 |
|
|
|
|
|
|
|
|
 |
|
Motor Casting tools |
|
The casting tools we use are of two types; Tools for our unique design motors that we make our liners for and tools for commercial liner motors. Due to the 24 hour cure time for Sorbitol, sufficient quantity of tools will be need for one casting party |
||
|
|
|
 |
|
These tools are for our motors that we roll liners for. We have this type of tools in 24, 38, 54 and 75 mm sizes. The liners are not always (almost never) round, so a short length of motor tubing is used to support it. The base is bored for the mandrel and a step cut for the support tube. |
||
 |
|
|
|
These tools are for our commercial liner motors, Kosdon/AMW clones. The liner is more uniform and doesn't need support, so they are less demanding to make. The base is drilled to hold the mandrel and the cap plug is drilled to fit over the mandrel, we have found that forstner bits work the best. For mandrels we have tried PVC pipe and Delrin/Acetal plastic rod. PVC is way cheep but we have not been able to make it work, we have polished it with 2000 grit wet & dry paper in the lathe, waxed and sprayed it with silicone mold release but the propellant still sticks to it and has to be pressed out! Polished Delrin/Acetal rod is more money but works well and will last a lifetime. If anyone has had better results with PVC please let us know the details.
Cap plug info; http://www.caplugs.com |
||
|
Casting Tubes |
||
|
Some of our motors are unique sized, so we have to roll our own casting
tubes. For the smaller ones we use file folders, on the 54 mm and 75 mm we
use painter's rosin paper, it is thicker than masking paper and has a
unique property of expanding when glued and shrinks back to size when dry,
making it slip right off the mandrel. |
|
 |
 |
|
Cut the paper to size, the width is the finished length of the grain. The length will need some trial and error to wrap around the mandrel plus 1/8" overlap and still fit in the case. For the 24 and 38 mm motors we use two wraps and three wraps for the 54 and 75 mm. For mandrels we use PVC pipe turned to size and polished so the glue will not stick. |
|
 |
|
|
Mix the glue, we have had good results with Elmer's Pro Bond mixed about 50% with water. Pull the paper over the edge of the bench to give to a curl and have a damp rag handy to clean up the excess glue or everything will be sticking to everything! |
|
 |
|
|
We use a binder clip taped to the bench to hold the paper. Wrap it around the mandrel, roll it up and check the alignment, unroll until there is one wrap tightly around the mandrel. Paint the exposed paper with glue and roll it up. Release the clip and press the glued edge to the bench until it tacks enough to hold, then immediately remove from the mandrel and stand on its end to dry. |
|
 |
|
|
Here is a batch of tubes drying, when they are dry enough to handle we paint the outside with the leftover glue, it seams to further inhibit the grain and makes the tubes more ridged. |
|
 |
|
|
We tape the grains together with two wraps of masking tape and tape the
nozzle end leaving about 1/8" overhang which forms a crush seal, we also
tape the forward insulator on. The tape forms a Trailer Trash liner and
makes clean up easier. This load is for the J400 54 mm 3 grain that flies
in the Crayon and the 3" tube fin test rocket. |
|
 |
 |
|
Here is the load in the case seen from the delay bulkhead end. The case is 2 ¼" x .120 wall 6061-T6 tube turned down to fit into the 54 mm mount. The case only has a .060" wall, but that has never been a problem (knock on alloy), we run it with a 250 Kn at 500 p.s.i. The right picture is a tube from one of our first 75 mm test fires, all that hard work burned up in 2.5 seconds! On the 54 and 75 mm Kosdon/AMW clone motors we are using casting tube sets from John Lyngdal also available from Aerocon http://www.aeroconsystems.com/misc/motor_making.htm#liners and Missile Works |
|
