Shop Projects

Introduction

In this post we are talking about the design of a DIY gantry crane. We will cover some of the basic design concepts and the CAD drawings for the crane itself.

I covered how the beam was selected in a previous post, so you might want to read that first.

Finding The Right Beam For Your Project

Design Goals

As with any project, it is important to define your goals. If you are unsure of your goals, you can define goals and thresholds. The goal is what you want to achieve and the threshold is what you’ll accept. For this project, I didn’t list any thresholds, because I needed the crane to support the designed weight.

Goals:

• Lift capacity of three metric tons (3000 kg) or 6600 lbs.
• Cheaper than buying one ($2500 – $5000)
• Adjustable height, up to 12 ft
• Wide enough to fit a semi trailer underneath.
• Mobile
• Can be dissembled.
• Future upgrades.

What Is A Gantry Crane?

A gantry crane is a type of crane that has its own support structure and therefore is freestanding. A gantry crane does not rely on a building or expensive foundation to work. Although, heavy duty gantry cranes do need special preparations for the surface on which they operate.

The gantry crane utilizes two uprights at each end of the main beam, which is the load lifting structure. The main beam usually has a trolley that can move the load back and forth between the two supports. In most cases, the entire gantry crane can be moved back and forth, or in any direction depending on the wheel setup.

Gantry cranes come in many sizes. The crane in the image above is a Mazzella 30 ton, capable of lifting 60,000 lbs. Many home shop gantry cranes are in the one to two ton size.

My Design

The design of my crane does a fairly good job of achieving the goals that I put in place. Some of the goals will come with upgrades over time. Right now, I need to get the crane operational as soon as possible, so I will defer some of the more difficult build items for now.

Dimensions

The most important dimension (for me), and the one that most other consumer grade gantry cranes fall short on, is the distance between the uprights. Why is this important? The gantry crane can lift heavy objects. Things that would come on a semi truck or even a large trailer. In order for the crane to be able to lift that load, the trailer and the load has to fit under it.

A standard semi trailer in the U.S. is 102 inches wide (8.5 ft). The distance between the wheels of my crane was set to 114 inches (9.5 ft). That would give me a clearance of 6 inches on either side of a semi trailer. In between the vertical posts of the crane is 124 inches (10.33 ft), which should give plenty of clearance between any tie-down points on the side of the trailer.

Height is also a consideration when dealing with a semi trailer. Semi trailer decks are 5 ft off the ground. Meaning that the the crane would need to be much higher to lift a load of considerable size off the deck. Unfortunately, I couldn’t get my crane to be more than 12 feet off the ground so, I will be limited on the height of object I can unload, but is should still be substantial.

Main Beam

For the main beam, I decided on a wide flange beam. A wide flange beam has flanges (top and bottom of the beam) that are flat, not angled like a traditional I-beam. Wide flange beams, like I-beams, come in a size and a weight. For example, the wide flange beam that I had originally decided on was a W10x12. The “W” is the designation for a wide flange beam. The “10” indicates that the beam is 10 inches tall, and the “12” means that the beam weighs 12 lbs per linear foot.

Unfortunately, when I went to purchase this particular beam, it was not available. Fortunately, I do know how to do math, so I was able to run the number to get another beam that was suitable. In this case, I went down to a W8x15, which is a slightly shorter, but heavier beam. I knew that a W8x13 would work, but the deflection under load was too much for me. The deflection of the W8x15 beam is only slightly higher than the W10x12.

Telescoping Uprights

To make the gantry crane adjustable in height, I needed to make the uprights telescoping. Telescoping tubes that are pre-made are very expensive. But one can make their own telescoping tubes by being intentional with the purchase of the correct size and thickness of the materials.

In my case, I went with a 4″ square tube that was 3/16″ thick as my outer tube. The four inches is the outside dimension and the thickness takes away from the inside dimension. This gave me an inside dimension of 3-5/8″ square. For the inner tube, I used a 3-1/2″ square tube that was 1/4″ thick. That left 1/8″ between the inside and outside tubes. That is more slop than I like for such an application, so I will have to weld some 1/16″ flat plate to at least one side in each axis to take up some of the slack.

If you’ve never worked with steel tubes like this, but you know how to do math, I already know what you’re thinking. If I just got the 4″ tube in 1/4″ thickness, that would be a perfect 3-1/2″ for the other tube to slide in. Unfortunately, these tubes are manufactured by bending the steel into shape and welding the ends together along the length of the tube, leaving a small, but distinct bump down the inside of the tube. This bump gives so many craftsmen nightmares. While you may be able to file down the bump a few inches in, if you have tube several feet long, there is no practical way to get rid of the bump.

Legs and Feet

For the types of gantry cranes that people have in their home workshop, there are two main designs for the legs and feet. The first is just an A-frame with wheels on each end. The second is an tee design where the vertical post intersects a ground beam that runs parallel to the ground. The wheels are attached to the ground beam. Most cranes of this design also have diagonal bracing between the ground beam and the vertical post.

For my design, I went with the A-frame because it uses less metal than the ground beam design, and offers more flexibility when moving it around a cluttered shop. Where I differ in my design is with the wheels. I didn’t want to attach a single wheel to each leg. If I disassembled the crane for any reason, the vertical uprights would not be able to stand on their own. So I added a small cross beam at the bottom of the legs and put two wheels on each cross beam.

Height Adjustments

To adjust the height of the main beam, I will utilize two boat winches, one for each vertical upright. Unfortunately, modeling this idea in Fusion is time consuming, so I have not shown this. In the image below is the rest of the components of the system, including the lifting rod, shackle, and the retaining pin. I turned on component colors to help you see the pieces a little better.

The yellow component is the lifting rod and will push on the underside of the top plate, where the main beam will attach. At the bottom of the lifting rod is the shackle. The winch hook will attach to the shackle and then go up and over a pulley (not shown) at the top of the vertical frame (dark purple) and then back down to the winch (not shown). The green component is the retaining pin, which will be one inch in diameter. The holes in the telescoping vertical component (light purple) are 6 inches apart, giving me half foot increments of adjustment.

Other Components

As much as I like to design and build things, I can’t do everything. So I will purchase the main lifting components of the system. I will purchase a 3 ton trolley, which will attach to the main beam. Attached to the trolley will be the chain hoist, which will be used to raise and lower the load. And finally, the lifting straps and other rigging hardware will be purchased items as well.

Current Design

Future Improvements

Above is the basic mechanical design to get the crane operational. However, this will not be the final design. Some future upgrades may include an electrical system to motorize the lifting of the main beam. Also, potential motorization of the trolley and lifting hoist. But the bigger potential upgrade is to install a method to lift the entire crane and load it on a trailer. I buy heavy equipment to fix and sell, and sometimes there is no assistance in loading the equipment on a trailer. It would be nice to take my crane with me, to load the trailer. I’m not sure how I’ll accomplish this one yet, but I’ll figure it out!

Thank You

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