Help with frame modification

[48Rob]

I need, or would like to modify the frame I'm working on.

The tongue is too long for my needs, so my idea is to extend the frame a little farther forward to gain another foot of floor space.
What I want to do is cut the steel out that is between the tongue rails.
This area is/was the front of the trailer. The piece in question is about 1/8" steel, in a rough "U" shape which is welded to the main frame rails, the tongue rails, and a heavy box section that stretches across the trailer side to side.



The tongue rails are an inch smaller than the main frame rails. The heavy box section is not currently welded to the tongue rails.
I can weld a brace between the box section and the tongue rails to make up some strength.
I'll also have a piece welded under the tongue a foot further forward connecting the two tongue rails so there will be a support for the floor.

I can't see where I would be losing much, if any rigidity across the front.
It appears the piece I want to partially remove is there to keep the front of the trailer/the frame square.
If I only remove the center section, and add more support a foot forward, will that make up for it?

Rob

[Martiangod]

I don't see where removing it would cause any grief, is it neccessary to remove it???

[48Rob]

Chris,

Thank you for your thoughts.

No, I don't "have" to remove it, but it would be of great help to the design if I could.
Further information is needed on my part to explain;

The frame as viewed from a normal trailer frame viewpoint is fine. The problem comes from me not placing the floor on top of the frame as is standard practice, but rather at the bottom of the frame, in order to achieve a dropped floor of sorts.

The floor between the tongue rails is just below those rails, and extends to the front of the trailer where the piece in question is located. As you may be able to see in the picture, there is another brace run between the tongue rails a foot forward of the original front of the trailer, the new front.
If I can remove the offending section, the same floor level can be carried all the way to the new front. The brace run between the tongue rails on top, can now be placed on the bottom, allowing me 1 more foot of same level floor space.

This is an old drawing, one of many ideas that I may or may not use...but it shows the frame configuration I have to work with;



The floor runs below the main frame rails, then steps up 3 inches to the bottom of the tongue rails.
That level extends to the original front of the trailer, where it steps up another 8 inches.
If I can cut out the plate between the tongue rails, I don't have an 8" step up, between the tongue rails.
Out side the tongue rails it has to, but won't mess with my floor plan.

Rob

[angib]

I would not remove that centre cross-member as I think it is an important part of the connection between the tongue and the main frame.

Any upward load in the tongue is transferred to the front cross-member because it is continuous from side to side. Take away the middle of it and the tongue can flex up and down by just twisting the side rails of the main frame and the two transverse stubs you will leave behind. What you are adding is as strong as spaghetti by comparison - it may be plenty to hold up the floor, but it doesn't connect the tongue to the main frame.

I can't swear that cutting out the middle will cause a problem, but I very much doubt anyone who says it won't........

[48Rob]

Andrew,

Thank you for your thoughts.

That general theory makes a lot of sense.

I've looked at a lot of other trailers, and they all have the critical front plate to tie the frame rails together. Some also tie the tongue together, underneath, or through the plate.
Very few have the additional beam welded underneath, tying the frame rails together.
Here is an example of the standard design, one in which cutting out the center section would certainly cause catastrophic failure;


I had hoped that by welding a connecting piece from the 6x2 beam to the frame rails, it would more than make up the lost strength, since the 6x2 has to be providing a tremendous amount of extra stiffening over and above the thin plate, no?

Rob

[MtnDon]

I'm thinking that if the piece marked as "leave this piece" was placed forward under the piece that you want to remove, that would be better. Welded and gusseted to the original frame members.

[48Rob]

Don,

Thank you.



The piece marked "leave" is already welded to the bottom of the main frame rails, it is not in any way connected to the tongue rails...except for being spot welded to the front plate, which is welded to the tongue rails.
My thought was after cutting out the center section of front plate, If I connected the tongue rails solidly to the piece marked "leave" that I will have replaced the section/strength lost by removing the plate.

Maybe these pictures will help show what I'm working with.







Rob

[MtnDon]

something like this, using angle iron welded to the "leave this piece" and the tongue. That would be stronger than simply welding the A-member to the "leave" piece. Both sides of the A-member.

The tongue A pieces are continuous through that crossmember that is to be removed, right?



(need to doctor up another of those images to complete my train of thought. will post .....

[48Rob]

Yes Don,

That is what I had in mind.
The tongue rails are continuous.
The piece that is to be cut out can also be shortened and welded back in a foot forward, with plate connecting it to the "leave" piece if needed.

Rob

[MtnDon]

gusset in the marked area, or an overlay plate on the bottom to cover most of the triangular area. From the "leave " piec back to the acute angle.



Just my thoughts

[48Rob]

Thank you Don.
Your plan sounds quite reasonable.

I'll try to work on the drawings a bit to provide an easier to understand and visualize plan.
I'd really like to hear more from anyone skilled in this type of building.
I don't want to/will not build something unsafe. However, if there is a way to make it happen, I'd like to hear the ideas.

Rob

[KCStudly]

The side view of the lower "leave" in piece makes it look like thinner formed channel.

I'm with Angib. It would be much better to stiffen against the tongue members twisting. Rather than just attaching the leave channel to the tongue rails with angle clips, truly gusset them from the outside top of the tongue rail down to the vertical legs of the "leave" channel.

Since that flat "leave" member does not do very much in that axis, I would add another of the smaller rusty square tubes running across at the bottom of the tongue rails, and gusset these together on each side with a couple of short shear webs, or do like you say and put the cut out/cut down piece there.

Might be okay. You will have to be the final judge.

[48Rob]

How about this?

[KCStudly]

Yeah, that would probably do okay, and you probably don't need to go all that thick. I'm thinking 16 ga sheet, not plate.

The angle clips on the inside still won't add as much as diagonal gussets on the outside.

The thing with this is that you are confining the twist to the short section of tongue rail between the new front kick area and the original front. Shorter is stiffer so it might do the job.

There is an awful lot of box tube adding weight behind that "leave" in channel. What's that all about?

[48Rob]

KC,

Thank you.

The diagonal gussets you mentioned, will the white triangles in the photo do?

The box tubing behind the leave piece are to support the 1/2" plywood floor in that area; the bathroom.
The larger area box tube is the main living area, where multiple people may/could end up standing in the center of the span.
Both are at different levels.
These pics may show it better.

Rob