Please give me your thoughts of this concept frame...

[rdkng07]

Hello, I’m working on plans for a trailer that I want to build. At this point it will be shaped like a KenSkill, only it will be 60” wide inside. I may lengthen it a bit and make it a little taller, I haven’t decided yet. The frame is made using 1 x 2 x 3/16” channel. It is not the material or size I wanted, but I can get a few long pieces very cheap. The 2” web is too short and the 1” legs are not enough to comfortably work with.
This is bar channel with a uniform thickness in the legs.

If I had to use standard channel, which have a tapered thickness in the legs, I think I would use something else.

The frame is made completely from channel except two mounting plates that are 11 gage or .1196 in thickness. I will have to weld two additional channel pieces to the tongue to make tubes for strength. I am not sure yet the strength of two of these channels welded into a box, but I think that because of the channel’s profile it will prove to be stronger than standard tubing.


The outside tongue channel runs from the coupler to the end of the frame. It is one continuos piece that will be notched, bent, and welded. The inside tongue channel runs from the coupler into the joint that is created from the bend in the outside channel and welded into place along with the front cross member.


I am no structural engineer and have no trailer building experience; I can however cut and weld as I used to fabricate sheet metal and structural components for a living.

The frame weighs 131.8615 lbs. I don’t know if this is considered heavy or not. The goal I gather is to have a strong but light frame, and I’m sure I’m not doing that. The trailer could grow to somewhere between 1500 and 2000 lbs. I hope it doesn’t and am concerned about the A-frame tongue being adequate. The weight stated does not include the two axle brackets in the drawings. The two channel gussets welded to the tongues forward of the cross brace should not be necessary. That would be nice because there is a lot going on in that area already.



I’m counting on the galley partition to strengthen the floor in the rear. If I find that I need additional floor support it might be in the way of oak lumbar.

Because of the short 2” web height on the channel, I’m worried about the frame twisting. Hopefully between the strength of the cabin box and the axle, this will not be a problem.

I’m sure I didn’t explain this very well, so please ask any questions. It is evident that I don’t know what I’m doing but I want to learn, and I am having fun! I value any and all input. This is just the first brush at a frame and I’m sure it could be simpler. The nice thing about using CAD is that you can play all you want.

Sorry for the book…

Rodger

[Guy]

Dear Rodger,

Everything would probably be fine except for one item. Ninety percent of the weight of a teardrop is rear of the axle, unlike a typical utility trailer. Therefore you may wish to consider that and either move your support back or put another in. The double gussets are superfluous. You could get rid of one and use the weight savings to add strength to the rear.

[angib]

Rodger,

That looks like a sound plan to me. I have tried to run your A-frame through the (Aussie rules) tongue strength page and here's what I got. In your design, it isn't obvious what the tongue length is - I've taken it from the forward floor mounts and I reckon that gives around 46" to the coupler centre.

So you want a capacity of: 0.5 x 46" x 2000lb = 46,000 lb-in

Your 1"x2"x3/16" channel has a vertical capacity of 9,800lb-in and you'll have four of them, two on each side of the A-frame. That gives you a capacity of 39,200lb-in, so that's 85% of the requirement. I reckon that's good enough.

130lb isn't at all bad - it would be hard to get a tough frame this size under 100lb, so you're not missing the mark by much. You can embarass Mike by asking him what the Baja Benroy frame weighed - it wasn't this low!

The one area that I could have some concern about is the joint at the back end of the A-frame - those welds are taking a lot of load. If your welding is professional standard, then there's probably no problem, but I would want to add a gusset running across that joint, connecting the vertical leg of the channels.

As the teardrop body has massive torsional stiffness, all those corner braces are superfluous - that is, unless you want to use them to mount the body, but they don't seem to help much in doing that.

Andrew

[angib]

Ninety percent of the weight of a teardrop is rear of the axle, unlike a typical utility trailer.

Guy, you've been out in the sun too much!

If 90% of the weight were behind the axle, the tongue weight would not be positive!

Rodger, your plan to use the galley bulkhead (partition) as a structural member, and so not needing any frame member underneath, is exactly right in my opinion. The only requirement is that the floor-to-bulkhead joint is of decent quality. Stick with what you've got.

Andrew

[Guy]

Dear Andrew,

You are right, I have been out in the sun, so eat your heart out.

[Chuck Craven]

Hi Rodger!

I am with Guy. I would add another cross piece just behind the spring hanger.
That should stop any twisting. I would also add a fishplate on the outside where the notch is made for the front cross member and the A frame starts. That should make up for any strength lost from cutting the notch, bending and welding in that critical area. I would go with an 8” long fishplate, 4” on each side of the notch/bend. Do a full weld to the fishplate. Your frame is a lot lighter than my frame. My frame, which is 58” by 10’, comes in at approximately 500lbs with axel, springs and tiers.


Chuck

[mikeschn]

You can embarass Mike by asking him what the Baja Benroy frame weighed - it wasn't this low!
Andrew

Hey, be nice...

That Baja Benroy frame was designed for rockhopping! (Well I had to have a good reason, didn't I?)

Mike...

[rdkng07]

Guys, thanks for the input, that is exactly what I was looking for. I slid a cross brace back and lengthened the channel that is welded on the inside of the frame for the axle brackets so that it can connect with it. That should take care of any potential droop in the rear.








I deleted the channel gussets in the body area, and I deleted the channel gussets that were up by the tongue. It seems they were in peel anyway. I added fish brackets to the tongue area both inside and out. Is the bracket added to the inside the needed weld reinforcement you were referring to Andrew? We're now at 129.2389 lbs.

Oh, if I end up rock hoppin it's because I took a bad turn...

Thanks again guys,

Rodger

[grant whipp]

... Because of the short 2” web height on the channel, I’m worried about the frame twisting. Hopefully between the strength of the cabin box and the axle, this will not be a problem.

Hi, Roger!

I don't know why, but this issue (frame twist under the body) keeps creeping into discussions (no offense meant to you, believe me, just wanting to clear this thing up one more time!). But the bottom line is that a properly built teardrop body is a rigid torsional box ... you could build the under-body part of the chassis out of bed rails and you'd be O.K., as that part of the frame is only there to mount the axle and the frame tongue. The critical parts of the chassis are the tongue itself and how it's tied to the under-body framework.

Admittedly, a lot of us overbuild our frames, and there are any number of reasons why (from a commercial standpoint, a lot of it has to do with liability ... ;-} ;-} ...!), but I think for what you are building, and for your purposes, your frame design is adaquate. I do, however, echo the suggestions to add gusseting and fish-plating to the A-rail/side-rail joints and maybe an added piece of the channel below those joints that spans them.

Good Luck with your build! In the meantime ...

CHEERS!

Grant

[Chuck Craven]

Andrew and Grant are right when it comes to overbuilding most of us do it.

I have built several utility trailers for people that wanted a 1000 lb load trailer.
Later they brought it back with the axel bent and the frame twisted at the spring shackles.
I asked them what they were haling? One answered rocks! The other answered sand!
How much? To the top of the side rails! Turned out to be 4000lb of rocks and 5000lb of sand in a 1000 lb trailer. So now I way over build them.

You can call it habit or experience. That experience took me out of the trailer building business.

Chuck

[Nitetimes]

A gussett like this on the bottom of the frame is what I usually use when I build a frame with that style tongue. 1/8" or 3/16" should make it plenty strong.

[angib]

Nice gusset, nitetimes! (It is OK to say that here, isn't it?.....) I would be happy with gussets half that size, but bigger is never a problem.

With those gussets, you can skip the fishplates, Rodger - it's an 'either, or' thing. Either way I would drop the inner fishplate you added, as there's little load going from the tongue to the cross-member - it's mostly going back into the side rail.

Andrew

[Arne]

For simplicity, I'd go with the external fishplate, and get better purchase between the frame rail and the x-member. Easier to construct, and more welded surface by running the x-member into the frame rail to the vertical wall... if you go with a gusset, you only have face to face welded contact with the x-member and the gusset.

That is what I plan to do with my new 5' wide h/f trailer when I widen it. I'll use the supplied parts that come with the 4x8, where the x-members height is the same size as the measurement of the inside of the frame rail... so the x-member fits snugly into the channel of the frame rail..

[Nitetimes]

Nice gusset, nitetimes! (It is OK to say that here, isn't it?.....) I would be happy with gussets half that size, but bigger is never a problem.

Sure, why not. They are the way I prefer to do them as most of the cracks I've seen on this type of frame start on the lower leg of the channel and work their way up the side.

Either way I would drop the inner fishplate you added, as there's little load going from the tongue to the cross-member - it's mostly going back into the side rail.

Very true, that would mostly be a waste of time, effort and material.

Andrew

For simplicity, I'd go with the external fishplate, and get better purchase between the frame rail and the x-member.

I don't see where you're getting that but...

Easier to construct, and more welded surface by running the x-member into the frame rail to the vertical wall...

Not really... and more 'welded surface' does not neccesarily make a stronger joint.

if you go with a gusset, you only have face to face welded contact with the x-member and the gusset.

That's all you need

But you obviously have more experience with this than me so we'll do it your way.

Now I'll give you my humble opinion here. The 2" channel is definitley strong enough for the frame itself however unless you plan to fit every joint inside of the channel by clipping off the flanges so the x-member inserts into the frame rail it makes a very flimsy joint. I have built lots of this way and it works just fine but it's time consuming. Unless you are getting the channel for free it would be much easier and less expensive to use 2"x2"x1/8" angle. Less fabricating and more surface area for mounting to work with.
Then use your tongue as you have it only slide it back under the trailer 18" and forgo the gussetting all together.

[rdkng07]

I don't know why, but this issue (frame twist under the body) keeps creeping into discussions (no offense meant to you, believe me, just wanting to clear this thing up one more time!).

Grant, your right about the body of the cabin adding to strength. I’m somewhat new to this and I keep thinking utility trailer.

Andrew and Grant are right when it comes to overbuilding most of us do it.

Hi Chuck, I tend to overbuild other things as well. If it's a design for work then I will look at material usage and cost. If it's a one off like something for myself, than I'm not nearly as critical. Although I do want to see how light I can make this frame. I'll admit, it's a lot easier to add a bracket out of something already laying around than to worry about failure and repairs after the build.

A gussett like this on the bottom of the frame is what I usually use when I build a frame with that style tongue. 1/8" or 3/16" should make it plenty strong.

Nitetimes, thats a good idea. I think that gusset would solve my problems.

so the x-member fits snugly into the channel of the frame rail..

Arne, good idea and I will notch the cross members so that they extend inside the side rails.

I am also playing with the thought of adding an inner brace to the tongue itself. You fellers have me thinking about the end weld on the inside tongue channel. Not a good idea I’ll admit.



What I could do is extent the inside tongue channel member beyond the notch and weld of the outer frame channel. This would move the end of that piece of channel past the welded joint and also give me 1.75” of end welding surface where I only had about .75” before.



As far as a inner brace goes, I would weld it to the inside tongue channel before I welded the tongue halves together. After the tongue halves are welded I would weld the other side of the inner brace to the outer frame channel. It seems to me that the inner brace would transfer the load of the inside frame much better than just the end weld I had before.