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Old April 22nd, 2012, 08:38 PM   #1
Kodiak450r
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Default DIY gantry crane question.

I'm in need of some insight in determining a weight capacity for a wooden gantry crane i would like to construct. My question is how can i determine the load capacity of a single 4x4 in the center of an 8 foot span? It would look something like this. For anyone wanting to know just why i wanna build one. I need to remove the body from my S-10 to strip the chassis and don't have access to a hoist

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Old April 22nd, 2012, 08:39 PM   #2
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triple 2x6, not single 4x4
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Old April 22nd, 2012, 08:41 PM   #3
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triple 2x6, not single 4x4
i just used the 4x4 as a starting point. i was thinking of stacking the 4x4's to make a 4x8 and bolting them together every 12" apart.
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Old April 22nd, 2012, 08:44 PM   #4
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have any trees in your yard?
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Old April 22nd, 2012, 08:44 PM   #5
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you want your height to be a single piece of wood, the piece on each side help stabilize it.
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Old April 22nd, 2012, 08:53 PM   #6
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i just used the 4x4 as a starting point. i was thinking of stacking the 4x4's to make a 4x8 and bolting them together every 12" apart.
If you do that, make the 4x8 by using 2 * 2x8s instead. The 4x4s will allow slide/flex between them, and won't gain you nearly the strength of the 2x8s, unless you laminate them together with glue.

A double 2x8 should be just fine for lifting a body. Less load in that setup, compared to, say spanning several feet as a header in a load bearing wall.

Boards are cheap, just go a little extra on it.
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Old April 22nd, 2012, 08:54 PM   #7
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you want your height to be a single piece of wood, the piece on each side help stabilize it.
so 3 2x6's or bigger if i can get them placed vertical next to each other would work? think it can handle the weight of the cab? it weighs around 800 lbs.
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Old April 22nd, 2012, 08:59 PM   #8
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Quote:
Originally Posted by Haggar View Post
If you do that, make the 4x8 by using 2 * 2x8s instead. The 4x4s will allow slide/flex between them, and won't gain you nearly the strength of the 2x8s, unless you laminate them together with glue.

A double 2x8 should be just fine for lifting a body. Less load in that setup, compared to, say spanning several feet as a header in a load bearing wall.

Boards are cheap, just go a little extra on it.
ok cool thanks for the input on that. now how about the uprights? 4x4's strong enough for that? i already have those so i was hoping to be able to use those. i'm going 10 feet high with this idk if that has any factor on capacity.
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Old April 22nd, 2012, 09:02 PM   #9
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Quote:
Originally Posted by Kodiak450r View Post
I'm in need of some insight in determining a weight capacity for a wooden gantry crane i would like to construct. My question is how can i determine the load capacity of a single 4x4 in the center of an 8 foot span? It would look something like this. For anyone wanting to know just why i wanna build one. I need to remove the body from my S-10 to strip the chassis and don't have access to a hoist

is the bed already off of it? if so, couldn't you just use floor jacks to get the body clear of the frame, set it on 4x4's that are resting on jack stands or w/e and roll the frame out from under it?
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Old April 22nd, 2012, 09:06 PM   #10
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is the bed already off of it? if so, couldn't you just use floor jacks to get the body clear of the frame, set it on 4x4's that are resting on jack stands or w/e and roll the frame out from under it?
X2. We've done that Many times.
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Old April 22nd, 2012, 09:06 PM   #11
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Me and a buddy pulled the stripped cab off of his S-10 by putting 2 2x4's thru the cab and picking it up on our shoulders. A standard cab S-10 shell isn't that heavy.

If you are taking a completely assembled cab off the chassis, that's a bit heavier.
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Old April 22nd, 2012, 09:08 PM   #12
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is the bed already off of it? if so, couldn't you just use floor jacks to get the body clear of the frame, set it on 4x4's that are resting on jack stands or w/e and roll the frame out from under it?
not yet. bed is coming off next. i'm doing this all by myself. i don't have any help for lifting things like that.
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Old April 22nd, 2012, 09:22 PM   #13
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not yet. bed is coming off next. i'm doing this all by myself. i don't have any help for lifting things like that.
Seriously, do not do this alone.

even if you are using some kind of winch with the gantry, if something goes wrong you can be seriously injured. Even if it's just the GF with a cellphone, have help available.
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Old April 22nd, 2012, 09:28 PM   #14
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for the bed,use a cherry picker and build something like this:
http://truck-bed-lifter.brutmfg.com/

for the cab, use (4) 4x4's and (4) bottle jacks, and lots of cinder blocks or more 4x4's cut to 1' sections for cribbing (much better then cinder blocks). Set up the cribbing and use the bottle jacks to raise the cab enough to slide (2) 4x4's under it, then reset the cribbing and put the bottle jacks under the 4x4's, raise and support those 4x4's (block off to the frame), then reset the cribbing and repeat the process with the other (2) 4x4's. When its high enough, crib the last set of 4x4's far enough out to roll the frame out from under it. Its much slower, but much more stable then using a homemade gantry crane, especially when working by yourself on something that is difficult to guess the balance point. It also leaves it elevated and sturdy enough to leave sitting right there.
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Old April 22nd, 2012, 09:31 PM   #15
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Or you could just unbolt it and heave it over on to the old mattress in your yard.


















You had to know that was coming
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Old April 22nd, 2012, 09:33 PM   #16
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i have taken the doors off and used a cherry picker to lift off the body, wasnt easy but i did it ( by myself too)
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Old April 22nd, 2012, 09:41 PM   #17
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I can look through my notes from last term and see if I can find the section where we covered bending moments in a wooden structure.

When we have pulled cabs we just used a cherry picker with two straps to pull a '76 F series cab.
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Old April 22nd, 2012, 09:47 PM   #18
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Used a cherry picker to pull the tub on my YJ.




It folded in half
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Old April 23rd, 2012, 08:11 AM   #19
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Quote:
Originally Posted by Kodiak450r View Post
not yet. bed is coming off next. i'm doing this all by myself. i don't have any help for lifting things like that.


Cry me a MF'in river.

Build a wood cradle for your cherry picker.
Profit.
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Old April 23rd, 2012, 08:19 AM   #20
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What about calling a local tow company with an extended boom? A few straps up it comes safe and secured.
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