bending 4x4x.250 sqtube

[muddstopper]

2000 lbs on the end will deflect 1.8" at the end, and .33" at the cylinder attach point. 2,000 lbs won't cause a permanent bend (60,900 psi stress vs 74,000 psi strength). So Mudd your gut feel for 4x4x.250 is pretty good. But you want a safety factor of 3x or 4x and all you have is 1.2x.

If you add the truss over the top your strength will increase by about 3 or 4x, then you will have the safety factor you need. You could use 3/16" flatbar for the truss. It would look nice with a 3" x 1/4" truss.

Your cylinder mounts probably should be independent of the strengthening elements. They should be set to fit your cylinder ends. The bracing can be its own unit on the topside.

SODO, you nailed the drawing to a tee. You lost me on everything else. Since I am not sure of what you are talking about, lets go with the truss system you suggest. Which I had already actually considered. I think its a good Ideal, but I intend to plate the sides of the root boom from the top of the tube to the distance needed to mount the cyl pins. I know that plateing both side of the 4x4 tube will increase bend strength. Also not having to drill any holes in the tube it should be able to maintain full strength. Anyways, Considering a 1/2x 6in plate by ever how long it takes to use the plating for the cyl mounting point for dipper boom cyl., It should be possible to not need a top truss.

 

[Shield Arc]

The truss on top is a very common practice. You see it on jib cranes, engine hoist, just to name a few.

 

[muddstopper]

I have seen the truss in a lot of applications. I have no problem using trusses if they are needed but, My thoughts are that if the plates, welded to the sides of the boom, are already needed for cyl mounting points, are the trusses still necessary.

 

[Sodo]

Saying it another way, with no truss (and no plate), your safety factor for 2,000 lbs on that 4x4x.250 is 1.2. Basically 2,000 lbs will flex it 1.8" at the end, but 2,400 lbs will permanently bend it at the cylinder support (49"). This 1/2" plate would have to be pretty long to spread out the "point load" caused by the cylinder.

A flat plate welded onto the 4x4 will strengthen it but its more efficient to add material farther away from the neutral bending axis. I don't think it's prudent to do the strengthening function with your clevis mounts. It's on the compression side, and you want the strengthening in tension. With all the key welds in compression or shear, not tension. The strap type truss welds are all in shear. I think the truss strap will "look right" too. Your cylinder clevises (4 inches apart) will not fit the cylinders in an ideal manner.

Maybe I'm not understanding you. Can you sketch your idea with a pencil and post a pic?

You could do it like this but the truss over the top is substantially stronger with less weight. Notice the 'blocking' to support the webs (which are in compression, not the ideal configuration but maybe 1/2" thick, needs no blocking). You will have to monkey around to get your cylinder clevises across that 4". 4" is perhaps too far for the pin size. Ideally the webs are tied into the 4" sides of the rect tube. Or you could bring it a little in but it can't be narrower than the big end of the upper cylinder.

 

[muddstopper]

Sodo, the problem with me sketching a pic and uploading is I dont own a digital camera to take a pic with. I have tried in the past to take pic's of drawing with my phone, but they never turn out. Let me see who I can get with a smart phone to take a pic. Might take a while since no ones around.

 

[Sodo]

If the hydr cyl is ontop it's protected from a swinging load. This lets the mounting clevis function as the truss in tension. Kind of a neat unit, extend-a-hoe method.



You can use bigger Sq tube, but that cuts into payload. Here's one by Lemco.

 

[muddstopper]

This drawing is not to scale and I havent checked the length of the 1/2" plate to see how long it will actually be. I'll try to draw it up in autocad later.

 

[muddstopper]

If the hydr cyl is ontop it's protected from a swinging load. This lets the mounting clevis function as the truss in tension. Kind of a neat unit, extend-a-hoe method.

well your pic didnt show up, but A cylinder on top is under load while retracting. This reduces the amount of available tonnage the cyl can pick up since it is pulling instead of pushing. At one time I had considered using a backhoe attachment to make the knuckle boom, but gave that up because of weight of unit and actual lifting power. With the backhoe attachment, the root boom cyl was mounted to pull the boom up and while this particular attachment was probably more than capable of the loads I would be lifting, the overall weight of the unit was over 3000lbs and not something I wanted to add to the tongue of a trailer. Weight is also why I am trying to get by with 4in sqtube instead of opting for something heavier. I havent calculated the total weight, but just a quick guess I should be under 1000lbs. 4x4x1/4 tube is about 13lbs per ft. Multiply that by 16ft= 208lbs. Rotator is 41lbs.. Grapple hasnt been built yet, but 100lbs+/-. swivel and mast, I guess at 400lbs, add another 100lbs for cyl weight, throw in some hoses and I'll be close to that 1000lb guess. And I forgot the out riggers, so maybe a tad over 1000lbs.

Ok, after your edit, the pic showed up. The lemco boom is exactly how I had this planned

 

[muddstopper]

Dang, i hate autocad. Been trying to draw the entire boom so I can get the measurements for both the root and dipper boom cylinders. I cant remember how I even drew up the sketch I already posted. Driving me nuts!!!!

 

[FarmWrench]

My 1960'sRyerson steel data book says 4x4-1/4" weight/foot 12.51 and will take 14.5 kips @ 6'

10x2-3/16" is a pound heavier @14.65#/foot but will take 27.4 Kips.

Go skinny and deep may help with visibility and Welding the ends?