Assembled AK-47 Kalashnikov.

Ствольная Коробка — Резки

Receiver Fabrication — Milling

We are building a Kalashnikov receiver, the Ствольная коробка, or stvol'naya korobka, the "barrel box" as the Russians call it. We have bent a flat into the overall shape. Now we need to mill the top rails of the receiver to carry the bolt. This is one in a series of pages about reconstructing an AK-47, Автомат Калашникова 47, Avtomat Kalashnikova 47 or Kalashnikov Automatic Rifle 1947 Model.

This picture shows why this part of the project is required, and how far we have progressed so far.

The original receiver has been cut into three main pieces with a saw and a torch, and most of the central part is missing.

Destroyed Romanian AK-47 Kalashnikov receiver, and a new receiver being built.

Above that is a new receiver being built from a flat. As shown on the preceding page, the receiver flat has been built into shape.

The next step is to mill the top rails of the receiver to the proper dimensions.

AK-47 Kalashnikov receiver and adjustable parallel.

An adjustable parallel will keep the receiver from collapsing while clamped in a vise and cut with an end mill. Red marking dye is on the top rails, and they have been scribed with the end points of the needed cuts.

The flats are intentionally made too wide, so that even if your bends are somewhat rounded or misplaced, there will be enough material left to provide the needed rail width. Not that the receiver will work if the bends are too misplaced or ill formed, but at least you won't be lacking the needed top rail material.

The receiver is in the vise in this mill. Right now it is resting on a pair of parallels. Because it is tapered, that means that the top rails are not level. We will rotate it so the top rails are roughly level, and clamp it firmly in the vise.

The adjustable parallel is slightly below the top of the vise jaw faces.

Scrap pieces of index cards are between the work piece and the vise jaw faces. These prevent marring and better grip the work piece.

AK-47 Kalashnikov receiver clamped in a mill.

A carbide end mill bit is cutting the rail. Start by making one pass that just barely touches the rail, to produce a straight surface aligned with the table's direction of motion. We then used a commercial receiver as a reference, comparing the reference and this piece to calculate how much needed to be removed.

Do the cutting in multiple passes taking away about 0.025" on each pass, intentionally aiming for about 0.005" oversized. Then one more cut should put you within 0.001-0.002".

Remember that you can always cut more away, but you can't put it back.

AK-47 Kalashnikov receiver being cut with an end mill.
AK-47 Kalashnikov receiver being cut with an end mill.

We added a small clamp for some of the cuts, to reduce the chatter when cutting near the ends of the rails.

AK-47 Kalashnikov receiver being cut with an end mill.

Cut just a little at a time. After cutting away another 0.025" or so, deburr the cut and measure carefully.

This is the notch at the rear of the top rails.

AK-47 Kalashnikov receiver after being cut to the proper dimensions.
AK-47 Kalashnikov receiver after being cut to the proper dimensions.

This is now a properly dimensioned receiver.

The rail dimensions we used, in inches, are shown in this table.

The end mill is round, so there is a radius rather than a square step. The quoted distance from the end is to the deeper edge of the radius. That is, to the narrower segment of rail.

Left Rail   Right Rail
Width Distance from rear Width Distance from rear
N/A 0.000-0.305 N/A 0.000-0.305
0.135 0.305-0.597 0.135 0.305-0.597
0.085 0.597-1.758 0.085 0.597-1.758
0.192 1.758-3.575 0.192 1.758-3.575
0.175 3.575-4.375 0.175 3.575-4.375
0.192 4.375-6.989 0.192 4.375-6.580
0.163 6.989-7.560 0.133 6.580-7.560
0.097 7.560-end 0.097 7.560-end

Next step: Riveting and heat treatment

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