Thoughts/opinions on my trailer frame design (1 Viewer)

[Layonnn]

I am getting ready to start building an off-road tear drop style (but not shape) camping trailer. I've went ahead and added some tools to get prepared for it (built large workbench, vise, drill press, chop saw, welding accessories). I'm going buy the steel this Friday and get started.

Do y'all have any suggestions or see anything very bad about my frame design?
The cross tubes where the hitch tube goes I plan to cut and weld them so they provide the bracing and more support (vs putting the hitch tube under the frame).

 

[LAMBCRUSHER]

thought I was the only guy who still used graph paper...seems like it'd be stout enough. I'm almost certain that someone who knows more than I do about the science would suggest you place the receiver tube below the plane of the frame to improve resistance to bending under loads, and that I would tend to think it to be a logical suggestion...other than that, I like the idea, and have a similar box in the cooking-up stages for my flat bed...a lot of guys try to keep their track width down, but that cuts into comfort in a live-in box. Also, not certain about what the right answer will be, but you might need to move your axle forward a bit to keep optimal tongue weigh...

 

[cmck]

Take this only as a consideration because I'm not an engineer or an expert. I have been planning a similar expo trailer build so I have been considering designs as well.

I see quite a number of trailer frame that have some triangulation to support the tongue.

Think about your suspension, as shocks normally mount to a frame rail behind the axle and its location might differ from the standard 2' you show.

I stress these are things to think about only.

My plan is to actually buy the axle and suspension 1st, then mock the frame up full size in 2x4's and screws. This sounds like an extra step but it's cheap, fast and will confirm the key points of the design.

Good Luck and enjoy the satisfaction of building your own trailer.

 

[Pascoscout]

You need to triangulate the tongue bar as suggested above. I'd take it from a foot or so behind the hitch point and end it where the first grate meets the wall if not further back. That tube may be heavy but with that long of a lever sticking out it can bend under the stresses taking this type of trailer off road will create.

Have you sourced a hitch for the 2.5" square tongue bar? Seems like most I have built have been for 2" square tube. If you triangulate you could reduce the size and probably the thickness of the tongue tube.

Most trailer designs go with the tongue bar (triangulated) under the frame because you can attach it in more points. With a lightweight trailer it may not be a big deal but consider how much this will weight when loaded with gear and supplies. Remember that water is just over 8 lbs per gallon so its weight adds up fast.

Otherwise looks like a pretty cool project.

 

[LAMBCRUSHER]

keep the 2.5 and weld the hitch to a piece of 2x2x1/4 and pin it into the receiver tube...if you triangulate, you can end the 2.5 at the point of the triangle and use a long piece of 2" to have an extendable tongue...its what I do, but I haven't triangulated...yet; I only have a 4x6 box and haven't felt the need...I'd end my gussets at a point where I could still achieve full 90*+jack-knife without hitting the pull rig, and have the tongue make up the difference to the hitch...another note...flat top fenders are great tables...

 

[ntsqd]

The line of the greatest bending moment in a trailer frame is right across the front-most cross-member. The frame needs more Section Modulus there to live a long life. Easiest way to get that is to run the tongue under the main part of the frame. If you are going to triangulate it them the diagonals are best used when they tie into the forward spring mounts or outer link mounts. The cad sketch below shows these features.

A lot of homebuilt trailer frames butt the tongue onto the front end of the main frame. They only get away with that because of the light loading and use. Note that the military 1/4ton trailers all have their tongues designed and built like the below pic. It isn't an accident that they're done this way.

I don't know what you're planning on using for suspension, but if it is leaf springs then the typical trailer leafs are way too short and stiff. Eggs and beer will take a beating with those. Use a longer, softer leaf spring and include shocks in the design. Stand them as straight up as possible. the more they are leaned over the less effective they are. Past 45° and you're wasting your time even bothering with them.

EDIT:
The tongue tube should, at minimum, extend to the first cross-member. Can go all of the way to the rear of the frame if desired. To gain more weld bead length if the tongue doesn't go clear to the rear I suggest a plate like the one shown here:

 

[LAMBCRUSHER]

the trailer whisperer has joined us...

 

[TroutBum03]

Was reading your post and thought about a recent camper I saw on Craiglist that mimics what you're design. I thought it was a very cool off road camper. It's a Taxa TigerMoth. May give you some more ideas.
TigerMoth Camper Trailer - Made in the USA by TAXA Outdoors

 

[Layonnn]

thought I was the only guy who still used graph paper...seems like it'd be stout enough. I'm almost certain that someone who knows more than I do about the science would suggest you place the receiver tube below the plane of the frame to improve resistance to bending under loads, and that I would tend to think it to be a logical suggestion...other than that, I like the idea, and have a similar box in the cooking-up stages for my flat bed...a lot of guys try to keep their track width down, but that cuts into comfort in a live-in box. Also, not certain about what the right answer will be, but you might need to move your axle forward a bit to keep optimal tongue weigh...

I love me some graph paper haha.
So the main tube for the hitch will be uncut. The parts where it goes "through" the crewmembers i had planned on cutting out the space for the hitch tube to go through and then welding to either side.
I don't plan to build the fender sections til I have my timbren axles in place and check about weight. The box will have cabinets and such in the rear so that will add a little balance but I may try and move it up a tad forward.

Take this only as a consideration because I'm not an engineer or an expert. I have been planning a similar expo trailer build so I have been considering designs as well.

I see quite a number of trailer frame that have some triangulation to support the tongue.

Think about your suspension, as shocks normally mount to a frame rail behind the axle and its location might differ from the standard 2' you show.

I stress these are things to think about only.

My plan is to actually buy the axle and suspension 1st, then mock the frame up full size in 2x4's and screws. This sounds like an extra step but it's cheap, fast and will confirm the key points of the design.

Good Luck and enjoy the satisfaction of building your own trailer.

I was kind of hoping the strangulation of the front rack would be sufficient but recently added to my drawings additional bracing to the front of the tongue as also a spot to mount a nose box (for batteries or electronics).

Suspension will be timbren 2500hd with electric brakes.

You need to triangulate the tongue bar as suggested above. I'd take it from a foot or so behind the hitch point and end it where the first grate meets the wall if not further back. That tube may be heavy but with that long of a lever sticking out it can bend under the stresses taking this type of trailer off road will create.

Have you sourced a hitch for the 2.5" square tongue bar? Seems like most I have built have been for 2" square tube. If you triangulate you could reduce the size and probably the thickness of the tongue tube.

Most trailer designs go with the tongue bar (triangulated) under the frame because you can attach it in more points. With a lightweight trailer it may not be a big deal but consider how much this will weight when loaded with gear and supplies. Remember that water is just over 8 lbs per gallon so its weight adds up fast.

Otherwise looks like a pretty cool project.

For the hitch, I'm using a max coupler. So it needs a 2" x2" internal dimension, so I went with 2.5" x2.5" 0 .250 wall tubing.

I'll add some extra bracing,triangulation to the front of the tongue, was unsure how far forward it needed to be in relation to the hitch.

I'm still not sure if the reason some manufacturers mount it below the main trailer is due to strength or because it's a LOT easier to build it that way (compared to the way I'm wanting to do it). I have seen quite a few built the way I'm planning. Though, for the weight i plan on the trailer being, it will be overkill regardless haha

keep the 2.5 and weld the hitch to a piece of 2x2x1/4 and pin it into the receiver tube...if you triangulate, you can end the 2.5 at the point of the triangle and use a long piece of 2" to have an extendable tongue...its what I do, but I haven't triangulated...yet; I only have a 4x6 box and haven't felt the need...I'd end my gussets at a point where I could still achieve full 90*+jack-knife without hitting the pull rig, and have the tongue make up the difference to the hitch...another note...flat top fenders are great tables...

Flat top fenders definitely. Plan on building them out of 1" square and some 14 gauge.

The line of the greatest bending moment in a trailer frame is right across the front-most cross-member. The frame needs more Section Modulus there to live a long life. Easiest way to get that is to run the tongue under the main part of the frame. If you are going to triangulate it them the diagonals are best used when they tie into the forward spring mounts or outer link mounts. The cad sketch below shows these features.

A lot of homebuilt trailer frames butt the tongue onto the front end of the main frame. They only get away with that because of the light loading and use. Note that the military 1/4ton trailers all have their tongues designed and built like the below pic. It isn't an accident that they're done this way.

I don't know what you're planning on using for suspension, but if it is leaf springs then the typical trailer leafs are way too short and stiff. Eggs and beer will take a beating with those. Use a longer, softer leaf spring and include shocks in the design. Stand them as straight up as possible. the more they are leaned over the less effective they are. Past 45° and you're wasting your time even bothering with them.

EDIT:
The tongue tube should, at minimum, extend to the first cross-member. Can go all of the way to the rear of the frame if desired. To gain more weld bead length if the tongue doesn't go clear to the rear I suggest a plate like the one shown here:

 

[Hornd]

Here's Mine
I put a storage under the floor and expanded metal up front.
I did the Y Design for the Tongue.

 

[Hornd]

Are you going Water Supply?
Are you Going Fridge?
Are you including an AC?

Included a bunch of pics from my design folder of ideas I saved

 

[Hornd]

I made mine 5' wide so it would fit a queen mattress.
If your using 4x8 Stock this needs to be considered.

I used Torsion Axles from Ebay ($100) and welded them on.

Another great site to get ideas:
Teardrop Travel Trailers by Camp-Inn
Search Kuffel Creek Cubby 8 Plans too.

I will try to answer any questions you might have about trailer design.

 

[ntsqd]

......
I'm still not sure if the reason some manufacturers mount it below the main trailer is due to strength or because it's a LOT easier to build it that way (compared to the way I'm wanting to do it). I have seen quite a few built the way I'm planning. Though, for the weight i plan on the trailer being, it will be overkill regardless haha

It is done that way for strength. It actually is a tattletale in detecting a trailer built by someone who doesn't fully grasp the forces involved in a trailer frame. I would never build a trailer any other way, but the custom frame under our camp trailer was built that way. It is only because of the light loading and overkill frame design (all .250 wall 2X3 tube except the receiver tube that runs full length) that it has lived this long and in 20+ years of service shows no sign of fatigue. Some pics of its frame:

The tongue was built to extend, but the only time I've ever used that feature is when I'm moving it around the yard by hand.

I've also cut off that (too) short receiver on the end of the sliding tube and have gone to pulling it with pintle using this rotating lunette:

Sadly the camper has largely superseded the trailer and it rarely leaves the yard these days.

 

[Hornd]

I bought cork 1'x1' Panels form inside flooring. It's soft, quiet and insulates.

 

[Layonnn]

It is done that way for strength. It actually is a tattletale in detecting a trailer built by someone who doesn't fully grasp the forces involved in a trailer frame. I would never build a trailer any other way, but the custom frame under our camp trailer was built that way. It is only because of the light loading and overkill frame design (all .250 wall 2X3 tube except the receiver tube that runs full length) that it has lived this long and in 20+ years of service shows no sign of fatigue. Some pics of its frame:

The tongue was built to extend, but the only time I've ever used that feature is when I'm moving it around the yard by hand.

I've also cut off that (too) short receiver on the end of the sliding tube and have gone to pulling it with pintle using this rotating lunette:

Sadly the camper has largely superseded the trailer and it rarely leaves the yard these days.

Ah, that makes more sense then. Thanks for all the information.
I do plan on adding a little more bracing from what's in my sketch. Keep in mind my goal weight of the trailer is less than 1250lbs fully built.
The steel for the frame in total is less than 350lbs. I doubt the wood box/cabin will be much more than 4-500 lbs.

Here is where I got so far and about half of it is tacked in place.

 

[Layonnn]

I bought cork 1'x1' Panels form inside flooring. It's soft, quiet and insulates.

View attachment 1543215

View attachment 1543217

I had saw that picture over at tiny travel trailers site. My plan is something similar to the simple cleat design so that the walls are sitting on the floor.
My wall design will probably be 3/4" plywood middle that will be skeletonized to save weight and make room for insulation. Inner wall will be plywood and outer wall will either be just a sheet of aluminum, or aluminum over a thin sheet of plywood, not sure yet.

For attaching the floor to the frame, I was thinking of doing nutserts in the frame rail and counter sunk bolts in the floor. Not positive on this yet either.

 

[Layonnn]

Are you going Water Supply?
Are you Going Fridge?
Are you including an AC?

Included a bunch of pics from my design folder of ideas I saved

View attachment 1543190

View attachment 1543197

View attachment 1543198

Water tank - not yet, but possibly added later.
No fridge, just yeti cooler.
No AC.

 

[Layonnn]

Where can I find the little bit of metal to weld at the end of the hitch tube that prevents it from wallowing out?
The enlarge portion at the end of this tube.

 

[Steve83]

Either buy a premade tube with that reinforcement; or cut a strip, wrap, & weld it on. It's not on the website now, but my local NT has a 4~5' receiver tube for ~$40.
Towing Hitch Adapters | Northern Tool + Equipment

On my mini-trailer, I used 3" tube for the tongue because that's what the tongue fit onto. It also has plenty of room inside for the e-brake handles (which I haven't added yet, but the axle has the cables). I used a Dodge Caravan rear axle because of its drop design, simple suspension, shocks, brakes, & common rims.



Because of the large tube & light axle, it didn't need triangulation; and because there's no tongue box, it has a ~93° jackknife angle (before the tongue hits the tow vehicle bumper).

 

[Hornd]

Lets see your axle layout.
If you are concerned about strength add gussets in corners.
You could put a full plate where Hitch Tube leaves frame and weld entire underside to the gusset.
You are likely fine.
Did you see the Gussets in mine? They are likely way overkill but I did not pay for the steel.