Gantry design ?

pineyfolks

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Waiting for it to warm up to start on a gantry crane for my shop , the I-beam I have is 10' long the overall height will be 9' 6". My question is how long do I have to make the base of the legs to be safe? Is 5' enough? I don't want to make them longer than I have to so it will be easy to get around in the shop. But I don't want a crash! Its going to be 1/2 ton cap.
 

Ray C

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Bill,

The dimensions are really based on how it's used. If you can give some idea on how you intend to use it, I can help with some basic guidelines. As always, they are guidelines and any gantry used beyond it's design parameters is a dangerous thing.


Ray

Waiting for it to warm up to start on a gantry crane for my shop , the I-beam I have is 10' long the overall height will be 9' 6". My question is how long do I have to make the base of the legs to be safe? Is 5' enough? I don't want to make them longer than I have to so it will be easy to get around in the shop. But I don't want a crash! Its going to be 1/2 ton cap.
 

pineyfolks

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Mosty I'll be using it to unload my truck , load and unload my machines and weld table, things that are just to heavy for one old guy. Its just my hobby shop . I'll be using a chain hoist and trolley. my upright post will be 5" OD 1/4" wall tubing with bracing to the casters forming a frame like the HF ones. The I beam was off a 1 ton jib crane.
 

Ray C

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level ground or slant on your driveway?
 

Uglydog

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I am in the same spot.
Have been thinking about a build summer 2013.
I've been looking at this link as a source for build information.

http://www.beacontechnology.com/gantrycranes/

Also, consider looking at the last edition of "Home Shop Machinist" they devoted an article to several considerations.

Remember this will be above your head, I hope you are a good welder.

Or are you going with bolts? If that's the case remember that each hole weakens the material. That's why riveted bridges, while once the standard, fell out of favor. The holes became a limiting factor.
 

Ray C

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If you stick to 1/2 ton on level ground and if the distance between the wheels is 5', you'll have some limitations. You'll need to lift the weight, drive the truck out, lower the weight as low as possible then, move the gantry. In other words, keep the weight low as much as possible while moving it. Of course, don't let it swing back/forth.

For gantries that are to be moved with the weight at higher elevations, you need considerably more leg length.

Now the other factors are the strengths of your connections and placement of the struts etc... Without knowing the materials, its hard to know how much twisting is going on.


Ray


Its level its going to be used inside.
 

pineyfolks

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Alot of good info there Uglydog. Thanks ,Fitting and Welding will be no problem but Thanks for the word of caution to those less experienced.
 

November X-ray

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I had a similar situation, and what I did, while only a level concrete floor, is use ratchet straps to tie the load to the outer bottom frame in a criss-cross fashion to keep the load from swinging with the load as low as possible. I would never try to move a load on a rough surface with a gantry crane.
 

Ray C

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Here's a gantry that was designed for dead lifts of my old diesel engine/generators that weighed up to 2 tons. I know the gantry can do more than that. It's 7.5' tall, 4 feet wide and has base legs 4'. I have used it for rolling things by putting wheels under it but, use very cautiously with the weight very low. The biggest problems you face are swaying of the weight and twist/stress on the struts. If something fails, it crumbles.

In physics, there's something called a free-body diagram where you draw the weights and supporting members and calculate the forces to determine the basic geometry. Then you need to calculate the forces on the welds and bolts. It's about ideal to have base legs that are about 2/3 (or more) of the maximum height. But when it comes right to it, the leg length really depends on how it's used.

Take a look at the gantry that Harbor Freight sells. The geometry is pretty good but due to component quality I don't think it's good for everyday, industrial use. Also keep in mind, it's almost certainly made of alloy steel and thus the seemingly thinner gauge metals.

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