Tube or Solid rod for roll cage/tube chassis?

[TITANIUM94010]

I'm going to be making a full brazed metal roll cage for my Prerunner, my question is do I use 3/16 tube or 3/16 solid rod for a roll cage /chassis?

Ive looked around, some guys say tubing is strong enough, others say that it'll dent the first time you drop your rig.

The cage I'm making isn't very structural, as the chassis is still held up mainly by scx10ii C channels, but the cage will still take a lot of impact. (I may end up brazing the cage to the chassis later)

It would be preferable to keep the cage on the lighter side, but I'm willing to take a few extra pounds to avoid from it being destroyed in a large crash.
I am going to be reguarly hitting 15-20+mph so it does still need to be strong.

If I have to go with solid rod, would welded stainless tube be stronger than solid mild steel? I would prefer to go with brazing, but if there is a drastic difference in strength between welded tube and brazed rod, then I may consider switching.

Also, where do you guys get your tubing/rod from? For a different project, I got a 3/16 brake line from an automotive store, but it was pretty overpriced for a few feet.

Thanks!

 

[durok]

I see multiple threads here that should help:

RCCrawler General Tech - Tools, and Procedures at RCCrawler.com

 

[DRED805]

I haven't been brazing long enough to answer those questions from experience, yet.

As far as materials, I'm using 3/16 .035 wall 4130 tube from https://www.mcmaster.com/. They'll have whatever else you might want.

 

[TITANIUM94010]

I see multiple threads here that should help:

RCCrawler General Tech - Tools, and Procedures at RCCrawler.com

Ive checked a couple of those thread with the searchbar, but it appears I forgot about browsing through the actual subsection. :roll:

I'll take a look

 

[TITANIUM94010]

I haven't been brazing long enough to answer those questions from experience, yet.

As far as materials, I'm using 3/16 .035 wall 4130 tube from https://www.mcmaster.com/. They'll have whatever else you might want.

Thanks!

Is the 4130 chromoly good for brazing? I read that something about the grains of the metal during cooling causes cracking?

 

[DRED805]

Thanks!

Is the 4130 chromoly good for brazing? I read that something about the grains of the metal during cooling causes cracking?

Hadn't heard that. I ordered that steel because on the website it's named "easy-to-weld 4130". I was planning to get a welder eventually, so I thought it'd be a good all around material to work with.

 

[Lashlee]

I've made two "rear cages" on a couple of trucks, one out of solid rod, the other out of hollow brake line (both 3/16"). Obviously the solid rod is heavier, but I don't feel I've sacrificed any strength in using the hollow brake line. I brazed the brake line and tigged the solid rod (my tig skills still need some help, but it works!).

 

[TITANIUM94010]

I've made two "rear cages" on a couple of trucks, one out of solid rod, the other out of hollow brake line (both 3/16"). Obviously the solid rod is heavier, but I don't feel I've sacrificed any strength in using the hollow brake line. I brazed the brake line and tigged the solid rod (my tig skills still need some help, but it works!).

Thanks for the info, I think tubing is better in my case.

Is tubing especially hard to weld? I know that thin metal is hard to weld, but was thinking that since you are joining the edges of tubes rather than sheets it would be easier?

 

[themountain]

Is tubing especially hard to weld?

you braze it ...its not welding ;-)
For 1/10 scale hollow tubing is more scale because same size solid tube would be too heavy. Thats the reason all fabricators use brake line..its cheap, light and easier to work with.
Good video here ---> https://www.youtube.com/watch?v=NcZ9khg9iXo

 

[TITANIUM94010]

you braze it ...its not welding ;-)
For 1/10 scale hollow tubing is more scale because same size solid tube would be too heavy. Thats the reason all fabricators use brake line..its cheap, light and easier to work with.
Good video here ---> https://www.youtube.com/watch?v=NcZ9khg9iXo

I've brazed tubing with relative ease, but I found that all the flux causes pretty big mess, and brazing doesn't work well too with stainless, so I've decided to move on to a tig setup. From what i've learned so far it would seem that tig welding thin metal takes a lot of skill, but is that the same case for small tubing? It dosent have to be nice and clean, im fine with a small glob at the joints as long as it holds.

 

[smog]

I would not consider myself an expert, but have brazed both using tube and solid rod. Rod is significantly heavier. For a full cage I think just way too much weight. Tube is also much easier to work with given that it heats up faster.

If there will be a lot of direct impact its most important is to make sure you design the cage with proper bracing or it will bend in a hurry whether it’s rod or tube. I feel it’s better to use tube and build in solid bracing. But again this is my opinion based on personal experience.

A large enough tumble will bend or dent whatever you build. It’s metal and doesn’t have the flex of plastic. In my opinion the dents are what give the rig it’s character and make it look more
realistic anyway. "thumbsup"

Edit: I also use brake line. I looked at steel tube from Metal Depot here locally but found it no cheaper

 

[Lashlee]

Thanks for the info, I think tubing is better in my case.

Is tubing especially hard to weld? I know that thin metal is hard to weld, but was thinking that since you are joining the edges of tubes rather than sheets it would be easier?

You can certainly burn through (trust me...) but if your machine can get down to the 20-30A range you should be good. My machine needs about 20A to start up then can drop down to 10A after the initial strike. I was using a 3/32" tungsten, you might fare better with smaller tungsten.

 

[TITANIUM94010]

Is 304 stainless a good material or is it better to stick with normal mild steel? I figured it might look cleaner but I may just end up painting or powder coating over it.

 

[Lashlee]

Just for the sake of ease of purchasing, I just use simple brake line from the local parts store. The metal supplier that I use for other projects is a 30 minute drive each way so it's simpler for me to stick with mild steel. Stainless would look better, but not worth it in my book!

 

[TITANIUM94010]

A different question, but I didn't want to make a new thread,

is it better to use 0.125 (3mm) or 0.16 (4mm) 7075 aluminum plate for my chassis plate? Originally I was going to use 6061 at 4mm because 7075 was way too expensive, but after checking our some metal supply stores, I found 7075 at both 3 and 4mm at reasonable and much cheaper prices. I would go with 3mm, but the front diff/ifs mount will not be supported.

Example:

Cyconxc's build has a solid metal bulkhead for the diff bolted to the chassis,

My chassis will not have that (I cannot find the part), and will just be a flat extension of the aluminum plate with the diff bolted on top, so I'm not sure if 3mm is enough.

Thoughts?

 

[Lashlee]

I'm no scientist, but flat things flex. There are ways to prevent it, especially with tube. I would make a few pieces and see if you can get a portion of the chassis together to give it a whirl. If anything, some dimple or bends in the flat plate could get you enough stiffness.