This is a brief overview of how my two-part printed Lower Receiver is assembled into a fully functional Lower Receiver.
You’re going to do what now?
I’m going to assemble an AR-15 Lower Receiver from parts. The lower Receiver is the part of the AR(Armalite Rifle)-15 civilian firearm that contains the fire control group, the magazine well, and attaches the stock to the Upper receiver which holds the bolt and the barrel. On its own, the Lower Receiver is hardly recognizable as a firearm. One would be more likely to confuse an upper receiver by itself for a firearm than a lower. But the Lower Receiver is the part on which the serial number is stamped, and of all the distinct components of the complete rifle, this part is legally considered to be ‘the gun’ even without all the other parts. Thus, a firearm transfer is required to just this part from anywhere outside my state(legally, you’re buying a firearm from out-of-state). But one is legally allowed to make one of these for personal use(not with intent to sell) without needing a firearm manufacturer’s license from the BATFE. It is less expensive to print my own than to buy one.
These are the parts I will be using.
Parts which will make a stripped Lower Receiver a fully-functioning lower.
After printing both parts of my two-part lower Receiver, I must remove the support material which I added to the models to facilitate printing. This support material was added by me in the model itself, so the model was sliced and printed without automatically-generated support material. It was only necessary in a few specific areas, and milling material out of every qualifying cavity is very time-consuming. And unnecessary with my modeled support.
A view of the model showing the support. And the beards for printing to prevent warp.
The support material can be broken away with a screwdriver.
A pair of pliers can pull the support material out easily.
The support material is fully removed.
What once was on the part as support material.
After the support material is removed, the magazine well is tested for fit. The printed model has artifacts from printing, and interior spaces seem to be slightly undersized after printing.
Once magazines fit properly in the well, the magazine catch is installed.
Magazine catch, spring, and button
The catch installed in the lower.
Magazine catch button in lower
After the magazine catch is installed, the official guide says to do the bolt stop, but I did this a little out of order. It doesn’t really matter. The fire control group is next.
The Trigger, trigger spring, sear, and trigger pin.
Trigger, sear, and pin as they appear in the lower.
hammer, hammer spring and retaining pin
Hammer , trigger, and sear as they fit together in the lower.
fire control installed, the cocked hammer is visible as I open up the hole for the bolt catch pin.
bolt catch, spring, and nub
inserting the bolt catch pin carefully with pliers.
with the bolt catch in place, I squeeze the pin through the other hole.
Next up is the front pivot pin which holds the Lower Receiver to the upper.
Carefully drilling the pivot pin holes. They were mostly the correct size as printed, but with the drill i can clean up any artifacts and make sure the pivot pin slides smoothly.
Pivot pin slides smoothly.
hand-turning this drill bit, I clean out the pivot pin retainer spring and pin hole.
Pivot pin, retaining pin and retaining spring.
Pivot pin installed.
Buffer tower part of my two-part lower. An older version and the latest print.
4mm bolt and nut which I use to attach the two parts of my lower together.
nut held captive in the front part of the lower.
Two parts bolted together.
Now that the rear part of the lower is assembled, I can install the safety in the fire control group.
Safety parts
The safety goes into the hole behind the trigger, just in front of my two-part attachment bolt.
takedown pin, retaining pin and spring.
Cleaning out the takedown retaining spring and pin hole
Buffer and retainer visible in the lower receiver
Safety and takedown pin installed, along with the buffer assembly
Some would consider the lower to be complete at this point(minus the handgrip). You may notice a captive nut in the handgrip area. This nut I added to my printed lower after stripping the plastic threads of my previous versions of printed lower receiver.
Now I will add my combined grip and stock to the lower and have it fully completed.
My combined Grip and Stock attach to the printed lower.
Parts needed to finish attaching the grip and stock to the assembled lower.
sling mount attached. I don’t need it to attach a sling, but it does have threads for the nut that holds the butt in place on the stock.
Butt attached to stock
Attaching an upper receiver first with the front pivot pin.
Closer on the pivot pin. It slides so smooth like butter.
Attaching next with the rear takedown pin. filing down the mating surfaces of my two-part lower made this pin also slide in very smoothly. Previous printed lowers had been very difficult to attach here.
The Complete Rifle. This is a .22LR upper.
That redesigned handgrip/buffer tube area looks a whole lot better than the previous version. Just a couple quick questions:
Which bits did you use to drill out the various holes?
Are you going to post the files for your new designs?
Thanks for this post though! It looks like a pretty good project to undertake. I’m going to try after I move (Spring)
3/16 for the bolt catch roll pin and retainer springs
9/64 for the safety detent
17/64 for the pivot and takedown pins
files posted.
awesome job. thank you!
It looks like you made this to take a rifle buffer tube, is that right? A1 or A2?
Thanks,
Mike
I think its a2. I bought the buffer assembly used on gunbroker.
OK, thanks. I’ll get an A1 tube with an A2 spacer just in case.
I know this is a lazy question, but i gotta ask. BOM available for the build?
lazy answer:
http://www.ar15.com/content/index.html#guides
Thatll work, thanks for the quick response!