Comparing Designs for a Small Gantry Crane
In reviewing the options for building or buying a small gantry crane (2-ton capacity), two designs for the uprights seem especially common. The basic shapes are an inverted "T" and an inverted "Y". In most cases, the basic shapes are supplemented with bracing.
I'm wondering if there are any significant advantages or disadvantages to either of these designs, especially in terms of stability and strength.
Rough dimensions are 10 feet long and 8 feet tall. Assume similar materials, size of beams, and quality of welds.
I like my upright "As". Easy, sturdy. I supplement these with diagonal braces to near center of beam, on spreaders at top so chainfall can pass.
Yellow gantry in photo on left.
Thanks, John. The "A" design seems to be another popular one, and as you say, it's easy and sturdy. I've added it to my short list.
There will be significant differences between the T design and the rest. but the rest, not so much difference between them. The T design is going to be the worst for a moment but the best for a purely vertical load, if you asume equal joint strength in all
Thanks. Forgive my lack of engineering background, but when you say 'worst for a moment', do you mean the T design will have more of a tendency to tip if the load is not purely vertical?
I built mine about 1979 and it has proved to work very well. It is the inverted T shape of square steel tubing with generous triangular plate gussets welded at the base intersections. The advantage over the Y-shape is that it made it easy to weld pads at the four corners to carry large iron-wheeled casters. Mobility is a very valuable feature for a gantry.
I also made the columns with inner tubing that telescopes for height adjustment. There are built-in winches on both columns to raise and lower the I-beam. I can roll the gantry in and out of the garage and then raise the beam for loading a mill or surface grinder to or from the truck. Adjustment is quick, but there cannot be a load on the hoist while adjusting.
It is hard to make an A-frame with adjustable height, though I think I have seen a commercial product (Wallace?) made that way. Actually adjusting the height is difficult.
I also have found that electric hoists like Budget are very heavy, so not suitable for a mobile gantry.. Aro air hoists, Little Mule electric hoists and manual chain hoists are light and easy to lift up to hook them into the trolley.
The moment comment is relevant when using the gantry an a slope. With the I-beam across the slope, the gantry will tend to tip and the legs of a T-type will have more bending stress than when the gantry is on a level surface.
Thanks, Larry - very helpful info.
I've been on the fence about making the height adjustable — it adds some complexity, but I'm certain it could be very useful at times.
How difficult was it to get tubing that would telescope? Were the weld seams on the inside of the outer tube a problem? For example, will 3.5 x 3.5 x .25 tube fit inside 4.0 x 4.0 x .25, or is that cutting it too close?
I'm only expecting to use a chain hoist, so the weight of the hoist will not be an issue.
I bought my tubing, plate and I-beam at a scrap yard, picking material that looked like it would work. It did. I found the two sizes of tubing that would telescope by trying out what they had on hand. They have some clearance. I have forgotten what I calculated for capacity, but my hoist is 1 ton and and my biggest machine is about 1400 pounds, so I never had a problem.
I will also mention that the I-beam is carried on bolted clamps at the top of the columns. The width is adjustable and the beam can be taken off the legs for transport. I can lift each leg and one end of the beam so I can take it apart and put it back together myself.
I did the braced inverted T here and made it all so that I can assemble and disassemble it all by myself. Having the pieces made so that they can balance themselves helps with that, and simplicity
My gantry is an upright A style. I chose that style as I felt it would be more stable when pushing it while loaded, sometimes on a floor that leaves a little to be desired.
For those of you who think powered hoists are to heavy, don't forget to add the live load caused by pulling on that manual chain hoist.
I copied the Wallace adjustable design when I built mine, as I have had it in various different locations with different ceiling heights, I have found the ability to change the height very useful.
This seems to work best with a hybrid of "A" and the Inverted "Y" design.
Thanks, gbent and Ries. The hybrid A-Y is an interesting approach.
Unless I'm mis-reading the scale of Ries' gantry, it appears to be more readily portable than many. Is that true?
What kind of weight will it support?
Factory made 1 to 3 ton gantrys we used at work were all the braced inverted y style with the center square tube a slip fit on the upright post. A spring loaded pin adjusted the heighth with a hole drilled about every 6" in post. A cable come along was used to adjust heighth on each end. Pay particular attention to the post to beam connection as that is a weak point when pushing from the end. You may not need all this flexibility. Ours were moved often from job to job.
The inverted "T" with triangulated bracing design is strong and stable.
I used this design instead of the classic "A" design (like John Oder's)
because my beam height on the poles is adjustable.
Note I used 4 casters on each "T" that makes them very stable.
Easy to roll them around when they are broken down too.
Thanks Doozer. Good idea about the quad casters.
I made an inverted T with braces. The base spreader on mine is flange-up channel, which gives me a place to store chains, eyebolts, and shackles. My casters were discontinued by Grainger, which cut their cost to less than 50% of original price. Both my legs bolt to the top I beam so the crane can be dismantled for moving. Be sure you can stop the crane from moving when you want it to stay in one place - my casters came with brakes that don't really stop it from moving. My "tomorrow" list includes welding up some screw type supports that I can run down when I want it to stay where it is.
My crane is fixed height -- 2" under the fluorescent lights in the shop. I've used adjustable height cranes in the past, and I usually used a forklift to adjust them. I prefer the increased rigidity of a fixed-height crane.
I located a 1/2 ton ARO air hoist on Craig's list for $ 75 that is all I usually use, but I have manual hoists that I can hang when I need the capacity - the crane usually lives stradling my welding table, and I don't need more than 1/2 ton capacity very often. When I do, I can hang one or two hoists directly from the I beam.
Mine is only a 1 ton design. 4" square tube, with a 3 1/2" slip fit inside for the adjustable height.
Mine does disassemble into two ends and a beam, and I have even taken it in the truck to buy a lathe, set it up in the former owners driveway, and loaded my truck, then taken it apart. I do not have diagonal bracing for it, as its only 1 ton and mostly used for lesser loads, but for a two ton I would definitely add removable bolt on diagonal braces from the upright to the load beam at each end.
I think the difference here (as far as bracing) is in the usage as well.
Originally Posted by Ries
When Reis lifted the machine to load a trailer, he probably just lifted it, no movement of any kind, and then
backed the trailer under the load, then set it down.
Using these "a" frames to roll around a load needs more bracing.
If you ever have a chance, observe the casters how they jiggle, when a full loaded gantry
is rolled about, especially on a rough floor.
For what it is worth...
See in my pic, that I lifted the machines and rolled the gantry loaded with each machine
and placed them on the bed of my 28' trailer. I had another person to help me, and we
each rolled one side to keep things even. It felt really stable, maybe a tribute to my many
casters. Also a flat concrete driveway was a good thing there also. Those are actually
"V" groove caster wheels. I figured I could run them on 1/2" pipe or angle iron, but it
really rolled well on the concrete. Biggest machine was 3500 lbs. The casters are 6"
Albion casters bought from McMaster Carr.
I also used the inverted T design, mainly because it was easy to size and build with adjustable height.