Starting my 31 ford 2 door sedan build and it came with a 2x3 rec tube frame with stock mustang II front end. well all that has to go... Now its time to start the frame and im looking at either finding a set of stock rails and just boxing them or next option is building a set of rails out of 2x4 rec tube. Rec tube is running close to 7 bux a foot plus the time and energy of building the curves and contours into them. I straighten frames and build suspensions for a living so its a little hard to get excited about doing it all day and then doin it at night to. As i dont know what the going rate is for stock rails right now which would be the most economical way to go ? How hard is it to come up with stock rails ? Strengh isnt really an issue for me, a boxed frame vs. Tube as with my set up in mind traction and major frame flex should be minimal..
Yeah but i want the straight rails of the 31's down, 32 up have a bow. I have already channeled my floor which should give me right at a 3 inch lower stance.
Model A frames are straight runs I think. Unless you are building a high hp engine 2x3 1/8" is enough. I know there are those who say 2x4 3/16" is the only way to go. But if you measure out most stock frames from the era you will figure out 2x3 is enough.
At $7 per ft. it will cost $140 for material. if you use an A frame it will cost for the frame and boxing material. If you can find a really good frame the labor will be about the same either way. With box tube you will need to pie cut at least the front of the frame to look right. When it is welded together there will not be as much heat distortion as a full boxing plate on the inside of the frame rail that will cause the inside of the rail to shrink, causing it to bow out in the middle and not line up with body mounts. I have had to straighten boxed frames after someone botched the job, not fun! Jim
Man, I'll give you an educated opinion. If you are building a fenderless car, (and it sounds as though you are) go with the 2X4, and step it up to 3/16" wall. The extra wall thickness really helps stiffen stuff up, and the softer radius of the turns on the walls look much more like the stock stuff we expect. Tapers are pretty easy to do, and you have the bonus of being able to make your frame anything you want it to be. I am not a huge fan of boxing stock "A" rails. I know everybody has been told to do it for years, but there are several reasons not to. First, as you weld, the weld shrinks the heat effected area. Look at most boxed "A" rails and you'll see a very gradual curve to what should be the straight sections. Second, like model "T"s, the composition of the metal in stock "A" rails is running fairly close to what we would now call spring steel, and due the differences in composition with the mild steel used for boxing plates, the welds are very crack prone. Third, in honest terms, Boxing really only helps with beam strength in these frames, which really isn't a large problem. Most of the time where boxing "helps" with torsional strength is in the areas where it is attached to the cross members at the front and rear. Simply welding these cross members to the side rails will dramatically stiffen the average "A" frame. Honestly, a lot more can be done to strengthen these frames with a well designed tube or plate "X" member with a lot less weight than boxing.
Like Chip,I thought boxing a Model A wasn't necessary until a friend of mine placed my frame on two concrete blocks,one under the left front frame horn and the other under the right rear cross member. He then stood up on the opposite frame horn and told me to stand on the opposite rear cross member,I was shock to see just how much the frame flexed! This probably would be OK for a Flathead but with a large displacement, rip snorting V8 I will always box a Model A frame. HRP
Boxing won't help as much as it should (metalurgy aside), with torsion, because those frames are so small in section. Also they don't have enough cross members even before removing the X. Boxing a slightly larger section rewards far more than you'd think if your only reference was a boxed Model A.
I've done three model A's, one with 2x3 tube, another with 2x4, and the last a boxed factory A frame. The fabricated frames were much quicker to build. And the 2x4 frame was the nicest driving and handling of the three. Posted with a Merganthaler Linotype.
I'm working a chassis for a track style T roadster. Using portions of an A frame, horns to the firewall, and sections of a mid-fifties GM pickup frame 6 inches in height, I'm splicing it together, and adding material for a profile similar to Deuce rails without the reveal. Once finished I'll bend both rails to conform to the lower lip of my '25 T body, then add a 'Z' section in the rear for an A cross-member and T spring. Inside the frame I plan to lattice it with a zigzag of strap, stitch-welded along edges where it meets the frame, for reinforcement. Then I can add a boxing plate drilled where the strap is exposed to the holes and rosette weld that, and weld the along the edges of the boxing plate, and grind it all smooth. I expect it to be a little heavier than a plain Jane boxed frame but it should be rigid as a bride groom's weenie on his wedding night. I had the frame pieces. Right now, rectangular tubing is out of my price range or I might have gone that route. All this requires a helluva lot of work, trust me; but with time and a welder, fabricating parts trumps using something that kinda fits.
Absolutely why I much prefer an X-member! I have done the same thing with the cinder block/jack stands and stock "A" frame, and it's shocking how much they do move. But, run a weld between the rail and the cross member in the back, and that movement is halfed. Do it again on the front and the movement is halted further. that is what usually provides the magic "stiffness" on a boxed frame, where the boxing plates are tied to the cross members, not the plates themselves. Now, theoretically, grab another stock "A" frame and watch it twist again. Then either build a full tube X-member that ties the faces and lips of the rails all the way around, and every last bit of twist is gone without several miles of welding and warping.
Thanks guys, yeah i figured the 2x4 tube would be the most rigid, i just didnt kno what 31 frames where selling for. Figured i would find out first before spending a bunch of money either for the oem frame or the tubing. If i build it i will lenghten it 3 or 4 inches and leave my firewall in place..
As always, great info just when I'm getting ready to build a frame. I was thinking 2 x 4 x 3/16 and now my mind's made up. Gotta love the hamb!
Quin is exactly correct that a good X member is better than boxing the frame. There are a few things you need to do correctly but the X beats boxing every time! I did K member in my lakes roadster and also a very strong rear cross member and it is very stiff in torsion. Rex
That's a very cool frame. Definitely a hybrid design. In the 80's we built lots of conventional boxed and channel ladder frames at Manlift, and I was designing the jigs & fixtures to build them. Guess what? The weld fixtures are ladder frames with the very same issues. If they flex, you build crooked frames. A boxed frame needs either thick walls (heavy!) or big sections in the rails and cross members to be stiff. They can be very light wall, but if they're too light they need internal stiffeners which are a PITA to weld 3' into a 6' long tube. Look at a P15 frame which is fully boxed and swells to a whopping 3.5"x6" in the engine bay. That replaced a much smaller frame, which was unboxed, but had the x-member. The convertible was still to flimsy, even when thicker metal was pressed for the rails and the skip welding increased, so they put the X back in. Torsion in a ladder frame is largely absorbed by torsional rigidity of the cross members. Adding sturdy cross members helps a lot, whether rails are boxed or unboxed. My '59 Edsel was a freakin' tank, frame-wise. There were 7 massive cross members as I recall. But structurally speaking, the x is more efficient. IMO, Detroit started avoiding them because it was easier to assemble a car where things don't have to negotiate the X. It was a situation where the manufacturing engineer overruled the mechanical engineer: a situation that mass production often demands. Our company designs buildings, not cars, but we often put in more steel than we really need, because it makes the production cheaper if you don't have a lot of odd sizes. So, when you modify anything, remember that the OEM design was more focused on fast production and the least use of precision methods.
stock rails ive seen lately are from $300-$600. for a decent non warped one I would expect around 4-500. plus you can buy boxing plates for $150ish I think. Posted using the Full Custom H.A.M.B. App!
While a 2x4 tubing frame is easy to build and probably cheaper it will never look like a real "A" frame; if that has any bearing on your final vision. Full fenders would be OK as the frame doesn't show; but on a fender-less early hot rod, race car, or an A V-8 a tubing frame would look out of place. IMO
You're building one car, not 1 million. Cost should not be an issue. $100 here or there should not influence your decisions. Using original rails with title will make the car easier to register in most states now and in the future. Use the AA front crossmember it's so much more rigid. Design and build a fully flowing X-member that flows into the frame like a 1940-48 X-member. Rivet it in place to avoid welding. I have a thread here on installing an X-member. Remember you can't build a beautiful car if you don't start with a beautiful frame.
Yeah the looks are defianitly have a bearing on it. I agree that the look of an original frame is hard to beat. If i go the a-frame route it will have an x-member set up running thru the middle. Yeah the early cars had one mean frame under them. I hate seeing one come into the shop and having to straighten them, especially when they are diamond. P.I.T.A with all capital letters. Oldest frame i have ever straightened is a model a 4 door, it was a peice of cake. The hardest ? Later model dodge pick ups..
Car frames and structural tubing are quite different, one being hot-rolled directly from an ingot and the other stamped from sheet metal. The common Grade 50 tube (called HSS for "hollow steel section" in the books now) is probably not as rigid as the more work-hardened frame stampings from River Rouge.
Most RHS/SHS/CHS/etc. we get around here is cold-rolled and seamed. An advantage is that there are advertised numbers for yield stress, section moduli, etc. I can't really know if a stock frame will give me the same 430MPa (units in use here) or more, or less; I don't know where it's been for the past 85 years, which might have affected the characteristics of the material. Of course this assumes that you'll be doing that level of structural design. I'd expect that whatever difference there is is likely to disappear into any decent safety margin. Something not yet mentioned on this thread is that frame torsions due to suspension inputs can exceed first-gear driveshaft torque by an order of magnitude or more. This is especially true if the suspension has been modified to demand more of the frame than the original set-up did.
Sorry, I was a bit off when I wrote that. Actually we do use a lot of ASTM A500 Grade B, which is cold formed, and as far as I know you can't get seamless here. It's all seam welded.
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