2015
02.15

PIR foam for Stratasys build trays

Filament is the primary consumable on Stratasys machines, but not the only one – the build trays are also considered consumable.  On newer machines that use plastic trays, the official recommendation is to use them for only a single print, but that starts getting expensive fast, so users will wipe them down with acetone or try sandblasting them to freshen up the surface for more use.  The old FDM series machines that I have don’t use plastic trays as a build base, but rather a foam square.  I had already investigated alternate materials with poor results, and John Branlund had started to look into craft store foam instead, as it seemed to be the material to beat.  We eventually concluded that the foam is most likely General Plastics FR-7104 modeling foam based on the sample kits that the company provides.  I haven’t pursued this further, however, as I can’t imagine that shipping on a 4′x8′ sheet of rigid foam could be anything close to ‘low cost’, and I have about half a dozen extra foam bases anyhow.  However, I’ll be turning the FDM 1600 loose to be used by other Makerspace members very soon, and I’d like to give them the ability to simply replace the foam bases as they deem necessary without burning through what I have left.

Some time back, fellow Makerspace member the_digital_dentist was experimenting with various slurries and sprays to improve part adhesion on his very large scratchbuilt 3D printer.  I gave him a Stratasys foam base to try, and it worked like a champ (almost too well, since the ABS support doesn’t break away nearly as easily as HIPS support).  I mentioned my woes in trying to source more of the foam, and he suggested trying the foil-sided polyisocyanurate (PIR) foam that you can find at some home improvement stores, and gave me a few pieces to try.  I cut a 12″ square, peeled the foil from one side, and sprayed the other side with 3M 77 adhesive before pressing it onto my material testing plate.  I put the tray into the machine and let it heat up before testing it.

Unfortunately, I failed to take differential thermal expansion into consideration.  With the chamber heated to 70 C, the foam expanded ever so slightly, buckling upwards due to the foil still being attached on the underside.

I removed the foil from the underside, and lacking anything better, used a bunch of paperclips around the perimeter to secure the foam.

While the PIR foam surface isn’t as smooth as the Stratasys bases, it’s ‘good enough’ for my needs and a test print went fine.

The part and support removed from the PIR foam very easily with just a little tearing of the substrate.  Overall, it’s still not quite as good as the FR-7104 foam (tears more easily and doesn’t grip as well), but for a cheap, readily available material, it’s the best thing I’ve found so far.  The only drawback is that locally available sheets are only 1″ thick and I need 1.25″ of thickness, but shimming up the base from the bottom shouldn’t be much of an issue.

2015
02.15

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…

2015
01.03

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.

2014
09.07

Aviation

Perhaps I haven’t mentioned it a great deal on my blog, but I guess I should come out and say it if anyone is wondering: I love airplanes.  I suppose I always have.  Growing up on the shore of Lake Michigan, our house was under a frequently used training flight path for C-130s and A-10s, and the sounds of Hercs or Hogs was enough to send me running outside to see what was passing overhead.  Some of my favorite early memories are of spending time at EAA Oshkosh with my uncles and grandfather on a foggy summer morning.  I distinctly recall seeing sometime in the very early 1980s an F-14 flying with wings swept in formation with a group of WWII warbirds (it may have even been a full Grumman ‘cats’ formation), then pulling out with an immense roar in the most memorable ‘missing man’ formation I will ever be witness to.

As a kid, I actually got kind of annoyed when going to the EAA airshow – I really wanted to see the jet fighters, but my uncles always dragged me first to see the WWII warbirds.  To be honest, I didn’t see their fascination with those old, propeller driven machines, when there were fast, exciting F-15s, F-16s and other such cutting edge combat planes as seen in An Illustrated Survey of the West’s Modern Fighters to look at (I swear, I absolutely devoured that book).  Many years later, I finally came to realize that it wasn’t a fascination at all – it was a deep respect and reverence for the planes and what they had accomplished so many years ago.  Now, when I go to that very same airshow, it’s not the modern jets that I go to look at first – it’s those old warbirds that so enraptured my uncles and grandfather.  The sound of a P-51 equipped with a Merlin V-12 is simply as magical as its engine name would imply.  Seeing the majority of airworthy P-38s in existence lined up together is the very best reunion imaginable.

I still love the jets, of course.  Oddly enough, many of the jets I knew and was fascinated by as a kid are now parked in that same warbird section – you might see an F-4, a MiG-21, or even a Sea Harrier in that area.  Sadly, with heavy restrictions now in place on what can be sold off into the civilian market, it seems quite likely that in another 10 or 20 years, there will still be more WWII vintage planes flying than the fighters I grew up with.  Apparently the government thinks shredding its heroes is for the best, and don’t even get me started on the USAF curtailing practically all airshow participation due to budget cuts (or so they claim – meanwhile, Canada was happy to send a few warplanes and even their phenomenal jet team to the Rockford air show).

Beyond my childlike desire for the sound of afterburning turbofans, I simply love airplanes in general.  I’m one of those weird people that simply have to look skyward when they hear something passing overhead, no matter how pedestrian.  I’m not even very good at being able to tell what type of plane it is.  It’s flying in the air, and that’s all that matters to me.  I’ve tried to scratch the itch – my bookshelves sag with books about airplanes, my hard drive is packed with flight simulators, and I have a pile of RC planes (and parts of RC planes, but I suppose that’s to be expected).  And yet it simply has never been enough.  I need to fly for myself.  I find it absurd that the concept of ‘aviation’ can be encoded into one’s DNA, yet the similar fascination of my uncles and grandfather appear to serve as at least anecdotal evidence that perhaps such desire is more rooted in one’s being than might normally be considered.  To be slightly more blunt, perhaps aviation is indeed in my blood.

I’ve been saving up for several years for flight training.  Flying isn’t cheap – despite the dreams and aspirations of optimistic 1950s post-war America, it’s not something you can pursue on a whim (and expect to succeed), unlike getting a motorcycle license (2 Saturday afternoons of training, a DMV test, bam – you can ride a bike).  I’ve heard that getting a private pilot certificate today actually requires more time/training than getting a commercial rating 50 years ago.  Despite the cost, I knew that this was something I simply had to pursue.  Stephen Force is an utter poet of piloting and has about the best summation that I can possibly imagine – “what do you owe to your 10-year-old self”.

No matter who who are or what are your own passions, I think this is a remarkably succinct distillation of what your true pursuits as an adult deserve to be.  If you had a time machine and visited yourself at 10 years old, what would disappoint them most about you?  Seriously consider that for a moment – looking at not a stranger, but yourself, 10, 20, 30, 40, 50, 60…  however many years younger than you now are.  What would you have to admit to your own self that you hadn’t even attempted, much less accomplished?  In my case, it would be “why didn’t you ever become a pilot?”  I would have to tell my 10 year old self that I had always wanted to, but you know, never quite got around to it, or some other bullshit answer.  And my 10 year old self would have looked at me with the most utter disdain imaginable.  They… you…  had dreams unrealized.  The opportunity was right in your face, yet you never grasped it.

I finally realized that in some way, I had made a promise to myself long ago.  I was going to either become a pilot or make the very best attempt at it that I could.  Your 10 year old self still lives inside of you, after all, subdued though they may be.  And I wasn’t going to let mine down.

Today I hope I did the 10 year old that lives inside of me proud.  I can’t verbalize the experience in any meaningful way, so I hope a simple log entry will suffice.

6 SEP 2014 – First solo – J-3 N42522

2014
06.16

Carbs

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.

2014
05.11

Finally, a semi-working FDM 2000

Continuing from the previous installment

Even after thoroughly cleaning out the problematic support nozzle with appropriately sized tiny drill bits from either end, the nozzle would still clog and jam.  I did indeed have a single spare T12 (0.012″ orifice) nozzle, and installing it exorcised the demons that have plagued the machine for the better part of a year.  *sigh*  It’s always the last thing you suspect.  Frankie notes that when he had nozzle clogs, he used a torch on the nozzles as a ‘take no prisoners’ approach to cleaning out foreign matter.  I think I’ll have to try this method if for no other reason than to exact thermal revenge.

Last week, after verifying that both nozzles were feeding without any jams, I started a test print as a good ’shakeout’ of the system.  Printing Duchamp chess sets are all the rage right now (more on that in an upcoming blog post), so I thought it would be a good inaugural print.

When I stopped in at the Makerspace the next day, I was relieved to see that the print had completed successfully, and I didn’t have a chamber full of ‘3D printer barf’.  The print quality isn’t as good as I’m currently getting with my FDM 1600, but that’s to be expected since I have to fully calibrate the XYZ location of the support nozzle in relation to the model nozzle.  There’s also a fair bit of rippling in the prints that I think may be due to a slightly loose drive cable.  Finally, the layer adhesion is quite poor, but this is standard P400 ABS, not the MG94 (P430 ABS+) from Coex that has me absolutely spoiled (yet another upcoming blog post).

2014
05.11

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.

2014
05.06

Support extruder reassembly

After discovering the semi-blockage in the support extruder, I carefully drilled it out with an appropriately sized drill bit and followed up with several pipe cleaners loaded with Mothers Mag & Aluminum Polish.

I then carefully cleaned the extruder tube, and pressed on the last spare inlet buffer I have (made from Vespel, again by John).

I carefully slid the heater coil back over the extruder (and tried to twist it as much as I could in order to keep it as tight as possible on the tube), re-attached the stud for the solenoid paddle, and re-attached the thermocouple probe.

Then I wrapped the woven fiberglass insulation back around the assembly.

The original foil was unusable, so I tried using plain old ‘heavy duty’ aluminum foil from the grocery store.  It wasn’t as thick, so I doubled it up and did my best to wrap it as tightly as I could (using pieces of 3M high-temperature flue tape to hold it all in place).

The next step was to re-insert the pins for the heater and thermocouple back into the circular connector (I had pulled the pins out in order to more easily re-attach the heater and thermocouple to the extruder tube).  Note that the correct insertion/removal tool is the Amphenol M81969/14-01 – it took me several orders from Mouser to finally figure out the right size.

I then used a few zip-ties to neaten up all the wires.

Everything got reassembled back into the housing.

Re-attach the motor drive blocks.

After putting the head back in the printer, I ran a few feet of support filament though the extruder to flush it out.  Things were looking good…  …until I attached the nozzle and tried running more filament through it.  Just as before I started the extruder teardown, it jammed, kinking the filament off to the side between the drive wheels and inlet buffer.  Seeing that the buffer was also now cracked, I said a few choice words and called it quits for the day.

Upon reflection, I figured that the extruder probably wasn’t the issue in the first place (assuming that I had done the rebuild correctly) and that the motor drive block or the nozzle was the culprit.  I removed the motor drive blocks and set the head in the machine so that I could power it up and try feeding the filament through by hand.  I was able to push the ABS filament through pretty easily, but the support filament I could barely budge.  So I removed the support nozzle and put the model nozzle on the support extruder.  Wonder of wonders, I was able to feed through the filament just as easily – the nozzle must be the problem!  I reinstalled the motor drive blocks and sure enough, the support drive was able to feed support filament through the support extruder and model nozzle with no jamming whatsoever.

I’ll try clearing out the support nozzle with a 0.011″ drill bit (even though I know I’ve done so once already), and I believe I have a spare T12 support nozzle floating around in case that doesn’t work.  At least I’ve finally found the core issue and I’ll hopefully have the machine fully functional in only a week or two.  [insert something about 'famous last words']

2014
05.05

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 – mashable.com 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.

2014
04.13

Well, there’s your problem…

Since my previous post on the stubborn clog on my Stratasys FDM 2000 support extruder, I made a rather shocking discovery.  But first, what I managed to accomplish before said discovery…

The first step was removing the Torlon inlet buffer from the extruder tube.  John’s inlet buffers are a very nice tight fit to the tube itself – unfortunately, removing it pretty much requires destruction as a result (sorry, John!).  I figured I could just break it off, but I’d be left with the ‘nipple’ of the inlet buffer still embedded in the tube.  So I used a heat gun to warm up the tube to loosen the material that had leaked out between the tube and inlet buffer while trying to twist off the buffer itself.

Apparently I got things a little too hot, as my gloved hand left imprints in the sides of the Torlon buffer when I finally broke it off.

Unfortunately, I also left a good bit of Torlon stuck inside the inlet, just as I had feared.  At this point, I stuck the extruder tube in a jar of MEK for a good long time and sloshed it around every so often to help soften up the material still inside the tube.  I also occasionally would use a pick to dig out chunks of the Torlon.

My plan at this point was to model the extruder tube in CAD so that I could conceivably machine a replacement in case this one was entirely ruined by internal buildup, gouges, or some other problem.  Alan C. was kind enough to share his FDM 2000 nozzle model and drawing, so I didn’t need to do any work on determining the nozzle threads.  I’m guessing that the threads are actually 9/16″-24 rather than 14.22mm-24tpi, but Alan used a CMM in doing the reverse engineering and his custom made nozzles work perfectly, so who am I to argue with success?  I also noticed that on my 2000’s support nozzle, the central 0.154″ protrusion on the back side of the nozzle actually sticks out by a few thou, whereas Craig noted his is dead flat with the outside ring surface.  There may have been some loose tolerances at work during manufacturing, especially in light of what I found on the extruder tube.

When using some short lengths of wire (old solid core phone wire worked well) as a pseudo pipe cleaner to push/pull out softened polymer goop from the hole that runs through the center of the extruder tube, I noticed something rather odd – the wire would tend to ‘catch’ when I pushed it through from the nozzle end.  It was almost as if there were a constriction in the extruder tube.  After digging out the last bits of Torlon from the inlet side, it still looked like there was some buildup on that end of the extruder.

After trying to clean it up further with a pick, and looking at it through a lighted magnifying lens, it became quite clear to me that it wasn’t buildup at all, but aluminum – the extruder tube was poorly made in the first place!  Here’s an image showing exactly how this extruder tube would appear if you sliced it in half:

The extruder tube appears to have been turned on a lathe before having the 90 degree bend done, with the central hole having been drilled through from each end (1/16″ drill from the nozzle end and 5/64″ from the inlet end as best as I can determine).  Apparently one of the holes was drilled just a few hundredths of an inch too shallow, leaving a nice conic restriction just past the inlet.  No wonder the blasted contraption had been jamming like crazy!  Pushing a .05″-ish diameter wire though the fully functional model extruder showed that there was no such restriction.  I can’t think of a single reason why you could conceivably want such a restriction in the first place, so I can only assume that this was extremely poor quality control on the part of Stratasys (apparently the horror stories of people returning malfunctioning heads for replacement only to get back used heads with just as many problems are not at all unfounded).  I’m at once really disappointed in the manufacturer yet relieved that the problem and fix is so blindingly simple.  My solid model probably won’t be needed after all as reference for creating a new hot end, but in case it would be useful for anyone else, here’s the .sldprt as well as an IGES model and a measurable eDrawings .eprt:  FDM2000 heater tube (includes the manufacturing defect just in case I’ve been entirely wrong)

Now, where did I put my number-sized drill set….