Tube chasis ?'s

[akdiesel]

Who has made their own tube chasis and A arm suspensions?

I am looking at making a tube chasis out of 3/4" .095 ss tubing for a two seat sand rail design with a snowmachine engine/clutch.

I have never made anything like this but I have seen some on line and It has been a project I have wanted to try for about a year now.
Wondering if the 3/4" would be strong enough to support this set up for a two seater chasis.
I figured I could get a hold of an early 2000 snowmachine model in the 700cc range and use most of the parts including steering, brakes, shocks, etc...
The Snowmachine engine/clutch set up seems to be the best power to weight ratio and easiest to modify.

 

[35mastr]

You will have better luck over at the sister site on this.

www.jalopyjournal.com/forum

 

[adam728]

I know a guy that built his own. He is an engineer by trade, and did a **** load of research and had been around mini rails a while too. If I remember correctly he went with mostly 1-1/4" tubing, in a mix of .095 and .120 wall thickness. Some gussets and stuff were smaller diameter.

In my opinion 3/4" will work if you are building a little 5 hp briggs & stratton kart for around the yard. If you are dumping 120+ hp in there and intend to use it, you'll need more beef than that.

What grade of stainless would you be using? Low end stuff like 304 (common for tubing) is weaker than 1020 steel (common for DOM chassis tubing).

 

[ghnl]

You may (also) want to peruse the forums at MetalMeet

 

[akdiesel]

Thanks for all the info.
The tubing is from Swagelok. It is 316 ss. It seems to be high grade. I know the .095 3/4" tubing is rated for 4900# working pressure and I have done some simple tests with 4' long pieces.

 

[zmotorsports]

Thanks for all the info.
The tubing is from Swagelok. It is 316 ss. It seems to be high grade. I know the .095 3/4" tubing is rated for 4900# working pressure and I have done some simple tests with 4' long pieces.

The material may be rated for 4900 lbs., however, when bouncing through whoops and going over moguls the pressure exerted may exceed the 4900 lbs. rating. I have build a few and a lot will depend on how long of a chassis you end up going with as well as how you tie the tubes into each other and/or gusseting. On my sandrail chassis that I am getting ready to build I plan on using 1.5" 4130 chromoly .083" for the main rails (primary) and 1" X .065" secondary tubing. The wheelbase will only be 120" so not too long and the whole car will be under 1000 lbs. (actually trying for closer to 900lbs.). I know S/S has a lot of nickel in it and actually moves or springs back a lot more than 4130 tubing does so also take that into consideration. The welded joints will also be extremely critical as how it is welded will determine the overall integrity of the components. With S/S make sure that the weld is backpurged when welding or the weld will become contaminated from the atmosphere attaching the weld pool.

Attached are a couple of quads that I have build. The green bike is all 1" X .065" 4130 tubing primary and .750" X .065" secondary tubing. The suspension is .875" X .065" lower control arms and .625 X .065" upper control arms. They have held up extremely well, however, they are drag/hillshooters and we don't jump them. I tend to overbuild everything due to safety and I couldn't live with myself if something happened to my son or wife on something that I built.

 

[RobSmith]

Personally, I'd give the Stainless steel a miss and go for chrome molybdenum tubing. It tigs up ok and is much more rigid.

 

[akdiesel]

zmotorsports,
Very nice work.
I have not had any experience with tiging chromoly. Is it available at the local steel shops or is it a limited supply with certain locations.
I realize that the pressure rating is not exactly the correct way to determine the strength for this application but it is all I have to go with for that product since it is mainly for internal gas and fluid applications.
With your front suspension do you feel you get the proper travel with those heim joints, and no issues with snapping them off?

 

[moonpool145]

I would suggest a pass on the Swagelock tubing. I have used a great deal of this for piping projects and besides being very expensive, it is formulated to be somewhat elastic (not sure of the exact metalurgical term), that is its not very stiff, though it likley appears that way when you are just looking at a 4 foot piece. Also, the .095 is quite heavy. This stuff is designed to carry high pressure gas/liquid and is not intended for structural applications. Chomoly is cheaper, lighter, easier to work and has the physical properties you are looking for.

 

[zmotorsports]

zmotorsports,
Very nice work.
I have not had any experience with tiging chromoly. Is it available at the local steel shops or is it a limited supply with certain locations.
I realize that the pressure rating is not exactly the correct way to determine the strength for this application but it is all I have to go with for that product since it is mainly for internal gas and fluid applications.
With your front suspension do you feel you get the proper travel with those heim joints, and no issues with snapping them off?

Thanks. Actually 4130 is much easier to work with in my opinion due to the fact that it is not necessary to backpurge your welds. I have built a few exhaust systems from S/S and it is much more work than chromoly.

As far as where to purchase it, some of my local metal supply houses can get it but I have found it is cheaper to buy from somewhere like Chassis Shop or Chassis Engineering. I have bought from both of them and even with freight it is cheaper than my local metal supply.

The heim joints work well. I have about 7" of travel on the front suspensions of both quads. I did the front suspension for a friends sandrail last year (it had a VW beam and I converted to a dual A-arm style) and used a VW ball joint on the lower and heim on the upper. It worked well but the heims would probably work just as well. If needs be you can use mis-alignment spacers which give the heim joints another 5-10 degrees of angle. Mike.

 

[speed bump]

Considering 316 has a yield of 30 KSI and an ultimate of 70 KSI your better off with even basic A36 for what you want to do as far as strength goes. Also it has a 40 for an elongation % factor so for every two inches of tubing it can be stretched 0.8" as opposed to most of the stuff commonly used which is generally less than 25%.

 

[akdiesel]

I will have to see the availability of the chromoly up here. I am sure it around but it may be expensive due to shipping and the amount used up here.
Part of the reason I was/am considering using ss is because I can get it at a discount at the local Swagelok distributor and they have a very nice tig system specially made to join two sections **** or cross. They made a very nice truck rack for a crew cab long bed truck. The welds are very clean and they haul alot of heavy loads on it, but it mainly out of 1" tubing.

 

[GN4WHLN]

Only skimmed the posts, but I am going to suggest DOM. 4130 needs post welding stress relief or you will likely develop cracks. 4130 has a better strength to weight ratio, but is more difficult to weld and harder on cutting tools and a bender. To build a chassis, you will most likely need a frame table and a tubing bender. I'm not saying it cannot be done otherwise or trying to discourage you, I'm just trying to bring some perspective. Without a jig or clampdown fixture, you will probably have some misalignment/warpage problems.

Also, as far as strength of materials, you should get a Machinery's Handbook. Some of what I read looked as if you were considering a pipe material for construction. You need tubing, pipe is not meant for structural applications.

A good site to check out is http://www.offroadfabnet.com/index.php Many of these guys build professionaly and are very helpful. There is also a section for mini buggies like what you have in mind.

Whatever you decide to do, post some pics, it sounds like a cool project!

 

[drive em]

Here is the mostly tube chassis I built for my '27 Track T. It is made of 1 3/4" x .120" wall, 1 1/2" x .120" wall and 1 1/4" x .120" wall mild steel round tubing. All the bends were done on my JD Squared bender and it was MIG welded using CO2 on my L-Tec 225 amp MIG welder:

 

[akdiesel]

Thanks for all of thel leads and info. Alot of helpfull stuff.
When I get the material to do this it will take some time to practice so any progress will be posted.

 

[zmotorsports]

Here is the mostly tube chassis I built for my '27 Track T. It is made of 1 3/4" x .120" wall, 1 1/2" x .120" wall and 1 1/4" x .120" wall mild steel round tubing. All the bends were done on my JD Squared bender and it was MIG welded using CO2 on my L-Tec 225 amp MIG welder:

Very nice work. Mike.

 

[zmotorsports]

4130 does not need to be heat-treated if you use 'normalized' tubing under .120" wall thickness. Mike.

 

[DelmarvaOffroad]

I don't know much about sandrails but for rock crawlers we used 1 3/4 DOM.

One thing I suggest too is get some software. This is a backhalf'd Jeep chassis we are working on in the shop.

It is fairly easy to design on the computer without wasting tube and once you are ready the software will tell you where to cut, bend, notch... Makes chassis work alot easier. Also if you ever bend a tube down the road it make a replace alot easier to re-make.


Let me know if you have any questions on benders or the software. We are a dealer for both.

 

[akdiesel]

Thanks for the info Delmarva.

 

[catmech]

You might be interested in this site: http://www.desertkarts.com They have plans and parts. You might also search drakart, they have some radical stuff and were using Rotax engines and chain boxes that were modified for reverse. There should be no shortage of mod sleds in Anchorage to cannibalize.

 

[JamieK]

They were talking about this book over on the HAMB today... it might help and its a cheap $10.

http://www.jalopyjournal.com/forum/showthread.php?t=419568

http://www.tbucketplans.com/

 

[iknownothing]

Here's the front end a friend and I built for our senior project. As zmotorsports mentioned, it was also a VW kingpin front end, but I wanted more travel...I'm no fabricator and there are some things I would change the second time around, but it was a lot of fun.

We used 4130 1.5" x .120" for the chassis and lower A-arms and 1.25" x .095" for the upper A-arms and bracing. We designed it in Solidworks and analyzed in FEA. We also tested the A-arm in a 100,000 lb press in the civil engineering lab. Also, eveyone we talked to (off road and circle track chassis fabricators) said you don't need to relieve the welds.

We could have used lighter tubing for the A-arms but I don't think I would consider 3/4" for anything. Two reasons, 1) safety, 2) I'm lazy, I don't want to have to build things twice. If I'm going to spend the time, effort, and money building something like this, I don't want it bending/breaking and having to re-build it. But that's just me...

 

[Justanoldguy]

You will have better luck over at the sister site on this.

www.jalopyjournal.com/forum

HaHa.

Snow machines.. 700cc .. The HAMB

He will get eaten alive.. lol

They are a tough ole school rodders bunch there.

 

[kartracer55]

I'm currently working on my 2nd FSAE car build, so I am no pro but I have definitely done enough work to give at least a little input.

1) Id stay away from stainless. As was mentioned, welding can be difficult and it is much more difficult to work with than, lets say a 4130.
2) 4130 in the area of .125 SHOULD definitely be relieved. There is enough info on the internet about "DIY" stress relieving
3) I would consider 1 inch tubes at the minimum
4) Do not mig 4130

Asking if 3/4 tubes will be strong enough isn't really a valid question, its dependent on your own knowledge of chassis design. I can tell you that we do manufacture our own chassis and A arms (and pretty much everything else), but that they are also drawn up in solidworks and FEA'd. Many of the members of our chassis are .049 tube or .065 and the chassis is still sufficiently stiff, but as a result of hours and hours of simulation and optimization.

This can definitely be a risky thing, especially not knowing your personal fabrication skills. I would think twice about this whole project, but if in doubt, overbuild. Look up BAJA SAE in google and check out what those guys do...

 

[akdiesel]

Thanks kartracer, I have been looking at TIG machines and have worked with the machines at my work and the help from our fabricators. I still have a lot to learn when working with a TIG machine.
I have never delt with 4130 material. Does 4130 have more nickle in it? It sounds a lot like Duplex.

 

[zmotorsports]

4130 is an alloy and has more carbon in it than mild steel. It is actually considered a medium carbon alloy. The carbon is what gives it the strenght. Mike.

 

[GN4WHLN]

4130 does have more carbon in it (.28-.33% as opposed to the .10-.20% found in 1010 and 1020 mild steel tube) which, like zmotorsports pointed out makes it a medium carbon steel. Medium-carbon steels have from 0.30 to 0.45 percent carbon. Increased carbon means increased hardness and tensile strength, decreased ductility, and more difficult machining. 4130 is called Cromoly because it contains chromium and molybdenum as alloying elements. The 4 refers to it being a molybdenum steel and the 1 refers to the major alloying element of chromium.

Nickel steels are 2XXX or nickel-chromium steels are 3XXX . There are some triple alloy nickel steels that begin 86XX, 87XX, 93XX, ... Never had any experience with those.

 

[jmastersinc]

For anything tube you can't beat http://www.offroadfabnet.com/ between this site and Bent Tech you can't loose, everything you ever wanted to build you can get help from some one on this site

 

[Cobradriver]

4) Do not mig 4130


As of five years ago,per a conversation at Oshkosh,Aviat Aircrat MIG welds all their aircraft.

Seriously.

He did say with the really thinwall 4130 it takes quite a while to get a person up to speed.

Chris

 

[swgray]

The "do not mig 4130" caught my eye, too. Why? I do it at work. Granted, its not life or death stuff, but still. A quick search turned up this.

 

[gte718p]

I've mig welded a metric but ton of chassis in 4130. Most of them are still together. Several FSAE, Mini BAJA, solar, and offroad cars.

4130 actually weld really well. Its easy to weld and easy to screw up. I've heard the warning against migging steel. I think it comes from the concern about the operator more then the metal. TIG almost guarantees a good operator. Any idiot who can hold a pensil can mig 4130. It may even look good, but have no strength.