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Unread 01-11-2007, 08:49 PM   #1
Matt in TN
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Front Bumper Build

I've been needing some front recovery points for a long time, and while I did the power steering and was fooling with that end of the Jeep anyway, I decided to build a new bumper and practice my very basic welding/fab skills.

It started as 48" of 2" x 4" x 3/16" rectangular tubing, and I cut 6" off each end and angled them up and back slightly and welded it back together, facing the ends with 2" x 3/16" flat. I then cut holes for the clevis mounts to go fully through. These were made out of 7/8" x 2" bar stock and were a full 7 1/2" long - long enough to go all the way through the bumper and bolt directly to the frame with 3/4" and 1/2" grade 8 bolts. Running a basic shear stress calculation (I'm an engineer - I can't help myself!) told me that just one 3/4" bolt would more than handle a 10,000 lb load, and that assumes no clamping force and friction - so I feel safe with these bolts. The 1/2" bolts are more for keeping the bumper from tilting up and down, but will add a little more strength in shear as well. I also did a few quick calculations on the frame itself to make sure the bolts would not rip the thinner frame material out, and they look OK too (especially sandwiched into 7/8" thick steel).

I welded it all with only my 110V flux-cored welder, but was careful to fully bevel all the 3/16" stuff and pre-heat the clevis mounts with a torch to get more penetration. That stupid spatter had me grinding a lot, but it turned out OK.

Anyway - nothing fancy, but it gave me the needed front recovery points and let me practice my welding skills a little more.





The mount:


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In the garage, waiting for hell to freeze over so I can finish the installation: Waggy front D44, AMC M23 rear

Last edited by Matt in TN; 01-22-2007 at 09:29 AM..
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Unread 01-12-2007, 05:17 AM   #2
rickr
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please don,t take this the wrong way. i do like your calculations, but,will those 110v mig welds hold up? they do look good.
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Unread 01-12-2007, 05:52 AM   #3
Matt in TN
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That's the question of the day!

I think they'll be fine - the rear bumper (made similarly, but without the direct bolting of the clevis mount to frame) has held up just fine and had some pretty good jerks on it. For the front the welds really aren't critical, as bolting the mounts to the frame (not the bumper to the frame) will transfer almost all of the load directly through and not put much stress on the welds. The bumper acts more as a crossmember instead of a hard mounting point - stiffening the frame and keeping it from flexing/twisting.

I wish I had a way to test penetration and know for sure, but the theory of pre-heating is sound - basically the more you pre-heat the steel with a torch, the less work the welder has to do getting the steel hot enough to penetrate fully with electricity. (learned that from BESRK - thanks!).
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In the garage, waiting for hell to freeze over so I can finish the installation: Waggy front D44, AMC M23 rear
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Unread 01-12-2007, 08:07 AM   #4
JJs99TJ
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looks damn good IMO

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Unread 01-12-2007, 08:34 AM   #5
igofshn
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Quote:
Originally Posted by rickr
please don,t take this the wrong way. i do like your calculations, but,will those 110v mig welds hold up? they do look good.
110 welds will do just fine.
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Unread 01-13-2007, 07:04 AM   #6
BESRK
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I like that! I did the same thing to my little CJ5.. ran longer clevis mounts thru the bumper to catch the bolt holes on the side of the frame. Think I'll do that on all my front CJ bumpers from now on.
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Unread 01-13-2007, 07:34 AM   #7
Matt in TN
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Good point, BESRK - I forgot to mention that the 3/4" bolt holes in the frame were already there and the perfect size! What were those originally for, a snow plow?
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[B]'79 CJ-7, 304, T-18a, Dana 20, AMC-20 w/ Yukon 1-piece axles, and Dana-30, 33x12.50x15, 1" Body Lift w/ heavily trimmed fenders, full cage with seats and harnesses, CJ/Wagoneer power steering upgrade, custom front and rear bumpers, body armor, and belly-up skidplate[/B]
In the garage, waiting for hell to freeze over so I can finish the installation: Waggy front D44, AMC M23 rear
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Unread 01-17-2007, 08:50 PM   #8
Havasu Living
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Nice, I'm hoping my miller 135 110v mig works too. The front bumper is on my list. I like the look
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Unread 01-19-2007, 08:46 PM   #9
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that looks awesome....glad to know my 110 fcaw will do that until i get the conversion kit to do gmaw......looks good
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Unread 01-20-2007, 01:17 PM   #10
famicom21
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wow! calculations!


...i bodge

i find a bolt that looks good enough, and just throw it on...


(i will use grade 8 for important stuff like suspension and seatbelts though)
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