material selection for axle truss?

[xj92]

That truss looks strong, but I picked up my steel today for $19, versus the $150 + shipping of that one. I can't tell, but that one looks like it might require more lift than I have to accomodate the larger profile also. I'm working on cardboard cutouts first, then I'll draw the pattern on the steel.

 

[Mr.OverKill]

best pic i have but it is under the jeep and works well and it is only 1/4 inch taller than a stock XJ44

i will try to get a fresh pic tomorrow or over the weekend.

 

[xj92]

Did any of you guys use a jig to set the axle in while trussing it? I talked to a local hot-rod builder that can weld the cast part for me, but he was concerned about it warping too much due to the heat. I can do small stitch welds a little at a time on the tubes to make sure it doesn't get too hot, but he said he uses a metal spray process to weld to cast and that he would have to heat it up, and it should have a jig to hold it in place while it heats up and cools. If I decide to build my own truss, he said I can just use a huge I-beam and weld some brackets onto it that will hold the axle in place. The cost of the steel alone for the I-beam would be too much though, especially since I'm only doing one axle on it. Any suggestions or comments from those that have trussed their own?

 

[Mr.OverKill]

no jig, i just back steped as i welded and jumped around to keep the tubes from warping. on the dif i left the cerrier in place and bolted tight the dif cover as well was left in place and bolted tight then i heated the whole dif at once and i filled all gaps i found after fit up by welding to the truss to fill them, once the gaps were closed then i welded to the tubes and dif.

if you use thick enough material for the truss and you tack ( 1.5 to 2 inches ) in enough places ( about every 6 inches ) the truss will work like your jig. if you have confidence in your abilities and think it through you will do fine besides it is an axle, if you dont over think it, you will do fine.


p.s. tack where there arnt any gaps first and fill the gaps as i described above letting the truss cool before you weld where you filled to the tubes and housing this will prevent the extra shrinkage that might cause the truss to pull the axle out of shape.

HTH and good luck, pm me your phone # if you need clairification.

 

[Tommy_Harrell]

simple 1/4" plate, still fine tuning the brakelines


Tommy

 

[XJEEPER]

I'm starting a truss project on my soon to be installed HP30 and rear 44 and I'm thinking of going with 2 rows of 1/8" plate, capped with 3/16" plate. I'm also planning on punching holes in the plate prior to welding that I can insert sections of tube in to add strength without weight, ala prerunner fab........
http://www.race-dezert.com/skunkz/mm/6.jpg

http://race-dezert.com/skunkz/newhan/27.jpg

Thoughts?

 

[XJ_ranger]

I'm also planning on punching holes in the plate prior to welding that I can insert sections of tube in to add strength without weight,

correct me if im wrong, but the weight that you saved with cutting out the circles on either side will be less than the weight that you add with the tube - correct?

and the tube being mounted inbetween the 1/8" plate will be in the wrong direction to add any strength to the truss doing the job of a truss...

if you have issues with your current mounts ripping off the axle because they flex too much, then the tubes would be helpful...

personally, the speed holes and tube seems like a lot of work for no gain, other than bling factor...

 

[XJEEPER]

correct me if im wrong, but the weight that you saved with cutting out the circles on either side will be less than the weight that you add with the tube - correct?

and the tube being mounted inbetween the 1/8" plate will be in the wrong direction to add any strength to the truss doing the job of a truss...

if you have issues with your current mounts ripping off the axle because they flex too much, then the tubes would be helpful...

personally, the speed holes and tube seems like a lot of work for no gain, other than bling factor...

Not going to argue that the circles save weight, they are there to increase the ridgidity of the overall section and as you've stated, reduce flex. My lack of engineering knowledge leads me to overbuild most of the stuff I've fabbed........since I've yet to have any of it break, this must work.

Bling factor VS structural benefit? I'm not an engineer, but I am a thinker. The go-fast desert fabbers use this method to keep reduce the overall weight of the car while maintaining the structural integrity. Could it be built as strong or stronger with thicker plate/tubing? Probably, but thinking in simple terms again, weight VS HP is always a consideration.

As for my trusses, there will be no significant HP loss in using heavier plate.......but I haven't factored in the bling benefit yet either......and I could paint it a really bright color so my extra work won't be overlooked.

 

[SCW]

Jeff, when the plate is dimpled for strength, it is "dimpled", not just a few holes whacked in it. The dimples create a ridge around the hole that provides strength, similar to a sheet of tin with a slight fold is stronger than flat tin.

I'm sure someone will correct this if it's wrong, but I don't think you'll see any strength gain from simply whacking flat holes in the plate.

The pictures look like aluminum?

It looks like they are basically building an I-beam with an extremely wide center section, built up of two peices tied together by the tubing. this increases the Moment of Inertia of the beam. Stress = my/I where M= moment, Y is distance from center. As the moment of inertia increases the moment can increase to put the same load on the beam. The tubing connecting the two prevent the double-layered center section from buckling locally, the plate is much stronger tied together than the individual parts are.

I don't know that it would be worth it. Maybe if you had some dimple-dies for the plate but building an involved truss system like that is a lot more work than I'd put into it. Won't hurt though!

 

[XJEEPER]

The other picture shows arms made from aluminum, which I used merely as a pictoral reference. The examples shown in this use the same principles, just with steel. I didn't make a reference to dimpling because I wasn't planning on doing this, because it really doesn't fit the truss model. Note that all whacked holes are then filled with a section of tubing and welded on both sides, which make the 1/8"? plate engineered rectangle tube more rigid, while keeping the overall piece lightweight. I'm sure someone has a nifty engineering term for this application? Share if you do.

The main reason I brought this up was the strength from bulk VS strength via engineering a less bulky material. Doubt I'll go to the effort of testing this idea out on my trusses, since I have a lot of rig to build and not that much time to get r done.

 

[SCW]

I doubt that this truss would save any weight, you are replacing the holes with quite a bit of steel and as you said, the option is a very bulky material to start with. This is very strong though so you are correct that this would keep weight lower (but not "low") and be very strong.

You mentioned not wanting to dimple, but that might be your best bet if you are planning to save weight and get a little more strength out of your steel.

Keep in mind I'm looking at this completely from the academic perspective. I've never built an axle truss and likely never will. That said, where do axles typically bend? I've seen several trusses that cover from perch to perch and some that are a simple tube only bracing over the pumpkin. If you expect problems with twisting the short brace can be ok, but if you are really trying to keep the axle from bending in an arc from wheel to wheel, you should plan on using your truss to absorb as much of the force out on the end as possible.

For example, if you are trying to resist bending the axle in the arc and you have 2000# on one wheel and brace A is 18" from the wheel, it will have to resist twice the loading as a brace that starts to absorb the forces from only 9" away. A brace that only coveres the pumpkin and a few inches of the tube such as this one-

probably won't help resist bending moment much.

One like this-

will begin resistance to upward bending much sooner and could have more capacity, but it is thin enough on top that it would have to be well anchored to the pumpkin to displace the upward energy you are trying to divert. In my (unexperienced) opinion, there should be bracing all the way to the perches to absorb moment as far out as possible. Also, it should have enough steel on top to help resist the bending moment in the brace, not just transfer it to the pumpkin. That big ugly sail that someone had (G Sequoia?) was actually pretty good imo. It went out far enough to do some good and had plenty of steel above the pumpkin to transfer the bending through the brace rather than back into the axle.

 

[Captain Ron]

...
That big ugly sail that someone had (G Sequoia?) was actually pretty good imo. It went out far enough to do some good and had plenty of steel above the pumpkin to transfer the bending through the brace rather than back into the axle.

Damn, just when I thought there was no common sense left on this subject, you come along and ruin it for me.

--ron

PS: You left out one thing though. It's light too.

 

[Jump This]

Damn, just when I thought there was no common sense left on this subject, you come along and ruin it for me.

--ron

PS: You left out one thing though. It's light too.

Wait a second, Geoff knows how to weld?


Now I gotta' try to find a picture of Sequoia's junk.....

 

[XJEEPER]

Agreed. Sorry to hijack the thread and swerve it off towards weight savings theory, which has been fun......but I'll prolly just go this route for simplicity

and more triangle shaped like Brett's, but attached near the perches. I can then fill in between the tube and the axle tubes with plate for obvious reasons.

 

[SCW]

I can then fill in between the tube and the axle tubes with plate for obvious reasons.

For a sail? What stickers will you be using?

 

[XJEEPER]

For a sail? What stickers will you be using?

I'll keep it sticker free, may dimple punch some bling holes in it to lighten it up a little.......:shocked:

 

[Mr.OverKill]

i say get a 3 ft piece of 2X5 unobtanium .010 wall and cold fusion it to the axle, that should strengthen it by a factor of 1000X :gee:

just kidding, the tube is a tried and true design that has minimum wind resistance and is fairly low peofile and if done like i did mine will evenly disburse the loads over the length of the truss and axle evenly, i went all Mr.Overkill on mine and used .250 wall but .125 would work just as well for a lighter application like ours.