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Thread: wooden a frame teepee hoist
08-09-2011, 03:18 AM #1
wooden a frame teepee hoist
once upon a time i made a 4x4 wood a frame to use with chain hoist to unload my 1800 lb nardini lathe from back of pickup. worked marvelously. it was simply 4pcs of 12' 4"x4" with 5/8" all-thread through the ends & splayed like a teepee. with chain hoist on rod.
I now want to load/unload from skid loader type trailer a 5800 lb vmc.
gives compressive loads.
says 4x4 x 12 are good for 3,300 each, at #2 grade. (i'm sure menardws is LOW)
of course I cant ensure my teepee is completely uniformly loaded per leg,
4x6 is 5200 lb @ #2 grade
shall I uprade my design to 4x6 or 6x6?
Last edited by dsergison; 08-09-2011 at 11:10 AM.
08-09-2011, 04:13 AM #2
The values listed account for the column buckling potential with long columns. Note that for a short column, the values are quite high. Solution. brace the 4x4's with X-bracing and you should be OK.
08-09-2011, 04:27 AM #3
The beauty of his design is that it conforms to unequal surfaces and is easily changed for very different situations.
Wouuldn't X bracing take away alot of the open space since to be most effective you want to place it roughly mid span?
- Especially with a VMC being relatively tall compared to a lathe being long and slender.
I'm no engineer but 6x6 looks like more than enough.
You could also do 3 2x6 nailed together to make a full 4 1/2 x 5 1/2 post
You wouldn't need about any short grain issues then where the grain runs across the post weakening the entire post.
Don't forget to think about the rod dia also
08-09-2011, 04:42 AM #4
oooh thanks! for the laminate suggstion. 3pcs 2x6 x 16 are even cheaper than 1 6x6x12
i do like the laminate beam idea. that will also get me a taller frame, and less crappy grain issues from the #2 wood. the extra headroom is a real help.
08-09-2011, 04:53 AM #5
Now we need pictures...
on edit...Now if you really want to make something strong make a box out of 4 2x6s
08-09-2011, 05:08 AM #6
I'll need a crane to lift my crane.
08-09-2011, 06:34 AM #7
Lean 'em against the truck and assemble them in place? Just cut the weight by 75%.
A fabricated square (or truncated pyramid) steel cup with a long eyebolt in the center would make assembly easier and would be stronger. A lag screw or two into each leg with a cordless, would keep it together.
I wouldn't swing the machine a lot though...... Straight up, straight down.
Tripods give better weight distribution, but might require too much height.
08-09-2011, 07:27 AM #8
The tripod design is good, but the loads are not pure compressive, there is also a bending component. The reactions at the ground either need lots of friction to stop the legs from spreading, or those forces can be self equilibrated by adding a tension tie between the legs, and close to the ground is best.
That leaves a delta shape on each side of the truck or trailer supporting the load. Then the column loading can be dealt with, and although the legs are still beam columns, the bending loads are much smaller. All that might be needed to insure the legs don't buckle is another (light) tension tie about mid height to increase the buckling strength of the legs.
I don't believe in cutting corners during overhead hoisting. More structure is more better.
08-09-2011, 07:37 AM #9
4"x4" is plenty but more important than lumber size is how you tie them together at the top. a simple piece of all-thread in a hole will want to split the wood IMO. some kind of cap as robert mentioned above needs to be thought out.
08-09-2011, 05:37 PM #10
There's a way of noosing the top of a tripod with six or 8 turns of rope that's more effective than readi bolt. Can you get, 3 straight knot free 6" logs (big end measure) in your area? Logs may be scarce in conifir-less Peoria. If they are straight, logs are a bit superior to dressed lumber for column loads. If they come off someone's woodlot they may be free. Do NOT cheap out when selecting tripod legs for a heavy lift of very expensive equipment.
Can you borrow 4" pipe and return it to the yard after the lift. Noosing and rigging a tripod won't mar or damage the pipe and you need have no fear it would break at a knot.
Look on page 33 of this PDF: http://www.globalsecurity.org/milita.../14251_ch6.pdf
Note the use of anti-scoot preventers connecting the butt ends of the legs. Those of you wishing for a handy resource for rigging information should copy this PDF for their library. I Googled it using "rigging a tripod". There's lots more information on the topic of safely lifting, rigging, and locating heavy awkward loads.
How far do you have to straddle to clear the trailer you want to back under it? The legs should be 2 1/2 to 3 1/2 times the straddle distance. Too wide a straddle and the butt ends may scoot out because of the horizontal component of the load imposed on an angled member. Depends on the surface (dirt, rough or smooth concrete). Do you need foot pads to keep the legs from driving into soft soil?
I submit 5800 lbs is about the safe limit for home-made tripods.
Last edited by Forrest Addy; 08-09-2011 at 08:28 PM.
08-11-2011, 01:19 PM #11
I had hoped one of the guys who had built a lifting horse would chime in and describe its construction. It's like a giant saw horse built with 4x4 legs and something more stout for the cross piece. I've never been able to understand the description of the bracing for one of these. A picture or diagram would help. The lifting horse would give you a better span over the trailer and the weight distributed among the 4 legs would be only around 1500 lbs per leg.
08-11-2011, 01:40 PM #12
RLamparter, I assume you mean a gantry crane, basically two A - frame ends coupled with a beam across the top. Because of the span of the beam, the beam would have be very large or a truss.
08-11-2011, 02:00 PM #13
With the kind of weight you are dealing with. I would have a pro come lift it and put it where you can handle it. Let us know how it works out. Kenny
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08-12-2011, 12:14 PM #14
Calling Davey Crockett
08-12-2011, 12:59 PM #15
If it was me doing this, I would do the following: Fabricate a gantry rather than a pyramid. Use laminations instead of solid wood for all elements. BOLT the laminations do not nail except to keep things in alignment. (important). Instead of using one chain fall or lift at the center of the beam, I'd use two, spaced as close to the end frames as practical. If you can borrow or scrounge a good piece of I beam I'd use that instead of a laminated beam. Using my two ton, commercial made gantry as a swag, I'd use at least a 10" beam, since mine uses a standard 8" for the relatively short span of 8'.