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So when you are fabricating something that needs to handle a certain load...how do you know if what you built is strong enough or should I say, how do you know prior to creating that it will be strong enough?For example, I am currently doing a dump bed and am at the point of the pivot hinges and next will be the scissor hoist. These are the key pieces for the dump to work / handle a load. Also I need to build a gantry hoist, which will use a 3 ton chain hoist. I want it to be 10' wide and have an adjustable height for 10', 12' and 14'. I know what to use for the 10' wide Ibeam (found what other 3T/10' wide hoists use), but not sure what to use for the legs.How do you guys when designing stuff know that it will handle the required load?
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Reply:I use on line charts, or copy the design of a manufacture. But sometimes there is just no way around it, you have to hire an engineer.Dont pay any attention to meIm just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Most of this is covered in most basic structures classes. Engineers have a variety of formulas and calculations that tell them if a given member will carry a given load. They take those calculations and refer to tables that will tell them which member will be suitable for the task at hand.Basic formula for a beam in bending would be M=(Pl)/4 where M is the maximum moment, P is the load in Kips, and l is the length of the beam in feet. You take M and look on a chart for the beam that meats this minimum number for the length you have.Legs would be a bit trickier. You would have a given load applied to the legs. You have to determine for each length whether the leg is stiff enough to resist buckling for the diameter of the section and the wall thickness. It's been way too many years since I had to do those calcs, and most of the ones I did were on straight not angled columns. The angle will complicate the matter as there is both a vertical as well as a lateral load to consider in buckling.There are also some computer programs that will do the math for you, but most are not cheap..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:In the UK we can get a company that can do a load test for you and provide you with a safety certificate for that design with the maximum safe working load.They will testRunway Beam TestingLift Shaft Beam TestingSupport Steelwork TestingSWL alterations and re-markingEyebolt Load TestingLifting Equipment Test and InspectionDestructive and Non-Destructive testingDedicated Inspection regimes, DataBase ReportingSafety Equipment Inspection and MarkingLoad TestingSWL Testing (Safe Working Load)Compression Testing of Hydraulic EquipmentTensile Testing of Lifting EquipmentTesting on-site using calibrated Test weightsDeflection TestingStatic Load TestingDynamic Load TestingSo basically if i need to come up with something, i try and see how its been made before or try and copy an idea and get a feel for the type of material, weigh, and supports i need.Then i would contact the company who would then collect the item for testing, Once you have the certificate of testing you can add the safety plate with the SWL rating on the item.I'm sure you have companies like this in the UShttp://www.trentlifting.co.uk/proof-load-testing.html
Reply:Look for "Strength of Materials" by J.P. Den Hartog.Full of all kinds of good info. Formula on figuring out just what you are looking for. Warning!! You should brush up on your math before reading this book. I still have a headache and only got to the 2nd chapter.....From the desk of Kevin CaronTrying to be the best me I can!www.kevincaron.comAHP Alpha Tig 200x MillerMatic 251Miller Syncrowave 200
Reply:Engineer ? seriously ? I work with Engineer and draftmen at work, we do large institutional and commercial steel project for building where a LOT of people are working, shopping and living in those buildings, i know how serious construction can be.But here we don't even know what't the deal with that dump bed, is it a dump bed that will carry heavy stones on the highway where thousands of people will share the road with this dump bed ?Or is it more like a lawn mower tractor trailer dump bed to move stuff arround the yard ?I think 1st you own logic will be a big part of this project!I grew up on a farm, and i saw hundreds of those farmer fabricating for themself stuff like logs trailer, tractor bucket, VTT trailers and never saw those things failed!I don't say that is stupid to ask an engineer, but before recommand an engineer ask for some drawing or hand sketch up, and ask to the guy what he'll be doing with this dump bed! Its like goind to the hospital for a broken nails. Attached ImagesLast edited by LayoutMan; 11-23-2012 at 11:21 PM.Calculator > Bevel Square
Reply:I get the impression that the item in question is going to be a DIY project due to the cost......if it fails and someone gets hurt, you'll end up being taken to the cleaners.......where's the savings then?Get an engineer designed plan and then get it made and tested etc.....approval and certificates of worthiness make more impression on a court when blame is being aportioned.BTW, your welding and fabrication credentials will also be called into question if it fails etc, especially if you go "cheap" on the materials or plan details.Ian.
Reply:Go to the truck lot and look at a truck with a dump bed on it. After so many years doing the same thing you pretty much just know how much weight something can handle by looking at it.Just remember to build it 1.5 times as strong as you intend and it should be tested the same.
Reply:LayoutMan, VPT, It's good to see that the belief of using common sense still exists. I've repaired more things in the last few years that have broken where they shouldn't have and a lot of them failed because they engineered the strength out of them in the name of cost saving and increased production.I work on farm machinery a lot and all you have to do is look at a lot of the things that are made today and a comparable model made a few years earlier.Trailblazer 302Hobart Stickmate AC/DCLincoln SP 135 TSmith torchSpoolmatic 30A
Reply:The dump bed is for a 1 ton dually truck.For the pivot I have 3x2x3/16 rectangular. One piece sits on top of the other. The top piece has a piece of pipe welded into it and the pin that will go in it is solid 1 3/8. Brackets now need to be made and welded to the bottom piece so the top piece will pivot up and down on the pin.I've attached 2 pics. One of the truck that doesn't show the top piece sitting on the bottom and a close up of what the top and bottom pieces will be like. Attached ImagesLast edited by diablo_svr; 11-24-2012 at 01:39 PM.
Reply:Mostly experience. Through lives experiences you'll remember stuff like, "That shop down the road has an gantry, maybe I'll go look at it", or "That trailer place down the road has dump trailers, there's a place to start". There is also the experiences that you catalog in the back of your mind when you see something that you may use in the future or peaks your interests. The latter is not recommended for life & limb builds.Millermatic 200Hobart Handler 120Victor O/A & Ramco BandsawLincoln 225 ACSnapOn AD HoodMiller XMT304/22AHypertherm Powermax 1650 G3Lincoln Idealarc DC600 w/Extreme 12 VSMiller Digital Elite "Joker"
Reply:Found some plans for an adjustable height 2 ton gantry crane. Think I will just get them. I realistically don't think I need more than the ability for 1-1.5. So far the most I have ever need to lift was about 1400 lbs.
Reply:Originally Posted by diablo_svrFound some plans for an adjustable height 2 ton gantry crane.
Reply:The comments I usually receive when I build something go along the lines of, "You obviously don't want it to break". I'm a worrier so I over engineer, but you do need a good mechanical mind too. I'm just about feeling the compression and tensile pulls of various parts of a fabrication. If you haven't got that then get someone to design it for you. There's other considerations too like where you weld (I still have a lot to learn in this area). Example I manufactured a weld on rigid grab for my little excavator. It's a big no no to weld across the stick, one guy did this and his stick snapped in two where he'd welded across. I welded mine lengthways at the edges of the box section. Some would have deep Vs on each end of a weld on grab so that the weld doesn't go straight across.As a layperson my general advice is build it so it's overkill or get someone with the knowledge to do the design. Then of course a chain is only as strong as its weakest link so the welds themselves are a big factor.
Reply:You guys should see the "device" I use to lift up my Welding Machines on to the back of my Welding Truck! HAHAHA., By no means in that thing professional - When I would lift up my 46' sae300, and - As a matter of Fact, I'll show the thing in action! That thing bows out and - wow! It can handle 3000 pounds with ease, but it is sketchy, sketchy - It was a 5 minute thing I slapped together and worked so well I never made new. Attached ImagesLast edited by Thorton; 11-24-2012 at 10:17 PM.46 sae30047 sa200 w/Wisconsin VF451 shorthood56 shorthood56 shorthood68 redface69 redface07 ranger 305G13 sae300Inconel/Hastelloy SS Duplex Chrome/Carbon Tig F3Downhand STT/RMD F3F4 B Pressure
Reply:try this for ideas...http://weldingweb.com/vbb/showthread.php?t=33239Page 1 has a good pic of the pivot on my dump trailer. There's a few pics of the scissor on page 3 and 4 I think.My name's not Jim....
Reply:Originally Posted by Boostinjdmtry this for ideas...http://weldingweb.com/vbb/showthread.php?t=33239Page 1 has a good pic of the pivot on my dump trailer. There's a few pics of the scissor on page 3 and 4 I think.
Reply:Mostly experience and failure. There are many loads that can't be engineered in my opinion. So I study other similar builds, and take the best ideas and reverse engineer most projects. Marinas for example, who knows when a 100 mph wind is going to hit, when a 6' wave hits at the same time a inexperienced boat slams into it? On your dump bed, you will dump an uneven load on a side angle all while driving forward. Your frame will have loads you just can't turn into numbers, in my opinion. Look around at what has worked for other projects. If you want simple beam deflection and strength answers A I phone has apps for that, but my gut feeling is what chooses the size or shape. I have had many design failures, especially on marinas, learn from them, move on.
Reply:Most engineers I have worked with don't really know steel shapes and capabilities. They don't understand some shapes are flexible and some are rigid. You get many over enginnered designs that are simply overbuild and wasted materials. You know you hit it right when you see people coming over to copy your design
Reply:Originally Posted by diablo_svrVery cool. What did you make the pivot brackets and scissor out of?
Reply:Originally Posted by blackbartMost engineers I have worked with don't really know steel shapes and capabilities. They don't understand some shapes are flexible and some are rigid. You get many over enginnered designs that are simply overbuild and wasted materials. You know you hit it right when you see people coming over to copy your design
Reply:Originally Posted by BoostinjdmPivot brackets are 3/8" with DOM bushings. I think I used a 1-1/8" pin.The scissor is either 10 or 11 gauge all boxed in with DOM bushings welded in.I've dumped loads weighing a little over 5K lbs with out any issues.I've dumped on slight side hills and the box didn't flex over at all.
Reply:This is my current gantry cane. So you can see why I want to build one. Attached Images |
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发表于 2021-8-31 23:40:28