Frameless Trailer/Torsion Axle Mount

[bdosborn]

Here's a nice picture of the bottom of a frameless trailer after the axle fell off at 60mph.


You pays your money and you takes a chance.

Bruce

edit note: Dohhh, Andrew beat me to it.

[Nitetimes]

How do you guys NDT-test your welds? You've got a record of your welder certification, right? Your metal frame designs have been passed by a PE?

Been tested, passed.
Some of my frame designs carry 50 tons

Metal frames, particularly home-made metal frames, are absolutely no guarantee of avoiding problems, as several posts on this forum will support. But they are certainly less likely to give you problems.

You are absolutely right on both counts.
It's also one less sue point if the trailer is mostly in one piece after an accident.

It's worth repeating that a frameless design is not something for the novice and requires a higher standard of build than a 'framed' trailer.

Agreed, and I'm not telling anyone not to do it. Just be certain you are up to the challenge. Good insurance is a good idea too.

Andrew

[doug hodder]

I think that if someone takes a good look at the bottom of the trailer pic that Bruce posted, and maybe I'm wrong on this, but I certainly don't see any real structure that an axle was bolted to...IE.where are the bolt holes that surely ought to have been there where the axle tore from? I'm only seeing what appears to be a 2X2. I would think that even if a lag screw were used, that there ought to be some visable tearout from it's sudden removal. A through bolted install with washers surely would have torn up the bottom side much more than is shown.

Oh well, everyone builds what they want, just don't compromise safety...doug

[asianflava]

There is a fine line between adding an extra margin of safety and overbuilding.

[bledsoe3]

There is a fine line between adding an extra margin of safety and overbuilding.

I agree. I guess it's just my nature to err on the side of overbuilding. I should have been able to build a couple of hundred pounds lighter.

[Arne]

I've only just started this, but it will give an idea of a minimalist frame. I wanted to bolt the axle to metal, and I wanted a cross member front and back for integrity and where the major weight would be in the back (a/c, battery, microwave, etc...)

Both x-members are laid flat to lower turbulence.

http://www.freewebs.com/aero-1


There was some weight penalty, but much lighter than the standard 1,800# h/f from from which it was made. The floor is built like a hollow-core door with 2x3s where I need to attach walls, etc. The floor is lighter than 3/4ply would have been, and is fully insulated with 1.5" foam.

[angib]

Doug, as far as I've found out, John just bonded the axle brackets to the underside of the floor and then laminated over them - hence my comment about peel strength as that was all that was holding the axle in place. Just four bolts with big washers would have been plenty to prevent this failure.

Interesting to see how strong the body was - almost unmarked from sliding down the road at 60mph - though that's no more than I would expect from epoxy.

Andrew

[Alphacarina]

There is a fine line between adding an extra margin of safety and overbuilding.

I agree, but at least when you 'overbuild' the frame, it lowers the CG of the trailer - Something you can't say in most other instances of overbuilding

Don

[angib]

but at least when you 'overbuild' the frame, it lowers the CG of the trailer

Yes.

It's also important to recognise that overbuilding does not necessarily make a trailer any stronger, it often just makes it tougher. If you make something twice as thick, it will feel much tougher to you - if you kick it, your boot won't go through any more. But it also now weighs twice as much as it did before and so when it goes over a bump in the road, it will experience twice the force. Twice the force working on twice the material leaves you back where you started - it can still only take the same bump. But of course you have to pull twice the weight around with you.

Some changes do make things more than twice as strong. It you make a roof spar twice as wide, it's only becomes twice as strong. But if you make it twice as deep instead, it becomes four times as strong. It's the structural equivalent of a favourite saying of mine "Work smarter, not harder".

Andrew

[Jiminsav]

My computer crashed and burned a month ago, and it took awhile to get Vista to work with apache, but I got it, and the frameless pics are in the album pics

[Alphacarina]

The only pictures which show much are #28 and 29

I think it's a bit scary without a one piece axle. The forces exerted on the half axles (and thereby on their wood mounting points) are much more severe than if it had a one piece axle which holds the wheels parallel to one another and maintains correct camber without depending on the wood to do that - You're asking an awful lot from just 8 axle mounting bolts. My 1400 pound Fexiride half axles use 6 bolts per side and those are meant to be bolted to some steel

With a one piece axle, the tongue welded to the center of it and a couple pieces of lightweight angle triangulating forward from the axle to the tongue and I'd not be scared of that setup . . . . plenty of 'frame' for me

Don

[Arne]

How much weight is saved by using stubs instead of a full axle?

I suspect if designed right, the weight savings isn't that much.. if you are using wood, you need a metal rectangle across the trailer to mount the stubs to..

If you are using a metal frame, the full axle could become a frame member eliminating one metal x member.... seems hardly worth the effort..

[brian_bp]

I agree with Arne... the two-piece axle approach doesn't help weight much. I'd go even further - I suspect that most of these designs are heavier than a one-piece would be. Jim has much better brackets on his than most do (I think that was the subject of an earlier disucssion thread); the more common design needs even more attachment structure in the trailer than his do.

I think the axle manufacturers offer these two-piece setups for an entirely different reason than they are being used here (eliminating the weight of the crossmember part); they are to allow trailer designs with dropped floors in the middle, non-standard track widths, or other novel configuration requirements. If the space between the ends of the fixed tubes of the separate axle parts are lined up with each other and nothing is between them, then there should be one cross-trailer piece of steel tubing.

[Jiminsav]

I agree with Arne... the two-piece axle approach doesn't help weight much. I'd go even further - I suspect that most of these designs are heavier than a one-piece would be. Jim has much better brackets on his than most do (I think that was the subject of an earlier disucssion thread); the more common design needs even more attachment structure in the trailer than his do.

I think the axle manufacturers offer these two-piece setups for an entirely different reason than they are being used here (eliminating the weight of the crossmember part); they are to allow trailer designs with dropped floors in the middle, non-standard track widths, or other novel configuration requirements. If the space between the ends of the fixed tubes of the separate axle parts are lined up with each other and nothing is between them, then they should be one cross-trailer piece of steel tubing.

very good Brian, thats exactly why I use half shafts, because I'm not sure about the finished width of the trailer, and using half shafts, I don't have to be worried about whether the wheels will fit when I get done.

they are actually harder to install, because you have to square up both stubs so it tracks right.

[Melvin]

I suspect if designed right, the weight savings isn't that much.. if you are using wood, you need a metal rectangle across the trailer to mount the stubs to..
.

The big advantage is you can get a custom axle width with off the shelve parts. Someone should make a torsion axle with an adjuster in the centre. Something threaded like a tie rod.