What is a fireworks rack?
A fireworks rack, contains a given number of aerial mortar tubes (aka "guns") of a given size. The racks are constructed from wood. The mortars are typically constructed out of one of three materials, namely HDPE (High Density PolyEthylene), paper, or steel. HDPE becoming the most common. Racks can only contain paper or HDPE tubes. Steel tubes must be buried 2/3 of their length. HDPE is used instead of say PVC or ABS due to its special energy absorption properties. The energy from a tube detonation goes into expanding and splitting the HDPE material, in contrast to PVC which would splinter and fragment throwing shrapnel and therefore be unsafe to use unburied in a rack.
The number of tubes per rack depends on the size (diameter) of the gun. Each rack has only one size of tube. Here is a general rule of thumb for mortar racks:
Less than 3" diameter, 5 tubes per rack
3" or 4", 5 tubes per rack
5", 6", 8", 3 tubes per rack
10" or larger get put in individual barrels of sand
How do you organize mortar racks for a show?
Generally, when using racks, you have to go in increments of 5 or 3 shots of the same shell size since that's how the racks come. This must be taken into consideration when a show is being scripted and racks are going to be used. An easy way around this is to just use the same size shell throughout the show. If your shooting a Pyrodigital (PD) show using a computerized firing system, all the racks of the same caliber can be grouped together and the computer picks and chooses which group to shoot from. This makes setup much easier. Racks can then be grouped in sets of 4 or 5, which saves time of not having to cleat each individual rack (although there are other methods to minimize this).
How do you secure the mortar racks for the show?
The only legal way to secure your racks is by "cleating" them together. What the heck is cleating?! It's quite simple actually. It involves taking a few pieces of wood (cleats) and nailing them to the racks. The name of the game is make the racks stable. If you have ever seen one of the videos of the mortars firing during a show, a finale in particular, you can see its extremely violent. So your cleating job has to ensure that the racks will not tip over or come apart while their jumping around. If your cleating an individual rack, or even two of them together, you will take one cleat across the bottom of the rack, making sure it is sitting firmly on the ground, and place two nails (in each rack if more than one are being cleated together) and then one cleat across the top (if more than one are being put together), with one nail in each rack. So, two nails in the bottom of each rack and one in the top of each rack. We use duplex nails (nail with two heads) so that we can pull the nails out with ease at the end of the show during cleanup. Finale racks are slightly different since they are usually cleated together at an angle (like a fan) so that you get a good spread and fill the whole sky. Same cleating method applies (two nails in the bottom, one in the top), with the one difference of fanning. Watch a video explanation of finale rack setup.