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The mandrels were designed in burnsim, and then CADed in Solidworks. The face of the grain was exported as a .dxf file from solidworks. The .dxf was run through this python script to generate a .dat file for the foam cutters. The foam cutter was run at .03 in/s at 20V to produce the mandrels. These values were determined by experimentation.
Making the Caps
The mandrel is held in place by 2 3D printed end caps. The aft mandrel fits over the casting tube and can be taped in place to seal that end. The foam mandrel is epoxied into the aft cap. The forward mandrel cap slides inside the liner tube and is designed to sit flush against the propellant. The mandrel slides through it. The forward cap contains captive nuts to allow it to be pulled out of place. Both of the caps were 3D printed from ABS plastic to allow them to be dissolved with Acetone should other extraction techniques fail. Both caps are designed to be an appropriate thickness so that the nozzle and seal disk can seat fully in the liner. Future improvements might include printing the aft cap to allow the propellant to match the taper of the nozzle converging section, or machining these from aluminum to make them more robust and extractable.
Nozzle End Madrel Cover.SLDPRT
Cutting the Liner to Length
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The motor was demolded by acetone. Acetone was poured through the core, and into the end caps after they were pulled most of the way off . The top end of the motor did not come out clean, as the propellant cured, it shrank, but some remained adhered to the top cap. This was cut off. A very manual process was then undertaken to create a .5 in recess for accomodating the forward closure.This started by using an exacto to shave in a spiral patter about .05 in at a time to get the the required depth. An exacto knife was further used to clean the face. This face was then sanded as smooth as possible. The resulting faces are pictured below.
Assembling the Motor
TBD
Firing the Motor
Main article here.