Topic: Is solid rod stronger than tube??

[manjisann]

The title kinda says it all. I'm thinking of makeing some very basic highway bars from solid round mild steel rod. Aside from weight, is there any advantage to tubing over solid rod? I'd use tubing, but I don't have a tubing bender, but rod can be bent with a torch and vise.

Thanks.

Brandon

[Duke McDukiedook]

Usually, no.

It depends upon the moment of inertia and the yield strength of the material being used.
 

[manjisann]

Cool I think I'll make me some then!

Brandon

[Duke McDukiedook]

What I meant was tubing (as long as it is not thin-walled) of the same diameter and material as solid bar is stronger.

[Gordon]

Seems like solid steel crash bars would weigh at least 20 pounds.  That's a lot of extra weight to be adding.

[mystic_1]

My understanding is that solid bar is stronger and heavier but bends more easily than the equivalent size tubing.  In other words tubing gives you better rigidity, up to a point.

mystic_1

[mlinder]

What I meant was tubing (as long as it is not thin-walled) of the same diameter and material as solid bar is stronger.

um, not to be contrary, but a solid bar with the same radius as a tubed bar will be vastly stronger.
It's only weight for weight that the pipe will be stronger, because a pipe having, say, 1/4" thickness but a 2 inch radius would have to be compared to a bar with 1/2" radius in that scenario. Of course the tube will be 'stronger' in that case.
But again, same radius, one pipe one solid, solid is stronger in every way by orders of magnitude.

[TwoTired]

Agreeing with Mark here.

The only caveate would be the specification of the same material for each example.

A tube of steel is stronger than a bar of lead, same diameter.  Alloy metal composition is crossing into the different material arena, as well.

Then there are heat treatments to consider, which can make a material stronger or weaker.

So, which is better and apple or an orange?

[mlinder]

I was assuming same material, Lloyd

[manjisann]

So, which is better and apple or an orange?

Pfft that arguement was settled years ago, it's the Apple, cause OJ'll kill ya!! 


ok, I think I'll try and combine the best of both works. I'll make the corners out of the solid rod since it can be heated and bent to a pretty extreme corner without collapsing. I'll then weld or braze the tubing to it.

Any thoughts on this plan?

Brandon

[Duke McDukiedook]

What I meant was tubing (as long as it is not thin-walled) of the same diameter and material as solid bar is stronger.

um, not to be contrary, but a solid bar with the same radius as a tubed bar will be vastly stronger.
It's only weight for weight that the pipe will be stronger, because a pipe having, say, 1/4" thickness but a 2 inch radius would have to be compared to a bar with 1/2" radius in that scenario. Of course the tube will be 'stronger' in that case.
But again, same radius, one pipe one solid, solid is stronger in every way by orders of magnitude.

The solid pipe of a same diameter as tubing would be stronger in tension and shear, but weaker in moment bending and probably torsion.
It's all about the moment of inertia of the structural member in question (If they are made of the same material).
 

[tramp]

you can run wires through a hollow tube

[manjisann]

you can run wires through a hollow tube

This is true, but I'm not planning on running wires in my highway bars.

Brandon

[BobbyR]

I think you need to define what you want these bars to to, and what shape are they going to be fabricated to. If you are talking about something to rest your feet on is one thing, protecting the bike in a tip over or crash is something else.

[myhondas]

You can go rent a pipe bender at a tool rental shop and if you put a spring of the interior dia. of the tube inside the tube when you go to bend it, it will keep the pipe from collapsing during the bend. Cheap way to make professional type tube bends.

[markjenn]

This is an interesting structural question.  Wouldn't be surprised if it is not on some college course final exams.  I took several structures courses on a way to a civil degree many moons ago, but who knows if that helps or hurts this response.

I vote that the solid bar would be overall stronger.  It has the same material as the tube and I don't see how adding additional material in the center would weaken it.  Granted the material towards the center wouldn't add nearly as much strength as the outer material and the thing would be very heavy for its strength, but I don't see how it could be overall weaker.

- Mark

[Ichiban 4]

Just adding my two-cents here..

Most of the comments about type of materials used, et al..seem right on. 

I can tell you from the old days when we made our own frames out of materials like Reynolds 531 chromemolly steel..that a 1/8" wall thickness of that stuff was stronger (and more resilient..don't forget that aspect) than a comparable diameter of solid iron (note: I said iron..not steel)..

As Myhondas was saying also..you can put either a spring (or fine sand) in the tubing (keeping it in there with a plug of clay, etc.)..and carefully bend it cold to the desired shape.  But a tubing bender seems much easier/straightforward.

I've found that if you check around a little for custom muffler shops that have their own benders..and assortment of dies..that they often can do custom bending for you..and @ a reasonable price.  You would need to make up templates/patterns in cardboard, et al..first..with the desired bends and angles you want..or just hope that the person doing the bending is skilled enough (often not).

Seems to me that solid bars would not only be heavy as hello as Gordon was saying..but vibrate and be uncomfortable to use..after a very short while.

If you actually go ahead on this..and research it out a little more..you'll be joining the leagues of the regular bike builders on these threads..I believe.

Let us know what you decide..and how it turns out..

Al / Ichi

[manjisann]

The idea of filling the tube with a spring, or sand to keep it from collapsing sounds like it would work. At least I think I understand what it's purpose is.

I want to fabricate some simple highway bars and hardbag frames, but lack a good tubing bender and have yet to find one locally. I've called a few places with no luck, but haven't exhausted the phone book either.

Here's my thinking. I understand that pound for pound tubing is stronger that solid rod. On a side note, I've also heard that hollow columns are stronger than solid ones. I know that solid rod can be heated and bent to more severe angles than tubing because there is more metal to stretch. I'm thinking that I could make the tight angles out of the solid rod and then slip the tubing over them and weld it in place. In my mind at least I would get the benefits of both worlds. I could make significantly tighter angles than tubing can do, but only weigh slightly more than if it was done out of tubing.
I would mount some pegs on the highway bars as well, for long distance cruising. And in the event of a wreck it'd be nice if the bag frame saved the bags, but at freeway speeds that may be wishing for the moon.

Thanks,

Brandon

[mystic_1]

For what you're planning, I don't know that I would bother welding in the tubing sections, I'd just make it all out of solid rod.  You're right that you can make tight bends in solid rod much easier than with tubing.  Once you've made the corners, you won't save much weight relatively speaking by making hte rest out of tube, and then you've got four additional welds per highway bar.  IMO the weight you'd save wouldn't be worth the trouble.

How are you planning on bending the bar stock?  Gonna need LOTS of heat to bend 1 inch bar.

mystic_1

[manjisann]

How are you planning on bending the bar stock?  Gonna need LOTS of heat to bend 1 inch bar.

I was gonna use 3/4 inch bar. I have an oxy/ace setup I was gonna use to do it.

Brandon

[mystic_1]

That'll work.  How are you planning to form the bends, do you have a welding table?

mystic_1

[manjisann]

That'll work.  How are you planning to form the bends, do you have a welding table?

I wish! I have a vise that is very securely bolted to a bench. I'll either bend it just using the vise to bend against (I've done this with similar sized rod before) Or I may make a "pattern" (for lack of a better word) that will clamp into the vise using some angle iron and tubing. It'll let me control the radius of the bend.

Brandon

[mystic_1]

I've seen guys with welding tables weld studs to the table to form a pattern and then progressively bend the bar along the pattern, seems like a nice technique.

Whatever you end up doing this sounds liek a very interesting project so please keep up posted.

mystic_1