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Thread: Telescopic dump flatbed questions

  1. #1
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    Telescopic dump flatbed questions

    I an planning a dump bed for my 1991 f250 and I'm trying to manage both weight and deflection while keeping the bed as low as possible to make loading easier and keep the center of gravity as low as possible.

    I already bought my cylinder, a 7 ton 90" stroke trunnion mount. It will mount right at the front of the bed and will have a small doghouse. I chose a telescopic cylinder because it used the least amount of pressure and I like it better than two parallel cylinders. I decided not to use a scissor because it added too much weight to the rear axle and required too much pressure to lift. I am using the p/s pump for this, so max pressure has to be below 1500 psi. The telescopic is about 500 psi and only weighs about 75 lbs, so it's perfect.

    My calculations show a deflection at max load (6,000 lbs+ bed weight) of ~.100". This is with an evenly distributed load over the bed and a cylinder to pin length of 87". Max tensile is ~10,000 psi at full load.
    I know someone will say "an f250 will never carry that much", but I am using 6,000 as a MAX with a good margin of safety. I want to trust this bed after years of wi salt.

    I don't have a cad program that does load testing for me, I am just doing it on paper. I can make up a cad file if someone wants to run it to see if my numbers are accurate.

    How much deflection should I design for or expect? Is there an industry standard?
    I am trying to have an safety factor of 3 inside the elastic range of the steel.

    My plan is to use this bed for firewood, mulch, logs, hay, pallets, gravel, etc... It's a farm truck and gets used for everything.

  2. #2
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    Re: Telescopic dump flatbed questions

    Are you the same isaaccarlson I sent some saveedge files several years ago? You were posting on Arboristsite.

  3. #3
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    Re: Telescopic dump flatbed questions

    Quote Originally Posted by flushcut View Post
    Are you the same isaaccarlson I sent some saveedge files several years ago? You were posting on Arboristsite.
    Yep, those files were awesome!

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    Re: Telescopic dump flatbed questions

    Seems like you are shooting yourself in the foot by using the PS pump. A 12v hydraulic pump can be had for $100-$300, they provide the right pressure, have easy controls and relief valves built in. You will spend more going your way and have a crappy system that takes forever to lift. As far as adding weight, just flip it around from the way you were thinking of doing it and you will be adding less weight than you will with that 9’ monstrosity. Its not too late to change your plan a little and end up with a much better product.

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    Re: Telescopic dump flatbed questions

    Quote Originally Posted by walker View Post
    Seems like you are shooting yourself in the foot by using the PS pump. A 12v hydraulic pump can be had for $100-$300, they provide the right pressure, have easy controls and relief valves built in. You will spend more going your way and have a crappy system that takes forever to lift. As far as adding weight, just flip it around from the way you were thinking of doing it and you will be adding less weight than you will with that 9í monstrosity. Its not too late to change your plan a little and end up with a much better product.
    How much weight do you think I will add with a good scissor and electric pump? The scissors I looked at were 300-500 lbs with a pump.
    What makes you think my telescopic won't work well? Do you have any personal experience with them? My cylinder will add less than 50 lbs to the rear axle.

  7. #6
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    Re: Telescopic dump flatbed questions

    Howdy!
    I would not use the PS pump just a lot of wear and tear and you can get a 12v hydro pump pack cheaply and would add maybe a 100lbs extra to our overall weight. If you have a 8' bed you can fit a full cord pretty easily it's the gravel you have to worry about 6000lbs isn't much gravel at all. And also consider your dump angle the steeper the better especially if you are hauling dirt. I had a Load Trail dump trailer that wouldn't dump dirt easily, a real pain in the azz. For the deflection add some more steel in the stress points and some airbags for the weight. to the build.

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  9. #7
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    Re: Telescopic dump flatbed questions

    You will spend more money in lines and adapters for your powersteering pump set up that you could get a monarch dump pump for. They are pretty reasonable on ebay. Scissors don't weigh that much either. I have built 2 flatbed dumpers from scratch and re-built one which was almost all new anyway. The best scissor I used was on the first one. I cannot find that company anymore. The second scissor was from Pierce. Total POS, I had to modify and reconfigure it to get it to fit, and it was specific for my application. The next one I do if I do one will me my own scissor. My monarch pump set up is in my side compartment alum toobox mounted to the frame. Best thing I ever did for protection from the elements.
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  11. #8
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    Re: Telescopic dump flatbed questions

    Seems like a hell of a lot of work for a 1991 F250

    I would throw in an easy dumper and be done with it.

    Iíve got one in my 95 F350

    It will lift 2 1/2 tons of stone.

    Which is plenty (for me)
    Any more than that you better beef up the suspension.
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    Re: Telescopic dump flatbed questions

    I just noticed you wanted A flatbed...

    Oops

    Still love the easy dumper though.
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  13. #10
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    Re: Telescopic dump flatbed questions

    The scissor hoist weight is the weight of that short cylinder, maybe 60 pounds, plus maybe 40-50 pounds for the steel structure, the pump weighs maybe 20 pounds.

    As far as your setup working, the PS pump is not a high volume pump, nor a high pressure pump. It is going to push you telescoping cylinder very slow at idle. You could add a high idle switch, but that plus the hydraulic control valve is going to cost more than an electric pump.
    Last edited by walker; 01-21-2021 at 07:55 AM.

  14. #11
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    Re: Telescopic dump flatbed questions

    I have built 2 chip-box dump bodies for myself. One was a f250 pickup with a dump insert, bolted thru the bed. The other was a F450 diesel with a 8 ft x 12 ft flatbed converted to a dumping flatbed with a chipbox, and toolbox bolted on top. Both had 12v hydraulic pumps(as does my present GMC 3500hd ) The F250 I used a 4"x24" logsplitter cylinder, 1-1/4" pins, and 1"(3) plates to make the lift mechanism. On the F450 I just used a old knaphyde hoist from truck being scrapped, it came with a PTO drive pump, and manual lever valves. purchased a new 12v hydraulic unit for it (northern tool). You just got to remember its a 250, only put the metal where you really need it. There are kits now to convert regular pickup bed to dumper, as well as for flat beds. If you don't purchase one then maybe you could copy the design.

    best of luck

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  16. #12
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    Re: Telescopic dump flatbed questions

    You could always find a farm dump wagon, remove the hoist out of it to use on your flatbed (copy the design of the wagon frame and hoist mount) and not have to invent the wheel with a telescoping cylinder and design wonderng if it will work.

  17. #13
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    Re: Telescopic dump flatbed questions

    Telescoping cylinders are a PITA to retract. I don't believe a little pickup body would provide enough weight to make it come down easily. Slight bind, and it'll hang up.

  18. #14
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    Re: Telescopic dump flatbed questions

    All telescopic cylinders single action? Just asking because I don't know.

  19. #15
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    Re: Telescopic dump flatbed questions

    No, some are double acting. Mine is single acting. I can easily move it by hand and the bed will have no problem pushing it back down.
    It will have a swivel cage on the trunnions, so there will be no binding.

  20. #16
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    Re: Telescopic dump flatbed questions

    Thanks!
    Have you stared fabbing yet?

  21. #17
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    Re: Telescopic dump flatbed questions

    Not yet. I am working on the cad file as I get time. I keep changing parts here and there.
    I will wait until warmer weather for fabrication.

  22. #18
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    Re: Telescopic dump flatbed questions

    So in June we should see some progress? LOL

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  24. #19
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    Re: Telescopic dump flatbed questions

    With the telescoping cylinder what are you doing for a resivour? Telescoping cylinders take a lot of oil. I would also worry about contamination wrecking a steering box
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  25. #20
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    Re: Telescopic dump flatbed questions

    I will make a reservoir. The truck is manual steering. I might convert to power steering, but if I do I'm not worried about contamination. The cylinder is clean. I will have a filter on the return line. I think this cylinder takes about a gallon of oil. It's not a big cylinder at all. It has a big stage of 3.75" and it works down to 2". At 5 gpm, it would take about 12 seconds to dump.

  26. #21
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    Re: Telescopic dump flatbed questions

    Seems like a lot of work and expense to put into a 30 year old 3/4 ton truck.

  27. #22
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    Re: Telescopic dump flatbed questions

    Seems like a waste to buy a new truck and spend even more. I own this truck and it has always served me well. The truck itself is great and I plan on keeping it for many more years.

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  29. #23
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    Re: Telescopic dump flatbed questions

    Absolutely... I repurpose equipment on the farm all the time. It's paid for, so why not put it to work? My water truck is a 57 IHC, my fuel truck is an 83 Ford, I've built log splitters out of old sprayer frames, and rebuilt cultivators with parts salvaged from other machines. Building a better mousetrap is part of the fun in farming. Never gets boring like a 9 to 5 office job. I do question your choice in pumps though. Looking at the ones on my grain box hoists, I think you're going to be looking for a bigger one shortly. The electric/hydraulic power packs seem to be the obvious choice. Not a fan of the single acting cylinder though. Had one and as the load slid to the back it would take it up over center. Double acting would prevent that and the binding during retraction.
    Last edited by whtbaron; 01-23-2021 at 11:44 AM.
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  31. #24
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    Re: Telescopic dump flatbed questions

    Quote Originally Posted by whtbaron View Post
    Absolutely... I repurpose equipment on the farm all the time. It's paid for, so why not put it to work? My water truck is a 57 IHC, my fuel truck is an 83 Ford, I've built log splitters out of old sprayer frames, and rebuilt cultivators with parts salvaged from other machines. Building a better mousetrap is part of the fun in farming. Never gets boring like a 9 to 5 office job. I do question your choice in pumps though. Looking at the ones on my grain box hoists, I think you're going to be looking for a bigger one shortly. The electric/hydraulic power packs seem to be the obvious choice. Not a fan of the single acting cylinder though. Had one and as the load slid to the back it would take it up over center. Double acting would prevent that and the binding during retraction.
    Had that and many other issues with our smaller dump trailer that is gravity down... every time we have to load a piece of equipment in it you have to chain the front down When we were first looking at dump trailers I thought the gravity down would be a plus because then if your dump battery was dead form the lift you could still get the bed down....Wrong!!! it don't take much binding/rust/angle to totally defeat the gravity part of the 'gravity down' LOL!!! Kinda like the regular full size dump trucks that haul something that is just a bit bigger than the vertical opening in their tailgate once you get something stuck in the back you're done driving for the day
    Last edited by ronsii; 01-23-2021 at 12:54 PM.

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  33. #25
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    Re: Telescopic dump flatbed questions

    Yes, I would spend a lot less time worrying about deflection, and more focusing on a unit that is going to work the way you want it to.
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