jb1390
Gold Member
Well the engineers at work claim my 4x4 tube will support 3800lb overhung braced in the middle of 8ft. I explained that 8ft is just the root boom and the dipper boom would add 8 more ft to the overhang, right off said then it was going to bend, but he would do the math and get back to me. Well he never got back to me so i still dont know what I need to know.
Looking at the Lemco and where the cylinders are mounted, well thats almost exactly what I had in mine. I feel the plating for the cyl mounts should add some strenght, but dont know how much. I am not opposed to the truss ideal, but would prefer not to use trusses simply because of eye appeal. I would rather it look ugly than fail, so the final build will probably include some sort of truss. The ideal of build it then add weight until it gives, then add a truss if needed, I had considered. Right now the only way I see not to use a truss is One, use bigger tube. Two, add plenty of plate in the middle of the boom for the cyl mounts and let that be the extra strenght. Three, use 2x4 tube and double it along with the extra plating. Right now I think all three methods will work, but will have to see what I can scrounge before actually building anything.
In general with this design, I would proceed with some caution. There are many, many possible failure points to be considered, some of which would have more significant consequences than if the tubing bends. The attachment point on the trailer, lower pin and hinge design, etc could end up being very dangerous if not designed correctly. And remember, just because it works the first time doesn't mean it will last 100 cycles.
You also will need to spend some time figuring out the correct mounting locations for the pistons so that you get the proper range of motion. When I design a scissor lift for a truck body, I normally spend hours calculating forces, running an analysis on the scissor arms, performing measurements in the computer to determine dump angle, all before I order a cylinder or start cutting parts. And I have a pretty powerful computer program at my disposal to do that.
That being said, as far as the arms go, I would weld a 1/4" strip down the top center of each arm. You can see from the analysis that I did how much of a difference that strip makes. This is with 2000 pounds at the end of the arm, which was about right for a 3.5" cylinder at 2000 psi.