This guide completes a forged AR-15 that is 80% lower. These steps also apply to the completion of the billet and the bottom of the AR9. We also use a popular elite builder jig that comes with an end mill bit and a drill bit. These steps describe how to use a drill press or mill to lower it by 80%.

Are you new here? Don’t know where to start? Check out these guides:

Are you using a drill press? Please read first.

What is 80% lower?

80% jig builder guide

You will need the following tools:

Drilling machine or milling machine

Vise for clamping 80% jigs

Machining oil for lubrication

Optionally, you can also use:

Digital caliper

Drill stop collar

Elite builder jigs include:

(1) 3/8 drill bit-5 inches

(1) 5/32 drill bit-3 inches

(1) 3/8 short end mill-3 inches

(1) 5/16 short end mill-4 inches

(1) 3/8 long end mill-4 inches

If you’re new to 80% bottom machining and don’t know what tools are needed or recommended, and why, check out this guide: Tools you need to finish the bottom. This section details the use of a drill press or milling machine. Both methods are explained here as well.

New! Video description

Feel free to use the in-depth instructional video along with this written guide. Learn how to use Elite Builder jigs and drill bits and end mill bits in drill presses.

Written instructions

Secure the bottom with a jig

Place it 80% below the jig plate on the right side so that the pins on the plate disengage from the inside of the rear takedown and the holes in the pivot pin. Secure the left jig plate to the other side and stand the assembly vertically.

Install the template plate holder

Next, attach the template plate holder. Install the holder over the jig so that the rounded edges touch the buffer tube housing. Bolt the holder to the side plate using the two largest hex bolts included.

Install the pilot whole template and vise

Attach the pilot drilling template plate to the template plate holder using two small countersunk hexagon bolts. This first plate is marked “3/8 DR 2.00 DEEP FROM THIS FACE”. Then tighten the jig and lower it to a vise for machining.

WARNING: Do not over tighten the vise. Only light pressure is needed to keep the jig from moving while working. If you over tighten the vise, the side plate will bend. This can cause the jig and bottom to be misaligned.

3/8 “Install the drill bit

Collect the included 3/8 “drill bits and attach them to a drill press or milling machine. Align the jig and bottom with the tool and drill 80% from each pilot whole guide on the template plate to the bottom receiver. Template plate Drill to a depth of exactly 2.000 “from the top of the. Set the depth stop of the drill or mill accordingly.

Drill the receiver pilot hole to a depth of 2.000”

Lubricate the template plate guides and receivers with machined oil to extend bit life in this step. You will need this bit to complete the pin hole on the safety lever. Drill exactly 2.000 “depth from the face of the template plate to the receiver. If desired, set a depth stop on the drill or mill and optionally use a stop collar and caliper to reach the final depth. Make sure that is 2.000 “. Once all pilot holes have been drilled, remove the 3/8 “bit and pilot hole plate. Replace the plate with the first milling machine template. Marked as” 3/8 EM1.375 “DEEP FROM THIS FACE.”

Mill the receiver to a depth of 1.375”

If you want to use a drill press, please read the “Drill Press” section first.

Replace the 3/8 “drill bit with a shorter 3/8” end mill bit. If necessary, attach a drill stop collar to the bit shaft and use a caliper to ensure that the cutting depth is exactly 1.375 “from the face of the template plate. The bit shaft is the internal shape of the plate. This will cut the shape of the receiver to the appropriate size. Apply a large amount of processing oil or lubricant to the end mill bit, the work area, and the template plate. It is recommended to remove the aluminum with a shallow incremental path, when the final cutting depth is reached to reduce bit run out and chatter.

Cut the receiver using a drill press

Unlike milling machines, which can cut almost any material laterally (left and right), drill presses are designed to provide only vertical machining. The milling machine uses threaded and locked quill, spindle, and chuck to prevent the tool from falling off the machine under lateral loads. However, many drill presses use tapered spindles and chucks that are press-fitted into the machine. Large lateral loads increase the risk of the press-fit spindle and chuck falling off the machine. There are two ways to safely cut an 80% lower fire control cavity using an end mill bit with a drill press:

Plunge cut

The attached end mill bit is a center cut. This means that you can cut both vertically and horizontally. Vertical cutting is easy. Just use an end mill bit like a drill bit.


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