Frameless construction

[angib]

unfortunately, dexter doesn't make off the shelf half shafts, however, the word custom doesn't fit either, i prefer to say they are made to order..

Which reminds me of a nice twist I saw on the FiberglassRV forum, from a guy who was replacing the rubber torsion axle on his Trillium. He had weighed each wheel of his trailer and had found, as do most, that the left side of his trailer was substantially heavier than the right - he has had his new axle made with the left side rubbered for 1500lb and the right side rubbered for 1250lb!

Andrew

[dwgriff1]

I wondered about that.

Do you think it was a worth while idea?

dave

[brian_bp]

I think the asymmetric springing was appropriate, although even load distribution between the two sides would be better. I have heard more than one trailer owner (including the previous owner of my travel trailer) comment that uneven loading (side to side) caused sway. Getting the thing to sit level has to help.

As for half-axles... a "frameless" trailer is the last place I would use these. The rubber torsion axles sold as one assembly are just two of the "half axles" sharing one steel tube (usually square) which joins them. Here are my reasons:

That tube keeps them aligned with each other, both in toe angle and in camber. Without a separate frame, the body would need to do this, but it is difficult to control the concentrated loads with enough stiffness. If I were to keep only one bit of framework across the trailer, it would be this tube.

The brackets on the full axles typically extend further towards the hub than away from it. If the bracket is long enough to extend to or beyond the hub line, the bracket takes all of the torque of the suspension load, and the trailer structure is just supported; if the bracket is short, like the little flanges on these half-axles, then the body is being twisted at that point by a torque equal to the load on wheel times the length of the arm.

There are reasons to use the half-axles, normally to get a odd track dimension, to accommodate a dropped floor down the centre of the trailer, or to otherwise work with an unusual frame requirement. To me, the "frameless" or unibody trailer seems like a good match to the "subframe" which is supplied as part of a full rubber torsion axle assembly, and a teardrop body which carries load to vertical side panels which would line up nicely with the full axle assembly's mounting brackets seems much better suited to those brackets than to the half-axle mounting flanges.

[brian_bp]

Andrew's vee-form structure (or subframe) makes sense to me, connecting the concentrated load points. The other way to do this is with a tee frame: a straight tube tongue extends all the way to the cross-tube of a rubber torsion axle, to which it is connected. U-Haul did this as sort of a subframe in their travel trailers. BPW (a major European trailer component manufacturer) sells the brackets to do this with their axles and tongues, and shows the result on their product overview page labeled as the "T-chassis" (the one like Andrew's design is the "V-chassis").

The tee design demands more of the floor structure, but the stress is in the plane of the floor, which is easy - the floor would act like a really big gusset for the joint of the tee.

[reiltear]

Hey Brian!

You are a thinking man! AND I like the fact that you are. You sound like an engineer.

Would you be so kind as to translate(or help us translate) the info in a couple of my previous posts into English(or Russian, I can still read it)?

Also, thank you for connecting the "axuls"(sorry Geron, I could name a few places you never heard of too, no insult intended, I just think it's fun to be from wherever we are and still be friends) to the "frameless" frame.

My main concern is the TD not falling apart(thank you, Geron), which is why I think(sorry, thinking hurts, so I try not to) I started this thread. So far I've only read about the "gut feelings" and great woodworking skills(THANK YOU Dave), and the honeycomb panels "that could sleep elephants"(Andrew, where are you?)

Happy holidays, and PLEASE, chime in, Ilya

[asianflava]

People have done it so I'm not saying that it can't be done. The problem with the wood is not it's strength, it's how resistant it is from the fasteners pulling thru.

I'm not a fan of the "Frameless" design. There is little advantage when compared to a "Minimalist" frame design.

[angib]

I'm not a fan of the "Frameless" design. There is little advantage when compared to a "Minimalist" frame design.

Yes, the weight saving is maybe only 20-30 pounds.

But I think the 'Minimalist' frame design is just a 'Frameless' frame design but with enough extra metal to convince onlookers that it's strong enough - the extra metal doesn't really do anything except allow the builder to make weak joints in the body - though that may be a useful benefit.

Andrew

[Arne]

Still planning, but the frame design is complete. and it turns out that it is pretty much a V frame (with each front to rear member having a jog in it), but really looks like a simple boat trailer without the cross members... I'm not gaining too much weight, I hope,and it ties the tongue to the suspension, with the tear as the box sitting on the top.

It may be over built, but it makes me feel better. And I can use the h/f 1800 parts to build it with... and if i don't like the way it sits, I can pull the springs and axle off and substitute a torsion axle at some point.

[dwgriff1]

I ran the hitch oak all the way to the back. That way I am using the strength from the back curved panels to strengthen the tongue. Everything ties into that tongue, this way.

That is basically the same thing you guys do who build a steel frame and bolt everything to that frame. I just have less weight all along the way.

dave

[brian_bp]

One more note on the half-axles: the Dexter units which Jim (in Savanah) showed us appear to have the same brackets as the full-width axles, which makes them (in my opinion) much more suitable than the others which I have seen - Andrew already noted this difference. Still, with four brackets instead of two, the whole suspension probably weighs just as much as a full axle assembly. The extra plywood plate apparent in Jim's design also addresses the toe-control issue (and to some extent the fastening issue), but again adds weight.

Ilya, your posts make sense to me - no translation needed!

My profile says "teardrop builder", because that's what the forum software uses as a label. I'm not actually building a teardrop, or other trailer, as I am just using and modifying my moulded fiberglass travel trailer for now. I find any vehicle technology interesting, and the depth which T&TTT members are willing to get into every aspect of design is impressive. Thanks, Andrew, for introducing those of us from FiberglassRV to this forum.

[Jiminsav]

OK..for the record, I didn't build a frame from metal, because the shop where I welded the first frame up at no longer was available to me, and I'm too scottish to pay someone to do it for me, so I sat down and thunk it through and came up with what I did..making it lighter wasn't an issue. making it at all was, because I already had the cabin under construction, and needed to do something now.

so, once again, what I have done was used a piece of 2 inch thick by 10 inch wide Oak to bolt the half shafts too..with stainless bolts and nuts, the nuts are under the trailer so I can crawl under and check them occassionally, the bolt heads are accessible if need be.
the sides of the cabin are glued and screwed to the oak, and also one cross member is mashed into the oak with the back piece of steel using 10 inch lag bolts.

the front steel piece is lagged into another cross member and the tounge is bolted to the steel pieces and lagged into the Oak.

[doug hodder]

I'm too scottish to pay someone to do it for me

Jim...good to meet another Scotsman...in a previous thread I mentioned that I wouldn't pay for something I could do or learn how to do...but you know what...I'll bet we know all sorts of shortcuts to getting things done on the cheap...Doug

[reiltear]

Hello, everyone!

Happy belated New Year!

To rekindle an aging thread, I found some sources for answers to my own questions. I still have to make heads and tails from a lot of this(it's been two decades since I had any use for math beyond 'rithmetic), it's a start.

I think much of this will apply to "regular" teardrop design and construction also and I truly hope I'm not being redundant by posting these links here. A word of warning - a lot of this info is very technical and geared towards building construction, but could be "scaled down" to TDs. Well, off we go.

The first link is to the "Wood Handbook" by the United States Forest Products Laboratory. As you already guessed, it has a plethora of information on wood. It's 486 pages long and is available in separate chapters or as a single 15MB download. I like the price too. $0.00 in electronic(PDF) format.

http://www.fpl.fs.fed.us/documnts/fplgt ... gtr113.htm

The next resource was "discovered" as a reference for some of the design chapters in the "Handbook" - it's the Engineered Wood Association. You will need to register to be able to download the PDF's, but it's easy and Freeeeeee...(sorry for getting carried away here...) And they haven't spammed me yet. The link is:

www.apawood.org

They have an inane(imho) numbering system for their articles and the ones I think are pertinent to TDs are these:

Y510 Plywood Design Specification - the "starting point", contains data on all kinds of plywood

S811 Supplement 1 (to PDS) - Design and Fabrication of Plywood Curved Panels (profiles and hatches)

U813 Supplement 3 - Design and Fabrication of Plywood Stressed-Skin Panels(floors, walls, doors and roofs and what caused me to start this thread - the desire to build something that has enough strenght for years to come, not weigh a ton, while avoiding a trailer and not being a guesstimate)

U814 Supplement 4 - Design and Fabrication of Plywood Sandwich Panels (same concerns as for U813)

Technical Topics TT-003 Bending Plywood

These articles are just the beginning, the APA website contains more info on plywood finishing, gluing, repair, crates, furniture frames and some transportation applications, too numerous to mention here.

I would really appreciate your opinions on this and also, if your "calculational" skills are more up-to-date than mine, some help in scaling the 2X4s used in the design examples to 1X2s, 2X2s, etc. If you "dare" to tread in these "dangerous" waters and think I overlooked an easier solution, please don't hesitate to let me know what a dodo I've been...

Thank you!

Ilya

[angib]

Ilya pm'ed me around Christmas and I promised I'd look at the links he supplied, but of course I then forgot about it. So I'll start with a public apology to Ilya for being so rude.

There is one easy answer to the question Ilya's asking, but it's not the answer he wants. The answer needs some explanation, and it's a repeat of something I posted long ago, so everyone's free to tune out.....

There are two main types of strength we need in a teardrop body and I'll use the floor as an example.

Firstly we need overall strength - the strength needed for the item not to be torn apart or damaged some other way. For the floor, the most (or the only) critical strength will be bending due to the weight on the mattress (no, I'm not calling you heavy....). This is exactly like the floor strength calculations in the APA handbook on plywood stressed-skin panels. But we know from Roly's 1/4-Nelson that a regular door with 1/8" plywood skins is strong enough, at least for the 40" width he was building, which shows overall strength isn't a big problem.

Secondly we need local strength which can also be called toughness or durability. I like the 'hammer test' method of describing toughness, which is how hard do you want to be able to hit the item with a hammer without damaging it or going through? A 'kiss', a light tap, an over-arm blow? 99% of the time with teardrops, this local strength will be the critical strength, not overall strength. That 1/8" double-skin floor is strong enough to hold you up sleeping, but if you kneel on it, you'll do damage*.

The difference between these two was clearly shown to me in Calgary 20 years ago. A hailstorm had happened a few weeks before we arrived and all the Japanese import cars that had been left in the open had hail-marked roofs, hoods and trunks, while the (heavier) North American cars didn't. The Japanese cars had perfectly good overall strength - they didn't fall apart when driven over a bumpy road - but they didn't have the same level of toughness or local strength as the North American cars.

Two skins of 1/8" plywood separated by at least 3/4" has enough overall strength for any part of a teardrop. For much of a teardrop, a single 1/8" skin with 3/4" deep framing will be strong enough. The only reason to go above these thicknesses/weights is if you want more toughness. And that's really a question of what you want, not what you need, so you have to answer it yourself.

Andrew

*Roly's floor is a slightly different matter as he used a hollow-core door. But that isn't actually hollow, it's got honeycomb paper core that actually provides a lot of local strength.

[reiltear]

Andrew, no apology was necessary. Thank you very much for the answer.

Ilya