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The liner was cut to 30 inches long for 28.75 25 in of propellant. The madrel caps are .6 inches thick. This should leave the propellant section slightly long to be trimmed back to the correct length. The inside of the liner was abraded with 150 grit sandpaper to improve adhesion of the propellant to the liner and avoid a debonding failure which could lead to the outside surface burning, and a rapid, unscheduled disassembly. The inside of the liner was then cleaned with Acetone to provide a good surface to bond the propellant to.
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The liner was measured to be 29.75 inches long and weigh 707gweighs 1.56 lb. The ID of the liner was measured to be 3.384 inches. This will serve as the OD of the propellant slug. The foam mandrel was measure to have a cylinder diameter of .956 inches. There are six fins, each .2 inches thick, protruding .474 inches from the cylinder. This is 215.06 in3 of propellant volume.
The foam core was expoxied into the aft casting cap with 5-minute epoxy. The 3D printed caps were coated with frekote.
During casting it was noted that the foam was quite flexible and could be bent easily. It was suggested to add a carbon fiber rod for additional stiffness, but after demolding, it appears to have not been an issue. The mass of the propellant and liner post demolding is 14.46 lbs. The liner weighs 1.532 lbs. The total propellant mass is 12.93 lbs. This suggests a density of 1,663.56 kg/m3.
Demolding
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