How do you attach your cabin to your frame?

[Krusty]

I'm building a light weight foamie hybrid with a fiberglass skin. Since the trailer will be so light I am thinking of making the cabin detachable so I can use the trailer for utility purposes too. What do you think would be the minimum method to attach the cabin to the frame without risking the two parts coming apart during travel?

I am building the trailer atop a harbor freight folding trailer. I'm thinking of using the 8 bolted on parts that are used for attaching a 2x4 frame along the outside of the trailer as mounting points. The plan is to attach some short 2x4 pieces to those mounting points and then run some carriage bolts through the sides of the trailer near the base. This would give me 8 mounting points. 2 points on each side.

The front and back would also have the benefit of the 2x4s preventing the cabin from sliding forward or backward. The mounting points on the side I will likely need to use some angle brackets to complete the mounting since the cabin is 3 inches wider than the frame so it wouldn't have quite as much movement impeding ability as the 2x4s on the front and back.

What say you? Would this be plenty of mounting goodness, or should I also run some carriage bolts through the floor throughout the frame? I'm trying to avoid this as it would obviously leave bolts in my floor and would be more difficult to mount and unmount.

[rowerwet]

my floor has four carriage bolts through the floor and frame, one at each corner, good enough to hold it on and easy enough to knock the bolts out with a hammer and lift the tear off.

[Kharn]

I have 8 carriage bolts holding down my bed area, 4 in the galley floor, 2 the forward storage and a few more will hold down the tongue box. They're all 3/8" carriage bolts with torque washers to spread the load and not strip out the wood, lengths vary depending upon location.

[Krusty]

Sounds like my 8 bolts will be more than enough then. Perhaps I'll throw one additional bolt into the exact center just to help hold the middle down as well. I should be able to tuck that one in the storage area.

[asianflava]

My 5X10 has 8 bolts.

[Disc Golfer]

I attached my build to my HF frame using the same method you described in your original post. Mine is a heavy build using 2 by 4's and 1/2 inch plywood inside and out. The 8 attachment points using 2 by 4 blocks bolted to the bottom of build and bolted through the trailer fence brackets has worked great for me.

[Wolfpack]

Is it possible to use the galvanized carriage bolts commonly found in big box hardware stores, or would those be too soft? Lowe's for instance, doesn't show what grade these are on their website.

[bobhenry]

I am sure the proof load strength of a standard off the shelf grade 2 bolt far exceeds the strength of the wooden member that it fastens to the frame. This chart shows the proof load strength of a 3/8 grade 2 at 4250 pounds. (The proof load is where the threads start to rip off of the bolt body). If you use 6 bolts it will take better than 12 tons of force to tear these 6 fasteners bald. I think that should exceed the normal stress demands placed on your fastners even in a high wind.

http://www.almabolt.com/pages/catalog/bolts/proofloadtensile.htm

[Wolfpack]

Thank you Bob Henry.

I can now put aside my unfounded concern, of the cabin becoming detached from the trailer.

[Corwin C]

I am sure the proof load strength of a standard off the shelf grade 2 bolt far exceeds the strength of the wooden member that it fastens to the frame. This chart shows the proof load strength of a 3/8 grade 2 at 4250 pounds. (The proof load is where the threads start to rip off of the bolt body). If you use 6 bolts it will take better than 12 tons of force to tear these 6 fasteners bald. I think that should exceed the normal stress demands placed on your fastners even in a high wind.

http://www.almabolt.com/pages/catalog/bolts/proofloadtensile.htm

With a grade 2 bolt, make sure that you don't overstress them when you install them. It's surprisingly easy to do and if you do overtighten, they will fail even earlier than the 4250#. This chart will help when determining the proper torque.

For example, a 3/8" Grade 2 bolt (coarse thread) is only recommended for 15 foot/lbs of torque. A young child with a regular box end wrench can easily produce more force. There are some 3/8" nylock nuts that require almost that much to turn them at all. Personally, I don't use anything less than grade 5 unless I want it to fail for some reason (shear bolt).

[aggie79]

There's no need to go overboard on securing your teardrop shell to your trailer. Remember that all that is holding your trailer to your vehicle is a single 1/2" or 5/8" pin.

You probably should have more concerns about the floor structure around your fastener, and its ability to keep the fastener head from pulling through the floor, than the shear strength of the fastener.

[Wolfpack]

Thanks for all the great information.

Grade 2 carriage bolts sound quite suffient for this job, and I will torque them accordingly.