Aluminum Trailer - Need help

[Neo]

Ok I think I've integrated all your measurements into my diagram (drawn on Google Slides) now. But if you don't mind there are 7 more I still need ... https://docs.google.com/presentation/d/ ... sp=sharing
Let me know if this looks Ok? .... Feel free to provide imperial measurements ... Sorry but I done the diagram in metric because that's what I'm used to.... with or without and beer

All the best.
Neo

[Tomfoolery]

My inclination would be to bend it cold, but I'd have to research it. Maybe Tom can weigh in on heating 6061 Aluminum to bend it. He's way better at Material science (and most other stuff too).

I actually have a second degree in Materials Science and Metallurgy, but since I've never worked in that field, I've forgotten almost everything over the decades other what's needed for common steel work.

I would suggest bending it cold. It's almost certainly 6061-T6, with a 40 ksi yield strength. The moment of inertia in the weak axis of that shape is only about 2.08 in^4, which means bending it to the point where the extreme fibers begin to yield takes about 4000 lb-ft, or 4000 lb at 1 ft from the point where it bends. Like in a press with the bottom blocks set 2 ft apart, with the arbor in the middle applying 8000 lb (force goes down as the blocks get further apart). Pretty easy to bend in that direction, relatively speaking. Take little bites to keep a large radius, so you don't cripple the flanges. I'd probably mark off locations, evenly spaced, so you can reliably do both beams the same.

It's about 2.5 times stronger in the strong direction in bending, by the way. Not that you'd want to bend it that way, of course.

And remember - I don't work in aluminium. So take everything I say about it with a grain of salt.

[Jimmyt]

Will work on the sketches this morning. English/metric conversion is problematic due to standard material dimensions for bunk wood. A 2x4 is really 1-1/2" x 3-1/2" (neither republicans nor democrats will accept the blame for this travesty). Similarly, a 4x4 is only 3-1/2 square cross section. So, when I tell you that a wedge block is a 5-1/2" 2x4, that gives you a certain angle. If your materials are different, and you're rounding mm, the result may be close enough, but I don't know that for sure. So, be careful when converting and rounding. This is particularly problematic since the drawings are not to scale.

Dimensioning to the center of a radiused bend is not really practical. The two bends need to be centered about where we dimensioned them along the 20 ft piece. After that, you won't be able to measure to the bends with any accuracy. Nor should you try.

I will measure the distance from the centerline of the hitch ball to the various points you requested. The distance fron the hitch ball to the axle, and the bunk and v-block distances from the hitch ball, will get you the original trailer balance. The draw bar, or tongue length has to be adjusted for different brake assemblies, hitches, etc. to maintain the centerline of hitch ball to axle, bunk, v-block distances.

I'll mark up the sketches and take pics.

Hope you can work out your material supply issues.

Since Tom says bending it cold is the way to go, hope you have a press. If not, you can probably afford one for what you'll save by building your own trailer. That's the story I always use to justify new tools!

Jim

[Tomfoolery]

I don't know much about aluminium, but I do know that T6 condition is the result of several heat treatments (quenching for hardness and strength, maybe followed by tempering for ductility and stress relief and/or whatever. So I definitely would not use heat to bend it, assuming it's not in the lowest strength (soft) condition, which I can't imagine any production beam would be.

[Jimmyt]

[Jimmyt]

[Jimmyt]

The dimensions down the left of the plan view are; centerline hitch ball to bottom of vblock. The next dimensions are from the bottom of vblock to center of front bunk and center of axle/center bunk. Axle bunk to rear bunk is on right side of plan view.

Critical to note the actual wheel center is 4-1/4” aft of the axle center. If you go to tandem axles or other system, make sure you center the wheel support assembly where the current stub axle is - not where the axle beam is.

Note that the strap at center bunk is bizarre, but bolted to the upper flange on both sides, and continuous across the trailer.

See how this settles in and get back with me. Got a few errands to run.

By the way, when you’re varnishing your furniture project, remember not to drop the can. . Get off my lawn!

[Neo]

Thanks so much Jimmy. Excellent point on the axle/wheel position.
And thanks Tom you're making my head spin with what you know ... It's all great reference information and I'm starting to sound like an "I-Beam expert" on the phone
Ok I've found an Alu I-Beam supplier about 80Klm from me. On their price list one beam (that weighs 21Kg) is a very close match but they'll only make it for a 250kg order!!... That's extra 10 beams I don't need!
The next Beam size up they have in stock but it's over 3" wide on the flange ... I know this is going to dramatically affect how I bolt the beam to the draw bar (and the bend angels) but what else would need to be changed to accommodate this? ... I guess a wider flange makes it even harder to bend too?

I've also found two fabricators that bend I-Beams... One normally only works in steel and he's pushing for "cut, brace & Weld". The other won't discuss details until I give him a full diagram ... So I need to get that finished

[Jimmyt]

Looks like shimming is allowed. Might require a bit of re-thinking, but a slightly wider flange would probably be ok - if you can bend it.

[Jimmyt]

Old Roger almost put a kink in this one when he bent it...

[Jimmyt]

Neo said: The next Beam size up they have in stock but it's over 3" wide on the flange .


The stock Mac trailer beams are 3-1/2” wide flanges. 89x127, flange thickness 7.37. Had enough beer where you’re doing new math?

You need to be looking at the bottom one, or the ones below that. Flange meat is the key. If you have the same web height, but less flange, it’s a no-go. Tom’s going to kill me for the low-brow factor of that statement....

[Neo]

Ok What a day !....Jimmy the photos are a big help ... "More meat" is best I appreciate that. That first Beam I chose was too thin, agreed. But there seems to be only two manufacturers of Alu I-Beams in Australia (SOMEONE PLEASE CORRECT ME IF I'M WRONG ). So if I can't find some form of compromise I'll have to abandon the whole project. "No Alu no build!"
Capral was the first company but second look at the other manufacturer "Ullrich" (who manufactures only five I-Beams types) and there's a possibility with their biggest I-Beam (UA4389) that has a fair amount of "meat" on the flange and the web.... What do you think guys? ... Thought maybe Tom could make some sense of the P, Ix, Iy and Mi measurements?



Jimmy I've updated my diagram. There are 3 more measurements I believe are import (highlighted in yellow)... But please, no rush for theses
https://drive.google.com/file/d/1m_lGP_ ... sp=sharing

[Tomfoolery]

Capral was the first company but second look at the other manufacturer "Ullrich" (who manufactures only five I-Beams types) and there's a possibility with their biggest I-Beam (UA4389) that has a fair amount of "meat" on the flange and the web.... What do you think guys? ... Thought maybe Tom could make some sense of the P, Ix, Iy and Mi measurements?



Jimmy I've updated my diagram. There are 3 more measurements I believe are import (highlighted in yellow)... But please, no rush for theses
https://drive.google.com/file/d/1m_lGP_ ... sp=sharing

The Ixx figure is the moment of inertia of the section in the strong direction, and the Iyy is in the weaker direction. MOI is a measure of stiffness of the section (when used with Young's modulus, a property of the material rather than of the shape*), and also of the strength of the section when used with other dimensions of the section and the yield strength of the material (again, a property of the material). The higher the number, the stiffer and ultimately stronger the beam. You can easily see which direction is the stronger from the Ixx and Iyy values.

The beam used in the Mac trailers, per the details posted earlier, have an Ixx value of 5,140,400 mm^4 (millimeters to the 4th power) and an Iyy value of 833,700 mm^4. Halfway between the last two entries in that table. You can ignore the P and MI values for this application. Beam weight as drawn is 5.2 kg/m.

*Young's modulus of aluminium is about one third that of steel, so the same beam in steel would be about 3 times stiffer, or would deflect about 1/3 as much with the same load on it. That's why things made of aluminium that are sensitive to elastic deflection, like bicycle frames and boat trailers, are generally made of larger members, even if the material strength is the same, which it often is.

[Jimmyt]

So, if I remember Materials 1 class correctly, Tom said, "if these are your choices, pick the last one".

You da man Tom!

I'm still cleaning up varnish...

[Neo]

Thanks Tom ... If MOI is a measure of stiffness of the section is it possible to calculate how much the Alu will be weakened when bent 14.5 Deg?... Can these numbers tell you if it's 6061 T6?
I'm guessing one advantage of a wider flange is it will not need to be bent as much?.. Maybe only two 13.5 Deg bends?
A higher web might be more problematic. It will create a deeper cradle and I may need to compensate with fatter bunk pads?...This technically raises the ground/water clearance which I was hoping to keep as low as possible for some of the shallow boat ramps I use.
I'll call Ullrich today and see how I go ... They don't actually state if their I-Beam is 6061 T6 ... or should I not be so concerned about that now?

Jimmy, Ok please explain the Varnish story ... Are you having a dig at Tom

All the best gents.
Neo