Dimples

• Magazine Well Dimples
• Feed Ramp Dimple
• Trigger Swell Dimple
• Safety Selector Dimples
• Axis Hole X and Y Dimples

There are several dimples that can be added to the receiver to give it that "complete" look.

Magazine Well Dimples

The receiver side dimples exist solely to center the magazine in the receiver, and to keep the magazine from wobbling and causing misfeeds.  These dimples are an "anti-wobble magazine alignment device"  :)

Dimples are optional so long as another means exists to stabilize and center the magazine.  Some people accomplish this by welding or screwing a metal shim to both inner sides of the magazine well. 

The dimples on the side of the receiver requires a stamping mold or jig of some sort that deforms the smooth sheet metal into the dimples.  

Some in the BIY community such as Machman have machined a stamping device from blocks of steel:

     

(this example is from Thud):

   

Dimple Dimensions as viewed from outside (from aceatm1nd):

• Approximately  0.150" deep 
• Inside step (narrowest part) length ~ 0.600" x width ~ 0.130"
• Outer edge (widest part) length ~ 0.965" x width ~ 0.475"

Remember you have 0.040" or 0.065" of material, so when making a jig take the thickness of the material into account.

Another dimple diagram from AKS-74U.com (credit to Keychain for the pic and jig info):

I have moved the information about my dimple jig to the Mag Well page

Comparison to my Norinco receiver.  Keep in mind that the Norinco receivers use the thicker 1.6mm receivers and so their dimples are more shallow than the 1.0mm Euro-pattern receivers:

Feed Ramp Dimple

You can make the feed ramp dimple by supporting the bottom of the receiver, allowing room around the mag well, and hammer it into shape with a scrap of stock or even wood.  Be careful as those who have done this have reported that the metal bends easier than expected.  You could also shim this and place the receiver in  a vise to apply pressure the the shim.

Some have machined or filed jigs to clamp the dimple into place.

This jig is from Thud: 

Here is how I did mine...

I started with a square-head bolt  that had a 1/2" bolt head.  I think it is a 5/16" or 3/8" bolt.

I had to grind the head down flat since the corners were chamfered, presumably to make it easier to turn with a wrench.

Using the de-milled feed ramp as a guide, I measured the size to be sure it would fit properly... the factory dimple is 1/2" wide at the flat.

    Measuring the bolt head for fit...     

Unsupported, you will experience flexing of the entire section.  A back support is required.

I have some scrap 1/4" plates I bought from a local metal salvage company... fits perfectly.  I would consider using some aluminum bar cut to the right shape as well.

I was able to move the side plates further back, creating a "notch" in the middle.  This notch is where the dimple will be formed.

Results...

Trigger Swell "Dimple"

This info is from Vulcan762:

The trigger swell is done by supporting the bottom, allow a gap to create the swell, drop a Craftsman socket of the size you want on its side and whack with a hammer. The metal really doesn't need to stretch that much and since it has not yet been heat treated works well.  Make them BEFORE the magazine opening is cut to avoid distortion. While it may not be needed, you may want to consider annealing the metal a little to make it easier to work.

His work:

My work... yes I know the trigger hole is too large - note that this is more of a test at this time.  Its ugly, but it should work. :)  I was going to use a socket but found that a discarded barrel pin makes a nice 'clean' look when used... a piece of 5/16" or 3/8" steel bar would work too.

I placed on the vise and opened the jaws just wide enough to allow the dimple to form.  I found that the entire section would bulge if unsupported, and moving the jaws closer helped to correct this. 

Safety Selector Dimples

3 different dimples, all pertaining to the safety selector.  All 3 dimples are optional.  The location of the safety selector stop and the top cover eliminate the need for these, as does the tension that the bend of the safety lever provides.

Left Side: Note the hole for the safety selector lever is in a recessed dimple.

Right Side: Note the oval-shaped dimple directly underneath the safety selector.  Note also the 'notch' that the front of the selector lever seats into when in 'fire' position:

Left Side

My first attempt at making the left side divot was more of a success than I had first expected.  Using the bottom side of my X-Y dimple "jig" (see below) I milled a 3/8" recess into the bolt after drilling the centering hole.  

Usage

NOTE:  Due to the size of this hole, it is best to make this dimple BEFORE drilling the hole to the final size.  It can be done after the hole is drilled, but I have observed that the hole will be cleaner since there is more metal there to "bite" against when pressing.  Use a center punch to align your hole, and perhaps a smaller drill bit or a centering drill bit.

Here's how the jig aligns...

Male "jig" in position.  

Female side In position.  As with the X-Y jig, I used a 3/16" transfer punch to "feel" the jig into position.  Note that I snapped this photo AFTER the final squeeze... Use a vise to insert the dimple, then squeeze.

Note the "flaring" of the hole since this dimple was made AFTER the hole was drilled... thus it is recommended to make this hole BEFORE the final hole is drilled to allow the dimple enough material to form:

UPDATE:  I think I have a better solution now - a barrel pin.  This is the second attempt, this time with just the pilot hole drilled - which was drilled off center... plan to mill the hole to final size ;)  

This time I used a barrel pin and the dimple came out nearly perfect.  The barrel pin has just the right diameter to mate properly with the 'female' jig to make this work:

Right Side

I milled a shallow channel in the other side of the mag well dimple die.  This aligns with the safety selector holes BEFORE drilling to ensure a nice clean bend.  Alignment after drilling doesn't look as clean.  

Here I used a normal punch to make the dimple and will clean up with a dremel polishing wheel.  I need to make a mating make jig to work with this die, and clean up the slot somewhat.  It *does* work in its present form, however.

This is an example of the right side dimple made AFTER the safety selector keyhole was cut.  Note how the edge of the dimple closest to the hole is slightly deformed.  This does not affect function of the safety lever, however the safety lever requires slightly more pressure to engage.  The negative effect is mainly cosmetic:

Axis Hole X and Y Dimples

Axis hole X and Y Dimples are completely optional.  I think they were originally intended to reinforce the FCG's axis pins and to aid in assembly (x goes here, y goes there) but no one has said for certain.  They are a requirement for those looking for the "authentic" look.

Aceatm1nd used a dremel router table and a cut-off wheel to make the punch, and a carbide burr to slot the die plate.  When done you will have a Y punch that also does X's, just turn it 180 degrees.

To use, hold the punch with a pair of vise grips and hit it good with a 3 pound hammer.  You should always wear a glove and hold the punch with vise grips, because if you held the punch with your hand and slipped, you would break bones at the very least - BE SAFE.

My work on the X and Y dimples...

Making the "jig"...

The male side is a piece of 1/4" stock with a raised notch milled into it.  You can also do this with a file.

I started with a 3/4" head bolt for the female side.  I wish it were just a bit larger - perhaps 13/16" or 1" head.  The ends of the grooves are really really close to the edge of the bolt head and it may not survive repeated usage.   

I cut the bolt down to 1.25", then cut it another .05" - the thickness of a washer.  This allows you to use the bolt when the rails are already installed: 

I used my mill to align and drill a 3/16" hole in the bolt, to allow me to center it in with the holes in the receiver.  I next used my mill to mill a 3/16" V-groove in the bolt.  The notch depth should be no more than one "thickness" of the receiver - I'm using older Ace blanks so I milled 0.04" depth.  This should work fine for the newer ones too.  Any deeper, then the dimples will not allow the shepherd's hook retaining wire to engage the pins.

To get it to fit properly, I shaved off part of the head to allow me to get it close enough to use on the trigger Y dimple.  I found that I still had to file a bit down on the opposite side, since the left rail was preventing the bolt head from aligning with both rails installed.  You can barely see the interference I am talking about here:

Removal.  I had to pry the receiver loose with the hammer handle.  I may shorten it another .05" and use two washers instead of one.  This will allow me to push out the washer, then the jig will fall free.

Align, Align, Align!!!  You want your dimples to "line up" and this method makes it somewhat difficult.  If you use a different male jig, it will be easier.  In the future I may use a bolt head to make a matching male jig.  Then just align and press.

My 5" shop vise had more than enough force to create the divots.  I positioned the male side and then secured with masking tape... this allowed me to visually inspect before applying the final squeeze to the vise.

I am using a 3/16" transfer punch to "feel" it into the center.  

Use a sharpie marker to align the holes on the jig, and transfer the lines to the side of the receiver:

Chase the hole with a "J" drill since creating the dimples will cause the hole to go out of round.

Results

           

Additional results.  Note the sharpie markings used to ensure alignment on the bolt head and on the side of the receiver:

Pins align good.  I'm going to polish it some with a flapper sanding disk to clean it up.