AR-15 Jig Instructions - Modulus Arms - AR

Transcription

AR-15 Jig Instructions
www.ModulusArms.com
October 6, 2014
Introduction
If your lower can accommodate an AR-15 upper, it is compatible with the Modulus Arms 80% AR-15
lower jig. The Modulus Arms jig utilizes standardized features within the lower receiver designed to
accommodate an AR-15 upper to properly locate the templates, resulting in a universal fit. A forged
lower completed with the Modulus Arms 80% jig using basic hand-held power tools is shown below.
For the first time user, the Modulus Arms jig offers increased safety (no milling with a drill press), a simple
and easy to use process, compatibility with commonly available hand power tools, and reduced risk of
failure.
For the experienced builder, the Modulus Arms jig offers universal fit, increased precision, and reduced
fabrication time. Modulus Arms also offers individual replacement parts.
The lower is easily completed with four simple steps to fabricate the : 1) the trigger slot, 2) the rear shelf
pocket, 3) the fire control pocket, and 4) the fire control pin holes (trigger pin, hammer pin, and safety
selector). To reduce the fabrication time and to improve the finish, a router with an end-mill is used to
finish the cavity that is first hollowed out with a drill bit in the first three steps.
Once any of the required finishing features are started, the lower is considered a firearm and all local,
state, and federal firearms laws will apply. It is your responsibility to check the legality of finishing and
owning an 80% lower in your area. Please make sure you are familiar with the safe operation of power
tools before using the Modulus Arms jig to complete your lower.
Modulus Arms Jig Part Description & Key Features
The Modulus Arms 80% Jig kit contains the following parts as shown in figure 1 and listed below:
1.
2.
3.
4.
5.
Template
Side Plate (2x)
Drill Guide
Front Support
Rear Support
6.
7.
8.
9.
10.
Buffer Support
Depth Gauge
Cap Screws [8-32 x ½”] (12x), [8-32 x ¾”] (2x)
Side Plate Support Cap Screw [8-32 x 1.5”] (2x)
Rear Take Down Cap Screw/Nut [1/4-20 x 2.25”]
www.ModulusArms.com | AR-15 Jig Instructions
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Figure 1: Modulus Arms Jig Kit Contents (in production kits, short and long screws are the same size)
Unlike conventional 80% jigs, all of the features that require milling with the ¼” end-mill are contained on
a single template that is designed to be used in two orientations (figure 2). The fire control pocket is
fabricated in one orientation while the rear shelf pocket and trigger slot are fabricated in the other
orientation. The template is attached to the front and rear supports. The side plates are attached with the
oval holes allowing for a universal fit regardless of variations in the lower receiver widths.
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Figure 2: Template Features
To speed up the milling process, excess material is removed with a drill. The drill holes are located with a
drill guide installed under the template as shown in figure 3. Since the template only exposes a limited
number of holes in the drill template, there is no chance to drill a hole in the wrong location.
CAUTION: The drill guide is not symmetric and can be installed upside down. For the rear-shelf pocket, all
three holes are fully exposed when correctly installed as shown in figure 3. If the drill template is upside
down, the right most hole will be partially covered by the template. For the fire-control pocket, there
should be seven fully exposed holes (the 8th – left most in figure 3 – should be partially covered and not
drilled). If it is upside down, both the 7th and 8th right most holes (figure 3) will be partially covered.
Figure 3: Drill Guild installed under template in both orientations
The same side plate is used on the left and right side as shown in figure 4. The rear takedown hole is
provided to assure proper placement for the drilling of the safety selector and the trigger group pins. The
side plate support holes are designed to reduce flex and marring with anodized lowers when the side
plates are placed in a vise to secure the lower during the milling process.
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Figure 4: Side Plate Features
The depth gauge is used for both drilling and milling as shown in figure 5. The gauge is used 1) to set the
drill depth using a drill stop on the 3/8” drill bit and 2) use to set the router depth for the final cut. Depth
gauge “A” is used to set the end mill so it exits the bottom of the lower for the trigger hole. Depth gauge
“B” is used for the rear shelf (depth = 0.630”). Depth gauge “C” is used for the fire-control pocket (depth=
1.249”). Production depth gauges will have engraved hash marks, the first hash mark represents the top
of the lower. Each hash mark is ¼” deep and represents the maximum depth of cut for a pass. The user
is encouraged to start at 1/16” - 1/8” of an inch depth of cut and work up to a comfortable depth that
should not exceed more than ¼” depth of cut. Typically, a deeper depth of cut requires a router with
variable speed so the end-mill speed can be slowed down for more control.
Figure 5: Depth gauge used to set the drill depth and end-mill depth
The following parts are required to complete the jig and can be purchased as an optional kit:
1.
2.
¼” x 4” 4-flute End-Mill with 1” Depth of Cut
3/8” Drill Bit (fire-control, rear-shelf, and safety
selector)
3.
4.
5.
19/64” Drill Bit (trigger slot)
5/32” Drill Bit (hammer/trigger pin)
3/8” Drill Stop
Figure 6: Optional kit required to finish the lower
The following tools are required / recommended (examples shown in the figure below):
1.
2.
3.
4.
Router (full size or laminate)
Drill (hand drill or drill press)
Vise (drill press shown)
3/64” Allen Wrench (for drill stop)
5.
6.
7.
8.
3/32” Allen Wrench (8-32 cap screws)
3/16” Allen Wrench (Rear Take Down Screw)
Philips Screwdriver (Side Plate support)
Front Take Down (pin, detent, & spring)
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C-clamp (optional if vise is not mounted)
Figure 7: Example of common tools that can be used to complete the lower
Modulus Arms Jig: General Assembly
Front Support: The front takedown pin is used to secure front support as shown in figure 8. For best
results, the spring and detent from the parts kit should be used install the pin. Optionally, the Modulus
Arm’s front bolt kit (not included) that contains ¼” bolt with the proper space and washers can be used in
lieu of a front take down pin.
Figure 8: Install front take down pin and use it to secure the front support like an upper
Rear Support: Thread in the buffer support (clockwise) until the buffer support is below the rear surface
of the lower (figure 9), then further turn clockwise until the two screw holes are at 12 o’clock. Cap screws
can be partially threaded into the buffer support for additional leverage. Using the long cap screws, attach
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the rear support. Make sure the buffer support is recessed so that the rear support touches the back of
the lower for proper alignment.
Figure 9: Install buffer support and rear support
Template and Drill Guide: The template attaches to the front and rear support using four small cap
screws. For milling, the template is used alone (figure 10, left). For roughing, the drill guide is used (figure
10, right). The first three of four steps involves installing the template with the drill guide to rough out the
pocket, then removing the drill guide to mill the pocket. Only the front support screws need to be
removed to attach or remove the drill guide. When properly installed (not upside down), the cap screws
that attach the front/rear support are flush with the top surface of the template.
Figure 10: Template only (left) or Template & Drill Guide (right) installed
Side Plates: The side plates attach to the jig through the template with four small cap screws (figure 11,
right). The jig is designed to accommodate different lower widths and should be pressed against the lower
before tightening the screws. For the first three steps, the main purpose of the two side plates is to allow
a vise to secure the jig, so the screw through the rear take down hole is not needed. For the fourth step,
the side plates serve as the template for the fire control group pins holes. For increased accuracy, the rear
take down screw/nut can be installed through the rear-take down hole.
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Figure 11: Side Plate Installation
6061 vs 7075 Lower: Commonly, most forged lowers are made with 7075-T6 lowers and billet can be
offered in either 6061-T6 or 7075-T6. In general, 7075-T6 is more difficult to work with requiring shallower
depth of cuts when using the router. Although a hand drill can be used with 7075-T6, a drill press can
significantly reduce the overall effort. If a hand-drill is used with 7075-T6, please be patient and go slow.
Step 1: Fully Supported Trigger Slot
Configure jig for drilling: The template is installed with the rear pocket template closest to the buffer as
shown in figure 1.1 with the drill guide installed.
Figure 1.1: Jig configured to drill he rear pocket and trigger slot
Trigger Slot Drilling: With the two exposed holes in the trigger slot, use a 19/64” drill bit to drill all the
way through the lower (figure 1.2, left). Figure 1.2, right shows the lower after completion. For best
results, start the drill after the drill bit is partially or completely through the drill guide to prevent
accidental damage to the template.
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Figure 1.2: Drilling the trigger slot holes (left), lower after drilling (right)
Configure jig for milling: The configured jig is shown in figure 1.3 after the drill guide is removed.
Figure 1.3: Jig configured to mill the rear pocket and trigger slot
Trigger Slot Milling: A router with an end-mill is used to form the cavity (figure 1.4, left) and the completed
lower with the trigger slot is shown in figure 1.5, right).
1. Adjust the end-mill to touch the top of the lower (using the rib between the two drill holes) – use
the depth gauge to set the depth and verify.
2. Important: Set the first cut depth to be ¼” (maximum) below the surface using the drill guide,
verify that the cutting surfaces of the end-mill are below the edge of the template. Modulus
Arms suggests that the user first start with 1/16”-1/8” cutting depth before working up to a
comfortable depth not to exceed ¼”.
3. Insert the end-mill into a drill hole and without the end-mill touching the lower, carefully turn on
the router allow the router to come up to full speed.
4. With firm downward pressure applied to the base, mill using shallow clockwise passes with light
pressure. The goal is to first adjoin the two holes, then widen until the end mill touches the side
of the template. Turn off the router, wait until the end-mill stops spinning, and remove from the
jig. Figure 1.5, left shows the lower after the first pass.
5. Increase the cutting depth ¼” using the depth gauge and repeat steps 3 and 4 until the end-mill
breaks out of the bottom of the lower. The “A” depth gauge can be used to set the final depth as
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shown in figure 1.4, right. Modulus Arms suggests that the user work up to a comfortable depth
not to exceed ¼” depth of cut based on adjustment of router speed and user experience.
Figure 1.4: Router to mill out trigger-slot ¼” at a time (left) and final cut depth set with “A” depth gauge
Figure 1.5: Example of partially milled trigger slot (left) and complete trigger slot (right)
Step 2: Rear Shelf
Configure jig for drilling: The template is installed with the rear pocket template closest to the buffer as
shown in figure 2.1 with the drill guide installed. DO NOT install the rear takedown screw/nut for this step.
Make sure all three holes are fully visible. If the right most hole is partially covered, the drill template is
upside down.
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Figure 2.1: Jig configured to drill out the rear pocket and trigger slot
Rear-Shelf Pocket Drilling: The three holes exposed through the rear-pocket template are drilled out with
a 3/8” drill bit (figure 2.2, right) to a depth set with the “B” depth gauge (figure 2.2, right). Finished lower
is shown in figure 2.3. Make sure to start the drill with the bit surrounded by the drill template to prevent
template damage.
Figure 2.2: Drilling the trigger slot holes
Figure 2.3: Drilled lower –most 80% lowers will have three holes. The lower in this example has additional reference
slot, which does not require the two right most holes.
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October 6, 2014
Figure 2.4: Jig configured to mill out the rear pocket and trigger slot
Rear-shelf Pocket Milling: A router with an end-mill is used to form the cavity (figure 2.5, left) and the
completed lower with the trigger slot is shown in figure 2.6.
1. Adjust the end-mill to touch the top of the lower (using the rib between drill holes) – use depth
gauge to set the depth and verify.
2. Set the first cut depth to be ¼” below the surface using the depth gauge, insert router into a drill
hole, and without the end-mill touching the lower, carefully turn on the router allow the router
to come up to full speed. Modulus Arms suggests that the user first start with 1/16”-1/8” cutting
depth before working up to a comfortable depth not to exceed ¼”.
pressure. First adjoin the three holes by removing the rib between the holes, then widen until the
end mill touches the side of the template. Turn off the router, wait until the end-mill stops
spinning, and remove from the jig.
4. Check the depth using the “B” depth gauge after each pass. The final depth is shown in figure 2.5,
right. Adjust the cutting depth by ¼” at a time and repeat steps 2 and 3 until the final depth of
0.630” is reached as indicated by the depth gauge. Modulus Arms suggests that the user work up
to a comfortable depth not to exceed ¼” depth of cut based on adjustment of router speed and
user experience.
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October 6, 2014
Figure 2.5: Milling the rear-shelf pocket (left) “B” depth gauge at the maximum depth for a 0.630” rear pocket
Figure 2.6: Finished rear-shelf pocket
Step 3: Fire-Control Pocket
Configure jig for drilling: The template is installed with the fire-control pocket template closest to the
buffer as shown in figure 3.1 with the drill guide installed. The 8th hole (left most) hole should be partially
covered. If the 7th hole is partially covered, the drill template is upside down.
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October 6, 2014
Figure 3.1: Jig configured to drill the fire-control pocket
Fire-Control Pocket Drilling: The five holes exposed through the rear-pocket template are drilled out with
a 3/8” drill bit (figure 3.2, right) to a depth set with the “C” depth gauge (figure 2.2, right). Finished lower
is shown in figure 3.3.
Figure 3.2: Drilling the Fire-Control Pocket Holes
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Figure 3.3: Lower with Fire-Control pocket holes drilled
Figure 3.4: Jig configured to mill the fire-control pocket
Fire-Control Pocket Milling: A router with an end-mill is used to form the cavity (figure 3.5, left) and the
completed lower with the fire-control pocket is shown in figure 3.7.
1. Adjust the end-mill to touch the top of the lower (using the rib between drill holes) – use depth
gauge to set the depth and verify.
2. Set the first cut depth to be ¼” below the surface, insert router into a trigger slot and without endmill touching the lower, carefully turn on the router, and allow the router to come up to full speed.
Modulus Arms suggests that the user first start with 1/16”-1/8” cutting depth before working up
to a comfortable depth not to exceed ¼”.
pressure. First adjoin the all holes to the trigger slot by removing the rib between the holes, then
widen until the end mill touches the side of the template. Turn off the router, wait until the endmill stops spinning, and remove from the jig. Figure 3.6 shows the lower after the first pass.
4. Check the depth using the “C” depth gauge after each pass. The final depth is shown in figure 3.5,
right. Adjust the cutting depth by ¼” at a time and repeat steps 2 and 3 until the final depth of
1.249” is reached as indicated by the depth gauge. Modulus Arms suggests that the user work up
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October 6, 2014
to a comfortable depth not to exceed ¼” depth of cut based on adjustment of router speed and
user experience.
Figure 3.5: Milling the fire-control pocket (left) “C” depth gauge at the maximum depth for a 1.249” rear pocket
Figure 3.6: Fire-control Pocket after the first pass
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Figure 3.7: Completed fire-control pocket
Step 4: Fire-Control Pin Holes
The last step is to drill the holes which accommodate the fire-control trigger and hammer pin as well as
the safety selector as shown in figure 4.1. A finished lower is shown in figure 4.2.
1. Insert the rear take down screw through the side plates (and through the lower rear take down
pin hole), and hand tighten the nut.
2. Using a wooden block or metal parallels, support the side so the side plate is parallel to the work
surface.
3. Optional: Clamp the bottom side piece in a vise, parallel to the work surface using wooden blocks
or metal parallel for spacing.
4. Using a 3/8” drill bit, drill through only one side of the lower (figure 4.1, left) for the safety
selector. (Try to make sure the drill is perpendicular to the jig before drilling)
5. Using a 5/32 drill bit, drill through only one side of the lower to form the hammer (figure 4.1,
right) and trigger pin holes (figure 4.1, center). (Try to make sure the drill is perpendicular to the
jig before drilling)
6. Turn over the lower and repeat the process.
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Figure 4.1: Drilling the fire-control pin holes using the side plate as templates to locate the holes
Figure 4.2: Trigger/hammer pin holes and safety selector holes
Helpful Hints
The completed lower is shown in the figures below. This section will focus on additional hints and
suggestions to improve the quality of the lower. The hints and suggestions may be useful to both the first
time novice as well as experienced 80% lower fabricators.
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Finishing Power Tools: The Modulus Arms jig is compatible with a number of different tools that can be
used to complete the drilling and milling process. Please make sure that you can safely operate the power
tools, and understand the manufacturer’s product manual.
A hand-drill or a drill press can be used to complete the 80% lower using the Modulus Arms jig. The handdrill is the lowest cost option, and its portability allows it to be easily borrowed from a friend or rented. A
drill press is a rarer and more expensive option, but results in reduced build time and increased precision.
 Drill Press
o Set the drill-press speed to approximately 2500 rpm.
o Make sure the drill bit is square to the table in both the x and y directions before using.
 Hand-Drill
o Using the low (2-speed) or medium (3-speed) gear option if available.
o Best results are obtained with a more powerful corded drill.
o Cordless drills will work; however, more than one battery and additional cool down times may
be required.
o For 7075 alloy lowers, the alloy is significantly more difficult to drill – a drill press is highly
recommended.
 General Guidelines and Recommendations
o Make sure the drill bits are sharp – sharpen if necessary. Dull drill bits will result in
considerably higher effort and excessive temperatures.
o To prevent damage to the template edges, start the drill when the drill tip is partially in the
drill guide. After drilling, stop the drill bit before moving to the next hole.
o Frequently clear the chips by pulling the drill bit up but not out of the drill guide. The space
between the drill guide and lower is designed to accommodate the chips.
o Clear the chips between the drill guide and lower after each hole to prevent chips from
accumulating and compacting.
o Cutting oil or WD-40 applied with a toothbrush can reduce the drilling effort.
o After each hole, use the drill guide to check the depth to make sure the drill stop did not slip.
For the milling process, the Modulus Arms jig is compatible with all common methods such as using a drill
press, router, or mini-mill. Using a drill press as a milling tool is NOT recommended and can be dangerous.
A router is common tool that is affordable and commonly used, making them easy to borrow or rent. A
mini-mill is a significantly more expensive option but results a significant reduction in build time, and an
increase in quality for the experienced user.


Drill-Press as a mill (NOT RECOMMENDED)
Router
o A router commonly used for woodworking with a standard ¼” collet.
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o
o
o
o
o
o
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The end-mill must be a 4” long, ¼” diameter end mill. Four flutes with 1” cutting depth is
recommended for best results. Longer cutting surfaces can damage the jig. Always check with
the first cutting pass that the cutting flutes are at least 50% below the jig template surface.
Routers with variable speed give the bests results, although fixed speed routers can be used.
Beware of inexpensive routers with quite a bit of flex – they can result in non-parallel walls
and damaged lowers.
The results in these instructions were achieved with a Bosch PR20EVSK Colt Palm Grip Router
with the speed set at 4.75.
End-mill cut in a clockwise fashion. Best results are achieved with light clockwise semi-circles,
trying to keep only ¼ of the cutting surface on the metal to be removed.
This jig has been tested with a number of different routers.

Mini-Mill
o A mini-mill with a Modulus Arms jig in a machine vise can be used. The x-y table offers
additional control, improved surface finish, increased speed, and reduce fatigue.
o Start with the end-mill in a drill hole and start the mill. Slowly move table front and back
without touching the jig wall to cut a slot. This must be done at a slow feed speed since the
end mill is cutting on both sides.
o Cut either toward the front or back without touching the jig wall, then move front to back
removing more material (should be done in about two passes on each side of the starting
channel).
o Carefully control both the x and y to generate a light pressure against the template for the
final pass.

General Guidelines and Recommendations
o The user should start with a shallow 1/16” to 1/8” depth of cut to gain experience before
increasing the depth of cut to a comfortable level that should never exceed ¼”.
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
o
o
o
Variable speed router is high recommended when approach the maximum depth.
The lower end mill speed allows for greater control
If the end-mill has larger than a 1” cutting surface, the first few passes need to be made
without the end-mill touching the end of the jig. Only once the cutting surfaces have cleared
the jig, should the end-mill touch the template edges to obtain the proper finished
dimensions.
The end-mill when working properly will feel like its cutting through butter. When the effort
increases, it is possible the flutes are clogged with metal. This can be removed with a small
pair of needle nose pliers.
The clogging effect can be reduced by
 Frequently coating the end-mill with cutting oil or WD-40 applied with a toothbrush.
 If possible, reduce the speed of the end-mill.
Misc. Tools: The following are suggestions based on our experience.
 Vise: The vise and work surface must not move or flex when routing. The vise needs to be either
clamped or bolted to the work surface. A drill vise shown in the figure was selected due to its lowcost, common availability, and low profile that reduces flexing.
 Shop-Vac: Great at removing chips and cleaning up the work area to prevent spreading of metal chips
 Toothbrush: Can be used to apply a small amount of oil on the end-mill.
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AR-15 Jig Instructions - Modulus Arms - AR

Transcription

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