Frame weight VS Cost, and a couple of other questions

[angib]

I think there are two issues at work:

1) Amateur welding - by running both tubes continuously, it avoids the need for 100% effective welds. The highest load is trying to close the joint where the tongue crosses the front cross-member (is that what you call a header?) as the failure mode is always coupler-up, not coupler-down.

2) Fatigue. The Australians know more about this than anyone with their washboard roads and the Aussie rules forbid any welding where the tongue crosses the front cross-member. Wherever there are welds, there are stress concentrations and the Aussies have found that the welds cause fatigue cracks that causes the tongue to snap.

If you look at the forces, it's only where the tongue crosses the front cross-member that there is a big load - all other joints are fairly lightly loaded.

[Trackstriper]

.....and the Aussie rules forbid any welding where the tongue crosses the front cross-member. Wherever there are welds, there are stress concentrations and the Aussies have found that the welds cause fatigue cracks that causes the tongue to snap.

Andrew, can you elaborate a bit on this? How do they recommend handling that joint, it it free-floating with just gravity assisting? Don't wish to get distracted from racermech's original questions but I think it might be germane, good time to learn what holds up best.

[bobhenry]

I can see where a square bottom "u" bolt would be a good choice here to prevent side to side movement without subjecting the tongue metal to the stress induced by welding.

[bobhenry]

I saved this picture of Plano vet's frame. I think this is one of the safest and stoutest tongue designs I have seen to date. The C channel sub frame continues from frame into the tongue to distribute the stress farther down each side of the trailer.

[angib]

How do they recommend handling that joint, it it free-floating with just gravity assisting?

Yes, that's it - but now I look for the evidence I thought I had saved, I can't find it.

Australians will frequently say that transverse welds at the tongue-to-cross-meber joint are not acceptable and only longitudinal welds should be used. Again, this is to avoid fatigue cracking.

A square U-bolt is a very nice solution.

[asianflava]

I think there are two issues at work:

1) Amateur welding - by running both tubes continuously, it avoids the need for 100% effective welds. The highest load is trying to close the joint where the tongue crosses the front cross-member (is that what you call a header?) as the failure mode is always coupler-up, not coupler-down..

This is exactly where my tongue broke. Granted my trailer was overloaded and the road was rough with expansion joints and compression dips.

2) Fatigue. The Australians know more about this than anyone with their washboard roads and the Aussie rules forbid any welding where the tongue crosses the front cross-member. Wherever there are welds, there are stress concentrations and the Aussies have found that the welds cause fatigue cracks that causes the tongue to snap.

If you look at the forces, it's only where the tongue crosses the front cross-member that there is a big load - all other joints are fairly lightly loaded.

The place that repaired my trailer plated the new tongue with a gusset to the front tube. I requested 2x3x3/16 but they used 2x4x1/4 because it's what they could get on such short notice. I was on the road and had to get going ASAP. Since they were using such a heavy duty member, I had them lengthen it back to my original length. I had removed 18in from the original tongue because I felt that it was inadequate. Backing with the shorter tongue was a PITA.

[bobhenry]

[quote="asianflava"[ I had removed 18in from the original tongue because I felt that it was inadequate. Backing with the shorter tongue was a PITA.[/quote]

Sometime gut instinct and kentucky windage is a good indicator.

I always felt the flex I had in the HF tongue on Chubby just too much.

It never failed but it just nagged at me until I installed the 2x2x3/16 center tube. It was welded to the center spine of the frame all the way back to the axle with 1" stitches about every 12 to 15 inches. I later had the opportunity to weigh Chubby and found out that loaded he was #1830 lbs. Now I know a bit better why I was concerned.

[racermech]

I did a little re work on the design. After looking around tthe web, and rubber necking every trailer that i saw on the road I decided to run the tongue under the header. While I still dont fully understand it. There must be a reason for all of it.

I ran out of time to do a couple of snap shots but I also decided to drop a few tubes to 1/8 wall and eliminated about 50lbs of weight. I am going to have my buddy clean up my model for me and then I will be able to create my shop drawings.