On Round Tower Techniques . . The Quest for the Round Tower
In 2008, I challenged myself to devise a method for creating round towers that could supplant the current methods. After one epiphany and a couple years of procrastination, Deborah Higdon beat me to the punch. But after the number of adherents to her technique started to grow, I was inspired to build again.
Of course, in order for my techniques to catch on, first I have to show people how they are done. So while I wait for a Bricklink order so that I can continue to work on my tower roofs, I'm documenting my technique.
The Wizard's Tower
The Wizard's Tower shows off some of the features that can be accomplished with this design. One of the large goals was to provide access to interior spaces. Unfortunately, the Wizard's Tower is incomplete at the moment. The interiors on the lower part of the central tower are yet to be constructed, but I can at least show off the break-away wall sections allowing access to the interior.
The Basic Trick
The tower is made by taking long strips with 2x2 tiles attached and connecting them to a central core. There are three functional components: the core, the facade, and the filler. The core is just the inner ring of tank tread. The facade is the outer shell, usually just made of 2x2 tiles. The filler is everything in between. Exactly how the filler is constructed is less important than the distance between the core and the facade. More filler means bigger tower. Less filler means smaller tower.
The two above examples show two different sizes with different amounts of filler. For the sake of convenience, call the first example a "size 30 tower", and call the second example a "size 39 tower". The size 30 tower has a circumference of 30 tiles and the core is made of 30 pieces of tank tread. The gap between the core and the facade is filled by a technic beam and a plate, the equivalent of 3.5 plates. The size 39 tower has a circumference of 39 tiles and a core made of 39 pieces of tank tread. The gap between the core and the facade is filled by a technic beam and a brick, the equivalent of 5.5 plates.
I try to get by with as little tank tread as possible. For one thing, it leaves more room for an interior. For another, tank tread is expensive. I usually put a full ring of tank treads on the top and a full ring on the bottom of the tower, and use a just a strip of tank tread to patch up places that wouldn't hold together otherwise.
Cutting a single hole in the tower is straightforward, as long as you don't cut into the rings of tank tread. The large hole on the left stops just short of the top and bottom rings of tank tread. If the hole was far away from the bottom ring, the facade might splay outward and require some additional reinforcement to stay together. In the pictures below, the hole for the balcony is built similarly. The hole for the window is reinforced a bit by the fact that the window construction fits snugly into the hole, although I doubt the facade was at much risk of splaying outward.
To have one hole above another takes some planning. Here I have strips of tank tread holding together the stuff between the holes, as can be seen a few pictures back. To hide the tank tread, I had to make the holes at least 5 studs apart. There is some sagging here, but it's not too bad.
Tiles vs. Plates
Most of the time I use tiles for the facade, but I figured I could replace a tile with a plate with no problems, right? Wrong. Since a tile has that groove at the bottom, the plate needs just a bit more room. It's not much, but when you multiply it by 30, it can make a difference. I'm fairly certain this isn't a problem with the size 39 tower, but it was for the size 30 tower. On the top of the tower to the left you'll see that I alternate between plates and tiles. My original design was just plates, and if you look closely at some of the pictures here they show the old design. The original design didn't work; there wasn't enough room for the plates and as a consequence some of the plates were not firmly attached and kept falling off.
But now that we know this, maybe it could be used to our advantage. One possible issue with this whole method is that a size 30 tower's circumference is not exactly 30, a size 39's circumference is not exactly 39. For sizes 30 and 39, this hasn't been a big problem, but should we run into a tower where the fit is too loose, we might add plates in strategic places to tighten it up a little. The size 18 towers in the Wizard's Tower are loose enough for gaps to crop up; some plates may help to even out the spacing.
Let's talk a bit about geometry and why the above stuff works. Whenever two pieces of tank tread snap together, the angle between the two pieces has many possibilities. It's our job to limit these possibilities and get the angle to be more or less what we want it to be. The tiles on the facade force this angle to turn inwards. The facade on the size 30 tower forces the second tank tread to turn inwards by at least 12 degrees (approx). Now when the ring of tank tread is completed, these turns must add up to exactly 360 degrees. It's not too difficult to show that the last two statements imply that at each connection, the direction changes by 12 degrees (approx).
The facade makes the tank tread turn. The fact that we have a closed circuit keeps it from turning too far. This means that if we don't want a complete circuit we have to find another way to keep the tank tread from turning too far. The quick and dirty solution: a brace to hold the two ends of the wall apart.
The example pictured is based on the size 30 tower. The curvature of the example is almost the same as the curvature of the size 30 tower, but not quite. This is because the brace pushes the tiles together more tightly, and thus changes it just a bit. It's not severe enough to try to fix in this example, but is something to be aware of.
The most straight forward way to make smaller towers in to replace the tank tread we've been using with smaller tank tread, then adapt the techniques we've already seen. However, the small towers in the Wizard's Tower use the method I've already documented here. It's a terrible trick if you want to have an interior, but otherwise it's a cool little trick.
Ignore the roofs in the pictures here, I have since refined the design and documented it here. I'm still looking for something better, but for now this is what I've got.
Bricks and Cylinders
The most ubiquitous technique is the old brick and cylinder trick. There are two basic types, one with 1x2 bricks and one with 1x3 bricks. For example, this one and this one by Eggy Pop.
The most straightforward way to make a round wall is to build a straight wall out of 1x2 bricks and bend it into a circle. The bricks only bend so far, so this makes large diameter walls. The Wizard's Tower uses this trick for the outer walls. The smallest of these walls has a circumference of 96 bricks, but smaller (Eggy Pop again) circles are possible. How small you make the wall depends on how skittish you are about damaging bricks. For the serious enthusiast, check out www.brickbending.com
Deborah Higdon devised an interesting method which gives a look similar to my method. (The rest of her photostream is also worth checking out.) This technique has shown up at least twice, here by busboy489, and here by Jordan Schwartz.
Nannan Z has an awesome variation that he used on this creation. The technique is perfect for making a snot wall that is just two studs high. It is parts intensive, and I'm impressed by the number of pieces used in his MOC to build that tower.
Here bikicsmilan offers a method for creating small towers with also gives a look similar to my technique. I plan on playing with this myself sometime in the near future.
Other scattered examples
Here's a fun one by Nathan Todd.
Bruce N H brought this one (by Nyu) to my attention back when I first started experimenting with round towers.
More fun with tank tread, by TooMuchCaffeine.
I accidentally ran across this one by Derfel Cadarn.
Here's a cool one by Hinckley et. al. On page 2 there's a picture of the round part from the inside for you to suss out how it's done.