Joystick Repair

I intended to post this a few months ago, but the old server had simply gotten too rickety to cope with new posts, much less OS or WordPress updates.  So I opted to roll an entirely new VM with an OS version published this decade.  Hopefully previous posts imported properly, but the site may be a work-in-progress for a while.

A friend’s all-in-one Namco joystick had broken, and they wondered if I might be able to fix it.

The issue was that the bushing that the joystick shaft is pressed into had split.  Since it looked to be Nylon, my guess was that just trying to glue it back into place (even with epoxy) would not last long as a fix.

While the manufacturer is still in business (though on a different URL), their site doesn’t appear to have any mention of this particular unit.  I wasn’t really expecting to find an exploded diagram and parts ordering form anyhow, but once in a while pleasant surprises pop up.  Not so in this case, so time to wield Phillips screwdrivers with careless abandon.

The joystick mechanism looks to be secured under that square base plate.

This turned out to be a far more complex mechanism than I had anticipated.  It wasn’t until I gave the unit back that I learned that this is due to the Pole Position game using joystick twist for steering instead of normal left/right movement.

My plan was to find some thinwall stainless or brass tubing to sleeve the outside of the bushing and thus collapse down the split section.  I didn’t have much luck in finding an appropriate size tube in the McMaster-Carr catalog, however.

No big deal when you have machine tools, though!  I found a piece of scrap stainless rod, faced the end, and drilled a shallow hole with a W size drill bit (0.386″, which is just the size of the bushing’s outside diameter).  I then thinned down the outside until I reached a point of ‘that looks about right’.  This turned out to be a wall thickness of around 0.017″ which I hoped would be thin enough to retain full movement of the stick.

After parting off the ring, I did a little light deburring.

The ring pressed snugly into place on the bushing, and the crack is practically invisible now.

I carefully hammered the joystick shaft back into the bushing when done.  Interestingly, the end of the shaft has both splines and ridges to keep it from pulling out and from twisting – that should have been a clue to me regarding the twist operation.

A few games of Galaga verified that operation is back to normal!

Gunsmithing the RAS-12 – Part 1

It’s no secret that I have a penchant for oddball guns, be they paintball marker or firearm.  Seeing a design that’s off the beaten path is always enjoyable, be it for mechanical ingenuity or sheer impractical novelty (though usually a peculiar blend of both).  During a recent visit to my friendly local FFL (always good for a rousing discussion and perhaps lightening of my wallet) a friend and I perused a distributor’s sale flyer and immediately spotted an intriguing item – a 12ga shotgun upper for AR-10 lowers.

For those unfamiliar with the AR-10, it is the bigger, older brother to the AR-15 rifle.  In fact, much of what was considered new or novel at the time of the AR-15’s introduction is properly credited to the earlier AR-10 design.  Unfortunately, there is far less standardization on the AR-10 platform than there is on the AR-15.  Eugene Stoner actually updated his AR-10 design decades later to have much greater commonality with AR-15 parts (resulting in the KAC SR-25), while Armalite (not the original Armalite that actually developed the AR-10, just somebody who bought the name and rights) developed the AR-10B using an upper from an SR-25, and somehow DPMS came up with a mashup of these designs, and then…  …yeah, I don’t really understand it all either.  We’re left with saying ‘AR-10’ as a generic terminology for something that looks like an AR-15 but fires a .308 round – as someone once wryly observed, “there’s an XKCD for everything“.

The important part is that the modularity of the AR-15 and AR-10 allows different upper receivers to be mounted to a common lower receiver (which is, as I’ve noted in previous posts, the one part that is itself considered the ‘firearm’ under US law).  While the AR-15 is far more standardized than the various AR-10 incarnations, the magazine well of the AR-15 limits what ammunition can easily be fed through it.  In fact, this limitation has been the underlying factor in the development of various new cartridges such as the .50 Beowulf, 6.8 SPC, .458 SOCOM, etc.  Although a 12ga shotshell by itself will just barely slip through the magwell of an AR-15 lower receiver, designing a practical magazine to feed that ammunition through said magwell is out of the question.  So, the next best thing is to scale up to the larger AR-10 lower receiver.

The ever-popular Magpul .308 magazines will happily accept a standard 12 gauge shotgun shell (extracting said shell is another matter, though).  The rimmed base of the venerable shotshell does not lend itself well to use in a box style magazine (as opposed to the tubular magazine that most traditional shotguns use).  As an aside, this issue isn’t unique to shotshells.  The rimmed base of the famous .44 Magnum round (feel free to insert your favorite Dirty Harry quote here) has limited its use in semiautomatic handguns to only 2 models in history, as far as I am aware – the iconic Desert Eagle, and Emilio Ghisoni’s masterpiece, the Model 6 Unica.

The designers of Kalashnikov derived shotguns (such as the Saiga-12 and Vepr-12) use special magazines with a fairly severe feed angle to improve reliability when stripping and chambering a round.  Unfortunately, that doesn’t translate terribly well to using a straight magwell and magazines designed for rimless ammunition.  The designers of the RAS-12 opted for a pretty radical approach to this problem – they designed their own ammunition.  Which is probably why I managed to snag this very interesting upper for less than a sixth of its original retail price – not much more than 2 years after announcing the product, the company doesn’t seem to be in business anymore.  I may write more on this later, but I’ll limit myself to covering just the ammunition in this post.

The ammunition comes in boxes of 5, with 20 boxes to a case.

The cartridges look very little like a traditional shotshell, and very much like a modern rebated rim pistol cartridge.  In this manner, it is reminiscent of the .50 Beowulf cartridge designed for the AR-15 platform.  The rounded nose and rebated rim makes feeding far simpler than with a standard 12ga shotshell, and allows for easy adaptation of existing magazines.

The most significant feature of the cartridges is obvious – they are not of metal construction, but polymer (US patent 9109850 calls out polycarbonate and nylon as suitable materials, though various online sources specifically note polycarbonate as the hull).  This feature alone is what made me take notice of the system, given that I’ve done a bit of tinkering with 3D printed polymers in gunsmithing applications.  Even if supplies of the original ammunition dry up *cough* Gyrojet *cough* Dardick *cough* EtronX *cough* it should still be possible to recreate the cartridges in a reverse-engineered fashion.  I’m somewhat surprised that the RAS-12 designers didn’t opt to ‘open source’ the design, as SAAMI standardization is precisely what has allowed previously proprietary cartridges to survive in the market if not outright flourish.

I carefully disassembled a cartridge to determine the weights (in grains) for all of the components:

  • Projectile half: 512.4 gr
    • Nosecone: 24.8 gr
    • Nine pellets of 00 buckshot: 481.2 gr
    • Wadding: 6.4 gr
  • Propellant half: 191.0 gr
    • Nitro card: 13.0 gr
    • Gas seal: 17.0 gr
    • Powder: 29.0 gr
    • Hull: 117.2 gr
    • Primer: 14.8 gr

…for a grand total of 703.4 grains for a fully assembled cartridge.  There’s certainly a bit of tolerance to these measurements, but they should serve as a suitable starting point for weights.  Now, to start measuring the hull and nosecone to draw up in CAD…

4-jaw chuck for the Keiyo Seiki

I recently had another Keiyo Seiki/Homach lathe owner contact me, and I mentioned that I had been meaning to get around to posting a copy of the manual that came with my machine.  It turns out that other owners have been looking for one, so hopefully this helps a few people: Keiyo Seiki Homach KM-1800C lathe manual

When I purchased my lathe, it came with both a 3-jaw and a 4-jaw chuck – the 3-jaw was mounted to the headstock and the 4-jaw was in a box.  However, the first time I wanted to try using the 4-jaw, I discovered that the chuck uses a D-6 camlock mount, not the A-6 mount that the lathe spindle actually has.  Apparently I had been given the incorrect chuck, but it had been long enough that I didn’t have the seller’s information anymore.

My first thought was to see if I could somehow mount the 4-jaw with an adapter plate of some sort – the jaw body itself mounts to a ‘spider’ that has the camlock lugs on it, so all I would need to do is to replace the spider with a backplate.  Well, in an ideal world, that would be the case.  The screws that attach the spider to the chuck body are attached from the spider side, not from the front face of the chuck.  Thus, using an adapter plate would be a mechanical impossibility with no way to reach the attaching screws.  So now I have a D-6 4-jaw that needs a new home, and I needed to start from scratch.  Off to Enco!

Enco did in fact have the sort of 4-jaw chuck I was looking for (I selected it based on the size of object it could pass – anything smaller than the headstock ID would be wasteful), so I purchased it during one of their free shipping promotions.  All I needed then was a backplate, which I procured from “Industry Recycles” on Ebay.  I think it was actually an Enco offering but I managed to snag it for about half price.  Score!

Unlike the backplate for the 5C collet chuck, this backplate mounted up just fine.  The trick, then, was mounting the chuck to the backplate rather than mounting the backplate to the lathe.  Mounting hardware was easily purchased from McMaster-Carr, and then it was time to start making holes in things.

Given my experience with the 5C collet chuck mounting, I decided to be a little more precision oriented this time around.  I started by measuring the hole locations on the chuck itself.  Using calipers and screws inserted into the mounting holes, I measured the distance across each pair of screws (both ‘inside’ and ‘outside’ measurements).

I found that the locations of the four mounting bolt centerpoints differed by about 5 thousandths of an inch.  Instead of just basing my cuts on a single measurement, I opted to use the average instead, which came out to be a bolt circle of 5.10425″, or a radius of 2.552″.  Easy work – put the backplate in the vise in an orientation that will clear the existing holes, indicate the center bore, and drill 4 holes at +X, -X, +Y, and -Y locations of 2.552″.

Wait, the Y handwheel stopped….

Noooooooooo!  I ran out of travel little more than an eighth of an inch from the lowest hole location.  I started to resign myself to moving the vise to a new location on the table (I hate having to re-indicate in a vise almost as much as tramming the head), when I realized “duh, just rotate the hole pattern by 45 degrees”.  So each hole would be at X/Y +/- 1.8045″.

After drilling, I ran a M14x2.0 tap through the holes.

The backplate mounts just fine to the lathe spindle….

And the 4-jaw mounts just fine to the backplate!  I started right in on drilling some Delrin for a new product offering.

FCG pocketing with CNC

A long-running project I’ve been tinkering with occasionally over the years has been machining an AR-15 lower receiver from scratch (or more precisely, a raw 0% forging).  I’ve made a fair amount of progress thanks to the excellent video done by Frank Roderus (which is a great machining tutorial even if you have no interest in firearms) as well as the Ray-Vin machining tutorial.  However, it’s really slow going, and I’ve made a few small mistakes.  Completing an 80% lower seemed like a good way to feel like I’ve accomplished something and would be a nice CNC project.

Drilling the holes for the takedown pins, selector, hammer and trigger pins, etc. is pretty straightforward after planing the top surface of the forging.  For an 80% lower, the takedown pin holes are already drilled and you can just use a drilling jig to drill out the holes on a drill press.  Call me a purist, but I still prefer just putting the lower in the mill vise as above, indicating from the front takedown pin hole, and drilling the rest of the holes with positions called out with the DRO.  The jig is invaluable for the various milling operations, though.

While the jig works great on the big manual mill, I can’t exactly clamp it into the diminutive vise on the CNC Taig, so I needed to determine a way to secure the fixture to the Taig table.

The 10-32 tapped holes on the A2Z tooling plate I use are spaced at 1.16″ intervals, and it turns out this spacing could be accommodated by the CNC Gunsmithing jig I use.  I drilled a line of holes for 10-32 clearance on the right jig half, and three 1/4″ holes on the left jig half (I used larger holes on one side to allow for slight differences in receiver thicknesses).  The magwell and trigger guard still stick out from the bottom of the jig, so I use a par of 1″ square bars on either side to raise everything up.

Generating G-code was pretty straightforward – I used HSMExpress to generate a path for the upper ‘shelf’ and a second path for the rest of the pocket.  Yes, I tend to make Z-steps very shallow, but hogging out material with a 3/8″ endmill with a fairly long length of cut is quite a bit for the Taig to handle, so I try to keep all the cutting lightweight, even if it means really long cycle times.  This was my first attempt to use HSMExpress, and I had no idea how well the toolpaths would work, or if the mill would suddenly take off on its own and carve a giant trough through the piece, turning a $70 part into 62 cents of scrap metal.  If only I had some sort of cheap plastic version for proving out the setup…  Quick, to the 3D printer!

I took a standard AR lower CAD model and filled in the FCG area to simulate an 80% lower.  I made sure to print the part with sparse infill to save plastic and time, but I still needed a way to have a ‘solid’ FCG area to provide material for the mill to actually cut.  I cut an opening over the FCG area and mixed up a batch of West System epoxy (I wish every hardware stored carried bulk epoxy supplies – luckily I live near one) loaded with a whole bunch of talcum powder.  I could have used some other filler, but I went with talc specifically to give minimal wear on the cutting tool – many common epoxy fillers can be quite abrasive (to say nothing of the fiberglass, carbon fiber, etc. that generally constitutes the matrix of a composite material layup).  I poured the epoxy/talc mix into the FCG area and let it sit overnight to cure.  In retrospect, I should have tried doing a vapor treatment on the part first, as the epoxy seeped out the sides a bit, but it wasn’t enough to affect the part’s purpose.

After reaming out the takedown pins, I was able to mount the printed 80% lower in the jig bolted to the Taig’s table.  I ran my generated program, and it worked great!  Right up until the very end, when the mill plunged right through the rear of the bolt catch area.  Precisely the sort of thing I wanted to test for, so it was all worthwhile.  I made a few adjustments to the G-code and ran the program through again to make sure that nothing else looked awry.

After that, I switched out the printed plastic lower for my partially completed 0% lower.  This showed me some other issues I hadn’t anticipated, specifically that the endmill liked to bog down in the aluminum.  I hit STOP right away, turned off the spindle power and took a step back to ponder.  The 4-flute endmill was probably not the optimal tool for this pocketing operation, but I had gone with it to increase rigidity due to the long tool length required.  The default toolpaths were also using climb cutting rather than conventional paths – this should result in less power required, but I’ve had bad luck before with climb cutting on the Taig and wanted this pocketing program to ‘just work’ even if sub-optimal.

With those changes made to the program and the purchase of a 2-flute endmill, I felt confident enough to subject a purchased 80% lower to the gauntlet.  One thing that proved very helpful were a pair of 1/4″ ground drill rods from McMaster-Carr that I could slide through the takedown pin holes in the left jig plate all the way through the holes in the lower.  This helped keep everything perfectly aligned while tightening down all the screws, and then I also used the rod to indicate in my X-axis position with an edge finder.  Make sure to remove the rear rod before starting the machining operation, though, as it sits right in the area to be machined.

Gripping a WD-40 sprayer in one hand, and Shop-Vac hose in the other, I exhaled deeply, turned on the spindle, and hit the green Start button in Mach3.  This operation makes a lot of noise, and I worried that something would seize up eventually, but my revised toolpath (I used a slightly different step-down path between Z-levels as well) seemed to do the trick.  When the program finished and the spindle fully retracted, I had no unintended cuts on the part and a nice, bright, shiny FCG pocket.

After washing it off, I installed the FCG components and did a safety check (make sure it will not fire if the safety is engaged, make sure the disconnector is working properly, etc).  Everything functions perfectly!  I’ll do a bit of identification engraving on the lower, and then it’s time to start picking out anodizing colors…

A pair of quick machining projects

It’s been a busy summer/fall/early winter, but I’ve managed to make a few chips in the shop over the past few months.  First up, dad had a front tractor axle that needed a little work.  The hole drilled through it wasn’t quite at the needed 5 degree angle to allow for proper assembly, so he ground out the sleeve that had been welded in and I gave the boring operation a try.

Clamping the part was a little easier than I thought it would be.  It’s a heavy beast, and is as long as the entire mill table.  There’s a pair of blocks near either end that worked great for aligning it on a a horizontal plane, then I just had to clamp the center section in the vise.  I tipped the head forward by 5 degrees to complete the setup.

I seem to have lost the feeler clamp screw for my trusty Blake Co-Ax indicator, so I used an edge finder to pick up the hole center instead.

I didn’t have a boring bar long enough to plunge all the way through, so I bought one just for this project.  I selected a bar tipped with C2 carbide since the cut would be interrupted due to being a slightly different angle than the original hole.  I started by setting the boring head to a small enough diameter that it would just start cutting at the bottom of the hole (where the offset between the existing hole and my new cutting axis is greatest).  I then adjusted the boring head to make the hole a little larger, set the powerfeed, and bored again.  It was long, slow work, but I finally got to the point where I had better than 50% circumference all the way through.  Finally, I turned a matching sleeve on the lathe that dad could weld into the axle hole for the whole assembly to ride on an axis pin.

A friend is assembling a new upper for his AR, and one of the components is a Sentry 7 adjustable gas block.  Unfortunately, the freefloat handguard he’s using makes adjustment of the metering setscrew almost impossible.  Dremeling out a simple slot would fix things just fine, but would look pretty ugly – milling the slot would look much cleaner.

The problem is, how do you clamp a round object while also properly indicating it so the cut is right over the central axis?  After a bit of pondering, I came up with the above solution.  I first drilled and tapped holes in a 1″ square aluminum bar and clamped that into the mill vise.  I used strips of tape on the vise jaws to protect the anodizing on the handguard, and then used a pair of 1/2″ bolts to secure the handguard – tightening the bolts works to wedge the handguard against the top edges of the jaw faces, perfectly centering and aligning the handguard.

At that point, milling the slot (really just removing the web from between two holes) was a piece of cake.


A few weeks ago I finally got the GS500 running for the season.  I rode with friends out to Madison and around the Kettle Moraine area as shakeout runs for a trip from Milwaukee to Minneapolis in a few weeks (should be interesting on little 500-650 cc bikes).  My bike, while it worked, needed some attention.

That’s the contents of my gas tank after draining it.  I’m surprised it ran at all – I needed to drain an entire Starbucks cup (thank you, parking lot litterbugs) worth of crud out of the float bowls in order to get home from Madison.  The second issue was the choke – it’s been getting progressively stickier until our 4-person ride to Kettle Moraine, where it seized entirely in the open position.  At stoplights I got to look like a tremendous jerk with my bike idling at 4000 RPM (and a Vance & Hines exhaust to boost the noise even further).  So after the ride I knew it was time to really dive into the bike guts.

After pulling the tank (and discovering the red-brown horror within), I removed the airbox and had a look at the carb itself.  The core issue was plainly obvious – a bent plate and choke plunger end on the left side.  So, just bend the end of the choke plunger back into pla… *snap*

Well, dang.  Fortunately, there’s a Suzuki dealer just down the road, and 2 weeks later I had a replacement plunger in hand.  Once I went to install it, though, something wasn’t right.

Yeah, the new plunger (top) was a bit different.  I don’t have another 2 weeks to get the correct part (if the shop can figure out the right part number), so I chucked the old plunger in the lathe.

A #43 drill and a 4-40 tap provided the threads I was after.  I installed the plunger back into the carb, and attached the plate.  A loctited 4-40 socket head cap screw finished off the assembly.

The carb, airbox, and most hoses are now reattached.  Once I put the gas tank back on and put fresh fuel in I’ll see if everything works.

Gunsmithing without a 3D printer 2

A friend had a Bushmaster rifle that they wanted to add a bipod to – unfortunately, the freefloating handguard has no provisions for mounting a bipod and even more, the handguard is integral to the barrel nut itself.  Still, I’m always up for a challenge.

To make things easier, I decided to leave the handguard/barrel nut in place and put the entire upper on the mill.  This way I could use the upper receiver as my horizontal plane reference.  I stuffed toilet paper down between the barrel and handguard to catch any chips, and used a strip of electrical tape on either side of the handguard to keep it from getting dinged by the vise jaws.

My first thought was to use a test indicator in the spindle against the two flats on either side of the upper receiver’s bottom to get it aligned vertically, then I realized that a much simpler method would be to chuck a large diameter multi-flute endmill and bring it down against a parallel while loosely clamped in the vise.  Then tighten up the vise while keeping a little pressure on the quill to keep things aligned.  Viola, perfect alignment without a test indicator.

Next step was to find the centerline of the handguard.  There wasn’t enough clearance to use a cylindrical edge finder on the jaw faces, so I flipped the edge finder over to use the conical tip.  I just had to make sure to set the stop on the spindle so that I used the same Z height on each side.  Also, this wouldn’t have worked if the top inside edge of the jaw faces was dinged up, since using the conical end of the edge finder in this way gives only point contact rather than the edge contact that the cylindrical end would have provided.

With the Y axis centered, I set my X axis zero as the end of the handguard and used a spotting drill to make a divot for the first hole 1.000″ in.

One of the ball end milled grooves on the handguard would be sitting right under the rail, but the groove is off-center by a little bit, so the spotting drill would be hitting the edge of the groove and not able to make a proper divot.  So for the two center holes, I used a 5/32″ endmill to punch holes all the way through (5/32″ is just a few thou smaller than the #21 drill used for the needed 10-32 threads).

After drilling through all 4 holes, I put a 10-32 tap in the drill chuck and loosened the collet so I could spin the chuck by hand (but still have it perfectly positioned in the X-Y plane).

After using a pick to dig out the toilet paper from inside the handguard, I attached the rail, and everything fit perfectly.  Remove from the vise, blow out any straggling chips with compressed air, and the job is done!  Ideally the screws should be installed with blue loctite (the metal is thin enough that you have to be careful about not torquing the screws too much and stripping the threads), but since my friend wanted to maybe start with having two stub rails installed instead of one long one, I’ll let him deal with the threadlocker.

Gunsmithing with a 3D Printer – Part 5

I realized it has been over a year since I last wrote on the subject (though to be fair, it seems it has been about that much time since I’ve written much of anything substantial).  Since I last addressed the topic in March of 2013, the apex of the “3D printed gun” story has been reached, and media interest in the concept has subsided.  Just as promised, Defense Distributed successfully created an entirely 3D printed firearm (save for a roofing nail used as a firing pin), proved the functionality, and released the STL files.

Naturally, I downloaded the files as soon as they were released last May.  Ever since Defense Distributed had stated their goal of designing, testing, and proving the possibility of a 3D printed gun, I had pondered how to actually achieve such a goal.  I had my own ideas in mind, and figured I could probably design something workable in a weekend, but testing and refining the design is something else – CAD is easy, but proving the model is hard.  My own line of thinking revolved around using a .410 shotshell as the intended cartridge, due to its extremely low pressure in comparison with other rounds.  This would have entailed building a fairly large gun with a rather long barrel (over 18 inches so as to not run afoul of the NFA), and would have taken quite a while to print.  As it turned out, DD came up with a remarkably elegant gun, far more refined than what I myself had in mind – something that stayed true to the intent of pushing the limits of 3D printing.  When I say elegant, I mean elegant in the Unix sense – not something that is beautiful to behold in an artistic manner, but something that has raw simplicity and efficiency in design and operation.

DD called their creation the Liberator, an homage to the FP-45 Liberator of WWII, an equally simple, straightforward pistol that was intended to be airdropped into occupied Europe for partisans to use in resistance of German forces.  The DD version is much chunkier in construction, but shares many of the same design intents – a gun that is able to fire a single shot with a centerfire metallic cartridge with as little mechanical complexity possible.

To this end, the Liberator is an impressive piece of work.  It consists of only a handful of 3D printed components:

  • receiver
  • barrel
  • breech block
  • grip
  • hammer
  • trigger
  • 2 hammer springs
  • trigger spring
  • firing pin

Plus a few pins that hold everything together.  Of these, only the firing pin itself is metal and is actually a roofing nail – since the firing pin needs to impact the cartridge primer and deform it enough to crush the compound between the primer’s cup and anvil, material hardness is a key consideration for the firing pin (and is a material property that escapes the current capabilities of FDM printing technology).

Since I had a number of journalists ask me for my take on the Liberator, I decided to print one for myself in order to give an accurate appraisal of the design.  My friend Joe (not his real name) was also interested in building and testing one to make a proper evaluation, so we collaborated on doing a proper test shortly after the design was released.

I opted to use up the rest of my MG47 filament for the various Liberator parts.  Unfortunately, I lost extrusion halfway through printing the receiver:

Rather than re-print the entire thing (which was over 30 hours), I decided to place the part in the mill vise and plane off the top, then glue on a replacement top half.

I took the opportunity to also glue in a metal block for compliance with the Undetectable Firearms Act.  I bought some 1″ square steel bar and sawed a piece off the end, then found a little bit of scrap to fill in the sides.  All told, I had 147 grams of steel, which should be more than sufficient to satisfy 922(p) (the specific section of US law codifying the UFA).

Insight is a powerful piece of 3D printing software, and I was able to go back to my sliced version of the receiver and delete all the layers from the file that I had already successfully printed.  This allowed me to print just the upper half of the receiver, and I printed a barrel at the same time for good measure.

Note that the .STL file for the Liberator barrel that was originally released is a smoothbore with no rifling (just like the original WWII FP-45 Liberator).  This theoretically makes it an AOW (Any Other Weapon) under the 1934 National Firearms Act (NFA).  The definition of an AOW is rather convoluted (and somewhat contested, given U.S. v. Davis), but it is intended as a catch-all category for firearms not otherwise defined by other categories (hence, ‘Any Other’).  A pistol or revolver with a smooth bore is generally considered an AOW, and for an unlicensed individual to make one, they need to submit a Form 1 to the ATF along with fingerprint cards, a passport photo, $200, and a sign-off from their chief law enforcement officer.  In other words, if you want to try printing a Liberator and don’t want a lot of hassle, make sure the barrel has rifling in it to avoid trouble.  Even modern reproductions of the FP-45 Liberator have tiny (and ineffective) rifling grooves in order to remain compliant.

I made sure to add rifling to the print itself, as rifling it afterwards would necessitate equipment that I simply don’t have (but would love to build someday).

Although the top half of the receiver printed without loss of extrusion, there was still a significant amount of warp on the bottom.  I opted to mix up a batch of epoxy with microballoons and colloidal silica (a thickener) to glue the two halves together.

I didn’t actually print the needed pins and just used some spare sections of metal tubing instead.

Meanwhile, Joe used his Lulzbot to create a remarkably robust receiver out of standard PA-747 filament.  He had tweaked his machine to provide extraordinarily dense prints with virtually no porosity.  We decided to test out his version to determine just how well the design works, its durability, and to get some velocity data to determine actual muzzle velocity.  Additionally, news stories on the Liberator seemed to generally claim that a $10,000 (or more) 3D printer was required to print the Liberator.  We wanted to dismiss this notion and show that even a $1000 printer is perfectly capable of printing high strength objects.

In mid-May of last year, we met up to actually perform the testing.  Our test rig consisted of an 80/20 frame to actually mount the Liberator to, which itself we clamped to a folding table.  In front of the test rig, we set up the sensors for my PACT chronograph (used to measure the speed of the fired bullet).  For safety, we used a 30 foot length of paracord to pull the trigger.  Note also that we used machine screws to actually mount the breech block within the receiver, rather than 3D printed pins.  Additionally, Joe’s barrel was slightly longer than the published Liberator barrel.

We had a great deal of difficulty getting the gun to fire in the first place, making nearly ten attempts to get it to go ‘bang’.  The first issue was getting the sear tail to actually release the hammer, so we replaced the trigger bar with one printed on my machine.  After this, the primer was indeed getting struck, but it did not seem to be igniting – we replaced the springs with ones from my machine as well.  We would wait 30 seconds after each attempt in case there was a hangfire (thankfully we never had one during the testing).  We wondered if headspacing could be an issue, so we pulled Joe’s barrel and put in one that I had printed on my machine.  We also replaced the .380 cartridge we had been using with a fresh one in case it was a dud.

Our next attempt did indeed go ‘bang’, and there was very little of the barrel left in the receiver.  My Stratasys FDM 1600 still has a bit of porosity in its output, and I hadn’t done a solvent vapor treatment on the barrel as was recommended by Defense Distributed.  Also, the round was a very tight fit and had to be pressed into the barrel – it’s possible that the bullet became dislodged, seating further down within the case and causing higher pressures when fired.  While the barrel was destroyed, we finally achieved primer ignition, so we put Joe’s barrel back in and continued testing.

With things finally working (if not smoothly), we proceeded to fire off as many shots as we could manage during the available sunlight.  Here’s a short video of the successful shots made: Lulz Liberator testing video

The video hints at some of the issues we ran into during testing.  We didn’t have the retainer for the firing pin installed, so the firing pin would rocket out the back during every shot.  We used a piece of masking tape on one attempt (you can see it fly up after the shot) to try and keep the firing pin in place, but the hole punched through the tape shows that this did not work at all.  We only had one roofing nail, but fortunately Joe happened to have along extra machine screws that he used for assembly and was able to fashion a replacement firing pin each time by cutting and filing it with a pocket multitool.  We had to make the firing pin longer each time as well, since each subsequent shot increased the headspace, with the cartridge becoming seated further and further down the barrel each time.

The 3 screws holding the breech block in place also became noticeably bent as testing continued, so we replaced them halfway through.

Here’s what the Lulzbot printed barrel looked like after its first successful firing.  The cartridge has actually been pushed back a bit (hence pushing back on the breech block and bending the retaining screws as noted).  You can also see white spots forming (known as crazing) as a result of the internal stress.  Finally, the primer has been pierced, allowing gas to erupt out the back of the cartridge, which is an undesirable behavior.  However, this is not a fault of the Liberator’s design, but a side effect of using a roofing nail or ‘field expedient’ machine screw – the sharp nose of the nail or screw actually punctures the primer cup, whereas proper firearm firing pins actually have a carefully rounded nose so that they dent but do not pierce the primer.  In fairness, however, pierced primers are not a great concern on a disposable firearm such as the Liberator or its WWII ancestor.  Continually piercing primers will allow the hot gases to erode the bolt face, firing pin hole, firing pin tip, etc. in a conventional firearm, but for a disposable gun designed to operate only a few times, this is admittedly a minor design quibble.

One thing the photo does not really indicate is how firmly the brass case is actually stuck inside the barrel.  In a conventional metal barrel, the brass does expand somewhat during firing, which is actually beneficial in sealing the case to the chamber walls in a process known as obturation.  The brass relaxes slightly as the bullet exits the barrel (which allows the internal pressure to drop back down to atmospheric levels), but since ABS plastic is much lower in strength than steel, the brass case expands greatly in the Liberator making conventional extraction all but impossible.  In our case, we needed to use a hex wrench and a rock to beat the expended cartridge out of the barrel.

Unsurprisingly, the walls had expanded so far that the case had actually split.

More surprising to us, though, was the fact that the barrel bore looked entirely unscathed (not only by the projectile, but by the hot propellant gases).  The photo really doesn’t show it, but in looking down the bore, the finish appeared just the same as in the unfired state.  Both Joe and I presume that there is so much bore expansion during firing that the bullet itself isn’t even touching the rifling.  Granted, the rifling would have done almost nothing anyhow (a copper jacket is still much harder than ABS plastic).

We only managed to record two shots with the chronograph (we weren’t using skyscreens, and they probably would have helped).  The captured velocities were 498.2 and 465.1 fps, for an average of 481.7 feet per second (146.6 m/s).  By comparison, the very same round fired out of a conventional .380 pistol will be well over 900 fps.  Consider that kinetic energy (or ‘muzzle energy’ in firearms parlance) increases as the square of velocity, and the difference is quite dramatic – the Liberator only achieves a muzzle energy of 49 foot-pounds, or roughly a quarter that of what a standard .380 pistol provides.  By way of comparison, a major league fastball delivers twice as much energy, and one person has actually died as a result of being struck with such a pitch (yet a year later, despite proclamations of mayhem and anarchy in the press, there have been zero deaths or even injuries from 3D printed guns).  In the end, then, the Liberator is not at all a weapon of physicality, but a weapon of philosophy, able to challenge preconceived notions regarding governmental control over the sharing of information.  Which, whether you agree or disagree with his views and actions, is precisely what Cody Wilson set out to accomplish in the first place.

Somewhat unsurprisingly, only a few days after DD posted the .STL files for the Liberator on their site, the US State Department sent a letter to Cody, demanding takedown of the Liberator files and 9 other designs that had been posted on Defense Distributed.  The authority for this stems from ITAR, the International Traffic in Arms Regulations, which controls import and export of defense related articles, including information related to such items.  That acronym may ring familiar to old hands of the internet, as it is the very same statute under which the US government blocked export of Phil Zimmermann’s PGP encryption software in the mid-90s, which saw Phil under criminal investigation for “munitions export without a license”.  While the case against Phil was eventually dropped (and Cody/DD have not been actually charged with any wrongdoing), the parallels are striking.  Like Phil’s case, it will undoubtedly be many years before the issue is resolved.

What struck me oddly about the State Dept. letter were the 9 other designs listed as takedown targets.  In my opinion, these were picked entirely at random in a perfectly transparent attempt to hide the fact that the Liberator files were in fact the sole items of interest.  Specifically, item 6, “Sound Moderator – slip on” was actually designed by noted RepRap contributor (and airgun enthusiast) Vik Olliver and is still available on Thingiverse.  If this was truly an ITAR violation, then why did the State Department not do anything when Vik originally ‘exported’ the file from New Zealand to Thingiverse servers in the US, and why has Thingiverse/Makerbot/Stratasys not received their own ITAR takedown letter for continuing to host this design?  I could opine a great deal more on the topic, but since I attempt to limit my blog writing to technical matters, I’ll curtail my musings.

Other interested people have printed their own versions of the Liberator as well – has a superb 8 minute documentary called “I Printed a 3D Gun“, which I highly recommend watching.  Travis Lerol (who has also experimented with printing AR lowers on his 3DS Cube) attempts to give his own Liberator a try, but it fails to ignite (spoiler alert).  Travis tells me that he has since managed to get a round to fire, though it took about 200 attempts.  A number of design remixes of the Liberator concept have also been posted online, though very few (if any) have actually been printed and tested.

I was very honored to be asked by Professor Hod Lipson to make a presentation at the Chicago Inside 3D Printing conference on the topic of 3D printed firearms on July 11.  I was scared stiff to do any sort of public speaking, but thankfully there weren’t many people in the audience, and I had a few friends in attendance for moral support.  I’m very glad I attended, as I was able to chat with so many notable people in the field – not only Hod Lipson, but Avi Reichental (of 3D Systems), Scott Crump (of Stratasys), Scott McGowan (of Solid Concepts) and especially Ralph Resnick (of NAMII) – thanks to you all for your time and attention.  Chatting with Scott McGowan and some of the other folks from Solid Concepts was especially interesting, given that only a few months later, Solid Concepts would release their own 3D printed gun, the 1911 DMLS.  As a fan of John Browning‘s entire portfolio of work (and especially the M1911 pistol), I was thrilled to see such an iconic, century-old design recreated with cutting-edge technology.  Solid Concepts is now actually selling the 1911 DMLS in a limited run of 100.  While I wish I could afford one as a collectible (Scott, if you have an extra, please drop me a line!), I’m simply happy to see the whole 3D printed gun media story finally reach its logical conclusion: 3D printing is simply another manufacturing technology, and its application to firearms is no different than the development of milling machines, investment casting, CNC, polymers, and on and on.

Addendum: I had initially wanted to cover much more of the work done in the past year by others exploring the intersection of gunsmithing and 3D printing, but this post took long enough to write as it was.  Fortunately, Andy Greenberg (who interviewed Joe and me for several stories last year, and is a superb technology reporter) has an excellent rundown of the various designs being experimented with by FOSSCAD.

Rotary Phase Converter – Part 3, aka 'What temperature do electrons burn at?'

When machining the scope mount spacer rings in a previous post, I had been planning to finish them when Max had stopped by one evening.  Simple enough – fire up the RPC and turn on the lathe.  Only thing was, the red ‘start’ button on the RPC was stuck and I couldn’t press it in.  What the heck?  Being in an impatient, Neanderthal-esque mood (I was hoping Max could take home all the parts for the project that night), I powered down the system and removed the button so that I could hammer it into a variable on/off mechanism rather than being restricted to the single, not-terribly-useful state of ‘off’.  With my ‘fix’ complete, I re-installed the switch in the semi-dangling sheet metal front panel (I plan to fully enclose the whole thing nicely one of these days, honest).

After throwing the mighty disconnect to ‘on’ once more, I pressed the just-tweaked red start button again, and the system fired up.  However, things were not sounding right, so I pressed the black stop button right away.  I surmised that the growling must be due to loose items sitting atop the plywood sheet that adorns the RPC cart (and acts as more horizontal storage space than I care to admit).  So I pressed the red start button again, and let the system growl angrily while I prepared to turn some perfectly good aluminum tubing into swarf.  After perhaps 10 seconds, there were loud popping sounds coming from the RPC, followed by me hopping around trying to turn off every electron flow nearby.  After I finally hit the main disconnect, I had a look at the carnage underneath the plywood sheet, where we both saw some rather impressive green flames emanating from what had been the bank of starter capacitors.

“Um, what temperature do electrons burn at?” he quizzed, a highly amused grin on his face.  After I had finished blowing out the flames (note to self – buy fire extinguisher for garage) and giggling over the absurdity of the situation, I determined that finishing the scope rings would simply have to wait for another night.  We pulled out the smoking remains of the capacitor bank and had a look.

So, that’s what’s inside an electrolytic capacitor – foil, paper, and magic smoke.  As everyone knows, once you let out the magic smoke, nothing works correctly, and you can’t get the smoke back into the component it escaped from.  After I checked my notes (that is, my previous blog posts on actually building the RPC), I re-familiarized myself with the circuit.  I had connected the starter capacitors directly through another pushbutton module, as I didn’t have a suitable relay at the time.  I recalled consulting with our EE at work about the use of just the pushbutton for the starter capacitor array, and he said that while it wasn’t ideal given the amperages in play, it would probably hold up just fine for several dozen to a hundred startups, which sounded just fine to me at the time (and then I promptly forgot about that limited lifespan).  I don’t know exactly how many RPC startups I’ve had since building it, but it’s certainly within that range – he gets major bonus points for accurate estimation of the failure mode and timeframe.

Really, I should have noted the signs of excessive current when I first pulled the pushbutton out of the panel.

The melted plastic housing right next to the screw terminal at the very rear of the module is a dead giveaway for “something ain’t right over here”.  So I replaced that module with a spare that I had, and decided to actually do things correctly this time.  Well, more correct at any rate – if it blows up again, I may have to reconsider my approach.

I used an Allen-Bradley contactor (the gray device on the left) with the 120v coil wired in to the start switch by way of the step-down auto-transformer (black box in the upper right).  The previous bank of ten 64mfd start capacitors (bits of their innards still sprinkle various components) has been replaced with three 208mfd caps (which I would have used initially if Surplus Center had them in stock at the time).  The big rectangular run capacitors remain unused, the poor things (well, it’s a better life than erupting into a cloud of electrolyte and flame).

Starting the newly repaired RPC was not quite as nail-biting an experience as the very first time, but still caused me to grit my teeth when pressing the red button.  Fortunately, all my work had been properly done, and the RPC started up in a flash without issue.  In fact, it seems to be even more reliable at this point – I’ve started it up perhaps 5 times or so, and each time was perfect.  I didn’t have to release the start button after 1.2 seconds because it didn’t sound quite right – every start has been confidently powered, with no hesitation.  The scope rings were turned with ease, and the system is better than ever!

Gunsmithing with a 3D printer – Part 4

Well, to say that a lot has happened since Part 3 would be something of an understatement.  To recap:

Defense Distributed tried printing my AR lower STL on an Objet machine, but it only held up for 6 shots.  While much was made in the media about this ‘failure’, I thought it was actually an excellent demonstration of material properties in the two different 3D printing technologies used.  My FDM printed lower used material with a higher impact strength, while the Objet printed lower was stiffer.  As a result, mine flexed and would not cycle properly with .223 ammunition, while Defense Distributed’s lower cycled perfectly with 5.7x28mm ammunition, but fractured at the root of a buffer tube thread (interesting how the extreme detail afforded by the Objet process actually created stress risers due to the threads in my STL model being perfect ‘V’ profiles with no filleting of the thread roots).  They’ve since refined the model to hold up for 600+ rounds, which is quite impressive for a photopolymer.

Representative Steve Israel started calling for renewal of the Undetectable Firearms Act, and has also called for making 3D printed firearms and homebuilt ‘undetectable’ polymer magazines illegal.  I’m taking this somewhat personally, as he keeps using a giant photo of my AR lower as .22 pistol during his press conferences – the least he could do is put my URL on the photo to provide proper attribution.  Given that some of the most popular rifle magazines commercially made today are of polymer construction, I’m not sure what he’s really hoping to accomplish by expanding a law that was passed due to media hysteria over the introduction of the ‘plastic’ Glock pistol.  Wait, media hysteria over plastic guns?  The more things change, the more they stay the same…

After the horrific shooting in Connecticut, Thingiverse pulled almost all of the firearm related files, including my AR lower and a Magpul style trigger guard I had designed.  I immediately contacted their legal counsel and pointed out that a trigger guard is a rather important safety device and has use in paintball and airsoft, not just firearms.  The response was ‘our sandbox, our rules, and we can change the rules at any time’ (but spoken in far more lawyerly terms).  An AR-15 grip that had also been taken down was reinstated a few days later, so I’ve been asking how to get my trigger guard reinstated as well.  However, my requests appear to be ignored, and I’m somewhat giving up on Thingiverse at this point.  It’s still a great community, but when I can’t use it to share with other gunsmithing hobbyists or even paintball and airsoft enthusiasts, my desire to use it naturally diminishes.  Meanwhile, Thingiverse appears to have no issues with people sharing drug paraphernalia designs, so maybe they’re attempting to cater to a rather different group of ‘hobbyists’.

For anyone interested, I have a copy of my original AR lower STL here (though I don’t really recommend it at this point – there are much better 3D printable lowers that have been designed and refined by other folks).  I have a copy of the trigger guard here.  It comes in two versions – one is the standard version that uses a roll pin through the rear holes, and the other I designed to be a tool-free version that uses angled studs to snap into place.  I’m actually rather proud of this version, and would be happy to hear feedback on it.

Back to the present – I really haven’t done anything further with the printed AR lower, as I’ve been experimenting with a different firearm platform.  Commenter Allen had asked “Could the Ruger 10/22 receiver be built the same way?”  This certainly got me wondering, as the 10/22 receiver, unlike an AR-15 lower receiver, is what the barrel attaches to, and contains the reciprocating bolt.  Additionally, the fire control group (trigger, hammer, etc.) is contained in a modular pack rather than having those components fitted individually to the receiver.  Plus, answering this question seemed like an excellent excuse to finally purchase a 10/22 – like the AR-15, it’s an incredibly popular rifle with countless aftermarket accessories available.  Additionally, it’s a great platform to learn the fundamentals of proper marksmanship (one of the many skills that I’d like to learn one of these days).

I found a very well used one at Gander Mountain for a reasonable price – the sling swivels had apparently broken off long ago and the receiver finish was a bit worn, but it looked to be in good functional order and would do well for learning how the rifle operates and is constructed.  When I got it home, I eagerly dug into the disassembly to see how it functioned and to give it a much needed cleaning.  The 10/22 is a semiautomatic, blowback operated .22 rifle.  The blowback operation means that unlike the AR-15, the bolt is not locked into place when the gun is fired and is only kept forward by means of the recoil spring.  A blowback bolt is also quite heavy in comparison to the cartridge used – this is to ensure that the bolt begins its rearward travel in the firing cycle slowly enough to let the chamber pressure decrease to a safe level before the spent cartridge is extracted.  The receiver itself is cast, though there are aftermarket billet receivers available for those looking to heavily customize the rifle.  In looking at how the bolt reciprocates in the receiver, it appeared that there should be no issues with a 3D printed receiver, provided that the print is made so that the layers are parallel to the barrel axis (to provide as smooth a surface as possible for the bolt’s travel).

For the printed receiver itself, I again turned to Justin Halford’s for an IGES file.  Unlike the AR-15 lower receiver, there weren’t any design features that I felt needed strengthening right away, so I created an STL file directly from the solid model and set it running with the same Bolson black ABS I had used for the AR lower.  I printed the receiver upside down so that the interior didn’t need any support material, and thus would provide as good a finish as possible.

After removing all evidence of support material, it was time to start fitting parts.  Chief among these is the barrel itself, but the hole in the receiver was slightly undersized (not unexpected, and better than being oversized).  I clamped it to the angle plate on the mill and indicated it in vertically with a dial indicator and coaxially with a Blake co-ax indicator before opening up the hole with the boring head.

After bringing the hole to appropriate size (I could just begin to insert the barrel shank), I tapped the barrel clamp holes with 12-24 threads (thanks to the blueprints at as well as the stock mounting screw hole in the front tang.

Next was to actually test installation of the barrel itself, which tightened up nicely, but I noticed that the barrel would visibly cant downward as I tightened the clamp screws.

After removing the barrel, I saw that there wasn’t quite enough clearance on the front counterbore, and the back of the barrel was catching on the top front edge of the receiver.  So it was back to the boring head to enlarge the diameter on the mating face slightly.

Then, it was time for a test fit of the bolt – it was a tight squeeze to get it past the rail on the inside right of the receiver.

As it turned out, I think the rear wall of the receiver in the original IGES file may be a touch too thick, as I also couldn’t get the trigger pack installed, so I thinned out the rear by perhaps 0.030″ until I could just get the retainer pins to go through the receiver and trigger pack (I had already reamed out the holes in the receiver at this point).

With that done, I could finally fit all the internals and actually dry fire the gun.

However, when I tried to drop the receiver assembly into the wood stock, it wouldn’t fully seat.  After fumbling with it for a few minutes, I noticed that there is an extra relief cut on the original receiver at the interface between the tang and the receiver front.  As it turned out, the original IGES file does indeed have this relief cut, but when I brought it into SolidWorks, I had run a feature recognition pass on the part.  For some reason, SolidWorks removed this feature – I should have just done a direct export to an STL file instead!  Oh well, one last machining pass on the mill took care of it.

The barreled action fit just fine in the stock, and both the 10 and 25 round Ruger magazines fit, though perhaps a little more loosely than desired.

Today I took it to the range and found an accomplice to act as a model.  Naturally, I let him burn through some rounds on the 3D printed AR receiver configured as .22 pistol first.  A .22 AR pistol is kind of a ridiculous contraption, but it is also ridiculously fun.

Next was the test of the printed 10/22 receiver.  As with previous testing, I started with only 1 round in the magazine and worked my way up.  Things were running just fine, so I put in the 25 round magazine and let ‘Secret Agent Man’ have some trigger time with it.

Generally, it ran nicely, though we did have some feed issues with it.  I think the fitment of the magazine could be to blame, as it seems that the front of the magazine is able to tip down a little too far.  Both magazines are also absolutely brand new (this was their first usage), and I’ve been told that 10/22 magazines operate better after an initial break-in period.

So there you have it – a 3D printed 10/22 receiver is entirely feasible!