Frame rails sizing - Vintage Mustang Forums
 
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post #1 of 8 (permalink) Old 07-08-2019, 06:20 PM Thread Starter
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Frame rails sizing

Whats up boys,

So I'm currently setting up my placement of my tubed frame rails i've made for my 1973 (Front of car is getting cut off because of rust). In order to secure them to the rest of the frame (that's not getting chopped) I am making a "sleeve" to weld the pipes to and then slide in and weld the sleeve to the existing rail.

The plan with the sleeve is to essentially make a box that fits right into the existing rail. Though I am not sure as to what size I should use to make it out of 1/8 or 1/4 in. sheet metal. The existing rail is 1/8, but am I better off using 1/4 or could that actually be detrimental?

Thanks
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post #2 of 8 (permalink) Old 07-08-2019, 06:41 PM
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You're in uncharted territory in this forum for a question like that. 1/4" wall tubing would be way overkill considering the rest of the car is sheet metal. Not sure which "rail" you're speaking of.

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post #3 of 8 (permalink) Old 07-08-2019, 06:59 PM Thread Starter
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Thats what I figured, I had already made one sleeve out of the 1/8 but just wanted to get some opinions.
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post #4 of 8 (permalink) Old 07-08-2019, 07:18 PM
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That sounds like a significant design for a street or even street stock. What are you going to do with the car?

A .120 wall tubing or 10 ga and above sheet are used in those apps in off road with mild steel. I'm using .1875 on my off road plate/boxing fab with mostly .120 DOM or .095 4130 tubing. Those trucks will take way more of a beating than a street or street stock classic Mustang. I used 14 ga to gusset the roller spring perches I just made for the Mustang. In circle track and sports cars depending on the weight of the vehicle it could be .095 wall tubing and 12 ga sheet. It's application driven depending on the what the part is supposed to accomplish. I don't have direct experience building drag cars but that's usually .095 to .120 4130 depending on the time of the car in a quarter mile.

The integrity of your design is going to depend more on how you tie the front and back together rather than the thickness of the material in and of itself. Another consideration would be how you are attaching the new rails to the existing structure. Without knowing the specific app, what the desired result is or how you're tying the front and rear together it's difficult to say at this point. I'd be looking in the .120 area and then doing at least some napkin math to make sure the loads and geometry is kosher.

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post #5 of 8 (permalink) Old 07-09-2019, 09:30 PM Thread Starter
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Right, so the cars honestly going to just be a driver, nothing crazy as far as now, as this is my first build. Just the stock 351C with some cams is the powerplant and I'll have to research what manual trans I can mate to it.

So the connection point from where I'm going to cut the car off is right at the firewall, so firewall forward will be gone. I'll post a pic below, but the point at which I am connecting the tubes to is a few inches forward from where the floor support begins. So I'll push a 1/8in thick box thats at least 8in long that I fabricate to fit within the frame and I'll seam weld the tubes to the box... thats once I find the right geometry of the tubes compared to original frame which I just about have. Then I'll just cut a couple spot weld holes throughout the box, weld those up to the frame and seam weld the edging of the box to the frame. After that I'll create a plate for the front of the connection, cut holes for the pipes and weld it up to the original frame to further strengthen the support for the rails.

Vega sounds like you have the experience, does that sound like a proper plan to you, if you can picture it? (By the way, whats up? I had talked to you a lot about bending tube a little while back). I'm working with a guy who has built plenty of drag cars with tubed frames so he's giving tips.
Tubes a 1-5/8 DOM .120 wall for the rails.



I bought this car off a craigslister, (yes sends shivers down your spine as soon as I say that, right) from what I could see looked pretty good, and to quote the seller "theres one hole the size of a golfball in the wheel well, other then that easy project". So... now I'm here... trying to bring her back to life.
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post #6 of 8 (permalink) Old 07-09-2019, 11:19 PM
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Interesting plan but remember that there isn't much support at the front floor supports. The bulk of the metal doing the work is the front fender aprons normally known as inner fenders. the frame rails push up against the aprons and they push back against the firewall keeping the front end from folding up like Bufurd T Justice's car in smokey and the bandit.


Everything is pushing against something else. It's not as easy as a full framed car it's more like a boat or airplane. The only thing holding the front floor supports is a couple spot welds at the cross member and a spot welds to a paper thin flimsy floor pan which doesn't really provide much support. The floor supports basically hold the cabin of the car off the ground.

So yeah you can make your own frame rails but make sure that you have support to replace the fender aprons or integrate the stock ones and you will be Ok.
I plan on adding the pipe reinforcement that goes from the firewall to the frame rail. Not sure if I will purchase the kit or make my own. I am familiar with bending pipe but for electrical... Dunnow will see when I get to that point. I like to do most everything myself because i can say I did it and I like having more tools and capabilities in the shop.


Here is a picture of my 66 with everything up front removed.

[IMG][/IMG]
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post #7 of 8 (permalink) Old 07-10-2019, 10:43 PM Thread Starter
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Oh great to see someone else working through this!
So where I 'll be welding up the rails won't be getting welded to just the floor support but a little remaining frame rail from the originals and tying it into the torque boxes. As far as the aprons I haven't made a set plan but was banking on bending a tube to make the aprons and tie in the strut tower. (picture below of what I'm looking to go for)


Now why did you remove the torque boxes, i'm assuming they were rusted?
Do you have a plan set in stone as far as how you are going to be tying in the new rails to the car if you don't go with the kit?
Will you be making the apron out of tube and how would you go about tying it into the car?
Just trying to get ideas.
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post #8 of 8 (permalink) Old 07-11-2019, 10:17 PM
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Mine is a 66 coupe so it didn't have torque boxes. The plan so far is to go with the stock frame rails and fender aprons. I'm not going all in on tube frame up front, that will be for a later toy project for a friend that involves lots of tubing big tires and a motorcycle engine. I haven't decided if I will go with stock suspension or a mustang 2 ish one.

I plan to do a reinforcing brace like the one MTF sells. I will probably build mine as the MTF one is very nice but doesn't fit the budget. It is a complex part to bend. Progress pics are on my build thread. I update it as I go. https://forums.vintage-mustang.com/b...sket-case.html

If you do the tube upper make sure to spread the load over a large enough area.


Oh and this reminds me when BlakeTX was over looking at my 66 shortly after I got it here he was trying to get me to do a race car look which has kind of grown on me and would look really cool with some structural tubing. But the better 3/4 will be the primary driver of this car so I gotta make it more what she wants... However she did give the car an infusion to the parts fund for it today so I can't complain. Maybe if I can find a cheap 68 convertible for the next one.
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