Bring It All Together

Introduction

In this post, I will cover the assembly of the DIY gantry crane. I will go through the steps of my build and some of the items that I had to redo or defer to a later date. As always, if you haven’t read the previous posts pertaining to the DIY gantry crane it would be a good idea to read those first to be up to speed.

Finding The Right Beam For Your Project
DIY Gantry Crane – Design
DIY Gantry Crane – Height Adjustment
DIY Gantry Crane – Prepare for Construction

Disclaimer: When I am working on a build, I rarely stop to take pictures of what I am doing. I’m trying to get better at this, but for now, just know that many of the pictures you see are taken after the fact.

Foundation

It is clear to see by any gantry crane design that the beam is the central focus of the build. But it is not the foundation. The strength of your beam relies solely on the supports holding it up.

Drilling and Tapping

The first step in the build, after cutting the pieces to the desired length and shape was to prepare those parts for assembly. The only thing I had to do prior to welding, other than cleaning the areas to be welded, was to drill and tap the holes for the wheel bolts. I chose to just drill and tap the beam itself as opposed to trying to weld nuts inside the beam.

This method can be tricky if the thickness of the material you are tapping into is not sufficient. I prefer to do this with 1/4″ thick material, but 3/16″ is just thick enough to take a thread. Plus, the forces pulling on these bolts will be negligible so I feel comfortable with this approach.

For your wheels, you may choose different wheels than mine. I would only use these wheels if I were working on smooth concrete. It doesn’t take much debris to stop the wheels from turning. Other than that, I would choose a more rugged all-terrain style wheel. Regardless of you wheel option, if you plan on putting two wheels next to each other as in my design, make sure you make your mounting points sufficiently wide enough so the wheels can’t hit together as they pivot.

Main Structure

Alignment.

I do wish I had pictures of the steps I took to make sure my frames were not only square and level on their own, but also square and level with each other. For this to work effectively, the holes where the retaining pins are had to be at the same level. The wheel base of each upright had to be the same, and neither post could lean inward or outward by any margin.

In order to assure the two parts were identical, I tacked the diagonals of one support in place and then I laid the parts of the other support directly on top of it. I made sure the holes I had drilled for the retaining pins were lined up, that the diagonal supports hit at the right place and that everything was at the right angle. Then I tacked those parts together. I flipped everything over and repeated. Every time I placed a tack, I measured again to make sure no adjustments needed to be made.

Welding

Only when I am confident that everything is as close to perfect as I could get, then I would weld. If you’ve never welded before, or never welded long welds on tubing, there are a few things you should know.

First, put lots of tacks to help keep things from moving. Make sure you put your welding tacks on all sides of the tube. Heat can make metal move quite a bit. Second, if you are making long welds, alternate sides. As a weld cools it tends to pull the metal in, causing it to cup on the side of the weld. Welding a pass on one side and then welding a pass on the opposite side, helps reduce this effect.

Welding Tubing

Lastly, and it’s not a big problem if the tube is big enough, but if you are completely welding a tube shut, you need to be careful. If you weld a tube too quickly, you’ll cause the air inside the tube to expand rapidly. This can do two things. One, it could pressurize the air inside the tube, which can cause problems with your welds. Another problem is if the tube is made of thin metal, and you seal it up when it’s hot, it creates a vacuum inside as it cools. That could cause thinner metals to collapse inward if the vacuum is sufficient.

There are a couple ways to combat this. One is to drill a small hole into the tube to vent the hot gases while you weld. Then when wait until the pipe cools and weld up the small hole. The second way is similar but doesn’t require drilling a hole. If I am welding square tubing, I weld three of the four sides on one end and all four sides on the other end. Then I let the pipe cool before I make the last weld. Pipes with large internal volumes and thick walls generally don’t have many problems, but this is a good habit to get into when welding tubing.

Telescoping Uprights

With the main frames completed and standing on their own (advantages to using four wheels instead of two), I could concentrate on the tubing that goes inside the main frame. This tube will extend up and provide the main support for the beam.

Alignment

Again, with the these posts, the alignment is the key to success. This time we need to make sure that the multiple holes that are drilled to accept the retaining pin are aligned both front and back and between the two posts. I spent several hours with the two posts lined up next to each other on saw horses, measuring and marking hole locations.

I didn’t have a drill that could drill straight through the tube to make both holes. Instead, I had to drill one side, flip it over and drill the other side. A total of 40 holes needed to be drilled between the two tubes and they had to line up perfectly. I couldn’t have done it without that mag drill! This is also where taking the time to measure carefully and mark precisely pays off. A metal scribe marks a more precise mark than a fat Sharpie. Aim small miss small. Once you have the mark, use a punch to make a dimple so you can line up the drill.

This tube doesn’t fit perfectly inside the 4″ tube. There is a little too much wiggle room. So I cut thin strips of sheet metal and tacked them onto the the sides of the tube to help take out some of that wiggle room. I only did the bottom 24 inches because that’s the length of sheet metal that I had. I just needed enough to keep the tube relatively centered in the 4″ tube.

Finishing The Part

To close out the telescoping tubes, I welded the diagonal brace and the 1/4″ top plate to the top of the tube. This will serve as the mounting point for the beam. The top plate already had holes drilled in it to match the mounting points on the beams. This is another area where alignment is key. If your top plate is crooked on one of your posts, that post will have to be crooked to line up with the beam. Also, make sure you weld your diagonal on the correct side of the beam. It needs to be perpendicular to the holes. Slow down and take your time when doing these assemblies. Do it right!

Assemble The Posts

I found it easier to lean the top of the main frame of the post down on a saw horse so that I could slide the telescoping tube down in it with less trouble. The telescoping tube, despite all the holes, is still quite heavy. Once the tube is in place, you need to retain it with your retaining pin.

Retaining Pin

Since I decided on a single pin for each side, I made my retaining pin out of 1 inch diameter 1045 steel. I tapered one end to help find the hole, and I welded a tube to the other end, and knurled it to at as a grip. I do need to drill a hole in the grip to put a lanyard on the pin so that it can’t be dropped and roll off while I’m trying to change heights.

Height Adjustment Mechanism.

I already have an entire post dedicated to this topic. DIY Gantry Crane – Height Adjustment. I encourage you to go read it as I am not going to repeat everything. At the end of that post, I highlighted a problem that at the time of that writing I had yet to solve. It turned out that I actually had two problems that were conspiring together, and neither one was what I thought it was.

The first problem was that the pulley used for the lifting cable just wasn’t big enough. Between the two pulleys it had the load capacity, but the diameter was very small. That made the force much more concentrated and caused one of the pulleys to not turn much at all. Instead the wire rope skid across it’s surface creating a lot of friction. So to solve this problem, I cut of the old pulley and designed a new mount for a much bigger pulley.

Better Components

This time, instead of using a small 420 lb pulley with a 1″ diameter on each side, I went with two 20,000 lb pulleys that were 8 inches in diameter. Yes, they are a bit of overkill, but there weren’t any pulleys available in my area in between these two sizes. To be fair, the 20,000 lb pulley is not intended to be used quite like this, but it does work. I used a snatch block (common in towing and recovery) as my pulley.

The snatch block is made to where the two plates on either side of the pulley twist to open up. This makes it easier to add or remove a snatch block to a cable or rope. Great for towing and recovery work, not so great to use it as a permanent pulley. I had to spend some time thinking about how I would attach this to the crane and keep both halves together. The hole is just too big to put a simple bolt through.

To solve this problem, I made a hook out of 1/2″ steel that was just wide enough that the two plates of the snatch block could sit down in it. This became both my mount for the pulley and my lock to keep the block together. I elected not to put some sort of retention on the top of the hook because the tension on the cable pulling down is enough to keep it in place. I have to let out a lot of cable to get the block out of the hook.

A Problem Still Remains

One of the features I wanted in this lifting mechanism was a way to lift both sides at the same time. I made a rod to extend between the two winches to synchronize their motions. When I tried it, it didn’t work. I thought that was because of the pulley issue, but it still seems to have trouble. Upon further inspection, I found that the bracket and the cranking shaft of the winch are flexing enough to cause things to bind.

Unfortunately, to fix this, I may have to remake the bracket assembly, which will take some time. For now, I just move back and forth between the posts to raise them a little at a time. Lifting and lowering the crane is not something I do a lot so it’s a minor inconvenience.

The Final Piece

Last but not least, I had to assemble the final piece of the puzzle. The beam. My crane is wider than most consumer-grade cranes. My beam is 136.5″ long and the opening for my barn doors are 137 inches, leaving me just 1/4″ on each side of the beam when trying to drive it though the opening with the tractor.

With the posts set at their lowest settings and the beam sitting on top of some 6×6’s on my tractor’s pallet fork, I was able to get it up high enough to set it on top of the two posts. With a little wiggling, we were able to get all the bolts in place and everything was straight!

How Much Did It Cost?

This is probably the most asked question when tackling a project like this. How much did it cost to build it yourself, and could you have purchased one cheaper? I’ve looked for 3 ton gantry cranes that are wide enough to fit a semi under them, and they are hard to find. The ones you can find are very expensive. Here are a few that meet my criteria with similar width, and height adjustment range compared to mine. I’ve linked to their respective sites so you can visually compare.

3 Ton Adjustable Height Aluminum Gantry Crane = $13,349.29
3 Ton Adjustable Height Steel Gantry Crane = $4,105.00
3 Ton Adjustable Height Steel Gantry Crane = $3,449.00
3 Ton Adjustable Height Steel Gantry Crane = $9,782.20

Another item that I have been able to make out of the leftover steel I purchased for the gantry crane is a load spreader.

3 Ton 4ft Long Load Spreader = $1660.99
3 Ton Adjustable Lifting Beam/Spreader = $1996.59
3 Ton Adjustable Lifting Beam = $2966.29

If I were to take the cheapest option of the cranes and the cheapest option of the load spreaders, I would have spent $5109.99 before taxes and shipping. Below are the items I purchased to build my gantry crane and load spreader. I lumped the steel and the fasteners in one category so I didn’t have to list each one with their quantities. If you need a list, let me know. The fasteners were all purchased at Home Depot.

Material	Qty	Price (each)	Link
Steel/Fasteners		$1374.97	Steel Supplier/Home Depot
1200 lb Winch	2	$41.59	Amazon
3 Ton Trolley	1	$105.00	Amazon
3 Ton Hoist	1	$79.90	Amazon
6″ Casters (4 Pk)	2	$121.98	Amazon
1/2″ Shackle	2	$5.99	Harbor Freight
Snatch Block	2	$29.99	Harbor Freight

The total for the gantry crane and the load spreader came out to $1958.97. Compared to buying a gantry crane and load spreader, I saved $3,151.02. These numbers are before taxes and shipping are figured in. All of my items came with free shipping (including the steel) or a run to the store.

Thank You

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