The part I tried last night using the sheet protector as a release film worked! The part was by far the easiest to remove, both from the mandrel as well as from the film. Additionally the part is of a size that it can be used with a friction fit motor, using a bit of tape. That makes me think that the motor block will also fit ok into the part. I am attempting to replicate this now with a bit of carbon.
It has been a while since I have worked on this project. One of the last attempts I did a while ago utilized a bit of release wax and PVA on an aluminum tube. The idea was to create a part with better tolerances, however that part seems to be permanently bonded to the mandrel. It was hoped that exposure to cold would shrink the aluminum mandrel more than the carbon, however it just wasn't enough.
Another attempt after that utilized the paper and tape method using an aluminum mandrel. This gave a nice part with good concentricity, but alas the ID was too large to be useful.
Today I decided to take a step back and make some fiber glass parts. I was hoping to have gotten the first carbon part fairly quickly, but it seems there is enough iteration that needs to happen that the first rocket might end up using fiberglass to reduce the cost of experimenting.
Instead of using packaging tape as my release layer with paper under it, I am trying to use a section of plastic film from a page protector. A section that allowed for ~2 wraps around the mandrel was cut from the protector, and wrapped around the mandrel. The film was then taped once in the center with a small piece of scotch tape. I am hoping that this with both be easy to remove, as well as not so thick as to make the part useless.
The most recent attempt at tube construction tested trying to remove 1mm of material from the mandrel. When constructing using the cash register tape and packaging tape technique this is about the difference in size noted between final part and target. This attempt went extremely poorly.
The dowel used has poor concentricity to begin with. In addition to this chucking it in a drill and sanding it does not work very well. This gave me a tapered rod. Those two things coupled together have lead me to finally order an aluminum tube to use as a mandrel instead.
The aluminum mandrel will allow me to use the difference in expansion/contraction with temperature to more easily remove the part. This eliminates the cash register tape from the process. However, as I wait for material to arrive the temperature has been dropping, thus increasing cure times.
The second attempt at a tube used a single layer of cash register tape lengthwise instead of spiral wrapped, and a spiral of packaging tape. The tube was made the entire length of the mandrel (20cm). Instead of the Adtech epoxy I tried using APC EZLam epoxy since it is easier to mix in small volumes.
The tube turned out slightly large still, however it is possible that it is usable to build an actual rocket out of it. The tube can probably be thickened with a single layer of paper epoxied into the interior, or the motor can have tape added to improve the friction fit. It also seems that the tube is much softer than the other tubes. It is unclear if this is due to the tube being stretch more, or the different epoxy, or the epoxy not curing fully due to the recent drop in temperature. Even though it is softer, it is still stiffer than a cardboard tube, and adequate for the forces it will see in flight.
My next thought is to try making a part using a 6mm rod with the normal paper and tape wrap. That technique was by far the easiest to remove. The single layer lengthwise wrap was difficult, and resulted in destruction of the dowel, whereas the other part was relatively easy to slide out.
After curing overnight the heat shrink was removed. Both tubes have a usable area less than the design spec for the rocket (10cm) due to fraying and what not at the ends of the tube. This will have to be addressed in future layups by making a longer initial part.
The first tube, made with just packaging tape, is proving to be very difficult to remove from the mandrel. If I had used aluminum I could do some tricks with temperature, however not so much with wood.
The second part was much easier to remove. The dowel slid right out from the paper and tape covering. I was able to use a piece of thin steel rod to release the paper/tape roll from the interior of the tube. However, the tube is a full carbon tube wall thickness off from designed. The first tube slides neatly into the second. This part is essentially not usable as is, however a layer of carbon could be applied to the interior to make it the proper diameter.
It was also much harder to get a perfectly concentric part out of the second layup. Though this might be something that changes with practice. A change in technique might help with dimensional issues. I am thinking instead of spiral wrapping the register tape, doing a single layer rolled lengthwise. The same with the packaging tape.
A wooden dowel wrapped in Scotch 3650 packaging tape is used as a mandrel. A 20 cm section of dowel was prepared by lightly sanding with 220 sandpaper both to remove imperfections as well as to slightly reduce the diameter. Then a layer of packaging tape was applied in a spiral wrap at >45 degree angle.
A single layer of carbon was prepared at 9 cm, with a total target length of 10 cm. Excess will be cut off when epoxy has fully cured. The sleeve was cut and folded inside out so that the seam is on the interior of the tube, and so any fuzzies could be removed. The sleeve was put over the mandrel and wetted out with laminating epoxy (adtech 820). Excess resin was removed with a paper towel. Treated heat shrink from Soller composites was then applied and heated from the middle.
A second tube was prepared in the same manner, except that a layer of cash register paper was put on the dowel prior to wrapping with packaging tape. This was done to aid in removal of the tube, should the first tube prove impossible to remove from the mandrel.