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Old 07-31-2018, 03:58 PM   #1 (permalink)
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cross member material and strength advice

sorry if this doesnt belong in the Hardcore section

going to make a cross member for my YJ that will have the Atlas support ring and my lower triangulated link mount in the center of it.

my current idea is to make it out of 1" x 3" x .25" box tubing.

1" will be the height of the crossmember and 3" will be the width.

will be fabing it so that it the middle straight section will be lower to clear pinion and also allow room for the Atlas support ring like this \_/ but only at 10 degrees of slope and bring the middle down 1.5" (as of right now)

so my main question is, is 1" x 3" x .25" box tubing sufficient?

2nd question, weld the crossmember to the frame or bolt it? i'd really rather just weld it on as of right now since it would save time and effort so i dont have to drill and sleeve the frame.

thanks in advance
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Old 07-31-2018, 09:01 PM   #2 (permalink)
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Drill and sleeve. Unless you like cutting things out. Yes it takes more time but you will be thankful when it comes time to pull the case out if/when you need to for some reason
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Old 07-31-2018, 11:35 PM   #3 (permalink)
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I used 0.25 wall when building something similar for my lower mount. Cut side off a short piece of 2.5x2.5x0.25 and welded to either frame in a "U". Cross member is 2x2x0.25 that drops into the "U" from above and gets bolted in. Can't remember the thread, but I got the idea here.

potato pic of cross member:


potato close up pic of mount:
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Old 08-02-2018, 08:53 AM   #4 (permalink)
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Quote:
Originally Posted by Chief Rocka View Post
I used 0.25 wall when building something similar for my lower mount. Cut side off a short piece of 2.5x2.5x0.25 and welded to either frame in a "U". Cross member is 2x2x0.25 that drops into the "U" from above and gets bolted in. Can't remember the thread, but I got the idea here.

potato pic of cross member:


potato close up pic of mount:
Your image links are broken. GDrive sucks for linking images. I suggest using https://imgur.com/upload. Once the image uploads click to expand the image, then right click the image and select copy image url. When you paste it here make sure it ends with the proper file type (.png, .jpg).
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Old 08-02-2018, 09:15 AM   #5 (permalink)
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better now?

used the get share links > BBCode (Forums)

[IMG][/IMG]

[IMG][/IMG]
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Old 08-04-2018, 10:49 AM   #6 (permalink)
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Ive seen it where people use bushing on the end and weld their tube to the bushing housing.

Really depends on what your goals are. I would build it to withstand my jeep slamming down and high centering. This means gussets and over-engineering.
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Old 08-06-2018, 03:40 PM   #7 (permalink)
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better now?

used the get share links > BBCode (Forums)

[IMG][/IMG]

[IMG][/IMG]
much better lol.

i get your idea now. ive been doing designs in my head according to what you said
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Old 08-06-2018, 03:45 PM   #8 (permalink)
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Ive seen it where people use bushing on the end and weld their tube to the bushing housing.

Really depends on what your goals are. I would build it to withstand my jeep slamming down and high centering. This means gussets and over-engineering.
i actually just installed a crossmember just like that this weekend for my transmission.

dont think i'd consider that for a 4link mount though



it's made my Genright and its pretty sweet. was able to jack my tranny up about 3" after i clocked the Tcase. I may even have enough clearance to not have to offset my link cross member down in order to clear the output.



just showing off my welds now







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Old 08-09-2018, 12:46 PM   #9 (permalink)
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I used 3" x 1.5" x .025 wall tube for my front skidplate support. It does flex slightly when you put a jack under it and lift the vehicle. You might want to do a test like that before investing too much time in the 3" x 1" tube...

I went with 4" x 2.5" x .025 wall tube for the rear skidplate support since it also serves as link mounting points. Its a bit overkill, but when you run the link calculator and see loads in the 10,000lb range it does give you a bit of comfort. Details here: https://www.pirate4x4.com/forum/jeep...-cj-7-a-3.html
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Old 08-10-2018, 02:28 PM   #10 (permalink)
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I used 3" x 1.5" x .025 wall tube for my front skidplate support. It does flex slightly when you put a jack under it and lift the vehicle. You might want to do a test like that before investing too much time in the 3" x 1" tube...

I went with 4" x 2.5" x .025 wall tube for the rear skidplate support since it also serves as link mounting points. Its a bit overkill, but when you run the link calculator and see loads in the 10,000lb range it does give you a bit of comfort. Details here: https://www.pirate4x4.com/forum/jeep...-cj-7-a-3.html
in that case i'll definitely beef it up. thanks for the advice, exactly what i was looking for
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Old 08-16-2018, 05:11 AM   #11 (permalink)
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I made my cross member/tranny suppport out of 1.75" .120 DOM

I figured if its good enough for frames it good enough for a cross member.

However I would use thicker tubing for skid plate purposes
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Old 08-16-2018, 07:30 AM   #12 (permalink)
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I would use 2x2x.25 for that rear cross member. Weld the ends and gusset to the frame. Make sure you have clearance so you can remove the transfer case. I would not attach the transfer case to it.
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Old 09-01-2018, 08:24 AM   #13 (permalink)
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Here's some I made, one out of square tubing and one out of flat plate welded to a cut factory crossmember both I was using factory trans mounts.
Attached Images
  
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Old 09-02-2019, 04:03 PM   #14 (permalink)
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2x2x0.25 is not surviving

Dangit, the 2x2x0.25 is bending! What are the odds I can straighten that out and sleeve with 1.5x1.5x0.25? If not, what's the fix?

TIA




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Old 09-05-2019, 08:45 AM   #15 (permalink)
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Dangit, the 2x2x0.25 is bending! What are the odds I can straighten that out and sleeve with 1.5x1.5x0.25? If not, what's the fix?
The crossmember is now junk, don't even try to save it.

First, check the 2.5" saddles you welded to the frame for cracks. If those are holding up here is what I'd do. Cut the link mounts off the crossmember and weld them to a fresh piece of 2x2x0.25 or better yet 3/8 wall. Then weld another piece to the front of it (it will be shorter, just the distance between the 2.5" saddles.

The engineering here is that your cross sectional area can support the shear but the section modulus isn't enough to prevent bending. Or something like that

Sleeving can help if you are close on strength, but since it is inside the original tube it doesn't contribute as much to the section modulus as you'd think - its not just wall thickness its resistance to bending. One thing that really helps is to weld the ends of the sleeves together so they act as one piece of steel. Otherwise you have two pieces of steel acting independently. For example you can bend a phone book easily since the pages slide past each other. Glue the edges and you can't bend it at all.

The quick fix is to get a piece of 2.5x2.5x0.25 and cutting one side out (the one with the weld in it). Slip this over the front of the crossmember and weld. Like above, it doesn't have to go the whole span, just saddle to saddle.
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Old 09-05-2019, 06:39 PM   #16 (permalink)
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I think the saddles are ok, the frame looks like it is starting to bend/deform slightly. I may need to spread the frame to get the straightened or new piece in and weld some triangle gussets.




The bracket is an Artec BR1006. I specifically asked them what wall tube to use and was told 0.25". Now that they have seen the pics, they are telling me it appears to have been used in a full size truck and a shorter piece in a jeep would have been fine. Maybe LJ's have a wider frame, I thought they were just a longer version of a TJ. Artec is saying to bend it back and brace it.



Fresh tube would be best but I'm not sure I can cut the tube out of the mount without destroying the mount. Against your advice to start over, I'm going to try to straighten first. Do you think a 20T btl jack and chain with some heat added will get it straight enough to brace with your 2.5x2.5x0.25 idea?

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Old 09-05-2019, 07:43 PM   #17 (permalink)
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Did everyone forget the "strength in shapes, not thickness"?

The bent crossmember should be 2x4x.188 or even 120 with some plating to spread the load out.

Also, it blows my mind that people build crossmembers out of 1.5 or 1.75 x 120 tube. It's a pain to build mounts for and it not strong enough for most crossmembers imo.
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Old 09-06-2019, 07:38 AM   #18 (permalink)
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I think the saddles are ok, the frame looks like it is starting to bend/deform slightly. I may need to spread the frame to get the straightened or new piece in and weld some triangle gussets.

The bracket is an Artec BR1006. I specifically asked them what wall tube to use and was told 0.25". Now that they have seen the pics, they are telling me it appears to have been used in a full size truck and a shorter piece in a jeep would have been fine. Maybe LJ's have a wider frame, I thought they were just a longer version of a TJ. Artec is saying to bend it back and brace it.

Fresh tube would be best but I'm not sure I can cut the tube out of the mount without destroying the mount. Against your advice to start over, I'm going to try to straighten first. Do you think a 20T btl jack and chain with some heat added will get it straight enough to brace with your 2.5x2.5x0.25 idea?
My guess is when the crossmember bent, it also got shorter and pulled the frame in slightly. Anything you can do to strengthen the saddles is a good thing, but that doesn't appear to be the weak link right now.

Artec want's 1/4" wall to prevent tear out. YotaAtieToo's suggestion of a larger cross section plated near the bracket achieves the same thing with less weight, but is a higher level of difficulty.

Yes, you can get that pretty straight with heat and a jack if you take your time. In fact, I would try it without the jack first, using a vise and a bar stuck in the end for leverage (you will have better control that way).

Keep in mind, YotaAtieToo is correct, you want to end up with a much larger shape so don't try to fit the 2.5x2.5 on like a sleeve, you want to end up with something nearly 4" wide so just slip it on far enough to get a good weld and clear your t-case/hose fittings/etc.
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Old 09-06-2019, 07:59 AM   #19 (permalink)
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Did everyone forget the "strength in shapes, not thickness"?

The bent crossmember should be 2x4x.188 or even 120 with some plating to spread the load out.

Also, it blows my mind that people build crossmembers out of 1.5 or 1.75 x 120 tube. It's a pain to build mounts for and it not strong enough for most crossmembers imo.
Note it is failing in both planes. I doubt the 2x4x.188 would have held up in this case, but it's possible. Seeing this I'm glad I went with 2.5x4x.25 tube on my heavy ass Jeep.

Choice of material depends on a lot of things. How big is the span? What are the loads? Will it be subject to impact on rocks? How much room do you have? I think if you are just supporting a transfer case in a narrow frame vehicle there is nothing wrong with a piece of 1.5 or 1.75 DOM. It's light and you already have a bender that can help with packaging. I would even consider it for a skid plate or links if braced properly...
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Old 10-01-2019, 02:33 PM   #20 (permalink)
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Thanks for the help all. It should be good now!
I got the cross member straightish with a chain and 20T btl jack.

[IMG][/IMG]

[IMG][/IMG]

[IMG][/IMG]

Then welded a piece of 3x4x0.3125 angle to it on an angle.

[IMG][/IMG]

[IMG][/IMG]

[IMG][/IMG]
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Old 10-01-2019, 07:08 PM   #21 (permalink)
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For the transmission crossmember I'm planning on using a 1/4 thick wall rectangular tube with about 5 inches wide by 2 inches thick.



I have an issue with the bellhousing on this project so it's at a standstill at the moment.
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