Finishing an 80% AR Lower Receiver – Part 2, by 2A Advocate

(Continued from Part 1.)

WHAT DO YOU HAVE TO DO?

You will need to create a space within this block of aluminum to install the fire control group: The trigger, hammer and safety selector control. Here is how that’s done:

Setup of the Easy Jig 2
Photo 1

So, the Easy Jig 2 is a very cool tool! It is extremely heavy duty. Several of the parts do double duty; it is very well-engineered. Assembly is simple: (Photo 1) attach the two square side plates to the top plate. The words “AR-15” are at the top and there is a right and left. (If milling an AR-10 lower receiver the plates are rotated and attached in the same location with the words “AR-10” facing up and out). The red buffer screw holder is attached with 2 bolts with the letters “AR-15” facing up. (Turn it over, rotate it and use the 2 outer holes for an AR-10). The drill extension pieces are bolted to the two side plates. (These are not used on the new Easy Jig 3). Start the buffer tube screw into the red holder. Done.

Insert the lower into the jig
Photo 2
Photo 3

Turn the jig upside down and insert your 80% lower (Photos 2 & 3). Thread the buffer screw through the red holder and into the buffer tube threads in the receiver. Leave it loose for now. There is a short pin with a ring on it: push it through the front holes in the jig and through the front pivot pin holes. It will lock into place.

Photo 4

The long pin goes through the hole marked “A” in the side plates, and through the rear takedown pin hole. (Yes, it’s the “A” hole – did they do that on purpose?) The long black bolt gets tightened between the 2 big side plates to keep them from moving in the vise and the buffer tube screw gets tightened securely. With these 4 attachments the lower is totally solid in the jig: no movement at all (Photo 4). Also, if you take the lower out of the jig and need to do more milling later the lower goes right back into precisely the same location in the jig. Ask me how I know this!

Pilot Hole
Photo 5

Lock the jig into a vise. I really liked using my drill press vise for this project. It kept the work plane at a comfortable height when I was seated. Right at a good eye level and comfortable for my arms when milling. Make sure everything is level. There is a metal block that bolts to the jig top router plate. It sticks up about one-half inch when bolted on (Photo 5). Use a 21/64” drill bit, with lots of cutting fluid in the hole and on the bit. Drill all the way through the lower receiver; about 1.3 inches. It took me 2 to 3 minutes to accomplish this.

Photo 6

Be patient, use a medium cutting speed on your drill, and just medium pressure. This keeps the bit and the workpiece cooler and prolongs drill bit life. You will hear the drill motor slow down as you near the bottom of the hole. In fact, it may grab and stop. You may have to reverse the drill; you may have to remove the bit, clean out shavings and relubricate. Use a corded drill for all the drilling steps. 80% Arms states that cordless drills don’t have enough power for the drilling steps. (However, I notice they are using a cordless drill in their new Easy Jig 3 video!) This pilot hole serves as the beginning point for each milling pass with the router (Photo 6).

You have now made one machining step on your 80% complete lower. Even though it is not functional at this stage, it is now legally considered a firearm!

Router set up

The router bit is proprietary to the Easy Jig 2. A router is used for the milling. A modern router will make life easier here. Really, don’t try to use your father’s 30-year-old router. I used a Makita RT0701C. There is a list of tested routers and comments about them here (See page 24, Appendix A). There is a small router attachment plate included with the jig kit. It does not fit all routers, so make sure yours is compatible. (They like the Dewalt DWP611 and the Ridgid 2401.) With the router cord unplugged, remove the existing round plate at the base of the router and install the plate that came with the jig with 4 non-tapered screws. (From the router or the ones included in your kit). The opening in the router attachment plate faces away from the router power cord. Remove the collar from the router and loosen the collet nut. Insert the end mill and tighten the collet nut very tight. Then tighten it again!

Milling the trigger pocket

Work in a garage or shop. You will get lots of aluminum shavings and some oil on your table or bench and floor. I read that the volume of the aluminum chips is 15 times the volume as a solid! You are also using cutting fluid, so it’s a bit messy. Attach your shop vacuum hose to the open end of the red 1-1/4” buffer screw support. (You might need to MacGyver it with duct tape).

Look at the top of your lower receiver (Photo 3). Is there a square hole already milled out right in front of the buffer tube threads? If so, it’s a generation 2 lower. If it is generation 2, move that long pin from the “A” hole into the hole in the router plate, as seen in Photo 1 near the letter “T” in “RIGHT”. This keeps you from milling too far back. You may have to loosen the buffer screw to get the pin out, then tighten up the buffer screw again.

If you have a generation 1 lower receiver, the whole top of the lower is flat. You must mill out that rear pocket, so leave the long pin in the “A” hole for now. Sorry.

On the jig top router plate are 3 pockets labeled “A”, “B” and “C”. Turn the router sideways and set the end mill tip into pocket “A”. Adjust the tip just to the first hash mark in pocket “A” (Photo 6).

Give a squirt of WD-40 or cutting fluid of your choice on the top of the lower receiver where you will mill. Turn on the shop vac. Make sure that you have your hearing and eye protection on! You will have to adjust the router RPM based on your judgment. 80% Arms suggests starting at 75% of maximum speed and adjusting to find your optimum setting.

Photo 7
Photo 8

Insert your end mill (in the router and adjusted for depth) into the pilot hole with the power off (Photos 7 & 8). Make sure the router attachment plate is positioned flush on the router plate (the top of the jig). You should be able to rotate the router around its axis, but it should not move in the x or y directions. Hold the router in a firm two-hand grip where you can reach the power switch with at least one hand. The grip is firm, to hold the router down on the router plate. It’s not a death grip; you must be able to slide the router around the plate to mill. Starting at the pilot hole make small CLOCKWISE circles working away from the buffer tube in the center of the pocket you are milling. When you reach the limit of movement, reverse travel direction back toward you, clockwise. Again, when you reach the limit, go around the edges with the end mill up against the router plate, again moving clockwise.

Photo 9

Give special attention to the corners and shoulders. I make a final pass through the center in case the end mill bit shifted at all. If the end mill extends, it goes deeper and can leave a slightly elevated ridge down the center. Turn off the router, wait for it to stop completely, then lift it out of the pocket. Check the end mill depth on the hash mark to be sure the bit isn’t slipping, or the collar on the router isn’t slipping. Adjust the end mill depth to the second hash mark on pocket “A”. Brush any remaining aluminum chips off the router top plate, the trigger pocket you just milled, and the bottom of the router. Sweep chips remaining in the trigger pocket toward the vacuum with a 1” foam brush. Give another squirt of WD-40, set the end mill in the pilot hole and make a second pass. Photo 9 shows the trigger pocket after a pass or two with the router.

Moving the router around is more by feel than by sight. Most of the time you cannot see down into the trigger pocket. When milling the edges of the pocket, just keep pressure on the router so the bushing built into the router adapter plate stays against the edge of the jig top plate opening. This will result in a very nice straight edge. It’s like running a pencil around inside a stencil.

Continue with each hash mark in pocket “A”. If you have a generation 2 router you just continue with pocket “B”. If you have a generation 1 receiver, now move that long pin from the “A” hole to the hole in the router top plate to protect that rear shelf area from further milling.

Photo 10

For pocket “B” 80% Arms recommends advancing just a half of a hash mark at a time. As the end mill gets extended more and more, there is less support on the end mill and more likelihood of a little wobble. Cutting less material at a time gives a much smoother job with less vibration and chatter. When you get to the bottom of pocket “B”, the trigger pocket is complete. Also, roughly halfway into pocket “B” you will see another hole appear in the trigger pocket (Photo 10). This is normal, it’s a hole that was drilled from the bottom by the manufacturer that will be used to secure the grip when you install your lower parts kit.

Milling the trigger slot
Photo 11
Photo 12

Now the drilling block is reinserted, this time upside down, so it fits down flush with the router plate (Photo 11). Adjust the end mill on the first hash mark in pocket “C”. This time the end mill goes through the oval opening in the drilling block. Again, put the end mill into that same pilot hole. Slowly make a few more clockwise passes, advancing until the end mill is at the bottom of pocket “C”. The milling steps are now finished! Next,  remove the drill block (Photo 12).

Drill the hammer pin, trigger pin and safety seLEctor holes
Photo 13

Remove the entire jig and lower receiver combination, vacuum off the worst of the chips, then reclamp on one side in your vise (Photo 13). Reinsert the long pin into the “A” hole. Make sure it’s level and use the 5/32” drill bit with cutting fluid on the bit and in the holes. Put the bit all the way into the hole against the lower receiver before starting the drill. Only drill through one side of the receiver. Again, just light pressure and about 3/4 speed of the drill. Do the same for the 3/8” hole. About half speed, just light to medium pressure. Turn the unit over and drill the three holes on the other side.

Done!

Cleanup
Photo 14

Go ahead and remove the lower receiver from the jig (Photo 14). Unscrew the buffer screw, remove the long and short pins from the takedown and pivot pin holes and remove the long black bolt running between the two side plates. The lower is quite messy with oil and aluminum chips. Don’t wipe it off; vacuum the worst and rinse with a hose over a bucket. Then wash it with dish soap so the finish doesn’t get scratched by the metal chips.

(To be concluded tomorrow, in Part 3.)

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