Custom Built Frame How-tos?

[69_Sportsroof]

Anyone know where I could find a lot of information on building your own car frame? I've already found that most people use 2x4x0.120 tubing, and have found a couple builds on here, but didn't know if there was a compiled list somewhere or another forum that specializes in that kind of project.

[19,69camaro]

I don't know of one but having gone that approach I can give a few pointers.

First off before you cut anything get the car on a level surface, then level the car and take as many reference measurements that you can. Wheelbase, width of fenders, fender lip heights, location of the firewall, you name it. And take pictures. You have no idea how much this will help later

Second figure out if you will have a cage in it or not. If so that will add a ton of strength to the frame and you won't have to go nuts with you materials. IMO 2x4 tube on a lowered pro-touring car will be a pain in the ass to fit floor pans in and not having them stick out the bottom like a truck frame. The other option would be to raise the floor which would mess with head room.

Lastly build as much of a full frame as you can including mocking up the engine, transmission and rear end while you have plenty of access to it all

[69_Sportsroof]

The thought occurred to me to take lots of measurements, but one question is: what points do i use to level the chassis? If I use something that is getting cut out obviously that's a moot point, would the rockers be strong enough?

2x4 does seem large, one of the questions I had was whether or not you could use 2x4 "main beams" down the middle, and support the rest of the chassis with smaller tubing, especially near the rockers and floor pan area.

[Zachalanche]

The thought occurred to me to take lots of measurements, but one question is: what points do i use to level the chassis? If I use something that is getting cut out obviously that's a moot point, would the rockers be strong enough?

2x4 does seem large, one of the questions I had was whether or not you could use 2x4 "main beams" down the middle, and support the rest of the chassis with smaller tubing, especially near the rockers and floor pan area.


Seems like there is some detail missing in your question. you could just throw a lot of material at it an you will have a truck when you are done. if you have an idea what you want the car to weigh, and an idea how to meet that goal, you can use that to help you design an appropriate frame. this is the perfect opportunity to build something super light which requires less power, less tire, less brakes etc. etc. all of those save money not only in initial cost, but operating cost. keep the whole picture in mind do some research and learn as much as you can about chassis design.

as for leveling the car (i'm assuming you are working on a 69 mustang based on your name) there are a few flat surfaces that seem like they are level (like the front frame section or the top of the tail panel). they might be, but don't trust them if you are using a small level. you could go off suspension mounting points if you are measuring form a level surface. the rockers should be a decent indication, but the pinch weld at the bottom has a lot of variation so measure to the actual rocker assuming it isn't bent. the frame rails should be good side to side, but it seems like there was a lot of leeway built into these old cars. It would be ideal if you had a table to set the body on.

[69_Sportsroof]

Ideally I would use as little material as possible, but I'd rather it be safe than light. I see art morrison and i believe chris alton use the 2x4x 0.120 so i assumed it was a good basis. I am an electrical engineer so I don't really know how to do a structural analysis of the chassis but I'm pretty good at on the fly fabricating. Done a fair bit.

Anyone have a rough guess what the outer body weighs alone? Doors, quarters, fenders, bumpers. I'd love to keep the car under 3000lbs. Just not knowing anyone who has done a chassis from scratch I don't really know the best combo of safe yet light. Would 2x3 work better? Been reading Jon schwarz' build but it starts with the frame already done.

[69_Sportsroof]

Also, this car will not be a "race car" competing in a class. Its just a fun toy I'll take to autocrosses, drag strip, HPDE. So I planned on a 4-6 point roll bar, but may benefit more from running bars over the doors thru the firewall and tying into the shock mount area. That would get rid of the 2D area between the front and back that cars typically suffer from.

[TheJDMan]

Judging from your question, it appears you have not yet read any of the suspension and chassis theory threads written by Ron Sutton. Ron does an excellent job of explaining how chassis and suspensions work and why they work. I would recommend that you spend some time reading and understanding his threads. It does not take much effort to find Ron's posts here on PT.com.

[raustinss]

i agree you definitely should spend some more time reading chassis design etc. my questions are , what fab skills do you have ,tools you own,tools you have operated , welding machines,skills. remember this could be your families life your playing with .

[69_Sportsroof]

I've read a lot of the suspension theory in the past, but I didn't realize he had chassis sections. I will go look. Also pulled out my intro to mechanical engineering book, along with how to make your car handle and secrets of solo racing books haha.

[69_Sportsroof]

I'm very comfortable mig welding, cutting, grinding, etc. I have more tools than the average car guy(including a Hobart mig) since I worked in auto shops part/full time for 6 years and have a 2 yr degree in automotive tech and was ASE master certified. Just never doing this before makes me pretty nervous, but I feel that's a good thing.

[MonzaRacer]

Most of the chassis kits I helped build with used 2x3x0.125 mild steel, if we could get mandrel bent OK if not we could cut and weld and plate, or slice and form, then weld and reinforce every joint.
See if yo put enough cuts in a pipe it can be bent in circle, just don't cut all the way through.
If its not too wide some of new Crown Vic's have bolt in front cradles, pretty popular in street rod crowds.
Or mimic Fox front end or SN and use one of tubular k members.
Twintorino swapped in bunch of parts from Mustangs in their Torino's. Adapted lots of stuff and got awesome car out of it.
I like the book "How to make your car handle." By Fred Puhn.
Learned tons of stuff from that book, even how to build chassis some.

[feeble]

If you want more of an engineering book, Race Car Vehicle Dynamics by Milliken is excellent. If you have CAD skills, I recommend laying out as much of the car as possible in a CAD system before you start building. it will help identify a lot of issues before you commit to steel.

[Yukon Cornelius]

Along a similar path. What is everyone using for floor supports when building a custom floor? 1"x2" seems a little large and heavy.

[Ron Sutton]

Steve (The JDman),

I tried sending you a PM, but your inbox is full. Clear it out & send me a PM please.

Ron Sutton

[Ron Sutton]

You really have 3 critical areas of planning when designing & building a new frame:
1. Achieving adequate torsional rigidity versus weight
2. Packaging everything well
3. Suspension design

I've covered a lot of stuff in my threads about suspension, safety, aero, etc ... but I don't know if a person can cover enough in forum threads to teach how to properly design & build a car frame from scratch ... for someone that has never done it. Building your own frame will be challenging, but fun & rewarding. I would suggest you map out where everything goes, figure out your suspension designs & gather as much info as you can before you start cutting & welding steel.

I think the most important first step ... before any of these 3 areas ... is to clarify your priorities & goals for the car. Because along the way there will be compromises & decisions that have to be made. Over the years I have designed & continue to design a lot of chassis ... and the one thing that is always a challenge is packaging. Every time you make something better, optimum or closer to optimum ... it encroaches on something else. Then you have to decide what gives. This is where having clarity of your priorities & goals for the car will help you make these tough decisions.

My tips are:
a. Be patient
b. Plan it out
c. Learn lots before starting
d. Have fun with it
e. If you get in over your head, reach out to veteran frame builders

Best wishes ! :cheers:

[69_Sportsroof]

Thanks for all the suggestions. I have a couple acquaintances with lots of CAD experience, I'll try to see if I can bribe them to do some modeling haha. I believe I am going to try to utilize a bolt in well known front kmember to avoid all the complications from designing a front suspension since I've never done any of this. If I get brave later on I can fab my own and remove the kmember.

I've read lots of drag guys use 2x3x0.085 but suggest 0.120-0.125 for street cars. I do plan on at least a 6 point setup, would 2x3x0.120 twin rail frame with some roll structure be a good starting point for design? If ive dine my homework right 2x4 is twice as stiff but weighs more and is harder to fit so I'm unsure if its necessary.

[69_Sportsroof]

Anyone else have input for this? Still trying to decide which route to go. It's either replacing the majority of the factory lower sheet metal and some frame rails, then modifying suspension, or doing a frame. I feel like it might be easier in the long run to do a frame but cutting the whole car apart makes me pretty nervous