Wednesday, January 9, 2019

T19 Build Guide - Part 3 - Breech Assembly

Previous: Part 2 - Cage Assembly

  • Hand Drill Motor
  • 9/64" Drill
  • 7/64" Drill
  • 6-32 Tap and Tap Handle
  • File
  • Knife
  • Dremel/Mini Grinder/Die Grinder with zip wheel
  • T19 Cage/Barrel Assembly - refer to Part 2
  • T19 Flywheel Motor Controller Cover x 2
  • T19 Breech
  • T19 Mag Release
  • 6-32 x 2" Socket Head Cap Screw x 1
  • 6-32 x 5/8" Socket Head Cap Screw x 2
  • 6-32 x 1" Socket Head Cap Screw x 4
  • 6-32 x 3/4" Socket Head Cap Screw x 4
Start by cleaning out all 6-32 through holes with a 9/64" drill:

Controller covers: 3 bolt holes each

Breech: 4 cage flange bolt holes

Breech: 4 drive section flange bolt holes

Breech: Right side, mag release bolt hole (Side with counterbore ONLY. DO NOT drill left side for clearance - this will be tap drilled and tapped later)

Mag release: Pivot hole

Then drill the following holes in the breech to 7/64" (or tap drill size to suit material) and tap 6-32 threads:

3 controller cover mounting holes per side (Note: Top two are through entire part)

Left side mag release bolt hole

Mating the cage and breech: Feed motor phase wires through the phase wire holes in the cage flange.

Bolt the cage onto the breech with 4 x 6-32 3/4" length SHCSes. Torque evenly.

Test fit motor controller covers and deflash prints if necessary. Note snap-fit around lower bolt heads - may be tight. Don't pinch wires that are currently here.

Remove covers afterward and put them aside (with their bolts inserted for safekeeping) - they will go on later after mating the breech to the drive section and installing the motor controllers in these compartments.

File the mag release slot in the breech and top layer of the mag release lightly to deburr. Hand fit the mag release further for smooth motion if required.

Mark a 6-32 x 2" SHCS to be cut to length as the mag release pivot bolt. Note: Do not substitute a shorter screw, unless the unthreaded shank length is appropriately long, which is the rationale for cutting a widely available, standard 2" socket head screw. Do not allow the mag release to pivot on threads!

Zip that to length, and deburr.


Do not overtorque! Apply only enough torque to prevent unwinding. Overtorquing the mag release bolt will cause mag release binding and can distort the magwell enough to make mags not drop free.

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