Chapter 1:  

The tools:


The following tools are required to build the KT Ordnance KT-15 lower receiver assembly.

1. A Drill Press;  (A cheap drill press will do.  A $50 or $60 drill press is perfectly adequate)

2. A small milling machine; (One can use a drill press and an X-Y table in lieu of the milling machine.  However, special care is needed.  This will be explained in the section entitled: “Magazine Catch Slot Machining”.)

3. A ¼” end mill;


4. Various small files including a small triangular file;


5. A pair of dial callipers.   An adequate pair of callipers may be had for $30.

6. A 12-18” long pipe wrench or other similar adjustable wrench.  (I believe that the word “wrench” is the same as a “spanner” in England.)  

7. The following drill bits are available from MSC Industrial.  (http://www.mscindustrial.com)  These bits are important and the builder should not use cheap bits.

¼” bit—part no. 60221496—Price: $1.75.  
13/64” bit---part no. 60221462—Price: $1.38.
1/8” bit---part no. 60221413----Price: $0.91.
5/32” bit----part no. 81181109----Price: $1.18.
3/8” bit---part no.  81181240-----Price: $4.55.
3/32x6 aircraft extension bit---part no. 01008424----Price: $1.32



8. A one and three sixteenths by sixteen tpi tap. This tap is available from Brownells as part no. 8K00CHD.  This tap is used to tap the buffer tube.  This tap costs $42.07
(http://www.brownells.com)

9. One AR-15 jig available from CNC Gunsmithing.  This fixture costs $90.00.   (http://www.cncguns.com)

Chapter 2:

The Jig:  

An essential part of any AR-15 or KT-15 build is the CNC Gunsmithing AR-15 fixture.  This precision tool consists of two aluminium blocks.  The blocks are machined on CNC equipment; they allow the AR-15 builder to precisely locate the various receiver holes that must be drilled.

Even though the holes are precisely indexed and located on the KT-15 receiver, the CNC fixture enables the builder to properly hold the receiver during various drilling operations. The very first operation is the tapping of the buffer tube.  But before detailing this step, I should first explain how to install the receiver inside the CNC fixture.

1. Before placing the receiver inside the CNC fixture, make sure that the two aluminium blocks are loosely attached to each other.  The two blocks screw together via two hex screws.

2. The left aluminium block is drilled with various holes.  These include the five main holes to be drilled on the KT-15. These holes are the front and rear takedown-pin holes, the hammer and trigger holes and the fire-selector hole.

3. The fire selector hole is at the rear of the receiver.  It is instantly recognizable as it is the largest hole that must be drilled.

4. Place the receiver between the two blocks.  The rear of the receiver is the end that features the fire selector hole.

5. Tighten the blocks slightly.




6. Turn the blocks and the receiver upside down.  Place the assembly upside down on a flat table.  The top of the receiver will bottom out and align itself with the top of the CNC blocks.

7. Once the top edges of the receiver are aligned with the top edges of the CNC blocks, one must align the rear of the receiver with the rear of the blocks.

8. Take a flat surface such as a machinist’s block, a plane of glass etc. and press said flat surface against the rear of the receiver and the blocks.  Make sure that the rear of the receiver sits flush with the rear of the aluminium blocks.

9. Tighten the hex screws and make certain that the screws are absolutely tight. Use an allen wrench to fasten the screws.  It is essential that the blocks cannot move during the drilling process.

10 Inspect the block/receiver assembly under a strong light.  
Make sure that the upper receiver surfaces are aligned with the tops of the blocks.  Inspect the holes and ensure that the “dimples” on the receiver are aligned with the holes on the left side block.  Once you are certain that everything is aligned, you are ready to start machining.

Chapter 3

Tapping the Buffer Tube:  


In the previous chapter, I explained how to place the KT receiver within the CNC jig.

With the receiver clamped within the jig, work can begin on tapping the buffer tube.

The first step in tapping the buffer tube is to clamp the jigged receiver in a bench vise.  Make sure to protect the sides of the jig by wrapping a rag around the sides of the aluminium blocks.  

Wipe motor-oil or cutting oil onto the inside of the buffer hole.  You should also wipe oil onto the buffer hole tap.  I used Rotella T 15W40.

Start the tap into the buffer tube using your fingers.  Take a pair of pliers or vise grips and grasp the shank of the tap.  Twist the tap into the buffer hole until the tap bites into the aluminium.  Once the tap bites the metal, get out your pipe wrench or other long adjustable wrench.  Use the wrench to grasp the shank of the tap and turn the tap as far into the buffer tube as it will go.

After turning the tap all the way into the buffer tube, withdraw the tap.  Then turn the tap into the buffer tube one more time.  After withdrawing the tap, clean the buffer tube area using canned air or an air hose.  You must remove all the aluminium shavings from the receiver.  Wipe down the buffer tube using a clean cloth.  And clean the tap and put it away!!

The buffer tube tap is an impressive tool but don’t let it intimidate you.  Keep in mind that the KT Ordnance receiver has a pre-tapped buffer tube hole.  The receiver is pre-tapped with larger threads and all you have to do is to chase these larger threads with your tap.  The larger threads will allow you to easily centre your tap within the buffer tube hole.  The


tapping operation is simple and should take less than 5 minutes.

The key things to remember: Clamp the receiver in a bench vise and use a long handled wrench.   You will need to generate leverage, so get a long handled wrench.  And make sure that you lubricate everything using cutting oil or motor-oil.  If you follow these steps, you will cut the buffer tube without difficulty.

Chapter 4:

Drilling the Receiver holes:  

With the buffer tube hole tapped, you are now ready to drill the receiver holes.  There are a few important things to keep in mind.

1. The quality of your work depends heavily on your tools. Do not use cheap Chinese drill bits.  You must acquire the best drill bits available.  The bits available from MSC are first class and you should consider ordering them if you cannot easily find proper drill bits. Do not buy cheap, common drill bits at your local hardware store!  I made this mistake with my first build.  From now on, I only use top quality US-made drill bits.

2. Before drilling anything, make sure that your drill press spins truly.  Inspect the press to see if the spinning drill bit wobbles.  You should get a new drill press if your press is a “wobbler”.

3. Do not even think of using a hand drill to finish your receiver.  It can be done, but trust me---it is generally a very bad idea to forego a drill press.

4. If you plan to use your drill press to mill the magazine slot, make sure to drill your receiver holes first.  The importance of this step cannot be overstated.

With the above caveats out of the way, let’s discuss the drilling.  Ensure that the jig is clamped inside a drill press vise.  The vise is orientated so that the drill bit can enter the pilot holes located on the side of the jig.  Drill the selector hole with a 3’8” bit.  Drill slowly and carefully; use lots of cutting oil.  You must drill through both sides of the receiver.  The drill should operate at slow to medium speed.  

The hammer-pin and trigger-pin holes are both drilled with a 5/32” drill bit.  The front and rear takedown pin holes are both drilled with a ¼” drill bit.  With all of these holes, you must drill

through both sides of the receiver.  I say again:  Use lots of cutting oil.

The final hole to be drilled is the rear trigger-guard-pin hole.   This hole is drilled with a 1/8” drill bit.  Drill this hole through both sides of the receiver. Be careful!  Do not apply excess force; if you do so, damage can result to the trigger guard area.  Do not drill the left front of the trigger guard area!  The  front of the trigger guard only has one hole; this hole is located on the right side of the receiver.  

In summary:

1. Make sure that the jig screws are tight before the drilling begins. Make sure that the jig is still perfectly aligned.  Do not remove the receiver from the jig once drilling has begun.
2. Use a drill press to drill the holes.
3. Inspect your drill press to ensure that it spins truly.
4. Do not use a hand drill.
5. Use lots of cutting oil.
6. The drill should operate at slow to medium speed.
7. Use only quality drill bits.
8. If you must use the drill press to mill the magazine release slot, make sure that you drill the receiver holes first.
9. Work carefully and slowly.


Once the drilling is done, the receiver is almost complete.

Drilling the Detent Holes

Chapter 5:  

When I first started, I had no idea what the heck a “detent” was.  I assume that you are in the same boat.  In the AR-15 context a “detent” is a spring-loaded pin used to retain some other pin.

The AR-15 lower receiver features 4 main detents.

1. The Buffer Detent:  This detent fits into the buffer stop plunger hole.  The buffer detent retains the buffer and spring in place inside the buffer tube hole.

2. The Front Takedown Pin:  This detent prevents the front takedown pin from falling out of the receiver.

3. The Rear Takedown Pin:  This detent prevents the rear takedown pin from falling out of the receiver.  When the rifle is fully assembled, the rear takedown pin detent is secured by the stock.

4. The Selector Detent:  This detent holds the selector shaft.  This detent prevents the selector from falling out of the receiver.  When the rifle is fully assembled the selector detent is retained by the pistol grip.

Drilling the Front Detent Hole:  ( Use a 3/32” drill bit)

Stand the jigged receiver up.  The receiver should sit on the rear surface of the aluminium blocks.  The front nose of the receiver should point straight up towards the drill press.   The receiver assembly is then secured within the drill press vise.

The front right side of the receiver features a round rib.  The front takedown detent hole is drilled into the front face of this rib.  The exact position of the detent hole is not critical.  You should “eyeball” the drill bit so that it drills directly into the centre face of this rib.  The drill bit should be drilled to a depth of 1.125”.   Measure the drill bit with dial calipers and mark the correct 1.125” depth with a piece of tape.  By “eyeballing” the

tape, you can assess the depth of the drill as it bores into the hole.

Drilling the Rear Detent Hole:  (Use a 3/32” drill bit)

Stand the jigged receiver up on the front edge of the blocks.  The rear of the buffer tube will point straight up towards the drill press.  There is a piloted hole on the right rear of the buffer tube tower.  This hole serves as a guide for the rear detent hole.  With the receiver assembly secured in the drill press vice, drill the detent hole located at the right rear of the buffer tube tower.  Drill until the detent hole reaches the rear takedown-pin hole.

Drilling the Selector Detent Hole:  ( Use a 1/8” drill bit and a 5/32” drill bit)

Underneath the selector hole at the bottom of the receiver is a shelf.  The selector detent hole is drilled through the shelf up into the selector hole.  The correct location for this detent hole is determined as follows:

1. Use a very sharp pencil or a scribe to mark the mid-point of the right hand selector hole.  Draw or scribe a line from the mid-point of the right hand selector hole down to the bottom of the receiver.  (Down to the receiver shelf) Turn the receiver over and continue this line along the width of the receiver shelf.  At the midpoint of the receiver shelf and along the mid-point selector hole line, mark a hole using a punch.  The receiver should still sit within the jig at this point. It should also be secured within the drill press vise. The CNC Gunsmithing jig holds the receiver perfectly square and if you do not use the jig, you run the risk of botching the job.  The receiver must be held absolutely straight.

2. Drill from the punched mark using the drill press and 1/8” drill bit.  Drill all the way until the bit enters the selector hole.  

3. Use a 5/32” drill to countersink the 1/8” diameter hole. Drill the 5/32” bit to a depth of 0.188”.   The 5/32” drill is marked with tape so that the 0.188” depth can be easily “eyeballed”.


Drilling the Buffer Stop Plunger Hole:


This operation causes a lot of difficulty for many builders.  The original Armalite drawing required this hole to be drilled at an angle of 6 degrees.  The KT Ordnance drawing is hopelessly confusing and to simplify matters I came up with my own method of drilling this particular buffer hole.

The buffer stop plunger hole is drilled directly at the foot of the buffer tube tower uprights.  The hole is drilled at the midpoint between the uprights. The hole is drilled with a ¼” drill bit.  The hole is drilled to a depth of 0.712”.

The reason why the hole is drilled at an angle is that the buffer tube tower would otherwise interfere with the drill bit.  In order that the drill bit clear the tower, the front of the receiver must be raised about one inch. When the front of the receiver is so raised, the rear of the receiver lowers and the drill bit will clear the buffer tube tower.  So here is what you ought to do:

1. Install a ¼” drill bit in your drill press.  Unplug the drill press.

2. Place the jigged receiver assembly beneath your drill press.  

3. Lower the drill until it brushes against the midpoint of the buffer tube tower.  

4. Raise the front of the receiver assembly until the drill bit just clears the buffer tube tower.  You will have to raise the front of the receiver about one inch.

5. Once the receiver is properly raised to allow the drill bit to clear the buffer tube tower, clamp the receiver assembly securely within the drill press vise.  The drill bit will clear the tower by the slightest fraction of an inch. ( approximately one cat hair )

6. Drill the hole.  Use care and lots of cutting oil.   The hole is drilled so that the right hand edge of the hole touches the first two threads of the buffer tube.

This completes the drilling of the detents.  There are four remaining operations:

1. Milling the magazine slot
2. Cutting the front receiver forks
3. Cutting the trigger guard slot
4. Drilling and tapping the pistol grip hole.

Cutting the Magazine Catch Slot:

Chapter 6  

This operation causes some builders to have problems.  I know; I was one of them.  The KT Ordnance drawing was impossible to understand.  However, through the actual measurement of a completed KT receiver, I came up with simple easy to understand numbers.  And my method has been proven to work with another recent build.

The top of the frame forms the Y coordinate zero. The left front edge of the magazine well forms the X coordinate zero.  The magazine slot is cut from (-0.939”, 3.075”) to (-0.939”, 1.575”)
The magazine slot is cut with a ¼” end mill.  The depth of the cut is approximately 20 thousanths of an inch.

The magazine slot should be cut with a milling machine; however, it can be done with a drill press and an X-Y table.  If you cannot use a milling machine, you should understand the limitations of a drill press.  

A drill press is not designed to withstand lateral loads.  If you try to make deep cuts with a drill press, you will ruin the machine in short order.  You should make very shallow cuts when using a drill press.  To cut the magazine slot with a drill press, you should make 5 or 6 passes while removing three thousandths of an inch at a time.  I call this “ the mouse cut”.  It is called the “mouse cut” because you must “nibble” away a few thousandths of an inch with each pass.  Do not get greedy!!

And if you make a habit of using a drill press as a milling machine, eventually you will cause the machine to suffer run-out.  If you must use a drill press to machine your magazine slot, you should drill the receiver holes first.  

And while on the subject of drilling holes, I prefer not to use a milling machine to drill holes.  It is a pain in the clinton to change bits in a milling machine; I also found that I needed more vertical travel than the mill would allow.  


Trust me.  Even if you have a milling machine, you need a small cheap drill press.  And if you don’t have a milling machine, you can mill the slot using care, an X-Y table and a drill press.

Finally one word of caution:  The numbers given earlier apply only to the KT Ordnance receiver.  These numbers do not apply to other versions of the AR-15 lower receiver.    

Chapter 7

Cutting the Trigger Guard Slot:  

Before I describe the cutting of the trigger guard slot, you should first take a close look at the left side of the KT-15 receiver.  Take a good look at the rear trigger-guard-pin hole.   When you turn the receiver over, you will see a rectangular pad that measures 0.687”x0.438”.  

When you turn over the receiver, also look at the surface underneath the front trigger-guard-pin hole.  You will see a “pad” of metal that measures about 0.690”x0.287”.  

These metal “pads” are important because in these areas one must machine the trigger guard slot.

The trigger guard slot is approximately 0.432” wide.  Now please do not worry about this number.  The trigger guard slot is a non-precision number.  There’s a lot of play in the various trigger guards available today.  And you can always fit a trigger guard to a particular slot.  So don’t worry about the 0.432” number.  That’s just what my particular KT-15 measures.

The two “ears” formed by the slot are both about 0.131” wide.  The depth of the slot is about 0.250”.  Now the exact depth of the slot is also not a critical number.

The cutting of the slot with a milling machine:

1. Turn the jigged receiver over onto its back;

2. Locate the rear trigger guard pad;

3. Fix a ¼” end mill in your milling machine.

4. Set the Y zero on the top edge of the rear trigger guard “pad”.

5. Set the X zero on the right hand edge of the rear trigger guard “pad”.


6. To form the upper trigger guard “ears”, cut a ¼” wide slot from (-.131”, 0) to (-.131”, -2.98”). The slot is cut to a depth of about 0.250”

7. To form the lower trigger guard “ears”, reset your X and Y zeros as follows:

8. The new Y zero will be the bottom edge of the rear trigger guard “pad”.  The X zero will remain the right hand edge of the rear trigger guard “pad”.

9. Form the lower trigger guard “ears” by cutting a ¼” slot from (.131”, 0) to (.131,-2.98”). The slot is cut to a depth of 0.250”.

This will complete the trigger guard slot.  At this point take an AR-15 trigger-guard and check the fit of the guard within the slot.  You may have to file the slot or the trigger guard slightly.

You should also realize that the trigger guard slot can be formed using a drill press and an X-Y table.  Just “nibble” away at the metal with multiple passes.  Do not get greedy and try to mill away .250” of metal all at once.

The trigger guard slot may also be formed with a small jeweller’s hacksaw, (coping saw) and some small files.  Here is how to do it:

Use dial calipers to scribe a line about 0.131” on either side of the metal “pads”.  Use a small triangular file to form small grooves at the scribed lines.  Use a small hacksaw to cut away at the small grooves.  Make the hacksaw cuts about 0.250 deep. Go slowly and be careful!!  Take a small triangular file and make a cut at the centre of each pad.  You will have small “fingers” of metal between the centre file-cut and each hacksaw cut.  Carefully remove the “fingers” using a dremel tool, small hacksaw or a file. If you do not know how to use a dremel tool, don’t even think about using one.  (I have a dremel tool and my skill level is such that I am afraid of using it.)

Carefully continue filing until the slot is properly formed.  File slowly and measure often.  Keep the AR-15 trigger guard handy and check the fit of the trigger guard.

Important Note:

The numbers above apply to the KT Ordnance KT-15 only.  Other receivers will vary.  Each KT-15 receiver is exactly the same, so these numbers can be used with confidence.

When filing aluminium, please remember that aluminium will clog your file.  Keep using a file card to remove aluminium.  You should also buy a bunch of cheap Chinese made files for this operation.  ( Who cares if you ruin a bunch of cheap files?)

Chapter 8  

Forming the Front Receiver Fork  

The front of the AR-15 receiver terminates in two “ears”.  The two “ears” also form the receiver “fork”.  The upper and lower receivers attach between the two ears.  The front takedown-pin fits between the upper receiver lugs and the lower receiver “ears”.  The front takedown-pin is also called the “pivot pin”.

To form the front receiver fork, I first had to get the numbers for the width of the “ears”.  Two separate Bushmaster receivers were measured and the ears measured as follows:

Rifle No 1:  Left Ear: 0.285”, Right Ear: 0.275”
Rifle No 2:  Left Ear: 0.283”, Right Ear: 0.273”

Before doing anything take a look at the front of the receiver.  Take note of a round cylindrical area between the two takedown-pin holes.  This is the area that must be cut for the front receiver fork.

Use dial calipers to scribe lines about 0.30” from the edge of each front takedown hole. (The lines are scribed onto the “cylinder”)  Use a triangular file to cut a small hole at the centre of the cylinder.  Use the triangular file to lightly groove both scribed lines.  Then use a small hacksaw to cut about .35” towards the magazine well.  Go slowly and be careful!!  After cutting both scribed lines, you will have small metal “fingers” between the hacksaw cuts and the triangular file cut.  Remove these metal fingers using the hacksaw.  Or if you are skilled enough you may use a dremel tool.  Form the rest of the fork with a file and remember to be careful.  You must file a slot between the ears. This slot must be flush with the front of the magazine well.

You should measure your upper receiver lugs in order to determine the correct width of your front receiver ears.  Then you should carefully file the “ears” to proper width.  




Again, you should use cheap disposable files and you must keep those files clean.  The aluminium receiver is easy to file.  Just keep filing away patiently.  Don’t be tempted to rush anything.

Of course one could also mill the “fork”; however, it can be tricky standing the receiver straight up and getting proper clearance on a small milling machine.  With a large milling machine, I would use a ¼” end mill to cut a slot 0.390” deep and to thereby form the ears.  

Chapter 9

Drilling and Tapping the Pistol Grip Hole  

Take one AR-15 pistol grip and fit it over the KT-15 pistol grip triangle.  You will see the pistol-grip-triangle located at the rear of the receiver beneath the fire control hole.  The pistol grip-triangle is marked with KTO’s logo and the date of manufacture.

If the pistol grip will not sit in place properly, file a little metal away from the back of the “triangle”.  Once the pistol grip fits properly, take a pistol grip screw and dip it in layout blue or paint.  Pass the screw into the pistol grip and allow the screw to come in contact with the bottom of the pistol grip triangle.  

When the screw comes in contact with the metal, you will have a mark identifying where to drill the pistol grip hole.

Turn the jigged receiver over and allow it to sit on the buffer tube tower.  Place a small wooden block under the buffer tube tower and in so doing you will raise the lower pistol grip triangle into a horizontal position.

Once raised into a horizontal position, the lower pistol grip triangle can be drilled.  The jig is secured within the vise and the pistol grip hole is drilled with a 15/64” drill.  The hole is drilled all the way through to the interior receiver fire-control pocket.  After the pistol grip hole is drilled, it must be tapped with a 1/4”x28 tpi tap.

When tapping the hole, use lots of cutting oil.    

Chapter 10

Drilling the Bolt-hold open hole:  

The AR-15 features a bolt hold-open device.  This handy gadget allows the bolt to lock open on an empty magazine.  Some military rifles such as the G3 and AK-47 do not have a bolt hold-open device.  Some people don’t like bolt hold open devices, while others love them.

If you do not want a bolt hold open on your AR-15, you don’t need to have one.  If you want to install one, here’s how.

At the outset, this step can be really tricky.  But if you approach matters the right way, you can drill those bolt hold open holes without much difficulty.

First of all, take a look at the left side of the receiver. Do you see those two cute little ears that sit at the top of the receiver just behind the magazine well?  Those ears are designed to retain the bolt hold open.  The two ears must be drilled with a 3/32” x6 aircraft extension drill.  But how?

Here’s how:  Take apart the CNC jig and remove the receiver.  Notice on the left hand block there are two slots.  These slots allow one to slide the block down onto the receiver.  The receiver walls slide into the block and the block fits onto the receiver.  To the left of the leftmost slot is a 3/32 hole that serves as a guide to drill the hold open ears.

How to drill the hold open ears:

1. Push the left hand CNC block down onto the KT receiver.  The slots on the block slide down over the receiver walls. Push the block forward until it stops just behind the hold-open “ears”.

2. Use a “C” clamp to fasten the block to the receiver.  The block must not slip.




3. With the block held fast, clamp the receiver in a bench press vise.  The receiver must stand with the buffer tube facing up.  The receiver must be clamped between wooden blocks within the drill press vise.

4. Fix the 3/32”x6 aircraft extension drill within your drill press.

5. Carefully guide the drill bit into the 3/32” hole that sits to the immediate left of the left hand block slot.

6. Carefully drill through the bolt ears.  Use slow to medium speed.  Be very careful not to break through the rear ear thereby striking the receiver with the drill bit.

7. Work slowly and carefully and use lots of cutting oil.


This completes the machining of the KT-15 receiver.   The next step is anodizing.

Chapter 11

Anodizing the AR-15 with the Caswell 3Ampere constant current rectifier.    

Introduction: The U.S military specification for AR-15/ M-16 anodizing is something called “MIL-A-8625A”.  This specification calls for Type III hard-coat anodizing.  Type III anodizing is beyond the scope of the homebuilder.  Type III anodizing requires cold temperatures and very high current densities.  This type of anodizing is potentially dangerous and is best left to commercial concerns.  On the other hand, Type II anodizing can be done at home using a relatively low powered supply as sold by Caswells’ Plating.  

The anodizing process as described below will result in a 20 micron thick layer being deposited on the surface of the receiver.  Although not as thick as Type III anodizing, Type II will provide a surface that is just as hard.  Type II anodizing will more than suffice for our purposes.  The lower AR-15 receiver is not subject to great stress and Type III anodizing is just not necessary.  Of course, once Type II anodized, the receiver will be dyed.  It can also be coated with a very tough layer of baked on gun-kote, but this is entirely up to the builder.  The resulting receiver will be extremely durable and attractive in appearance.

Note:  All these operations are performed while wearing gloves.  Skin oils will thwart anodizing.  And of course, gloves protect the skin from the dangerous, corrosive acid.   It is also important to keep large amounts of baking soda handy at all times during the anodizing process.  The baking soda is used to neutralize the acid in the event of a spill.  It is highly recommended that the anodizer have an assistant present.  In the event of an acid spill, one may have to immerse oneself in a solution of baking soda and water.  The presence of an assistant will advance the cause of safety and will allow for orderly and careful anodizing.  The anodizer and assistant should also wear proper protective gear such as chemical gloves, goggles and thick clothing.

Materials needed:

One Rubber Maid plastic tank:  ( Available from Walmart)
One sheet of aluminium.  ( Such sheets are commonly used to repair auto bodies. You can use aluminium foil for the anodizing cathode, but a roll of sheet aluminium is easy to work with.) The aluminium sheet should be about 24”x10”.
Battery Acid
Distilled Water
3A Anodizing Power Supply available from Caswells.  (http:www.caswells.com)
Anodizing dye. (From Caswells)
Anodizing sealant. (From Caswells)
Aluminium Desmut solution. (From Caswells)
12 g. aluminium wire available from Radio Shack.
1. Clean the AR-15 receiver by dunking it in a bucket of hot distilled water and detergent.  Use a toothbrush to thoroughly scrub the receiver. Rinse.

2. Repeat step1.

3. Once you are confident the receiver is clean, repeat step 1 and rinse again.

4. Immerse receiver in a solution of boiling tri-sodium phosphate. .

5. Rinse in distilled water.

6. Etch the receiver for 20 seconds in a lye solution.  (drain-opener)  This is an optional step.

7. Rinse and dunk the receiver in a bucket of distilled water.

8. While the receiver sits in distilled water, prepare the desmut solution according to the directions on the bottle.  The desmut solution is a liquid that is added to distilled water.  The desmut process removes impurities from the surface of the aluminium. The desmut process also de-oxidizes the aluminium surface and prepares the receiver for anodizing. ( Note: This is an essential step)

9. Once the desmut procedure is finished, rinse the receiver in distilled water.  Dunk it again in the distilled water.

10. Using a pair of needle-nose pliers, fold some 12 g. aluminium wire over onto itself.  This folded up wire is then forced into the pistol grip hole of the receiver.  The receiver is mashed down over the doubled over wire.  The wire is forced to take the shape of the pistol grip threads and you actually “screw” the receiver down onto the wire. It is very important that the wire is very tightly wound into the threads.  Unless the connection is secure, the correct current will not flow and the anodizing process will fail. But not to worry, it is easy to properly secure the connection.

11. Once the aluminium wire is tightly wound into the pistol-grip threads, you are ready for anodizing.  Place the receiver into the vessel so that it sits upside down. The aluminium wire attached to the pistol grip hole will stick straight up.

12. The cathode is a round sheet of aluminium metal.  The sheet is held in place by two clothespins.  The receiver is placed inside the ring of aluminium.  The receiver must sit about 3 to 5 inches away from the cathode.  The top of the cathode is connected to the power supply via an alligator clip electrode. The electrodes are attached to 12 gage copper wire conductors.  ( Note: the receiver should never touch the cathode.)



13. The receiver and cathode are covered with a water and acid solution. The water is added first. Pour in three gallons of distilled water.  After the water is in the tank, add one gallon of battery acid.  Remember the AAA rule.  ALWAYS ADD ACID. If you add water to acid, the acid may splash all over you.   (The acid may be obtained from stores that sell truck batteries.)  The cathode is not totally immersed in the acid/water solution.  The top part of the cathode juts out of the solution.  

14. The receiver is connected to the positive side of the Caswells’ 3 A power supply.  The cathode is connected to the negative side of the supply.

15. The power is turned on.  The current (amperage) control is set to minimum.

16. The voltage is set to maximum.  The load is connected and then the current control is advanced until the digital display reads 3 Amperes.  When you see 3 Amperes displayed, you know that everything is properly connected.  You should monitor the display at five-minute intervals just to ensure that the pistol-grip is still electrically connected.

17. The receiver is anodized at 3Amperes at a temperature of 72 degrees for 90 minutes.  The temperature of 72 degrees is important.  Do not try to anodize below 65 degrees.  At low temperatures, you will need much more current than the supply can deliver.

18. After anodizing, dunk the receiver in a bucket of distilled water and baking soda.  Then rinse, rinse, rinse in distilled water.  Dunk the receiver in distilled water and let it sit there until you are ready to dye the receiver. Do not let the anodized receiver dry.

19. Prepare the dye solution according to the product’s instructions.  Heat the dye solution to 140 degrees and dunk the receiver therein for at least 15 minutes. The receiver is hung into the solution using a length of 12 g. aluminium wire. The dying step is optional. You may choose to not to dye if you are going to gunkote.  ( But I think that dyeing is an important step.  The dye reaches places where gunkote may never reach.)

20. Rinse, rinse, rinse using distilled water.

21. Prepare the sealant solution.  The sealant is mixed 1 oz per gallon of distilled water.  The sealant solution is heated to 180 degrees F and the receiver sits therein for at least 20 minutes. Again the receiver is hung into the solution using the aluminium wire.  ( Note:  One can seal an anodized part by merely dunking the part into boiling water for 20 minutes or so. The use of a specialized sealant is optional.  I would just dunk the receiver in boiling water for 20 minutes.)

22. Rinse, rinse, rinse.



23. Hang the receiver up to dry.

24. After the receiver is dry, it can be gunkoted, but that is for another day.  It is probably best to wait several days before gunkoting.

25. Once the acid/water solution is no longer needed, it should be neutralized with lots of baking soda.  Keep adding baking soda until the solution stops fizzing.
It takes about 5 pounds of baking soda to neutralize a 5 gallon acid/water solution.  Once the acid/water solution is neutralized, you can safely pour it down the drain.

Chapter 12

Anodizing the AR-15 with the Caswell 3Ampere constant current rectifier.

Dealing with acid.  


Here are a few tips regarding battery acid.

You can purchase battery acid at your local NAPA store.  Please keep in mind that the store clerks may ask you stupid questions regarding your purchase of battery acid.  It appears that some Arab tried buying large quantities of acid and this set off alarm bells.

So when you buy your acid, just tell them that you bought a marine battery that was shipped dry.  This ought to satisfy them.

Depending on where you are, acid is sold in different containers.  A friend was able to buy acid in convenient bottles.  However, I could only locate a 5 gallon box of battery acid.  The box houses a heavy-duty plastic bag that containing the acid.  Inside the box there is also a rubber hose connected to the plastic acid bag.  The hose also features a plastic plug and a metal shut off valve.

Here is how I safely handled the acid:

1. I bought large quantities of distilled water.  The distilled water came in 1 gallon jugs.
2. I poured one gallon of distilled water into the anodizing tank and I kept the empty 1 gallon water jug.
3. I donned protective chemical gloves and goggles and so protected, I placed the acid box on a chair on my porch.  The acid box was slightly inclined.
4. I had lots of bicarbonate of soda and distilled water on hand in case of a spill.
5. I removed the rubber hose from the acid box. Very carefully, I cut the end of the hose and removed the plastic plug.
6. I carefully placed the hose over the mouth of the 1 gallon plastic jug and released the shut off valve.
7. The acid began to flow into the 1 gallon jug.  I used the shut off valve to control the flow of acid.  (I was very careful not to allow the acid to overflow the jug.)
8. With the jug full, I had one gallon of battery acid. I carefully shut off the acid valve and while wearing gloves, I flushed the small plastic plug in a solution of distilled water and bicarbonate of soda.  Then the plastic plug was pressed back into the acid hose.
9. I wiped down the outside of the acid hose with a sponge soaked in distilled water and bicarbonate of soda.
10. I withdrew the acid hose and placed it back inside the cardboard box.  The hose was sealed and I made sure that the valve was securely shut.  
11. The box was taped shut and the acid box was removed from the anodizing area.  
12. With the acid out of the way, I was ready to set up your anodizing cell.


13. The rubber maid container was readied with the cathodes in place and the prepared receiver sat in the middle of the tank.
14. The 12g. aluminium wire pointed straight up in the middle of the tank.  
15. I poured three gallons of distilled water into the tank.  Carefully pour the gallon container of acid into the tank.  ( Remember: Always add acid)
16. After anodizing, the acid was neutralized.  I dumped 5 pounds of bicarbonate of soda into the anodizing tank.  This will made the acid/water solution safe.  Once neutralized, I dumped the former acid/water solution down the bathtub. And then I rinsed off the cathode plates.