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Wood strength for a lifting arm

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Forum topic by richgreer posted 827 days ago 1029 views 0 times favorited 11 replies Add to Favorites Watch
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richgreer

4521 posts in 1575 days


827 days ago

I don’t know how to do drawings here, so bear with my written description of what I want to do.

Imagine a square steel shaft on an old tractor. The shaft measures 1.25” square and is 2.5” long. It pivots under hydraulic power. It was used to lift various pieces of farm equipment (e.g. a cultivator).

I want to use that shaft for some relatively light weight lifting. I want to attach an arm to this shaft that is about 12” long and I want to be able to lift about 400 pounds from the end of this arm. I don’t want to work with steel unless I have to. I’d have to hire someone to make it for me.

I envision using 8/4 hardwood. I envision using 2 pieces of wood with a cutout for the shaft. I would bolt the 2 pieces together around the shaft.

Does anyone have an opinion regarding is this doable and/or what wood would be strongest for such an application?

Also, would it be better to cut a diamond or square shape into each piece of wood?

My initial thought is to use maple and cut a square shape, but I don’t really know why I think that.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.


11 replies so far

View Jim Finn's profile

Jim Finn

1502 posts in 1423 days


#1 posted 827 days ago

Hickory is used for axe handles maybe that would work.

-- In God We Trust

View TCCcabinetmaker's profile

TCCcabinetmaker

896 posts in 856 days


#2 posted 827 days ago

12 inches long doesn’t seem like much of a lever. Only problem with hickory is it appears to only come in 4/4. You probably would at least need oak, but I’m still not convinced on a 400 pould load wood is the way you should go.

-- The mark of a good carpenter is not how few mistakes he makes, but rather how well he fixes them.

View Bill White's profile

Bill White

3187 posts in 2461 days


#3 posted 827 days ago

Why can’t ya just get a piece of square stock (hollow) steel that will slip over the existing arm(s)? Set screws or bolts to hold ‘em in place. That is if I’m understanding your need.
Bill

-- bill@magraphics.us

View casual1carpenter's profile

casual1carpenter

353 posts in 977 days


#4 posted 827 days ago

Rich, basically you are making an M&T joint where the 2.5” 1.5×1.5” square steel stock is the tenon. I agree with TCCcabinetmaker, that’s a lot of weight you are lifting. Perhaps you could thru bolt some steel flat bar to each side.

View Edwin's profile

Edwin

89 posts in 1499 days


#5 posted 827 days ago

Use steel tubing or angle iron. It is easier to work with. You can bolt it on or use C clamps. Thats the way I would do it and I’ve been working with steel for 40 years…
ED

-- Ed Port Republic

View Viktor's profile

Viktor

446 posts in 1920 days


#6 posted 827 days ago

Hickory would be the best (among easily available). If the drawing in post #4 is accurate wood is not going to work (to much stress at the joint and it can’t be glued). Use steel square tube as Edwin suggested.

View crank49's profile

crank49

3245 posts in 1472 days


#7 posted 827 days ago

I was thinking the arm would be 90 degrees to the way the drawing is showing it.

You will be applying 400 foot pounds of torque to that square hole. At 1.5” square you will be applying a spreading force of 3200 pounds. That will split your hole.

Use a pair of u-bolts (like large muffler clamps) to attach the crank arm to one side of the square shaft. Then you don’t have cut a hole in your arm. Put a piece of flat bar on both sides of the wood for the bolts to go through to spread the load. This would easily handle the load you are wanting.

-- Michael :-{| Diapers and politicians both need to be changed often; and for the same reason.

View Woodwrecker's profile

Woodwrecker

3470 posts in 2077 days


#8 posted 827 days ago

Well, I was going to throw my 2 cents in Rich, but you have some awfully smart engineers helping you out here.
lol

-- Three Rules of Work: Out of clutter find simplicity; From discord find harmony; In the middle of difficulty lies opportunity. Albert Einstein

View Jim Bertelson's profile

Jim Bertelson

3591 posts in 1665 days


#9 posted 826 days ago

I am like Eric, you have plenty of good help here.

But I just wanted to second the point made by Ed. For us not having steel working equipment or know how, there is a workaround solution. Angle iron, flat iron, threaded rod, iron pipe, etc. With a drill press, set of taps and dies, and a good hack saw, you can make a lot of iron stuff. I have been doing that kind of thing for 30 some years. I made a substantial roller for my garden tractor with a 12” in diameter 6 foot piece of pipe I found on my property in Fairbanks, capped it with plywood, filled it with sand, and made a yoke for it with pipe.

I don’t know anything about what you are trying to do, but some simpler metal projects can be cobbled together with stuff you buy at HD. I keep angle iron and threaded rod around for those oddball needs.

-- Jim, Anchorage Alaska

View Nomad62's profile

Nomad62

668 posts in 1459 days


#10 posted 823 days ago

The problem I see is the wood attachment would split; it will easily lift the 400lbs if you can get it to hold together. So, a couple of options; first, if you have the room you could make a very large piece, maybe 8” square (a big block to say the least) with a hole in it just big enough to slip tightly over the tractor stub; or a smaller block that is wide enough to run a couple lag bolts thru on each side of the stub hole to hold it together. I’d go with option 2, but would really sniff out some help with a steel guy first. If you do use wood, make sure to have the flat grain on top, like a bow is made, to help it bend without snapping.

-- Power tools put us ahead of the monkeys

View styrling42's profile

styrling42

2 posts in 820 days


#11 posted 820 days ago

Well Rich, your fulcrum (square steel shaft) is awfully small. It would rip right through a wooden hole. So I think that Crank49 had the best idea. Fender washers would even work if you didn’t have flat iron plats. No drilling into steel, that way, either. I would extend the wooden shaft out of the back side a little though so you could add weight or a coil spring to assist the lifting. Like a see-saw. I’ve done that when having to move big stones, except I was using a chunk of log and a tree trunk as the fulcrum and beam.

Have you considered just adding a PTO driven winch assembly? Northern Tools has one that bolts on, I think.

Good luck and post pics if you getting it working.

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