Liebherr mobile crane

Discussion in 'Other metal working projects' started by Rebekah Anderson, Dec 24, 2023.

  1. Hiya all,

    this is my project.
    Very ambitious but achievable.

    the boom is approx 650mm maybe longer. The ends have a mounting collar to mount guide frames that contain bearings for sections to run on. The same for the base of each section.

    I want to replicate the telematic system which will require some programming electronics using stepper motors.

    I bought a decent CNC router now so I can cut decent parts. I have thought about trying to CNC the boom in two halves and TIG welding them together but that posses another set of problems.
     

    Attached Files:

  2. Well, at least you chose an easy project! ;-)

    To me, it looks like the boom boxes on the actual cranes are weldments consisting of press brake-formed components. I can understand the attraction of using your new CNC to make those parts. But you will have a big pile of chips on the floor and a lot of dull cutters in a bin. Step bending a piece of, say 16 or 20 ga steel on a press brake with suitable dies to approximate the needed radii would seem like a good approach to me. The curve so formed would surely have visible subtle steps. But, I am pretty sure the full-size version is formed with a press brake, so it would be a true-to-life method. A simple brake of adequate capacity should not be that hard to find.

    It might be very practical to CNC a die set to form the radius. For a short run aluminum dies might work fine.

    Tigging the formed pieces together would be fine. But, for thin metal and long seams, I'd be busting out my mig for a much faster and easier joining method, at least in my non-pro hands.

    Forgive my butting in, please.

    Denis
     
    Last edited: Dec 25, 2023
  3. Hiya,

    thanks for replying. The CNC route I totally agree with you. £250 per half where 90% will be on the floor is definitely not where I want to go tbh.

    the press brake is certainly the first thing I want to try. I want to try with a former out of wood and sheet of aluminium and see how that works out.

    The welding aspect may force me to change material.



     
  4. Tops

    Tops Silver

    Hey Bex,

    I would think about a CNC cut mandrel for the inner dimensions and then vacuum bag it with lightweight fiberglass cloth and epoxy resin. Then use epoxy resin to attach the other external fittings. Nice thing being that if it works well you can make copies. You will have to look at the mandrel material and mold releases so the desired tube is not permanently glued to the mandrel.
     
  5. Hiya,

    thank you, hadn’t thought of that. I wasn’t sure what you meant so I googled it. First thing that came up was carbon fibre. So I’ve sent an enquiry to a company to further understand the process.

    repeatability is something I’ve considered because I might make more variants.

    thank you for the idea.


     
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I take it this is a scale model. What are the actual sizes of the parts you want to make? Does it need to be load bearing and functional or merely positionable? One thing about telescoping tubes, the outer and in tubes only need to be close tolerance on one side but the inner tubes need precision both sides so layup of reinforced fiber cloth may not be suitable for those since one side will not be closely controlled by the mandrel.

    Best,
    Kelly
     
    Tops likes this.
  7. Last edited: Dec 25, 2023
    Tops likes this.
  8. Tops

    Tops Silver

    Using a mandrel for the ID would give one smooth surface to slide against.
    Disclaimer: my other hobbies involve fiber glassing so I see solutions in that realm, not saying it's the only way.
    I imagine there will need to be 'pads' or bearings of sorts (like on the big ones) to align and allow the sections to slide.
    A full surface contact/slide would be really fussy, both ID and OD would have to be spot on.



    lieb_boom0.jpg lieb_boom1.jpg
     
  9. To go along with the fiber glass solution: Using urethane foam panels and sheer fiberglass (.75oz/yd) cloth combined with CNC'd urethane foam corner blocks would allow a dimensionally accurate inside surface and an smooth metal-like outer surface. If made in two mating U-shaped halves, the fit and finish of the inside surface could be refined and UHMW bearing blocks installed and tested prior to joining them to make a box. Just thinkin out loud.

    Denis
     
    Tops likes this.
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not sure how I missed this information in the first post.....but......

    It does potentially allow close tolerance ID tube only but merely shifts the required close tolerance mating to the outer bearing surface(s).....andon such mechanisms aren't there normally two bearing surfaces spaced apart that end up reducing the effective telescoping length to a fraction of the actual tube length?

    If you were to make the tubes by cloth/resin lay up on the outside of a mandrel, how would you get those tubes off the mandrel after they cure? Trying to extract that zero clerance tube from a 650mm long mandrel seems to be a bit of an obstacle. Making that mandrel is no small feat either, andmultiples are needed.

    Best,
    Kelly
     
  11. According to the info I found online the "big boys" do indeed use bearing blocks not full length pads---I am sure for the reason you state.

    To control dimensional accuracy of a boat foam (urethane) u-shaped assembly I think I would use a "strongback" arrangement of rectangular frames set at interval analogous to strip canoe fabrication.

    upload_2023-12-26_8-36-57.png

    The laminated foam/cloth assembly would be springy enough that it could be easily popped off the strongback.

    I am guessing casting is going to come into this project somewhere....

    Denis
     
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not sure I get the analogy for the boom tube shape. The mandrel would be a completely encapsulated D shaped tube.......except the ends. ??

    Best,
    Kelly
     
  13. rocco

    rocco Silver

    Not sure if this would be helpful or not but I've made a number of hollow fiber glass parts by laying the glass over top of a styrofoam core then dissolving or cutting out the styrofoam.
     
  14. The idea was to use a strong back with square stations rather than curved ones for a canoe.
    Foam core sheets would be applied to this strongback for the curved side of the boom. Partial depth table saw kerfs fairly closely spaced and running lengthwise would allow bending the sheet to a radius at the corners.

    upload_2023-12-26_17-28-12.png

    This strong back would allow construction of the slab-sided portion of the boom.
    upload_2023-12-26_17-31-42.png

    Glassing the sheets inside and out would make a very strong half-box. The two half boxes would be joined to make the boom box. ;-)

    I hope this makes sense. UHMW bearing blocks could be added to the inside of the boom as needed.

    Denis
     

    Attached Files:

  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    -Nope, dont get it.

    The fundamental issue is how you extract a lay up off a 25 inch long, small corss section (i.e. <<1 in2) mandrel of any profile with no draft............don't see what any of that discussion does for that problem.

    Do you think you could draw say a .25" wall lay up off a 25" long .5" diameter centerless ground round mandrel? I'd say it aint happening. But if the OP want's to give it it a shot......have at it.

    Best,
    Kelly
     
  16. ddmckee54

    ddmckee54 Silver Banner Member

    If you haven't done it already, you might want to check out this site. https://www.rctruckandconstruction.com/

    There have been several cranes that have been built in the Construction Equipment forum, and I believe that there are a couple currently in progress. There is a 1/24 scale Liebherr that might be of interest to you. https://www.rctruckandconstruction.com/showthread.php?t=13775

    He made his boom sections out of galvanized sheet metal that are soft soldered together with Teflon tape bearing strips - I think. I think he either formed the sections over a wooden buck, or he soldered them on the buck - don't remember which. He just finished it in early December. I don't know if he's done any load tests, but he does have a picture of the boom slewed to the side and fully laid out without any tipping issues.

    You might be over-thinking this. This is a model, you are not going to be lifting tons, a pound or two maybe - but probably nothing that would over-stress even a boom built up out of styrene sheet.

    Don
     
  17. Jeez, I do not think I used any of the words "centerless, ground, or mandrel."

    I am simply trying to suggest that two u-shaped in cross section box halves be made. Then joined to make a box boom section.

    If sheets of boat foam were laid on the strong back and joined together with a layup of fiberglass to make the red piece shown below, that would constitute 1/2 of a boom box section.
    upload_2023-12-26_21-47-15.png

    Similarly fabricate the green shell below:
    upload_2023-12-26_21-52-35.png
    Peel the red shell from the strongback and the green shell from its strongback. Glass them inside and make needed locating strips to align top on bottom etc. (Not sure how much detail to include in what is intended to be a suggested starting point idea.) But, I do believe this is feasible and a pretty good way to make a modestly strong box.

    Join them to make a box
    upload_2023-12-26_22-1-19.png

    Of course this is a crude conceptual drawing obviously not to scale or even precisely correct general shapes. (This is how I made a cedar strip canoe 16 feet long which constitutes half of a box exactly 50 years ago. I had it out on a lake with my grand kids this Fall a couple times. It is strong, very light and has withstood hundreds of bumps and scrapes on rocks, logs, fence posts, you name it.)

    Denis
     
    Last edited: Dec 26, 2023
  18. I've been thinking a bit more about how these booms are constructed internally. I haven't been able to find very much detail on online. though I think the question is quite interesting. when I was going to college in the summer years, I worked in a crane manufacturing plant near in my hometown, though we did not make at that factory extending booms as our Used in the model being discussed.

    I've sort of been making an underlying assumption that the boom sections had to telescope precisely throughout their whole length so that the boom would be rigid at any position.. But that is not necessarily the case. If you look at videos of how the crane sections extend, you'll see that there are discrete points where pins come out and lock the extension of the boom. It would be at those points that a close fit between the inner and outer section of the boom would be necessary so that there would not be undesirable slop and whipping of the boom. But for the rest of the distance of extension, there could be a pretty loose tolerance as load is not applied while the boom is being extended, but is only applied after it has reached those discrete points and pins come out and lock it in place. So in building the model if. blocks were placed at those discrete points where the inner and outer section of boom did fit up fairly well. and a pin placed then the boom would be quite acceptable for its use as a model much as it would be if it were a real crane. Once again, I'm not certain that what I'm saying is clear and it's late, so if if that doesn't make sense, let me know and I'll draw it out better tomorrow. The bottom line is that smoothly telescoping tubes are not required for the entire length of extension, and that makes construction quite a bit easier.

    Denis
     
  19. Tops

    Tops Silver

  20. OK, so I am having fun practicing my CAD drawing and thinking about box boom sections...

    Here is how wear pads might be arranged on nesting boom sections with the black thicker pad attached to the inner section and the yellow attached to the outer. The removable red pin locks the two sections preventing one sliding on the other.
    upload_2023-12-27_8-3-54.png
    upload_2023-12-27_8-6-52.png

    With the outer section of the boom slid off the inner is shown with its pad.
    {Trouble pasting image}

    You can see that there is clearance equal to the yellow outer yellow pad's thickness when the outer section slides off the inner pad during extension. The black pad can ride on the inner surface of the outer tube and need not be a tight fit. That allows the outer tube to have pretty loose dimensional tolerances. But when the outer tube is positioned so that an inner section pad aligns with an outer yellow pad and the pin placed all "slop" is taken up.

    It would be a whole lot bigger engineering and fabrication problem if the boom were intended to be able to extend while under load. That would require precision fitting the entire length of the boom section. But according to what is saw, first the boom is extended to a given length, a locking pin is placed, and then the load is lifted.

    Surely this is a gross approximation of how the real-life sections may fit together. But I'd be willing to bet that a precision sliding fit is not built into the entire length of each box section. Next time I see one set, since my curiosity is definitely piqued, I'll do my best to find out how they are actually engineered.

    Denis
     
    Last edited: Dec 27, 2023

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