Last time we finished discussing the parts required. The next step is to “manufacture” the receiver. For each case, I will include a link to a video or videos, and then add my comments.
Drill Press and Jig
The receiver was the reinforced polymer Tennessee Arms “Liberator”, pictured above, and the jig was the one which came with it. The jig is “sacrificial” or “one time use”, and it looks it. But then it did not cost that much, less than $25.
The package arrived in an incredible two days and at first glance looked and felt very nice. The engraving was so-so; not as big as it could be and not at all centered (I asked for a non-standard location and their equipment couldn’t handle it); the serial number meets the BATFE minimum character height, but “dense” characters such as “5” are kind of a blob. I advise you to specify a larger font for the serial number. Also, consider the fiber optic laser for the image if it has any detail; the CO2 laser cuts deeper but does not handle detail as well. The receiver has Safe/Fire markings AND safety selector stops on both sides of the receiver; a plus. Another plus is the enlarged trigger guard built in. There were no instructions in the package; it turns out they are supposed to be sent in an email, and they resent them upon request. I also found a link to the instructions on the site. Their return policy is VERY good; even if I destroy a receiver, a replacement can be had for the cost of filling out a form and shipping them the pieces (as required by BATFE) of the old one and $8.00 for the return shipping.
I’ve been told that one should avoid using lubricants with any penetrating additives on polymer as it may affect it, and acetone in any form, as it will eat it.
MY first concern was that the fellow did not use a vise; I’m astonished he did not ruin it, since on mine, at least, the bottom of the jig is NOT FLAT and rocks side to side. I strongly suggest using a vice. The vise will prevent the thing from tipping any from vertical, and can add mass to the unit, dampening the tendency to move in undesired directions. Before starting, it is a good idea to ensure that your (tilting) drill table is perpendicular to a drill in the chuck (using a right angle gauge) and the top of the jig in the (angle) vice is parallel to the drill table. A circular level is handy for checking this.
HIS first concern was that one of the bolts was not long enough. If you run into this, DON’T use a wood screw as he originally suggested. Call Tennessee Arms or go to the hardware store (or your junk drawer) and get a bolt, lock washer and nut which does fit. They do now include the longer bolt in the package, and mine came with all six screws, lock washers and nuts. It says to drill out the jig holes with the included 5/32 bit, and I did drill out and bolt all six jig clamping holes despite the instructions only pointing to five. Check for any gap at each clamp point; nothing I did could get rid of a gap between the jig sides on top at the buffer tube end. Tennessee Arms said this would be OK, as was my drilling and bolting the 6th jig hole.
The fellow in the video complained about the depth to drill which is somewhat odd. Perhaps he should take that up with Armalite who invented the receiver with those dimensions.
The depths ARE difficult to measure with a standard ruler, but a digital caliper makes it easier. Since these calipers generally have a built in depth gauge, it was easy to double check the depth of the hole before locking in the drill press depth stop. Drilling the holes produces a lot of big chips which fill up the cavity in the jig so you can’t see to place the next hole. After each hole, use a vacuum cleaner to suck out the chips, or pick up the vice and turn it over to clean them out. It was “impossible” to get exactly 1.22″ deep on the second pass; going over by 0.01″ or 0.02″ did not seem to be a problem, but don’t go any further. I also checked each of the second pass (final) holes to make sure the depth stop didn’t move on me. The masking tape marker is a good idea, although I used something with a bit more “stick” (metallic duct tape) as a guide for the first hole to set the depth gauge, and a safety check for the other holes. I should have used something with a distinctive color as the silver did not contrast against the drill. And, I used the depth stop on my drill press for both passes, as he did for the second pass. Using the depth stop on the second pass is critical; there are too many chips and not enough of the top surface left visible for the tape to be a reliable indicator on the second pass.
When milling, he held the chuck down with one hand and moved the receiver with the other, and my drill press does not have a quill lock either. I could have used the table elevation crank, but since it turned out to be quicker and easier to make shallow cuts, this was not needed. Be careful not to let the cutting part of the bit touch the sides of the template (the jig material is quite thin and soft) until the bit is deep enough that the cutting edges are below the template. The bit cuts better if you move it in a clock-wise direction around the jig cavity. The chips from milling are much finer than those from drilling, and you don’t need to see the bottom until near the end, so you can mill for a fair amount of time before emptying the chips out. The fellow in the video found that the buffer tube end of the jig did not allow him to mill to the correct depth. I think he had the bit chucked too far in; I had the end mill clamped in the chuck with nearly 2 1/2″ exposed below the chuck and it just cleared the high point of the jig. But you can cut the jig like he did if you need to.
I don’t know why he thought this task was so tedious. It looks like he tried to mill the entire .61″ at once, or maybe his drill press was not going fast enough; I set mine on 3000 RPM and the milling went quite quickly when lowering the bit perhaps 1/8″ per pass. Now fitting the hammer and trigger CAN be a bit tedious, because the shaft of the mill bit is slightly bigger than the mill itself, so when it rides on the jig, it will not cut quite enough from the sides. I used a Dremil tool with a rotary cutter to open up the sides enough for the parts to fit. The places where the width is critical are the areas around the trigger and hammer pins and above (a drop in trigger group would require a longer section to be the correct width). Places where a tight fit should be avoided are the narrow section where the trigger bar travels, and the front edge so as not to bind up the hammer (but not too much or you’ll break through into the magazine catch spring channel).
The trigger slot jig is not very good. It does not fit tightly in the top of the jig (maybe due to that gap in the main jig), so moves a bit when you use it, and comes out of the jig when you raise the bit. Also, the slot in it is the size of the cutters, not the shank, which has to go through it. This resulted in a too small trigger slot, which I had to lengthen and widen a little with the Dremil tool.
During assembly, he had some additional concerns. As mentioned, fitting the hammer (and trigger) is less tedious if using a Dremil tool with cutter and concentrating on only the critical areas. As for the safety latch plunger issue, it was indeed a tight fit and there was some flashing in the hole from drilling the safety hole. Rather than file on the pin, I just drilled the hole out slightly bigger with a number 30 drill (.128″). The flange (lower) portion of the hole was tight also, so I drilled 3/16″ deep with a number 28 drill (.140″) and the plunger then moved freely. For that matter, the safety was a bit sluggish in rotation although each side fit correctly by itself. It appeared the two holes were not quite lined up, so I took the 3/8″ drill and ran it all the way from side to side (by hand) and that allowed the safety to rotate freely.
His final concern was the need to fit the upper to the receiver, and this seemed to be a serious problem. I had to remove material from the front of the buffer tube socket AND the hole for the lug that the take-down pin goes through. If it was one or the other, and the instructions documented what to do, I might have accepted the claim that this was “to ensure a tight fit for maximum accuracy”. But since you can’t reliably tell where material needs to be removed and there are no instructions to guide you, you just have to hack at it until it fits, which seems counter to that “accuracy” claim as well as being a royal pain. It turns out that the upper I was using was not mil-spec and so needed more fitting than would normally be required, but worse was when I threaded in the buffer tube and found that it was not threaded far enough (no threading beyond the brass insert) to get the tube in enough to capture the buffer stop. I was able to “force” it those last couple of turns using a “strap” wrench, which “cut” the needed threads. But it was quite difficult, and without the stock lock of the carbine tube to keep the strap wrench from slipping and the buffer tube socket being thinner due to the material I removed from the back, I doubt I could have managed it. Trying this on another receiver which did not have any material removed from the back of the buffer tube socket, the polymer split above the brass insert.
This receiver manufacturing methodology worked quite well, but that was due primarily to the machine-ability of the polymer. I strongly suspect it would be very much more of a challenge for an aluminum receiver, particularly a forged one (see my experiences with one below). In this material, I could see this methodology being pretty good if the end mill shank was the same diameter as the cutter so it could ride on the jig and produce an accurate cavity. Unfortunately, although I can tolerate the deficiencies of the supplied jig because it does work adequately and better ones are available, and because the fixes are fairly obvious and easy, I found the amount of effort required to get the buffer tube installed to be unacceptable. This is a shame, because this really seemed to be an attractive option in so many ways. Although these receivers can be made to work, I can’t enthusiastically recommend this particular version of this brand receiver (I cut them in half and sent them back; we’ll see in the next part that the replacements live up to their potential).
Router and Jig
The receivers were an anodized forged receiver with custom logo from Atomic Engraving and another polymer Liberator, and the jig was the Easy Jig and its tool set. This is not a single use jig, and you can tell from how beefy it is. Good thing, as the price for jig and bits is nearly $200. You are supposed to be able to use it for up to 20 receivers, so the cost per unit can be quite reasonable. If you mess up a part of the jig, all parts have replacements available. Rather than “form fitting” around the receiver like the Liberator jig, this “universal” jig uses the take-down and pivot pin holes to index the receiver in the jig. Although more versatile, a potential problem is that a couple of the steps have you taking out the bolt through the take-down pin hole which could allow the receiver to shift in the jig. This did not occur in my experience. The instructions are clear and the process easy to follow.
The forged receiver was very nice; noticeably heavier than the polymer ones. The graphics were very good for the text, but the image was a “negative”. That is, the black area of the image was cut into the receiver in white, and the white area of the image was left uncut, colored with the black anodizing. A mil-spec upper fit perfectly in the forged receiver, but again not in the polymer one.
Be careful when drilling the two holes in the “rear” section (where the assembly lug of the upper goes). I noted that on the Liberator receiver, the rear-most hole in the jig looked like it would get really close to the buffer stop hole, so didn’t drill it. And when milling this area, I did not go all the way to the rear of the template because it was not necessary and would endanger the buffer stop hole. Not only was it too long (in THIS case), the template was also too wide. I found that I milled into the take down pin detent spring channel on the polymer receiver. On the Atomic Engraving lower, no milling of the take-down lug pocket was required, so I could not see if the problems with the Liberator were due to that particular receiver (most likely) or the jig.
The first step, drilling, was quite tedious in the 7075 forged aluminum with a battery powered drill. The same drill which did the entire set of holes in polymer on one battery charge with power left over was drained after only two holes in aluminum, and the pressure required was much greater, heating up the drill uncomfortably. I then tried my old corded drill, but it was much slower than the modern battery drill. I then tried my drill press. This worked pretty well for part of each hole, although I had to go to the slowest speed (about 500 RPM) to avoid serious smoking. But it would not go all the way to the bottom of the hole, having only 2 1/2″ of travel and needing at least 3 inches. The way I got it done was drill the first hole(s) with the battery drill (it was easiest, perhaps because the drill was sharper or perhaps because the holes were close to the chip channel allowing the chips to escape easier). Then I drilled the rest of the holes part way with the drill press and then removed the jig drill plate so the total depth was in range of my drill press. Using the first (completed) hole to set the drill stop, I drilled the rest of the holes most of the way on the drill press. Because of the tendency for the drill to bind, I left finishing the holes using the battery drill and the replaced drilling plate until after much of the milling was done.
The milling was quite easy in polymer, and even fairly easy in the 7075 forged aluminum with the router speed set to 26000 RPM, as the jig people recommended. But based on my drilling experience, I did take very shallow passes in the aluminum; I found that only 1/64″ per pass (very easy to set using the suggested Ryobi laminate trimmer) was fairly smooth while any attempt to go deeper than that caused chattering. Use the “tilt in” method from the second video rather than the “drop in slowly” method suggested in the instructions for the final (bottom) passes. Both the aluminum and polymer cavities resulting were acceptable as is, with no need for fitting any of the parts.
When drilling the starting hole for the trigger slot, the odds of messing it up are very high. It is HIGHLY recommended to get a center punch of the correct diameter in order to ensure the hole is centered. If it is not, the end mill will not go into it, and after you grind/file the hole sideways so the end mill will fit, there will end up being a notch in the side of your trigger slot. A drill press seems an adequate alternative to the correct center punch, and best would be to use both to ensure this critical hole is correctly placed.
With the exception of the take-down lug pocket possibly wanting to be too big (for the Liberator receiver, at least), this methodology can be a good choice, but it will take you a while (in forged aluminum anyway) unless you have better tools than mine. Maybe a billet receiver would be less tedious without the “hardening” resulting from the forging process. As for the Atomic Engraving receiver, it was an excellent choice, the engraving was pretty good, and the customer support outstanding. It did need the safety detent hole drilled out with the #30 drill like the Liberator did, but did not need the #28 drill.
Now that we have a complete receiver, let’s get it assembled and try it out. Tune in next time for the assembly process, and the results.