Part machined by Justin S. and completed on November 16th, 2019. This part is a segment of the Hermes 3 Nozzle Assembly.
CAD Design and Drawing
Manufacturing Procedures
Most of the operations regarding this part will be turned on a lathe. It is recommended that a four-jaw chuck is used due to the size of the starting stock. Use a dial indicator to center the part on the new chuck. Start by turning a piece of stock aluminum 6061 into a cylinder matching the outermost dimensions of the boat-tail (6.3 in. diameter, 2.4 in. length). Then use the center drill to clear a hole in the center of the stock to begin the boring process.
Change tools on the lathe to a boring tool. Make sure that the arm of the boring tool is not too extended. If the tool is fully extended it will cause vibration with the part which will make the finish less clean (as well as a deafening screeching noise). Start with the side which will mate with the nozzle carrier, making passes of 20 thousandths, boring from the center to the outside edge. Flip the stock to the other side and bore out with the same sized passes; this time making the passes inward. when this is complete you should have a piece of stock with a 4-inch diameter hole through the entire part, and a 5.5 inch insert on the top side as shown in the CAD drawing. then, switch tools to the finishing tool and use the chamfer function on the lathe to make the slanted portions of the boat-tail.
After the chamfers are machined, clean the lathe (especially if coolant was used) and remount the boat-tail on the radial indexer after calibrating it with a precision ground rod and dial indicator. After centering with the edge finder, use an H-type drill bit (0.266 in diameter) to make the 8 holes in the side of the part. make sure to space the holes accordingly so they do not overlap the chuck jaws. Use a countersink tool (82 degrees) so that the designated bolts lay flush with the side of the part when inserted. No tapped holes are required for this part.
Manufacturing Defects
There are two main defects in the completed part. The first is a stripped area on the inside of the 5.5-inch insert near the top edge where the tool cut too deep into the part (make sure go-to function is on when you are making passes). further yet less intense damage was made in the same area due to the fact that the boring tool was fully extended. this caused a large amount of vibration with the part when the tool was still, which produced an uneven finish. this was fixed in later passes for the rest of that particular operation. the defect was pointed out to the lead designer and he confirmed that the part can still be used.
The second defect is much smaller yet still worth mentioning. There is a very small lip (~ 20 thousandths) where the divergent section connects to the divergent section of the nozzle carrier. This portion is meant to be flush with the nozzle carrier and is the most critical part of this part. Fortunately, most of this lip was found to be mostly excess material from the chamfer operation, making the lip pretty much nonexistent. this defect has yet to be reviewed.
Possible Design Improvements
The outer chamfer on the boat-tail was arbitrarily chosen to be 7 degrees. if this angle is increased, more material can be removed and the part can be made lighter. this would shift the center of mass of the rocket up slightly and make the rocket more stable since this is the aft-most part. Increasing the chamfer angle to 15 degrees will also reduce base drag on the part.