Steel Sphere Which Is Easy to Make With the Help of Some Cement

I saw photos of spheres made out of scrap metal on the internet, but for quite some time I had no idea how I could make one myself.
I needed something in the shape of a sphere to hold all the steel parts in place while I would weld all pieces together. The material had to be strong and it should not melt or burn during welding. Fortunately, cement can do that.

Cement - just a small amount
Old towel
Large ball
Scrap metal - at least 150 pieces of 2x2 inch

I wanted to make a kind of bowl out of cement, so I could use it to support all my metal pieces during welding.
To get the correct shape, I used a large ball. I wrapped it in some plastic so the cement would not get the ball dirty. Then I used scissors to cut an old towel and get approximately the shape of a circle.

I used Portland cement, which is not yet mixed so I had to add sand and mix it. The amounts shown on the photo are the actual amounts that I used. The amount of sand is roughly twice as much as the amount of cement. I added the water from the bottle and mixed cement, sand and water in the bucket. The mixture should be quite wet.

I put the round piece of towel in the bucket with cement and made sure the towel was completely soaked with cement. Then I placed the towel on the ball so it can take the shape of the ball while it cures.

Portland cement takes quite long to cure. I let it sit on the ball for three days and then I carefully placed the ball upside down so the cement was at the bottom side and I removed the ball. That was easy because the plastic did not stick the the ball. Then I also removed the plastic and let the cement dry further for another 5 days.

If I would have used a quick drying type of cement, this step would have been faster but I was not in a hurry and since I only had the Portland cement I used that.

I used 3 meters (9 feet) of square tube of 5x5 cm (2x2 inch) and marked it at increments of 2 cm. Then I used an angle grinder to cut the tube into 150 pieces. It took 9 cutting disks to make all these cuts.

After cutting I had to clean the area from all the debris that was formed during cutting. Then I used a file to clean the inside of each of the 150 steel squares.

The cement had cured but it felt a bit brittle, so I made a pile of sand with a dent in the middle and placed the concrete on top. Then I placed the first few steel squares in the concrete bowl. The ground clamp of the welding machine was attached to a loose square part which works well to get a good ground during welding without hindering me.

I welded the squares at the point where they touched each other, then added a few more squares, welded them and continued adding squares. When the metal started to become larger than the concrete bowl, I rotated the metal so I always had the support of the concrete for the loose pieces during welding.

I continued to add more and more squares to the sphere until I had used all. I could have cut some more squares to get an entire sphere, but I decided that it is no problem that the sphere has an opening at the bottom side.

The concrete now has some brown areas which is dirt from the welding. The concrete also has cracked a bit but it still had the right shape and could theoretically be used once more.

I experimented a bit with how to place the sphere and took some photos during different moments of the day. I like it best with the open side facing downwards.

Since I did not paint the steel it will turn brown from corrosion very soon, but I like that.