What is stronger? Guesset or brace?

[ck85abc]

I want to strengthen my moon bars(bars that are above your head and connect the front roll bar with the rear roll bar)

My friends tell me I should just gusset them. I think I should just brace them with some 1 inch tubing. I also think the 1 inch tubing braces would make it stronger than gussets.

[rally bug]

In scca performance rally they will accept either method, which makes me believe that they are both structurally sound methods.

[vicsvw]

Ask before you install eather. The biggest problem we have with frame brakage is when some one braces or gussets in the wrong place. Some Bars must flex or the break. Vic.

[ck85abc.]

What I was planning on doing is the follow.

There is the front roll bar and rear roll bar. There is a moon bar on each side. I wanted to run a 1 inch brace at 45 degree angle from the center of the front roll bar over to each moon bar. Was not planning on doing it in the back because the rear engine cage goes up to it making it alot stronger.

[Guest]

By far the strongest thing to do is to triangulate the box in the structure ie the space the moon bars and roll hoops form. Do this by making an X out of tube to fit the hole with the 'legs' carefully shaped to fit the profiles of the tube intersections at the corners of the square. this will make four small triangles, the strongest shape in the chassis world. All the tubes in the X are then in compression and you will get minimal flex. This will stop the tubes lozenging or the square becoming a rombus because of deflection.

Take your time and get the tube end shapes perfect for a strong joint.

TIMBERWOLF

[Leatherneck]

Wish they had of posted pics on this one. Wonder what he ended up doing?

[Ol'fogasaurus]

If you don't mind I am going to add a bit more to this.

Basically, the "Mold Line" is the join point of a bend and the straight part of a tube, plate or what ever that has a bend in it that also joins another straight area or bend, say in the opposite direction. An "L-shaped" tube will have two mold lines, one on each side of the bend. There are two talked about joins, the IML (Inside Mold Line) and the OML (the Outside Mold Line) even though on a tube the join is all around the tube it is those two mold lines that are considered most important as I remember.

Guest talked about the front and rear hoops being joined by (usually) straight pieces of tube. The joins can be made perpendicular at/between the OMLs of the two hoops or they can be parallel with each other near or at the center of the hoops. The latter is usually referred to as T-tops and works best for getting in an out of the cage... but not the strongest way to do connect to two hoops; it is done that way more on street toys than off-road.

The joins between the two hoops done at the mold points is good for off-road especially for strength and transferring loads through out the cage. They also work something like tree bars when you tip into a tree (for example); they help limit the intrusion of the trunk of the tree or rock/boulder into the passenger compt.

On my blue buggy the builder of the cage (he built cages for race cars and also built rails before he retired from it) bent the outside join bars a bit to aid in egress. His wife also suggested a single bar (also bent) in the middle which is not wrong but turned out to be good for mounting my GoPro and for grabbing onto/helping with egress of the cage.

The "X" bars that Guest talked about actually creates 4 small triangles (and also 4 large triangles depending on how you look at it) as Guest said. The X" acts like the roof of a car to move loads from one side of the toy to the other and from the front to the rear or vice-a-versa.

Also don't forget the diagonal bar or better yet the "X" bar in the "B-pillar".

Gussets, as I remember, are more for support the joins of the tubes. We had a discussion on that a while a go as to where to place the gusset at the join but, as far as I can tell, the best gusset for tubing should be made of a same size bent tube with sides added. That is what you often see in the door bars on race cars, especially rally cars.

I hope this helps (and is right )

Lee

[bajaherbie]

Talk about a blast from the past! 2004!

Sent from my SM-G920R4 using Tapatalk

[Ol'fogasaurus]

I found this this morning after thinking about it last night.

The idea of placing the single gusset as shown still bothers me as I have seen this type of gusseting fail/break loose several times probably partially due to bad welding I guess but the edge/corner contact patch contact I still a bit leery of.

[bikesndbugs]

why not weld the ends of the gusset?
seems kinda odd to me

As far a bracing are we talking like a tube in place of the gusset. My friend has stuff similar to that in his 67 f250. just a bent tube where you would put a gusset looks nice and works as a good handle when you are getting in.

[Ol'fogasaurus]

I don't know Travis as it doesn't make a lot of sense to me unless it is for temperature growth or stretching of the tube but I would think that the rests of the welds will stop that too. I can think of other arguments against it too but to be honest.... I just don't know. Most of the gussets you see for tubes (do a search on them) are round or arced and round not sharp/broken corners.

[Piledriver]

Not welding the ends avoids a possible stress riser.
The point of a gusset is to spread the load out.

...So the answer to the original question would be:
Yes.
...gussets and more triangulation//cross brace tubing, with more gussets.

[Ol'fogasaurus]

Not welding the ends avoids a possible stress riser.
The point of a gusset is to spread the load out.

...So the answer to the original question would be:
Yes.
...gussets and more triangulation//cross brace tubing, with more gussets.

For what it is worth: a "stress concentration" is also known by the term we use: "stress riser".

With the 90 degree bent gussets I think I would agree but with "fitted" tube type of gussets is it still true? I've seen a lot of fitted gussets, done by supposed experts, that are welded full circumference.

I did a quick search on the subject and while being a bit confusing it might help doing a search on the subject. Stress concentration really became looked at when the British Comet passenger airplanes started crashing (I think the name was the Comet anyway) and they eventually discovered that the stress concentration at the corners of the square windows was causing metal fatigue/cracks which is why airplane windows are more rounded now. They even made a movie starring Jimmy Stewart loosly based on stress cracking concept.

I do agree that bracing joins should be gussetted also which is not always done. Kind of like the job is half done.

[PhillipM]

I weld them if they're bent/tapered tube as the end should be almost axial to the tube direction by then, so the stress is minimised anyway, if it's a straight gusset they don't get welded in the centre because that just leads to kinking the tube and an immediate massive rigidity loss associated with it.

[dustymojave]

Ny HiJumper original roll cage was built back in the mid '70s with "roll-formed" gussets at the corners. I thought then that was good. I later learned that made for dramatic stress risers (stress concentration points)at the ends of the gussets. It was strong as hell and survived a quadruple endo at high gear WOT (fast as the car would go). But when I raised the to of the cage to work with the next set of seats (better than the original fiberglass), I used tube gussets. When I built the cage in my Baja, I used flat plate gussets welded at the tangent line of the tubes instead of at the centerlines. This is best and adds joint strength without the stress risers at the ends.

Phillip is right that welding a flat gusset at the tube centerline creates a stress riser at the end of the gusset and tends to kink the tube at the end of the gusset. The gusset should be able to flex with the tubing if the load applied to the joint is greater than the flexural strength of the joint. It's far better for a joint to flex than to break.

I disapprove of the gussets used in FIA Rally cage door 'X's they put huge plates formed to the tubes and have gusset ends nearly perpendicular to the tubes. It makes the joint of the 'X' hella stiff. But it makes the tubes likely to break right at the end of the gussets.