Modulus Arms Heavy-Duty Universal AR-15 80% Jig Manuale utente
Heavy-Duty Universal
AR-15 80% Lower Receiver Jig
Instructions
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www.ModulusArms.com | Heavy-Duty Universal AR-15 80% Jig Instructions
2
Jig Contents
The Heavy-Duty Universal AR-15 80% Lower Receiver Jig contains the following parts:
1. 1x Top Plate (Al 6061-T6)
2. 1x Right Side Plate (Alloy Steel)
3. 1x Left Side Plate (Alloy Steel)
4. 1x Front Support (Al 6061-T6)
5. 1x Rear Support (Al 6061-T6)
6. 1x Buffer Support (Al 6061-T6)
7. 1x Drill Template (Alloy Steel)
8. 1x Router Template (Alloy Steel)
9. 1x Depth Gauge (Al 6061-T6)
10. 14x Screws [8-32 x ½”]
11. 1x Side Plate Support Screw [8-32 x 1.5”]
12. 1x Rear Take Down Screw [1/4-20 x 1.5]
Figure 1 Jig Contents
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Required Tools
The following items are required to finish the 80% AR-15 Lower Receiver:
(Available for sale on Modulus Arms Website as Jig Fabrication Kit)
1. ¼” Dia, ¼” Shank, 4” Long, 1” Cut, Square End Mill
4. 3/8” Drill Bit
2. 19/64” Drill Bit
5. 5/32” Drill Bit
3. 3/8” Drill Stop
Figure 2: Jig Fabrication Kit
The additional tools needed to finish the 80% AR-15 Lower Receiver:
1. Router (Laminate/Trim Recommended)
4. 9/64” Allen Wrench
2. Drill (Hand or Drill Press)
5. 3/16” Allen Wrench
3. Vise or device to hold Jig
4. Front Takedown kit or ¼” bolt
6. 3/32” Allen Wrench
Figure 3: Example Tools
Routers that we recommend to finish the 80% AR-15 Lower Receiver:
1. Ridgid R24012
2. Dewalt D26670
3. Makita RT0701C
4. Porter-Cable PCE6430
5. Porter-Cable 7310
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HD Jig Assembly
Front Support: The front takedown pin secures the front support as shown in Figure 4. For best results,
the spring and detent from the Modulus Arms AR-15 Lower Parts Kit may be used. Optionally, Modulus
Arms offers an AR-15 Front Takedown Kit. To install the Front Support using a Front Takedown Kit,
follow Steps 1-5 in Figure 4. If a Front Takedown Pin is not available, you may use a ¼” diameter bolt
(not supplied) to achieve the same result as Step 5 in Figure 4.
Figure 4: Front Takedown Pin Attachment
Step 1
Step 2
Step 3
Step 4
Step 5
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Buffer Support and Rear Support: Thread the Buffer Support into the Lower Receiver in the location
shown in Step 1. Thread the Buffer Support into the Lower Receiver (clockwise) as shown in Step 2.
Thread the Buffer Support into the Lower Receiver until the Buffer Support is below the rear surface of
the lower, then further turn clockwise until the three screw holes are aligned vertically as shown in Step
3. Using two of the ½” long screws, attach the rear support as seen in Step 4. Do no tighten, yet. Make
sure the rear support is in contact with the lower receiver rear surface. If it is not in contact, you must
thread the buffer support in further. On some lower receivers, especially polymer, the buffer support
can go in snug. Threading in two of the screws to use as a handle can help to install the buffer support.
Figure 5: Buffer Support and Rear Support Attachment
Step 1
Step 2
Step 3
Step 4
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Top Plate: Align the Top Plate over the Rear Support and Front Support as shown in Figure 6. Use four
½” screws to attach the Top Plate to the Rear Support and Front Support. Tighten the screws to 1 ft-lb.
Now, tighten the screws attaching the Rear Support to the Buffer Support from the previous step to 1 ft-
lb. The Top Plate should now be secure.
Figure 6: Top Plate Attachment
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Side Plates: Place the Left Side Plate into position and thread two ½” screws into the top through the
Top Plate as shown in Figure 7. Repeat for the Right Side Plate. Leave these four screws loose. Squeeze
the side plates together against the sides of the lower receiver. When they are tight to the lower
receiver, tighten the four ½” screws to 1 ft-lb. Screw the 8-32 x 1.5” Side Plate Support Screw into the
Right Side Plate and all the way through into the Left Side Plate as shown in Figure 8. Tighten to 1 ft-lb.
Do not install the ¼-20 x 1.5” Rear Takedown Screw.
Note: Many questions have been asked about the Side Plate Support Screw. It is used to prevent
the side plates from flexing in when clamped in a vise. That is why both sides are threaded.
Note: It is recommended to put masking tape or some other protection over the sides of the
lower before installing the side plates. Doing so will help prevent scratches or wear.
Figure 7: Side Plate Screws
Figure 8: Support Screw Location
Leave Loose
Left Side Plate
Screws
Right Side Plate
Screws
Side Plate Support Screw
DO NOT INSTALL
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Figure 6: Vise Screws
Drilling the Holes
Drill Template: Place the Drill Template into the Top Plate as shown in Figure 9. Thread two ½” screws
into the locations shown in Figure 9. Tighten the screws to 1 ft-lb.
Figure 9: Drill Template
Screws
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Drilling the Trigger Slot Holes: Insert the 19/64” drill bit into the drill and tighten the chuck. Place the
drill bit into the hole labeled “A”as shown in Figure 11. Drill through the Lower Receiver until you exit
under the Fire Control Group. Figure 10 shows the placement of hole “A”. The hole is also labeled on the
Drill Template.
Note: If a hand drill is being used be sure to hold the drill upright. If the drill is not held upright
blemishes may be visible in the trigger slot after assembly.
Note: Use a vise, C-clamp or other mechanism to hold the Jig.
Note: Be sure not to start spinning the drill until after the drill bit is placed into the drill guide or
premature wear will occur.
Note: Use plenty of WD-40 or cutting fluid and remove the chips regularly.
Note: All the above notes are true for all drilling and will not be repeated.
Figure 10: Drill Template Hole Placement
Figure 11: Hole “A” location
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Drilling the Fire Control Group Holes: Slide the 3/8” drill stop onto the 3/8” drill bit. Insert the 3/8” drill
bit into the Depth Gauge in the slot labeled “C” as shown in Figure 12. Make sure the drill bit is inserted
all the way into the slot and tighten the drill stop onto the drill bit. Next, drill the six holes labeled “C” in
Figure 10. The holes are also labeled on the Drill Template. Be sure to drill to the depth specified with
the drill stop and do not go any further.
Note: Be sure the drill stop is tight. Check the placement of the drill stop with the Depth Gauge
after each hole. This applies for all drilling.
Figure 12: Slot C
Figure 13: Hole “C” Location
Indice
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