3D Printing the Hellfire Lower, continued


Sometimes 3D printing is as easy as selecting a .stl file, pressing the slice button in your slicer, then hitting the print button.

Sometimes it isn’t.

I had some old printer filament that used to print wonderfully. I pulled it from storage and was trying to print with it. The layers were delaminating and it did not want to stick to the print bed. Likely the filament absorbed moisture during storage and is no longer good. So I opened up a new roll of marble filament.

This is the time I learned about the Hellfire lower, so I start printing one.

The nozzle clogged partway into the print.

I had been using that nozzle for a while, and it was overdue replacing, so I replaced it.

I had to re-adjust the height of the print bed after doing this.

Then I was able to print the good lower.

The Hellfire lower prints with a minimial amount of pre-made supports. It cleaned up rather quickly and mostly easily with a pair of plyers and a scraper tool. There were a bunch of little zits, blobs, and stringing in the magwell that cleaned easily. It was much easier to clean up than the slicer generated supports on that other lower I printed.

As I started printing the other parts, I had issues with bed adhesion. The parts filament absolutely did not want to stick to the bed of the printer. I had to cancel most of the prints a few minutes into them it was instant failures.

This part, for example, started good. But once I left it unattended it turned into spaghetti.

The rear of the receiver took two tries to print. Most of the others took several more.

During these prints I increase the amount of material in the first layer, and moved the nozzle closer to the print bed in an attempt to fix this.

I print on a mirror. I ended up bring in the nozzle too close and scratching up the mirror. So I threw away that mirror and installed another IKEA mirror that came in a pack of several.

The lower wasn’t the cleanest or best print. There was a little bit of poorly overhang filament that was preventing the rear of the receiver from installing. A moment with the scraper cleared off that plastic and allowed the rear of the receiver to slide on.

The two bolts seemed to me that they would hold on that section well enough. But I’m not sure how it will hold up under stress.

When the prints would stick to the bed, they still weren’t sticking well, and the would curl upwards away from the bed of the printer.

Despite this warping of the bolts and parts, they still went together easily.

If I could sing, I would sing complements of this design.

For the most part, I was able to assemble the lower like a standard AR15 lower.

The front takedown pin is extremely hard to open and close. Because the detent goes though a piece, it tends to hang up there causing me to struggle opening and closing it.

While I was working on it, I did the foolish thing of dropping the hammer with out the upper installed. This is something you are not suppose to do on a standard lower due to the chance of damaging it.

Immediately cracked the lower.

If the bolt catch had been installed, that might have provided the support necessary to prevent that area from having cracked. But either way, that won’t prevent function. I’m just going to leave it broken. I might rip out that chunk before I install a bolt catch.

This lower is somewhat rigid, but I can grab it and twist it a little, flexing it. I’ve read some people report their fire control group pins drifting out using use.

I don’t imagine this lower would last forever, but I have no doubt it would work. As for ergonomics, the thicker lower section where there are two bolts holding on the rear of the receiver extension makes the gun a little less pleasant to handle. But not terribly so.

Ignoring the various printing problems I ran into (that are not the fault of the lower), this has been one of the easiest 3d printer projects I have done. If you were new to 3d printers and wanting to print a lower, I would recommend this one.

I’ll probably go ahead and print another, nicer version of this lower sometime. But for the moment I am happy enough with how this one turned out.


  1. Now you start to appreciate why I believe that 3D printing isn’t the manufacturing revolution that some people think it is…

    For production of large numbers of parts/objects, it’s slow. It often needs a bunch of clean-up after printing. It might not hit sizes reliably.

    • “start to appreciate”? I’ve been 3d printing for years.
      Despite the issues I talked about. I probably only have about a half hour of labor into that lower. Starting a print is still only a few clicks of the mouse, and if it fails, it is still often only a few minutes of downtime before I am back up printing.
      If someone wanted to make a lower at home, I know of no simpler or easier way. To do something like buy a harbor freight minimill and attempt to mill one would take a great deal more skill and effort, not to mention cost. The cheapest minimills tend to run about twice what my printer cost me.
      It is a revolution. It is not magic, it has plenty of limits, but it can make many products that majority of people otherwise could not have.

  2. Thanks for posting Howard,

    I’ve printed several ‘Bolt’ and Vanguard lowers with encouraging success. I think I’ll try the HellFire and WildFire next.

    …so true
    “It is a revolution. It is not magic, it has plenty of limits, but it can make many products that majority of people otherwise could not have.”


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