{"id":1041,"date":"2012-06-28T22:22:37","date_gmt":"2012-06-29T04:22:37","guid":{"rendered":"http:\/\/haveblue.org\/?p=1041"},"modified":"2012-06-28T22:22:37","modified_gmt":"2012-06-29T04:22:37","slug":"gunsmithing-with-a-3d-printer-part-1","status":"publish","type":"post","link":"https:\/\/haveblue.org\/?p=1041","title":{"rendered":"Gunsmithing with a 3D printer – Part 1"},"content":{"rendered":"

\t\t\t\tI’ve used my Stratasys to prototype out various ideas for paintball gun parts, but the concept of using it for actual firearm parts hadn’t really occurred to me until early last year.\u00a0 I first thought of making some dummy 12 gauge shells to test out the action on a Remington 870, and then thought of using it to test out 1911 pistol grip panel ideas.\u00a0 Gun manufacturers<\/a> have been using rapid prototyping for years, and the concept is now making its way to the hobbyist gunsmith.\u00a0 To the best of my knowledge, this has been restricted to mockups (Justin Halford used a stereolithography made frame to test component fit for his fantastic Beretta 92FS<\/a> project) or less critical parts like furniture (grips, buttstocks and such). It wasn’t until I came across an AR-15 magazine follower<\/a> on Thingiverse that I began to wonder about the feasibility of making more functional parts with a rapid prototyper.<\/p>\n

The use of plastics in firearms is a relatively recent development as far as primary structural components go.\u00a0 Firearms have certainly used plastics early on (the use of phenolic ‘Bakelite’ was popular for grips and other previously wood furniture in the years leading up to WWII and well afterwards), but use of plastics for a core component took much longer.\u00a0 Consider a car analogy – we’ve seen plastic dashboards for many decades, but the use of plastic for something as critical as an engine block wasn’t attempted until the early 1980s.\u00a0 It wasn’t until 1959 that Remington (at the time owned by DuPont, hence having access to cutting edge polymer technology) came out with a .22 rifle that used plastic for the receiver (the core ‘body’ of the gun).\u00a0 This was the Nylon 66<\/a>, so-called since the Zytel-101<\/a> material used was a type of Nylon 6-6 polymer.\u00a0 While it was quite a popular rifle (selling over a million units by the time it was discontinued in 1991), and helped further the use of synthetic stocks among shooters, it wasn’t until Glock pistols became popular that polymer firearm frames\/receivers gained widespread acceptance.\u00a0 Today, polymer framed pistols outsell their metallic counterparts, and new rifle designs increasingly use molded synthetic receivers.<\/p>\n

The AR-15 rifle<\/a>, while designed to use an aluminum lower receiver, has such limited force imparted while firing that I guessed it could probably be made of printed plastic with little worry of breakage.\u00a0 After all, Orion’s Hammer<\/a> has successfully made a lower from HDPE<\/a> (after having limited success making one from a pine board<\/a>), not to mention the commercially produced polymer receivers such as Bushmaster’s Carbon 15<\/a> and Plum Crazy C-15<\/a>. It would easily fit within the build volume of the Stratasys, but my concern was whether or not it would have enough precision for all features to be usable (Orion’s Hammer didn’t worry about the takedown pin detents or bolt catch, for example).\u00a0 Rather than waste a lot of material on a failed idea, I took Justin Halford’s<\/a> IGES file of the lower, scaled it to 75% of full size, and set it running with PP3DP filament.\u00a0 The resulting print looked fantastic:<\/p>\n

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Figuring that my chances with a full scale print were excellent, I decided to modify the model by strengthening two areas that I was slightly concerned about – the front takedown pin lugs and the bolt hold catch lugs.\u00a0 Adding more material to the model in SolidWorks was pretty straightforward, and I finished it up by adding an integral trigger guard.\u00a0 I switched out the PP3DP filament for some black Bolson ABS – after all, the ‘black rifle’ would look a bit odd in ivory (more importantly, it’s easier to see\/photograph detail on dark material).\u00a0 After slicing the STL file, I sent it to the Stratasys and waited a few days (no speed demons, these old machines).<\/p>\n

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After breaking away all of the most easily removed support material, I had a great looking print.\u00a0 I had generated the STL file at a very high resolution, as I was wondering how well the buffer tube screw threads would actually turn out (having not yet tried printing any threaded objects).\u00a0 As it happened, perfect!\u00a0 A buffer tube screwed right into the threads with no cleanup required.\u00a0 Naturally, I wanted to share my results, but unfortunately firearms are presently a bit of a touchy subject.<\/p>\n

The concept of using a 3D printer to manufacture gun parts has not been lost on the RepRap community, and the topic has been debated a number of times on the RepRap forums.\u00a0 At this point, there is a policy proposal<\/a> to not allow weapon designs or projects to be uploaded to the RepRap library, and a line on the Health and Safety<\/a> page for the RepRap project states “the RepRap researchers will work actively to inhibit and to subvert<\/em> the use of RepRap for weapons production” (emphasis mine).\u00a0 On the other hand, Thingiverse once had a rule against weapons in their terms of service, but later removed that restriction.\u00a0 Afterwards, the Thingiverse upload page still said “Please don’t upload weapons. The world has plenty of weapons already,” but I assumed that this text was not updated after the TOS was revised.<\/p>\n

I decided to ask for clarification<\/a> on the Thingiverse mailing list.\u00a0 The phrase “kicking the hornets’ nest” aptly describes the resulting discussion, I think.\u00a0 In the end, Zach ‘Hoeken’ Smith (one of the Thingiverse founders) weighed in and clarified that such content is allowed, though discouraged. Fair enough. Apparently someone had taken notice of the commotion, and three weeks later, there was an STL file of a lower receiver posted to Thingiverse<\/a> in what could be described as a confrontational manner.\u00a0 Since the cat was out of the bag, I decided to upload my own STL model<\/a>, as I wanted to hear constructive feedback on how the version might be improved to better suit the current limitations of 3D printing.\u00a0 Well, apparently the resulting ‘weapons on Thingiverse’ debate raged hard enough that in February the lawyers were unleashed<\/a> upon the site’s Terms of Use<\/a>, and now uploading any content that “…contributes to the creation of weapons…” is verboten. Although that policy doesn’t appear to be enforced<\/a>, I suppose they could yank my uploads and kill my account at any time, hence I’m re-documenting my work here.\u00a0 Enough rabble-rousing – back to the fun stuff.<\/p>\n

I’m rather jealous of people who can print the lower receiver with soluble support<\/a>, as clearing support material from small diameter holes is a bit of a pain.\u00a0 I used a pin vise and an assortment of small diameter drill bits to clear out all the long cross drilled holes in the part, using Duke Snider’s receiver blueprint<\/a> for dimension references.\u00a0 With all traces of gray polystyrene eradicated, I set about cleaning up the larger holes, as they were ever so slightly undersized (better than being oversized).\u00a0 I ran a 5\/32″ drill bit through the holes for the trigger and hammer pins, and eagerly installed the fire control group.\u00a0 The trigger and hammer\u00a0 functioned flawlessly, with no slop apparent in the pins.\u00a0 The selector lever was a bit of a tight fit, so I worked it back and forth perhaps a hundred times to break it in.\u00a0 After tapping the 1\/4-28 thread for the grip screw, I attached the grip, keeping the selector in place by virtue of its detent.\u00a0 Similarly, the magazine catch was a bit of a tight fit, and I had to carefully work the part back and forth in the receiver to make sure that it would reliably retract under force from the magazine release spring.\u00a0 I then ran a 1\/4″ drill bit through the holes for the front and rear takedown pins.\u00a0 Unfortunately, I heard a quiet snap when drilling out the front hole, and sure enough, there was a break between layers.<\/p>\n

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On the plus side, this confirmed my suspicion that the takedown lugs needed reinforcement in the first place.\u00a0 I brushed on a bit of Weld-On 3<\/a> to fuse the layers together (delicately, recalling what happened when I dunked printed parts in MEK<\/a>).\u00a0 After running a drill bit through once more, the cleanup was complete, and I installed the takedown pin with its spring and detent.<\/p>\n

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Nice!\u00a0 Now, for the other area that had given me concern – the bolt hold lugs.\u00a0 Sure enough, when I pressed in the roll pin, I had layer separation.<\/p>\n

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Well, I never cared much for roll pins anyhow – they always seemed rather brutal (especially when driven into a blind hole – yikes).\u00a0 After touching up the damage with a few more dabs of Weld-On 3, I ran a 3\/32″ drill bit through the hole.\u00a0 I then threw away the roll pin and instead used a dowel pin of the same size.<\/p>\n

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A little bit of superglue on either end of the pin should suffice to keep it in place.\u00a0 Finally, there was the rear takedown pin to contend with.\u00a0 Justin’s model appears to have the recess for the pin head as around 5\/16″ or so, while the head on the pin from my DPMS parts kit<\/a> measures 3\/8″.\u00a0 No worries – I lightly clamped the receiver in the mill vise, centered the spindle over the hole, and carefully widened the counterbore out with a 3\/8″ endmill.<\/p>\n

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After this, the takedown pin fit perfectly.\u00a0 Since I don’t actually have a full AR-15 stock (and will be attempting to run this receiver as a pistol first), I needed a way to capture the detent spring for the rear takedown pin.\u00a0 I opted to tap 4-40 threads in the rear of the spring hole and kept the detent and spring in place with a 1\/8″ long 4-40 set screw.\u00a0 Unfortunately, the force on the detent was heavy enough that when I tried to slide the takedown pin into the receiver, the detent broke through the thin wall into the rear of the FCG area.\u00a0 It appears that extra 1\/8″ of spring compression due to the set screw may be too much.<\/p>\n

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I dabbed on a bit of ye olde Weld-On 3 and clipped 1\/8″ off of the spring to compensate before attempting to secure the pin again, but the detent still wanted to break through the wall.\u00a0 I’ll leave it out for the time being, but I’m considering drilling the hole out larger and sleeving it with brass tubing.<\/p>\n

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Overall, it’s looking quite promising.\u00a0 The upper receiver fits snugly, and magazines can be inserted and removed with ease – shown is the lower with an upper attached along with a .22 magazine that I intend to use with the CMMG .22 conversion kit<\/a>.\t\t<\/p>\n","protected":false},"excerpt":{"rendered":"

I’ve used my Stratasys to prototype out various ideas for paintball gun parts, but the concept of using it for actual firearm parts hadn’t really occurred to me until early last year.\u00a0 I first thought of making some dummy 12 gauge shells to test out the action on a Remington 870, and then thought of […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[2,9],"tags":[],"class_list":["post-1041","post","type-post","status-publish","format-standard","hentry","category-3d-printing","category-gunsmithing"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/posts\/1041","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1041"}],"version-history":[{"count":0,"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/posts\/1041\/revisions"}],"wp:attachment":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1041"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1041"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1041"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}