock frame i can get the same results, and normally, that is the route i would go for.
but unfortunately, my frame rails are trash, and since i have to remove them all, i figure why not take the opportunity to step it up a notch and give myself the option to beef up a frame that is already up to par with the original frame that has been modified to make it stronger, therefore allowing myself the option to make a frame that is severely modified if i choose to go the purely drag racing route.

i do hope this makes sense, its not that im aiming for a specific style of driving, its that i am attempting to give myself the option for change without a complete overhaul down the road, for now, i just want to drive it around town, maybe stomp on the gas for some fun down some back roads every once in a while, but essentially it is going to be a daily driver.
But i was under the impression that other styles of driving can be improved upon by simply altering the suspension setup to fit what you are trying to do. Naturally i understand that certain styles require more than just a different set of shocks for instance, but not much else if i already have a chassis and body setup that allows for not only current rigidity, but also modification when needed.

like i said, im not arguing, and i do apologize if i seem bullheaded, maybe i just dont understand the reasoning that yall seem to have in your mind, but i am trying to understand so that i dont go and make a stupid mistake that will cost me down the road.

and as far as using an old shell of another car, i have thought about that, but it seems to me to be pretty much the same amount of work if not slightly less, and i would not end up with a setup that i would be able to alter to fit my driving style as easily.

i do thank all of you for the advice and help, it has seriously helped me make some educated decisions about this project.

[Mike DC]

Hey, it's cool.  No reason for anyone to bash you for brainstorming some different ideas. 


The reason I was pushing you away from this idea is because IMHO the gains aren't worth it if you have an intact stock unibody.  But that is just my opinion and it sounds like you don't have an intact unibody.  So if you feel capable and if it's what you really want, then I say go for it. 

The floorpan issue will be major though.  The stock floorpans aren't exactly shaped to fit against flat rectangular tubing, so you are looking at fabricating almost the entire floor & rockers of the car.  (I wouldn't be surprised if you find yourself buying almost a full set of reproduction floorpans just for raw materials.)  This is no small job for even an experienced shop. 

I realize that investing a lot of work & money to recreate nothing more than a stock undecarriage is disappointing.  But what you are describing isn't just more work, it's A LOT more work.  Be sure that you won't get partway into this deal and start wishing you had just settled for recreating a stock chassis - because by the time you're partway into this deal, you would already have been finished with that job.

[71wrenchhead]

the floorpan issue was one of my main concerns, and i have debated a bunch of solutions for it.
i was thinking of essentially channeling them out and setting the frame inside it that way, the cab portion wouldnt be too horrible as it would be covered by the carpet and not protrude too much, the issue i feel is the rear wheel well area, i would have to have the frame jut into the interior of the trunk pretty far in order to give enough room to provide a proper weld.
thats not a horrible thing as i am planning on closing that area off in the trunk to cover the subs that i want to go there (nothing huge, just some 8s or 10s)
so that would cover that area.
input on this idea?

i do thank you for helpin me out, your points make me think about the complications i have to overcome, and dont worry, im not getting into anything until im absolutely sure

[HPP]

Okay, that makes a bit more sense to me that if you are going to need to replace the majority of your frame rails anyway, and probably some floors along with it, that building a frame from tube may be a more economical approach.

However, uni-body design was created not just for lower weight and less cost, but also because it can provide an increase in rigidity in a more compact design. Remember that these concepts were pretty radical thoughts 45-50 years ago. These days nearly all cars are made this way and they demonstrate significantly less flex and increased crash test capability as a result. Also consider that while this construction in passenger cars is called uni-body, in the racing world it is called monocoque and is the predominate construction method used by Formula and Indy cars. However...

We may also be splitting hairs about full frame, perimeter frame, and unibody frame. If you are simply using tube to replace the stock frame rails in the stock positions then this may not be too difficult a task. I believe this is what your original post was about. I think a later post did diverge about about alterations to the stock layout which lead me to believe you were making a body on frame design. Your latest post brings me back full circle to simple substituting sub frame peices so perhaps I was not following your logic correctly all the way through.

The suspension selection is a bit more involved than just tuning to the activity at hand. This is because some designs perform better at some tasks than others. If you are building a drag car, ladder bars or a four link will provide better performance and greater adjustability, but those same designs on a road course or autcross will be at a disadvantage. Conversely, a three link or leaf spring set up may not stand up well to high powered drag launches on a prepared track, but will provide greater lateral stability for handling appciations. If you changing out the stock suspension, putting in a replacement that will better support the predominate activity you will be using the car for will achieve better results and probably make it more enjoyable to use.

[71wrenchhead]

ok now that makes perfect sense
sorry for the confusion on my part, its difficult to keep all the ideas in line.
the suspension setup is still something thats a little ways off so i still have time to debate that and figure out which way i want to do, i was generally leaning towards the 4 link or 3 link setup, depending on the info i get form researching each one.

ok so, tubing - that makes sense on account of my lack of existing frame rails
creating a frame design that is essentially the same as the original rails - thats my game plan
unibody design - as in i will be welding the tubing to the body for added rigidity (i know i am going to have to cut out the floor pans to accept the straight tube, thats fine, no big deal from me

my only question now is, should i make the frame so that the front end is connected to the back end with tubing?
it would essentially be much like putting subframe connectors on an original frame.
Or should i leave it as 2 separate pieces that mimic the stock original frame rails.
And if i do put them in, on account of they will be straight tubing, so i attempt to move them towards the rocker panels to lessen the affect of having to channel out a section of the floor in the passenger area, or do i just run them straight back like they were plain old subframe connectors and attempt to minimize how far they protrude into the cab?

[HPP]

I'd run them over to the rockers instead of bisecting the floor pan.

[71wrenchhead]

thats kinda what im thinking, but i am not sure that will still give the added rigidity that you would get from subframe connectors on an original frame setup

[HPP]

Its actually better, if you tie them in to the rockers.

Subframe connectors were devised in the early 70s as means to reduce the damaged created by high powered launches and the ever improving tire compounds that were buckling quarter panels. The do not do so well in reducing torsion loading when compared to the rocker sills. The Direct  Connection Kit Car program of the late 70s devised a blue print for chassis assembly that made the rocker panels the major fore/aft structual members of the driver's compartment because of their size and the ease with which they could be reinforced to produce greater torsion resistance.

[Mike DC]

Yeah, SC's car mostly help beaming issues.  Torsional loads need the "torque box" plating.

Another big issue is the condition of the rocker boxes.  Subframe rails are pretty straigtforward, either they are solid or they're not.  But the rocker boxes are thinner sheetmetal with a lot of complex shaping and they are difficult to remove & install.  A lot of cars have semi-compromised rocker boxes that are only cosmetically fixed.  They still may not have the rigidity of the originals.  

[71wrenchhead]

 
this is why i come here for advice!
thanks guys, looks like i have a halfway decent plan now
i will definitely post a build thread when i get back home and start doing this, maybe it might help someone else down the road

[Chryco Psycho]

 This is another option http://www.roadstershop.com/products/1970-74-challenger/cuda-chassis