Here is a short description of my motor making process including making the paper tubes all the way to casting the grains. I have incuded pictures at the bottom to illistrate the process.
Paper Tubes
The process starts off by making the paper casting tubes and liners for the 38mm motors I plan to make. I use packing tape. 2 and 4 inch type non-reinforced tape with a water based glue works very well. All you have to do is wet the back of the paper and start laying it down. The mandrel prep consists of first finding the correct size (or making) mandrels for both the liner tube and the grain casting tube. Turns out that 1 inch emt pipe (cast tube) and a 1.25 wood dowel (liner) work get for both. Use a quick wrap of wax paper and away we go. Five wraps equals about .025 thickness. So I went for 6 wraps for a bit tighter fit on both liner and casting tubes. The can see the mandrels with the tubes drying. Once the tubes have setup for a bit, I remove them from the mandrel and remove the wax paper. Then I put them right back on the mandrel. The tubes will shrink a bit while they dry so the extra room is necessary. Once they are back on the mandrel I use a hot iron and roll the tubes. This helps dry the paper faster and smoothes the paper as it can tend to wrinkle as the paper dry. They may still even be a bit hard to get off. Another reason to leave them on the mandrel is they will warp as they dry and the mandrel will hold them straight.
Motor Building Prep
Next the casting tubes are cut to length for casting. You want to cut your tubes so you enough for how many grains you want to make, plus extra for cutting the grains and the top and bottom of the slug so you have nice uniform grains. It sucks to come up with one short grain so measure correctly and add a little extra. I then tape the ends or use the casting mandrel for the base of the casting tube. Don’t forget to cut your tube longer if you are using a casting base. I also print out the chemical lists with amounts for making the propellant.
Mix the Propellant
Making propellant takes a scale among other things to accurately measure out chemicals for making sticks of propellant. Always start with all your liquids and mix them well except the curing agent. Next carefully mix your metals taking care to know what you are working with. Some metals require being coated first. Then carefully mix in the remainder of your dry chemicals. Sometimes there is a certain order so again know your chemicals or seek qualified help when first starting out. After mixing for at least 40 minutes or longer, degas if your formula requires degassing or mix in your curing agent in the correct amounts. Just remember that the clock in now running and you may only have 40 minutes or less to get all the propellant packed before it starts to setup. This is only a problem if you have a big batch, make sure you have a couple of friends to help out. Once it is packed I put it in my curing box with a slightly elevated temperature.
Burn Tests
I usually make a couple of extra small (short) grains to burn atmospherically. I like to check the visible burn rate and color if it is that type of formula. You can kinda see from these types of burns how a propellant will turn out. Just so you understand if you are making colored flames, the color you see here may not be the color you see during the propellant under pressure. There are several factors that can change the color of the flame under pressure. Next would be to static test your propellant until you get good numbers. Then go fly since you haven’t do so in months.