Strength of round vs square tube.

[burninbriar]

I'm working on a design for a round bail transporter for my neighbor to use with his team of horses. One element in the structure will have a substantial amount of twisting type stress on it. I'm pretty confident that 2" square tube will resist bending better than 2" round tube of the same wall thickness but when it comes to twisting, I wonder if there is any difference.
I think the round shape would resist twisting better than a square shape, but the 2" square tube would have more stock around the circumference than the 2" round. I don't know if that would make up the difference or not. Truth be told, I'm not absolutely sure that a round shape would resist twisting better than a square shape in the first place.
Any help on this would be appreciated.

[RWC]

I beleive the round is superior for torsional forces assuming similar diameter to wall thickness ratios. You don't see many square drive shafts.
Russ

[CharliePantsOnFire]

For torsional strength you want to go with the round tube. Charlie

[burninbriar]

The piece will have stress in both directions. Thats why I thought maybe the extra material on the square would make up the difference. I was pretty confident that the round is better for torsion, thanks for affirming that.
I'm going to try to get a drawing posted if I can to show the piece in question.

[Laiky]

pound for pound, round is better for torsional loads. If weight is not a factor and bending is, i would use square.

[burninbriar]

These are not the best drawings but I think you can figure it out. The first picture is my original design, the second is my modified version due to the fact that the 3" axle has a very high crown in it and connecting the unit to it in 3 locations and still have it pivot would be difficult. I could replace the crowned 3" with a strait piece but I know the guy does not want to spend any more than necessary. I could also make a new pivot point just above thee axle that would be strait across all three points but thats more work and more weight, a big factor since the thing will be toted around with horses.

The way it will work is similar to a fork lift. The 2" arms that straddle the bail will slide side ways so they can be spread to back into the bail and then tightened to the bail. 1" solid round rods then push into the center of the bail.(not shown on my drawing) The bail can then be lifted for transport or drug along on the ground to unroll it for feeding.
The bottom drawing in the first 2 pics is the running gear, I tried to show the 3 point connection to the axle compared to the 2 point connection.

My first design completely eliminates the twisting on the top rail of the fork system but the second one is the concern. I spread the contact area by Y-ing the lifting arm where it contacts, I think that will help a lot. I don't think it will be a problem either way, but if it can be built better, why not?

I hope these pics are good enough to get the idea across. Oh yea, the small circle on the drawing represents the wheels.
The bails are 5' in dia. and 4' wide. I think they weigh 1000 pounds. I will use a 5 part rope block for raising it, that should work out about 100 lb pull on the rope to raise the bail after figuring the leverage into it. The tung should have around 300 lb down force when loaded. if I did my calculations right. I'm pretty beat, see you tomorrow.

[Smyrna5]

Burin - this was prepared for a far different purpose, but you may find the tables on use in your decision.

http://mnhpva.org/tech/frame_tubes.html

[JgishODU99]

Re Design

Good Afternoon,
If I may, I would suggest locating the traveling position of the bail to be squarely over the axle, (cg bail ailigned vertically with the cg of the cart as to not put a compressive load on the harness (zero tongue weight). As far as square tubing vs round, let me look at my m.e, design text and get back with you. Hats off to your neighbor. These ------ oil companies don't need any more money as far as I am concerned.

[burninbriar]

Burin - this was prepared for a far different purpose, but you may find the tables on use in your decision.

http://mnhpva.org/tech/frame_tubes.html

Thanks for that link, it was pretty good. Confirmed a few things and taught me a few. When I first glanced at it it appeared that the amount of material (weight per foot) is the most important factor. Then when I had more time to read it more carefully, I was surprised that the round tube is actually stiffer when wpf is used with the same wall thickness, but less stiff with the same dia.& thicker wall, even though the amount of material never changed.I guess I shouldn't have been surprised though when you look at how floppy solid round is.

Good Afternoon,
If I may, I would suggest locating the traveling position of the bail to be squarely over the axle, (cg bail ailigned vertically with the cg of the cart as to not put a compressive load on the harness (zero tongue weight). As far as square tubing vs round, let me look at my m.e, design text and get back with you. Hats off to your neighbor. These ------ oil companies don't need any more money as far as I am concerned.

I was thinking the same thing at first but he has another 2 wheel cart that goes between the horses and the 2 wheel wagon or implement essentially converting the 2 wheel implement to a 4wheel. Tongue weight becomes a non issue unless its really extreme.
The reason I chose to offset the axle on the running gear is so when he starts to lift the bail, it doesn't lift the tongue of the carrier. He will probably still need to stand on the tongue until it gets so high if he is not connected to anything.

Almost forgot. I will have a rope horn so he can tie it off at any point during the lift. My thinking there was more toward if he wants to move it by hand he can balance the load by stopping the lift when the bail is over the center line of the wheels, or at a balance point.

[JgishODU99]

Re tube recs

Hi Pete,
I tried to post a reply yesterday but got timed out. Anyway the four wheeled configuration sounds like the way as the bail would change the cart cg if centered over a two wheel as the cart ascends or descends and could be quite unstable.

[new2tig]

wagon design

if i remember correctly, the bale wagon i rode on that was hitched to a team of percherons a few years back was a frame with a platform to stand on at the front.
it had a pivot point close to the wheels for two arms that were connected together and had a cable going to a crossbar that was behind the reinsman where there was a cable winch attached.
he lowered the arms, drove pins in to the round bale though holes in the plates [ 2 ft long pins ][ more like pushed them in ]and cranked it up to move into the field.
when he got to where he was feeding the cattle, he lowered the bale , cut the strings and pulled them then without even being on the wagon told his team to step forward and rolled out the bale.
he left the team hitched all day and never started his tractor all winter.
he has been doing this for years

[2tay530]

don't know much about pure facts but common sense(witch isn't so common any more) would tell me that if square tubeing had better torsional strength that they would use it in nascar roll cages instead of round. But I asume that it would be diferent for diferent aplications.

[FusionKing]

don't know much about pure facts but common sense(witch isn't so common any more) would tell me that if square tubeing had better torsional strength that they would use it in nascar roll cages instead of round. But I asume that it would be diferent for diferent aplications.

Actually common sense is it (round) is lighter weight thus better in a race car