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Jason on Printer Issues

My goal was to try to come up with a design where if you had one of these low cost ABS printers, you could just download the file, print the parts, superglue them together, add the spring, and you’d have a working 32 round magazine.

Right now I’m at the point where you can download the file, print the parts, superglue them together, sand like crazy, add the spring, and you would have a somewhat finicky 20 to 25 round magazine.

The problem I’m having is a combination of ABS being a bit too flexible and software issues with tool path generation. The walls of the magazine needs to be at least a couple millimeters thick and solid in order to prevent excessive flexing. The tool path generating software (Skeinforge) doesn’t deal well with thin solid walls whose thickness is some uneven multiple of the print head width. For example, if the wall thickness is 3.5 times that of the print width, it will generate one pass along the outer surface of the wall, one pass along the inner surface, and then one more interior pass against either the outside or inside surface. But that leaves the remaining 0.5 of the wall thickness unfilled, and you end up with a hollow very flexible wall. What it really should be doing is a zig-zag like pass over the wall interior. I can trick Skeinforge into filling in the walls completely by lying to it about print head width, but the wall surfaces end up off a bit and then I have issues with the magazine fitting in the mag well or the rounds fitting in the magazine. So I’ve been tweaking the wall thickness and print head size setting in order to try to get Skeinforge to do what I want.

The right solution is probably to modify Skeinforge so that it will generate the correct tool paths from the correct model, rather than adjusting the model to try to make up for Skeinforge’s deficiencies.

Other than the flexing issue ABS seems to be strong enough. I have one magazine I printed which can hold the full 32 rounds and feeds fine, but it bulges so much when fully loaded that it won’t fit in the mag well. The one magazine rupture I had was due entirely to a mistake in the cad file that caused the printer not to correctly bond the insert pieces (where one section of the mag body fits into another) to the rest of the part.

20 Responses to “Jason on Printer Issues”

  1. Freiheit says:

    Can you use something off the shelf, like a square tube from mcmaster carr, and then use your machine to make a top and bottom adapter to fit that generic tube into the weapon and mount the spring?

  2. Freiheit says:

    Also regarding the bulging, what about reinforcing the mag with a steel plate or rod?

  3. DirtCrashr says:

    We have become way to tech-dependent. An illiterate kid in Lahore, Pakistan could probably hammer-out a working one in ten minutes from a Campbell’s soup can.

  4. PT says:

    Keep the updates coming.

    DirtCrashr: Sure a kid in Pakistan could make one out of a soup can. The idea I like here is that this technology could someday pop out a couple of magazines an hour right from your desk while you surf the web.

  5. Maybe you’re going about it wrong? Trying to use too similar a concept.

    (ie: cars had to evolve away from horse and buggies to really stand out).

    I am wondering if making stackable slices of the magazine might be better. In which case, you can make the wall thickness much thicker for everywhere but the feed lips/insertion point. So make that unit separate. And allow the rest to be added (stacked like LEGOs).

    You’d stacked them with the top piece and a bottom piece and as many middle sections as you want rounds to hold. There’d be a hole to run a wire through to “bolt” them together.

  6. I thought about posting this this morning but couldn’t convince myself to. Here’s the idea anyway.

    Instead of approaching it from the point of view how to build the magazine? What about, how do we build a mold, to then build the magazine?

    It will allow solve the limits of the printer allowing you to instead cast the entire magazine shell as a solid piece. You can use a potting compound that is considerably stronger and it can be the full wall thickness instead of just trying to shore up the result from the printer.

    There is nothing that says you have to go from start to finish in one shot.

    Just a thought, I could be completely off, I enjoy mechanical design, but I’m an EE, not an ME.

  7. emdfl says:

    Maybe use a couple of metal stiffeners like Glock does? Super glue them on the inside of the mag walls.

  8. Sebastian says:

    NUGUN:

    You’re fundamentally limited by two things here. One is the size of the cartridges you’re loading into the magazine. The other is the size of the magazine well in the receiver of the firearm. These were designed by the gun’s manufacturer with either steel magazines, or thermosetting polymer magazines in mind, which have different material properties than ABS, and have different strength quality than something that’s been extruded in layers.

  9. Sebastian says:

    Instead of approaching it from the point of view how to build the magazine? What about, how do we build a mold, to then build the magazine?

    There’s something to be said for this. There is a material you can get for this printer that will allow you to build a water soluble mold. But consider the design goals.

    The purpose here is to show that someone who is an enthusiastic hobbyist, who’s managed to purchase and assemble one of these 1200 dollar 3D printers, could download our design and print a working magazine, following simple instructions and using ordinary household tools.

    A mold is certainly within the realm of the hobbyist, but the problem with a mold becomes predicable results. The beauty of trying to do as much as we can on the 3D printer is that, once we find something that works, it should be easily reproducible for anyone that has this printer.

  10. Diomed says:

    I guess this is giving you a new appreciation for the trials and travails of firearms designers since the advent of the repeating firearm. Magazines are a bitch to design well – and even harder to get to the mass production stage.

  11. Sebastian says:

    I would say so, Diomed. I figured this would be a slam dunk after seeing the first results from the printer. But it’s hard, clearly.

    This is something that could never be mass produced. One of the difficulties is the several hours it takes to print a magazine. So if you want to try a change, it’s a three hour delay before you can see if the idea works. That’s not even counting the plastic you’re going through while you’re doing it.

    But the goal isn’t mass production. Mass production of magazines is a solved problem. A hobbyist being able to produce them is a different problem, and one we’re trying to solve, using this printer as the primary mechanism. That’s one reason I’m resistant to the idea of using shaped metal liners and such… we want most of the work, as much as possible really, to be done by the printer. Once you have to bring in other technologies and other skill sets, you’re making harder for a hobbyist to accomplish.

  12. Sebastian says:

    Jason is really doing most of the work on this project. My only real contribution was the follower, which was only a few hours figuring out how to use SCAD and some basic geometry.

    Jason’s been able to eliminate the need to use those base-stabilizing disks you see in the design. I’ll see if he has time to do another post talking about how he managed to eliminate the need for those.

  13. Jeremiah says:

    Very cool concept. This would take some modeling work (but is doable- not sure what types your system takes), but build a “smooth” internal wall and external reinforcing cross members (in the general shape of X’s when looked at from the side, start with 3 or 4 for the whole length for each side) below the magazine well. This will add a lot of stiffness without an internal volume, and utilizes the machine’s building function. (It will probably print slightly off the edge, allowing the external angles to be made.) The follower would be built so it had a larger head on it (for reduced angling issues) and a decent curve to the edge that contacts the walls (reduces snagging). If you can build this part with vertical ridges, the combination of ridges and gentle curve will reduce the likelihood of a snag and the resistance to movement through smaller frictional area. I don’t know how long it will work, but it should work at least once! ;-)

  14. armed_partisan says:

    I’m reading this, and I’m thinking “Gee, I wonder why nobody’s tried to make a magazine out of regular printer paper and glued it together?” It would take a lot of layers and a considerable amount of time, but you could conceivably make a magazine out of paper. Paper is the frame and glue is the binder. This is effectively what a laminate stock does. Has anybody tried this?

  15. SidViscous says:

    Now I don’t think we’ve seen the design. But one quick thought on something specific.

    Are you building it in the square format of normal magazines of the type your replicating. i.e. straight walls.

    You’ve got some room to play with, ,particularly around the ogive of the bullets to make the front internal more contoured and add some material for some more strength.

  16. buffalo bob says:

    This is cool. I think that this could put the nails in the coffin of the gun control debate – if the antis were susceptible to rationality. You can’t have an effective ban of X, if X can be made (or Grown – wink, wink) at home.

    Have you considered any hybrid construction techniques? Perhaps printing out a lattice and stiffening it with JB Weld or something? Combining two materials with different characteristics might be a way around the difficulties with ABS.

  17. wordcooper says:

    Internal ribs would give strength without requiring thick walls.

  18. dusty says:

    I would be extremely interested in seeing pictures, of somebody making a 30 round mag from cans (extra points for beer cans, but soup cans would be fine).

  19. Sebastian says:

    buffalo bob:

    I’ve heard Jason say a few times during this he needs a print head that extrudes JB weld :)

  20. Bryan S. says:

    instead of your toolpath being straight, can you zigzag or even spiral? think sewing machine.

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