The plug is the small fitting that the firebolt is screwed into. It contains the black powder charge and is inserted into the tee fitting during integration.

Materials:

  • 1/8 NPT Plug
  • 1/4-20 Bolt
  • #7 (13/64") drill
  • 17/64" or larger drill
  • Center drill

Procedure

  1. Securely attach the 1/8 NPT plug to a lathe. 
    1. It is recommended to use a lathe with an appropriately sized collet chuck (ask the shop staff) for greater stability. In this case, the head will be sticking out.
    2. If there are only three-jaw chucks, tighten the jaws onto the hexagonal head and make sure that the plug is perfectly horizontal and very secure. In this case, the threaded end will be sticking out.
  2. Select an appropriate rotation speed for stainless steel
  3. Use a center drill to create a small hole in the end of the plug
  4. Use the #7 drill to create a thru-hole in the plug. Make sure to go slowly and use a lot of oil.
    1. Check that a #7 drill is the correct size for a 1/4-20 tap
  5. Remove the plug and tap it with a 1/4-20 tap. The tap should be inserted through the head end.
    1. The threads only need to go about halfway through
  6. Place the plug back in the lathe it such that the threaded end is sticking out.
    1. You must use a three-jaw chuck lathe for this step, as it will not fit in a collet in this orientation
  7. Use a 17/64" drill or larger (up to 19/64") to widen the hole at the tip of the plug. Stop slightly before the head, make sure not to drill past the 2/3 point of the plug.
    1. This is to create enough space to fit the black powder. 
    2. Choose a drill that is small enough to leave a comfortable amount of steel radially
    3. If you drill too far, there will not be enough threads to insert the firebolt securely. 

Reference image of plug after machining:

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