Building a Wooden Trailer

[timm]

I'm in the design stage of building my trailer. Finding a trailer the dimensions I want for the price I want is proving to be more difficult than I expected. So I'm looking at building my own trailer, however, steel is quite expensive and I think for how much my trailer will weigh I should be ok to build the frame with wood. I'm thinking the weight will be about 450-650# not including the trailer. Have any of you built a wooden trailer or had experience with wood framed trailers?

This is what my trailer design looks like at this point. It has an outer frame of 2x3 beams with 1x3 pieces running across the middle. There is a 1/4" skin on the bottom and a 1/2" floor on the top.



The axle mounting areas are reinforced with 2" x 1 1/2" steel angle pieces. The tongue is two 6' sections of 3" x 3.5# steel C channel. The coupler will be a standard A-frame coupler. The frame also has a piece of the same steel angle reinforcing the front of the frame where the tongue crosses over.



The angle would be bolted to the frame and the C channel would be welded to the angle.



I would cover the underside and sides with PMF to reduce the likelihood of water getting into the frame as I don't want it to rot. The topside would be covered with the actual trailer build which would also be sealed with PMF. I'm probably going to use a leaf-spring suspension system as torsion axles are pretty expensive.

Do you guys see any flaws or problems with this design? I'm not planning on going off-roading with this as I'm towing it with a Honda Civic.

[GTS225]

Yes. A structure is only as good as it's foundation. Wood will twist and bend much more than steel, and the same dimensions of wood does not have the strength as steel.
While I'm not a structural engineer, I believe you should not short cut the foundation, (frame), due to cost. I'm lucky enough that I was able to scrounge up enough 2"x2" square tube to build my frame and tongue. I urge you to do the same, even if it sets you back in your schedule.

Civil law suggests that if that should break free from your tow vehicle, and runs into a soccer mom's minivan full of kids, you could find yourself in a world of hurt.

Just opinion.....Roger

[Ottsville]

If using leaf springs I would go build a steel rectangle for your spring hangers and side to side and attach the tongue to that.

A torsion axle would be the way to go dor what you are doing as the axle then becomes part of the structure. See the ultralight trailer design(maybe in deaign library).

[timm]

Roger, I agree that wood is not as strong as steel, however, I don't need it to be as strong as steel. I don't need the strength of 2x2 steel tubes, that would be way overbuilding for a trailer that only needs to carry about 500 lbs. I don't see how the frame being wood would cause it to break free from the car either, the tongue and coupler will be steel, if anything the frame will buckle and it'll start dragging on the ground.

Ottsville, the research I've done says a torsion axle puts more stress on the frame than a leaf spring suspension. Take a look at this website: https://mechanicalelements.com/trailer-axle-springs-torsion-axle/

[friz]

I think your idea is very viable. Early teardrop designs had a similar idea. My frame being a bolt together provides no torsional rigidity to my camper. Some of the welded ones might depending on depth of structure. In my case the frame hides my spare and battery and provides a surface to mount lights. I probably get a little shock absorbsion from it also.

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[friz]

Looking at your drawings, I think you will want a little more tongue. You dont want those corners hitting your bumper maneuvering in a campsite.

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[Ottsville]

Interesting link and lots of information on their site. I wonder why that analysis shows springs mounted directly to the frame though. Seems to me most have a shackle anymore which changes the stresses in the analysis(but that's not really relevant to this conversation).

The part that I think your frame is missing may be an adequate side to side strength - a solid connection between the axle mounting points from one side to the other. With a torsion axle you get that connection. I would think that leaf springs put more lateral and expansion forces on the points of connection and between them. I would tie the angle iron on the sides together just behind the rear shackle mount with another piece of steel.

[troubleScottie]

I am not sure if a wood framed trailer is legal.

The original teardrop may have been all wood.

However, the world has changed. There are rules on what you can and cannot do. I have no idea if there are regulations on what the frame must be made of, etc. I would spend the time and confirm that it is legal. And check other nearby states to make sure they allow it too.

Given that Harbor Freight (HF) has steel trailers in the $300 - $500 including axles, springs, wheels, frame and hitch, you would be silly not to go at least that way. Many here have built TD around this starting point.

[edgeau]

If cost of steel is a concern here is a tip. I got a lot for my build for free. The local motorcycle dealer let me have the packing crates the bikes come in - with steel frames.

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[Ottsville]

Does anybody have the link to the ultralight trailer frame? I know it was on here but I can't seem to find it. It was two diagonals for the tongue and that went straight to the torsion axle mounts. There was also a build thread that used that design.

EDIT
Found one of them. There was a different build thread too:
viewtopic.php?f=35&t=12220

[greygoos]

http://tnttt.com/Design_Library/The%20U ... hassis.htm

[rkanz]

I considered this approach when building my TD. I decided it was easier to use a NT aluminum trailer. Most of the weight is in the axle and wheels, the aluminum frame doesn’t add much weight. I did build a torsion box floor. My finished trailer is under 600 pounds and we can easily tow it with a Honda Accord.

[timm]

The coupler will extend the tongue out a bit, but I can also adjust the position of the C channel pieces before they're welded on. I'd like the tongue about as short as I can possibly make it so the aerodynamics are cleaner.

Adding a steel cross member would be fine. However, I could probably just increase the dimensions of the internal pieces of wood to increase the lateral strength. Is this about what you were thinking?



I've spoken with the insurance company and all they need for a homemade trailer is the receipts for all the building materials and a declared value, no official safety required. I'm up in Manitoba so I don't have easy access to Harbor Freight, I'd have to make a trip down to one of their stores which adds to the cost. The Canadian Dollar is also really weak right now so it's not that great of a deal.

I can try and track down steel for free, but if the wood box is going to be strong enough I don't really see the point of building it stronger.

That ultralight trailer design was where I drew some of the ideas for this one.

I'd like to build off an aluminum trailer, really that'd be ideal. However, the 5x8 NT aluminum trailer will cost me over $1000, which is far more than I had planned to spend on the trailer.

[rkanz]

I used 1/4” skins top and bottom. The pink panther foam, glued with foam adhesive to the skins, makes the floor very rigid. You can save weight by using 1/4” skins top and bottom.


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[timm]

I wasn't sure if 1/4" plywood with foam would be strong enough, I'll definitely do that then.