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Elmo

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Bridog View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bridog Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2019 at 12:40pm
We are still making progress on Elmo’s frame. After aligning the frame rails with each other and welding on the rear bumper we fabricated a crossmember that is located about where the rear leaf spring hangers will be at. The crossmember kicks up to the rear floorboard height to allow more room for the driveshaft and exhaust. Then we turned our attention to building some mounts that will tie the back of the roll cage and body into the frame. We built these out of 2” square tubing with an 1/8” wall. Plates which are 1/4” thick and 4” square will sandwich the body. The top plate will be welded to the roll cage and the bottom plate is already welded to the 2” square tubing. Then last week we started working on tying the front of the rock sliders and roll cage mount into the frame. To do this we first cut and drilled some 1/4” plates. Then we sleeved the frame rails where the 1/4” plates bolt up for extra strength and so that we do not crush the frame rails when we tighten the bolts. This week we will cut/notch some more tubing and weld it between the rock slider and these plates. Here are a few pics taken along the way with more progress and pics coming soon. -Dylan









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Post Options Post Options   Thanks (0) Thanks(0)   Quote rocnroll Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2019 at 1:00pm
That's looking really nice.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cj3bmutt Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2019 at 1:24pm
Looks good.  Enjoying the updates.  Can’t wait to see the finished 3B.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nothing Special Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2019 at 4:39pm
Originally posted by Bridog Bridog wrote:

.... Plates which are 1/4” thick and 4” square will sandwich the body. The top plate will be welded to the roll cage and the bottom plate is already welded to the 2” square tubing....

You might want to consider not having the top and bottom plates the same size.  When the sheet metal flexes around one plate as the chassis flexes it stresses the metal.  Then when it flexes the other way it bends around the other plate.  If the plate edges line up, the stresses are always in the same place and the reversing stresses will fatigue and possibly tear the metal eventually.  If the plates are different sizes the stress from flexing one way is in a different place from the stress flexing the other way, so the sheet metal will last quite a bit longer before fatigue would be an issue.
Bob

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bridog Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2019 at 8:46pm
Originally posted by Nothing Special Nothing Special wrote:

You might want to consider not having the top and bottom plates the same size... so the sheet metal will last quite a bit longer before fatigue would be an issue.


Thanks for bringing that up. I have heard this mentioned before, but I have been reluctant to buy in. The explanation you gave as to why such a failure could occur makes sense to me. I also understand in simple design terms about the stress being concentrated on the thin metal where it meets the plates. In our 20+ years of wheeling I just have not seen an issue where the body metal has failed around a pass through of a structural element done with equal sized plates. For that reason I question as to whether the magnitude and frequency of the metal bending back and forth at the edge of the plates is significant enough to cause the metal to failure prematurely. If failures have occurred I would be interested in knowing under what design and usage conditions the area was subject to and for how long.


At this point in the build it would be easy for us to make the top plates slightly larger and we are open to doing that. How much larger would you suggest if we decide to?     
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbjeeps Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2019 at 9:14pm
Awesome work Dylan, keep the updates coming!
1953 M38A1 (His)
1963 CJ5 Mk III Tuxedo Park (Hers)
1948 CJ2A "Targhee" (Under construction: looking forward to the Rubicon and Moab)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nothing Special Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jan. 2019 at 10:17pm
Originally posted by Bridog Bridog wrote:

Thanks for bringing that up. I have heard this mentioned before, but I have been reluctant to buy in. The explanation you gave as to why such a failure could occur makes sense to me. I also understand in simple design terms about the stress being concentrated on the thin metal where it meets the plates. In our 20+ years of wheeling I just have not seen an issue where the body metal has failed around a pass through of a structural element done with equal sized plates. For that reason I question as to whether the magnitude and frequency of the metal bending back and forth at the edge of the plates is significant enough to cause the metal to failure prematurely. If failures have occurred I would be interested in knowing under what design and usage conditions the area was subject to and for how long.


At this point in the build it would be easy for us to make the top plates slightly larger and we are open to doing that. How much larger would you suggest if we decide to?     

I don't have any personal experience with that type of failure in this type of application in a vehicle.  I know the theory is valid though - I've seen how it plays out in other cases.

Where it would be particularly critical is if you were just mounting the roll bar to the sheet metal, using the backing plates to spread the load.  In that case fatigued metal compromises the roll bar mount.  Since your lower plate is attached to the frame, fatigued sheet metal won't affect the strength of the cage, so I don't think it's a safety risk here.  Still, who wants to tear sheet metal?  If it doesn't hurt anything I'd make the plates a little different sizes just to gain the safety factor on that.

As far as how much bigger, I'd think an extra 1/4" on each side would be plenty.  Even 1/8" might be all you'd need.  You're just trying to keep the stress from reversing in the same location.
Bob

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepN95YJ Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jan. 2019 at 11:41am
Originally posted by Nothing Special Nothing Special wrote:

Since your lower plate is attached to the frame, fatigued sheet metal won't affect the strength of the cage, so I don't think it's a safety risk here.


This.

I don't see any reason to worry about this at all.  These bodies are so small and your mounts are so close together I don't see any way that you could produce enough flexing of the material to ever cause this type of failure during the life of the vehicle.  

On a unibody vehicle or a desert race truck this might be an issue.  But I just don't see this becoming an issue on your jeep. (A very nice build, btw!) 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jan. 2019 at 12:24pm
This thing is really looking good. I love seeing the progress. Keep the posts coming and keep up the good work Dillon and helpers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jan. 2019 at 2:25pm
You say that frame is 11 gauge right ? 
So that means you have 1/8" of wall thickness.
When multiplied by 2 vertical walls that would roughly equal a channel frame having 1/4" of wall thickness.
Compared to the standard frame with only 3/16" of web (vertical wall) thickness.
I also think your not going to see enough frame flex to make the body mounting a real concern.
Besides that the body will be mounted to frame  using rubber .... right ?

 
Currently building my final F-134 powered 3B .
T98-A Rock Crawler using exclusive factory parts and Approved Special Equipment from the Willys Motors era (1953-1963)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bridog Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jan. 2019 at 3:04pm
Originally posted by oldtime oldtime wrote:

You say that frame is 11 gauge right ? 
So that means you have 1/8" of wall thickness.
When multiplied by 2 vertical walls that would roughly equal a channel frame having 1/4" of wall thickness.
Compared to the standard frame with only 3/16" of web (vertical wall) thickness.
I also think your not going to see enough frame flex to make the body mounting a real concern.
Besides that the body will be mounted to frame  using rubber .... right ?

 



Yes, the frame is constructed of 2x3 and 2x4 both with 11ga wall rectangle tubing. Hollow structures like round, square, and rectangle tubing also offer better torsional resistance than channel. The rollcage tied into the frame in at least 8 places should also add some rigidity. I would anticipate the body and frame flex would be a fraction of that of a stock 3B.   The body will be bolted directly to the frame...no rubber mounts. Dylan wants to enjoy all that Dauntless has to offer including the vibration
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oldtime Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jan. 2019 at 3:30pm
I agree...Being tied into the roll cage will also eliminate a lot of frame flex.
Consider too that the overall tub will flex some too.

FWIW
I would add 1/8" of rubber on top/bottom to pad the tub sheet metal.
Otherwise the body will literally abrade itself thin from the friction due to any amount of lateral movement.


Currently building my final F-134 powered 3B .
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Zero aftermarket parts

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73 cj5 Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jan. 2019 at 1:35am
Very nice work. I'm building a 55 3B with YJ springs SOA and shackle reversal. Everything will be stock except the brakes. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bridog Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb. 2019 at 1:57pm
Originally posted by 73 cj5 73 cj5 wrote:

Very nice work. I'm building a 55 3B with YJ springs SOA and shackle reversal. Everything will be stock except the brakes. 

Thanks!  We are sticking with the springs under the axles, but will be doing a shackle reversal on the front. We are still kicking around some ideas of how to build the front spring hangers to help deal with the much longer YJ springs. Do you have any pics of the front of yours?  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73 cj5 Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb. 2019 at 4:33pm
I borrowed the design from another guy (with permission of course) and if you want I'll give you his  contact info. 
Here's where I'm at right now. I have some ways to go but this is about what it'll look like when done. Shackle mounts will be through the frame. Top plates are for my cage mounts. 




If I were to do it again I'd make the piece about an inch longer and have them cut on a cnc. Embarrassed


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