What's new
Florida sheriff encourages residents to shoot looters breaking into homes

AR-15 Lower How-to Guide For Drill Fixture

GunBuyer

Please carefully read these instructions in entirety before beginning.

Overview:

These instructions are meant to give you some direction in completing your 80% Lower Receiver. To complete the lower you will be drilling multiple holes and routing two pockets. To keep the lower receiver within tolerance, take your time and pay close attention to the measurements as you machine. We offer recommended speeds, depths of cuts, and tool stick out lengths on the final page of this manual. This guide will cover using the Optimus Defense Drill Jig to complete your lower.

fIGURE 1.png

Cutters:

These tools are included in the Optimus Defense Drill Jig:

  • 3/8” End-mill with a 3/8” shank
  • 1/4” End-mill with a 3/8” shank
  • 3/8” Stub split tip drill bit
  • 5/32” Jobber split tip drill bit
  • 9/64” Jobber split tip drill bit
  • K (0.281") Stub split tip drill bit
Other Tools:

  • Drill Press and Vise
  • C-Clamp (for securing vise to table)
  • Safety Glasses
  • Caliper and 6" ruler
  • Cutting Fluid such as A-9 or Tap Magic Aluminum
  • Manual Mill Drawings and Inspection Drawings (Click here to view the drawings).
General Machining Practices:
  • Use generous amounts of cutting fluid at all times, on the tool's cutting and rubbing surfaces.
  • Always peck drill to prevent chips from packing into drill flutes.
  • At times it may be necessary to clamp the vice to the table to prevent excessive vibration.
Figure 2.png

Procedure:

Assemble the drill jig


1. Using the two provided shoulder screws and one button head screw, assemble the drill jig with the lower sandwiched in between the two side plates. The shoulder screws go through the lowers take down and pivot pin holes, and the long button head cap screw goes through the magazine release hole. (See assembly drawing)

Drilling the trigger pin, hammer pin, and selector holes

2. Lay the drill jig on its right side and clamp in a vise.
3. Using the 5/32” drill bit, drill the hammer and trigger pin holes.
4. Using the 3/8” drill bit, drill the selector hole. Refer to Figure 2.

Fire Control Pocket

5. Stand the drill jig upright and clamp it in the vise. Fasten the Fire Control Pocket Top Plate to the drill jig in the "drilling position" (array of drilled holes closer to the buffer tube ear).

Note: the top plate and the left side plate have circular notches that align. This is where you will set drilling depth and final routing dept.

Figure 3.png
6. Set the 9/64” drill bit tool final depth using the exposed circular notch. See Figure 3.
7. Using the 9/64” drill bit, drill each of the 32 holes.
8. Remove the Fire Control Pocket Top Plate from the drill jig. Load the 3/8” drill bit and set the final drilling depth using the same circular notch as in step 6.
9. Using the 3/8” drill bit, drill the holes marked in Figure 4, effectively removing most of the material from the fire control pocket. Figure 5 shows most of the fire control pocket 3/8" drilled out.

Figure 4.png
Figure 5.png
10. Re-attach the Fire Control Pocket Top Plate with the routing pocket located over the fire control pocket area. See Figure 6.
11. Load the 3/8” end-mill and set the final tool depth using the same notch as in step 6.

Figure 6.png
12. Route out the fire control pocket using the top plate's routing pocket as a guide. The first depth of cut must be 1.375” +/-.03" below the top plate's top face, so that the flutes (cutting edges) of the end-mill does not cut in to the top plate. Move the cutter around the routing guide in a clockwise direction (conventional milling direction).

Warning: If the first depth (1.375") is not set correctly, the Fire Control Pocket Top Plate will be damaged. 13. Route next depths about 1/4" to 3/8" deeper until final depth is reached.

Trigger Slot

14. Remove the Fire Control Pocket Top Plate and fasten the Trigger Slot Top Plate to the drill jig in the "drilling position".

Note: The top plate now aligns with a different circular slot for drilling and final routing depth.

Figure 7.png
15. Load the letter K (dia. 0.281") drill bit and set the final drilling depth using the exposed circular notch. Before turning the drill press spindle ON, lower the drill bit through one of the holes until it is just above the floor of the fire control pocket. Then turn ON the drill press spindle and drill the hole. Repeat for all three holes through the floor of the fire control pocket.

Warning: If the K drill bit flutes (cutting edges) touch the Trigger Slot Top Plate while the drill is spinning, the drill bit will "grab" and damage the top plate.

16. Rotate the Trigger Slot Top Plate so that the routing pocket is above the drilled holes. See Figure 8.

Figure 8.png

17. Load the 1/4" end-mill and set the final milling depth as before in Step 15.
18. Route out the trigger slot using the routing pocket as a guide. Move the cutter around the pocket in a clockwise direction (conventional milling direction).

Note: The Trigger Slot Top Plate routing pocket is design for a 1/4" end-mill with a 3/8" shank.

19. After machining both pockets take some measurements and compare it to the inspection drawing. All dimensions should be within the tolerance noted on the drawing. If out of tolerance, carefully consider how it will affect the function of your lower.

De-burr

20. Using a suitable de-burr tool or sandpaper, carefully take down any sharp edges.

Warning:
Once you have machined any of the hammer, trigger and selector holes or the fire control pocket and trigger slot, you have what is considered to be a firearm. This firearm cannot be traded, gifted or sold without the assistance of a FFL. I assume no liability for the actions of the user of this product. You are responsible for knowing all laws and regulations in your area relating to this product. I am not a lawyer, and this is not legal advice.

Recommended Cutting Parameters:

3/8” End-mill
Speed: 2050 RPM
Stick Out: 2”
First Depth of Cut: 1.375” (below top plate's top)
Next Depth of Cut: 0.375” deeper or less

1/4” End-mill
Speed: 3050 RPM
Stick Out: 2”

3/8” Drill
Speed: 2000 RPM
Stick Out: 2”
Peck Drill: 0.190”

5/32” Drill
Speed: 4800 RPM
Stick Out: 2”
Peck Drill: 0.080”

9/64” Drill
Speed: 5450 RPM
Stick Out: 2”
Peck Drill: .070”

K Drill (dia. 0.281")
Speed: 2700 RPM
Stick Out: 2”

Calculations:
Definitions

RPM – Revolutions per Minute
SFM – Surface Feet per Minute
Dia. – Diameter of cutter

Formulas
RPM = SFM * 3.82 / Dia.

SFM for High Speed Steel cutting Aluminum is
200. (conservative cutting)

Recommended RPMs are based off the above calculation. You can use a slower RPM and compensate by lowering your feed rate as well.

Figure.png
Other Information:

Climb vs. Conventional Milling:


Conventional milling is recommended for manual machining since it keeps pressure against the table of the mill. For the fire control pocket, it is recommended to machine in a conventional pattern. This is generally moving the cutter clockwise around the inside of the pocket.

Tool Chatter:

Tool chatter may occur due to the long length of these cutters. If you are experiencing excessive chatter or getting a bad surface finish, reduce the spindle RPM and use more cutting fluid.

Cutting Fluid:

Using a cutting fluid that is made for machining aluminum, such as A9 or Tap Magic Aluminum, will greatly improve the machining finish, reduce tool chatter, and improve tool life.

Figure Manual.png
 

Frankie J

Member
Please carefully read these instructions in entirety before beginning.

Overview:

These instructions are meant to give you some direction in completing your 80% Lower Receiver. To complete the lower you will be drilling multiple holes and routing two pockets. To keep the lower receiver within tolerance, take your time and pay close attention to the measurements as you machine. We offer recommended speeds, depths of cuts, and tool stick out lengths on the final page of this manual. This guide will cover using the Optimus Defense Drill Jig to complete your lower.

View attachment 496

Cutters:

These tools are included in the Optimus Defense Drill Jig:

  • 3/8” End-mill with a 3/8” shank
  • 1/4” End-mill with a 3/8” shank
  • 3/8” Stub split tip drill bit
  • 5/32” Jobber split tip drill bit
  • 9/64” Jobber split tip drill bit
  • K (0.281") Stub split tip drill bit
Other Tools:

  • Drill Press and Vise
  • C-Clamp (for securing vise to table)
  • Safety Glasses
  • Caliper and 6" ruler
  • Cutting Fluid such as A-9 or Tap Magic Aluminum
  • Manual Mill Drawings and Inspection Drawings (Click here to view the drawings).
General Machining Practices:
  • Use generous amounts of cutting fluid at all times, on the tool's cutting and rubbing surfaces.
  • Always peck drill to prevent chips from packing into drill flutes.
  • At times it may be necessary to clamp the vice to the table to prevent excessive vibration.
View attachment 497

Procedure:

Assemble the drill jig


1. Using the two provided shoulder screws and one button head screw, assemble the drill jig with the lower sandwiched in between the two side plates. The shoulder screws go through the lowers take down and pivot pin holes, and the long button head cap screw goes through the magazine release hole. (See assembly drawing)

Drilling the trigger pin, hammer pin, and selector holes

2. Lay the drill jig on its right side and clamp in a vise.
3. Using the 5/32” drill bit, drill the hammer and trigger pin holes.
4. Using the 3/8” drill bit, drill the selector hole. Refer to Figure 2.

Fire Control Pocket

5. Stand the drill jig upright and clamp it in the vise. Fasten the Fire Control Pocket Top Plate to the drill jig in the "drilling position" (array of drilled holes closer to the buffer tube ear).

Note: the top plate and the left side plate have circular notches that align. This is where you will set drilling depth and final routing dept.

View attachment 498
6. Set the 9/64” drill bit tool final depth using the exposed circular notch. See Figure 3.
7. Using the 9/64” drill bit, drill each of the 32 holes.
8. Remove the Fire Control Pocket Top Plate from the drill jig. Load the 3/8” drill bit and set the final drilling depth using the same circular notch as in step 6.
9. Using the 3/8” drill bit, drill the holes marked in Figure 4, effectively removing most of the material from the fire control pocket. Figure 5 shows most of the fire control pocket 3/8" drilled out.

View attachment 499
View attachment 500
10. Re-attach the Fire Control Pocket Top Plate with the routing pocket located over the fire control pocket area. See Figure 6.
11. Load the 3/8” end-mill and set the final tool depth using the same notch as in step 6.

View attachment 501
12. Route out the fire control pocket using the top plate's routing pocket as a guide. The first depth of cut must be 1.375” +/-.03" below the top plate's top face, so that the flutes (cutting edges) of the end-mill does not cut in to the top plate. Move the cutter around the routing guide in a clockwise direction (conventional milling direction).

Warning: If the first depth (1.375") is not set correctly, the Fire Control Pocket Top Plate will be damaged. 13. Route next depths about 1/4" to 3/8" deeper until final depth is reached.

Trigger Slot

14. Remove the Fire Control Pocket Top Plate and fasten the Trigger Slot Top Plate to the drill jig in the "drilling position".

Note: The top plate now aligns with a different circular slot for drilling and final routing depth.

View attachment 502
15. Load the letter K (dia. 0.281") drill bit and set the final drilling depth using the exposed circular notch. Before turning the drill press spindle ON, lower the drill bit through one of the holes until it is just above the floor of the fire control pocket. Then turn ON the drill press spindle and drill the hole. Repeat for all three holes through the floor of the fire control pocket.

Warning: If the K drill bit flutes (cutting edges) touch the Trigger Slot Top Plate while the drill is spinning, the drill bit will "grab" and damage the top plate.

16. Rotate the Trigger Slot Top Plate so that the routing pocket is above the drilled holes. See Figure 8.

View attachment 503

17. Load the 1/4" end-mill and set the final milling depth as before in Step 15.
18. Route out the trigger slot using the routing pocket as a guide. Move the cutter around the pocket in a clockwise direction (conventional milling direction).

Note: The Trigger Slot Top Plate routing pocket is design for a 1/4" end-mill with a 3/8" shank.

19. After machining both pockets take some measurements and compare it to the inspection drawing. All dimensions should be within the tolerance noted on the drawing. If out of tolerance, carefully consider how it will affect the function of your lower.

De-burr

20. Using a suitable de-burr tool or sandpaper, carefully take down any sharp edges.

Warning: Once you have machined any of the hammer, trigger and selector holes or the fire control pocket and trigger slot, you have what is considered to be a firearm. This firearm cannot be traded, gifted or sold without the assistance of a FFL. I assume no liability for the actions of the user of this product. You are responsible for knowing all laws and regulations in your area relating to this product. I am not a lawyer, and this is not legal advice.

Recommended Cutting Parameters:

3/8” End-mill
Speed: 2050 RPM
Stick Out: 2”
First Depth of Cut: 1.375” (below top plate's top)
Next Depth of Cut: 0.375” deeper or less

1/4” End-mill
Speed: 3050 RPM
Stick Out: 2”

3/8” Drill
Speed: 2000 RPM
Stick Out: 2”
Peck Drill: 0.190”

5/32” Drill
Speed: 4800 RPM
Stick Out: 2”
Peck Drill: 0.080”

9/64” Drill
Speed: 5450 RPM
Stick Out: 2”
Peck Drill: .070”

K Drill (dia. 0.281")
Speed: 2700 RPM
Stick Out: 2”

Calculations:
Definitions

RPM – Revolutions per Minute
SFM – Surface Feet per Minute
Dia. – Diameter of cutter

Formulas
RPM = SFM * 3.82 / Dia.

SFM for High Speed Steel cutting Aluminum is
200. (conservative cutting)

Recommended RPMs are based off the above calculation. You can use a slower RPM and compensate by lowering your feed rate as well.

View attachment 504
Other Information:

Climb vs. Conventional Milling:


Conventional milling is recommended for manual machining since it keeps pressure against the table of the mill. For the fire control pocket, it is recommended to machine in a conventional pattern. This is generally moving the cutter clockwise around the inside of the pocket.

Tool Chatter:

Tool chatter may occur due to the long length of these cutters. If you are experiencing excessive chatter or getting a bad surface finish, reduce the spindle RPM and use more cutting fluid.

Cutting Fluid:

Using a cutting fluid that is made for machining aluminum, such as A9 or Tap Magic Aluminum, will greatly improve the machining finish, reduce tool chatter, and improve tool life.

View attachment 505
well done, this post i will share as so many people ask me how to do the jig process.
 
Top