Newbie just bought a Kart with potential

[5trucks]

i completely forgot to mention but it's really important to go with DOM tubing and not just ERW, as ERW can and will split at the seams.

Oh sweet Jesus! Not the seam thing. DOM does not have a physical seam after production. It starts life as cold rolled welded seam tubing and is cold worked after welding by drawing it over a mandrel to remove the weld flashing and further work harden the tube. Sometimes you can still see the seam, but it should not compromise the concentricity of the tubing. Hrew or Erw is fine. DOM is overkill for this application. I have been building rockcrawlers for years and have yet to have a piece of hrew split. I know it has happened but triangulation and design are major factors in preventing this. DOM is far better as far as psi and strength but you are talking 3 times the cost of hrew. With Hrew always bend with the seam on the inside of the die. Most splits occur at the bender not on the trail. This is due to placing the seam on the outside face of the die and that is the part that stretches the most.

 

[fluxcored]

Look at it this way, what do race cars use? Round tubing .120 wall hrew minimum. That's 1 3/4" diameter x 1/8"thick. There has to be a reason for this.

5trucks - been thinking about this for the whole day and night: Why, why, why, why!!

Could it be that round tube deflects impact stress across a wide area while with square it concentrates in a smaller area (the corners.). I mean do you want to be hit in the face with a square or a round tube?

That's the best I can come up with without doing a Googly. Anyways. my brain's starting to hurt.

 

[kibble]

I mean do you want to be hit in the face with a square or a round tube?

Hmmmm we'll have to test this out and get an honest opinion. Oscar! Come here boy! :toetap05:

I think I understand your theory and think it sounds ok. I guess it would be worth doing some sort of test with identical thickness pieces of square and round tubing and see how each one is affected by either impact or damage in certain places.

 

[AutoMX]

most of the commercial mass produced chassis use square tubing because they use large complex chassis jigs which allow them to easily and quickly put together a chassis and weld it together in hours not days. square tubing is cut in straight planes using standard saws, so it takes seconds, and then you pop it in and weld.

custom chassis makers (racing, offroad, etc) don't need to finish a chassis in less than 3 hours and each customer wants something different, so they can afford to use round tubing which can be bent in all directions and doesnt require as heavy duty of a bender as square. the chassis jigs used are usually much simpler and allow for modifications.

which is better isn't really a valid question, it comes down to opinion. formula 1 uses vacuum formed carbon fiber, and lotus uses glued together extruded aluminum for their chassis, both of which are extremely safe. ferrari and lamborghini use exclusively square tubing, lotus 7 type cars most often use round tube, and the saleen s7 i believe uses round tubing for the rear.
none of these are unsafe cars, they just appropriately used what they picked, and thats what needs to be done.

as for the DOM thing, i just heard it from a bunch of baja guys and i trust their judgment. i do agree that ERW is probably good enough for most cases, i know of a few people who used it out of desperation and never had issues (nor crashes) but my logic is safety first and thats what i suggest to others. my metal supplier actually doesnt even sell ERW so i'm stuck anyway.

 

[Jerryburger]

Hey! A fellow Spokanite! Well I was up until 84....
Perceptionist .... that is a cool gokart! I think you're right about the "Got to be a better way"... but short of starting over with the kart and re-using the drivetrain... who knows? I think you're definitely going to be the Top-Speed Champ of the home-builts!

 

[fluxcored]

Auto - I'm not qualified enough to argue your points but I believe that you're looking at safety as a function of design rather than whether a square or round tube is safer/stronger. My end goal is to build a Lotus 7 replica and most of them are square tubed, space frame chassis' - very light, safe and strong.

So, your points are more than valid but when it comes to roll cages, I'll rather bet my life on round than square.

GoKart Geeks Unite!!! Roy, you're not gonna comment?

Let's make love not war, eh!

Kibble, good luck with your experiment. Be scientific - verify the results at least 3 times!

Nice weekend dudes - I'm off!!

 

[oscaryu1]

Hmmmm we'll have to test this out and get an honest opinion. Oscar! Come here boy! :toetap05:

I think I understand your theory and think it sounds ok. I guess it would be worth doing some sort of test with identical thickness pieces of square and round tubing and see how each one is affected by either impact or damage in certain places.

Ya Kibs?

*goes back crying to mommy*

 

[kibble]

whether a square or round tube is safer/stronger. My end goal is to build a Lotus 7 replica and most of them are square tubed, space frame chassis' - very light, safe and strong.

Let's make love not war, eh!

Kibble, good luck with your experiment. Be scientific - verify the results at least 3 times!

Whoa! I wanna see that when you're done.

Second comment, I'm not so sure about.... :arf:

I'll be sure to conduct multiple experiments with various sizes of tubing.

Ya Kibs?

*goes back crying to mommy*

Get back here! That was just the 1/2" pipe, we're not done yet!

 

[perceptionist]

Hey Jerry, Thanks for the kind words, yes this project has motivated me to buy a 60 Gal air compressor, a Welder, A 20 gal solvent wash tank, and a whole lotta other tools to give this baby what she needs. I am looking into getting the air/manual 12 ton bender from Harbor Freight today after work:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=97433

Anyone ever see locking Manual Hubs used on an all terrain Kart? I am also researching Locking differentials but most I have found to be for heavy duty 4x4 truck use.

 

[AutoMX]

regarding the bender, the manual one at half the price is probably a better choice, it takes only a few seconds to pump it up, but more importantly you can feel the work being done. the dies on that bender are fine, but the anchor points (the stupid rollers) are not the best thing and push/crinkle thinner tubing pretty easy, so i wouldnt turst the bender to do a good job every time, especially automated with air. badly bent tubing = costly mistakes.

and yes a practical test should help see how much of a difference there is. i'm quite confident both are strong enough.

 

[kibble]

with AutoMX. I used the manual one to do all the work on my kart.

Yes it kinda sucks that the rollers make the metal bend in a bit where they make contact with the material. One other thing that sucks is that the thing doesn't retract automatically as it doesn't have the springs like that one you linked to.

It's not horrible though and gets the job done if you're careful enough.

 

[5trucks]

The HF bender is for pipe, not tube. Tube will kink or flatten if you don't modify the dies. I had said before that square tube for the bottom half of the frame would be fine. Square tube head hits SUCK!!!!!!! People this is all just my opinion here. Not trying to start an "i'm right you're wrong " war. Build what you can with what you have. just be mind full and ask for lots of design help. It may be the difference between life and death.

 

[perceptionist]

Ok maybe I am unclear on the difference between tube and Pipe, I will hold off on the bender till I am more educated. Help?

As for the square tubing head danger, is this not eliminated by enclosing all square cage tubing in that protective foam?

 

[5trucks]

Not really. Pipe is what you would use if you were a plumber. There is structural pipe and the crap stuff you buy at home depot. Structural stuff is strong. Pipe is generally heavier. Pipe is measured by inside diameter, tube is measured by outside diameter. Sch 40 pipe is .144wall where most people who use hrew/erw use .120wall (1/8") Strength tests usually come out the same but there is a huge difference in weight. Pipe will generally dent much easier also.

 

[5trucks]

5trucks - been thinking about this for the whole day and night: Why, why, why, why!!

Could it be that round tube deflects impact stress across a wide area while with square it concentrates in a smaller area (the corners.). I mean do you want to be hit in the face with a square or a round tube?

That's the best I can come up with without doing a Googly. Anyways. my brain's starting to hurt.

Square tube is designed to be used in structural applications, but because it doesn't have a completely uniform cross section (i.e. round) it isn't efficient. You will have to use heavier material to get the same overall strength if you go with square tube. The bends are considerably weaker than properly bent DOM or HREW round tube.

Round tube is stronger than pipe. Pipe is made of softer steel and has less cross sectional uniformity. Pipe is intended for carrying things inside of it under pressure. It tends to have thick sidewall, poor cross sectional uniformity, and is HEAVY.

 

[AutoMX]

i'm definitely sticking round around my head and elbows anyway, for safety reasons.
i also don't trust the strength of rippled bent tubing thus why i'm avoiding using it where structure is essential.

it's funny i saw a high end pro shop on TV using an HF bender on a rollcage for a SEMA show car

 

[jr dragster T]

Well if it helps my Junior dragster uses seamless round chromoly tubing everywhere including around the roll cage. I do agree it's best to have round tubing around the roll cage because I have hit my own head on it from the holeshot power.

 

[5trucks]

Well if it helps my Junior dragster uses seamless round chromoly tubing everywhere including around the roll cage. I do agree it's best to have round tubing around the roll cage because I have hit my own head on it from the holeshot power.

Chromo opens up a whole new can. If you mig weld 4130 for example. Without post weld treatment of chromo you basically have the ability to say "I built it out of chromo" but aren't getting any real benefits out of it other than the bling.

People do it all the time and mig welded chromo is strong. Again, do what you can with what you have.

 

[AutoMX]

from what i read its actually weaker if untreated after welding. oh and its 3x the price of typical steel. no thanks heh.

 

[jr dragster T]

I'm sure my junior dragster is built correct. It was built by halfscale dragsters in new jersy and NOT somone in there backyard with a mig welder. It was all profesionally TIG welded.