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This is a log of my somewhat lame methods in making one key element of a replica weapon; a 1930's pulp-adventure inspired double-barreled 45mm grenade launcher.
Above is a 3d render of the entire weapon. For this Instructable I will focus on the process of building the breech blocks.
Above is a 3d render of the entire weapon. For this Instructable I will focus on the process of building the breech blocks.
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Signing UpStep 1Designing the Breech
The client's drawing is shown here; the plan of attack was to take several surplus gun parts we had on hand, model them in 3d, extrapolate the rest of the weapon in 3d, and have that printed by Shapeways.
We decided it was worth it to have moving parts. 3d printing couldn't provide the necessary strength alone, not and stay under budget, so the evolving design used metal stock and plumbing parts as a sturdy skeleton, with 3d printings to carry the higher levels of external detail.
Many of the mechanical details simply had to be worked out in situ. Because of the lead time for 3d printing (at least 10 working days from completed and accepted model), I just had to count on building the actual working parts while the 3d parts were in production, and hope I could cut and glue them to fit them in place when they arrived. More or less, this is what happened.
DESIGN:
The first pass was a massing study; I modeled up the various shapes using primitives (boxes and spheres) in order to get a sense of what looked right. One of the first problems was that the centerline of each barrel lined up with the wall of the tube that ran into the butt stock. That meant the assembly basically "hung out" the sides.
As I developed concepts with the client with a lot of back-and-forth emails, we went back and forth on the concept of exposed hammers. We finally went with them, although they are not strictly period, as by the time we finally decided the 3d order had already been sent. Conceptually, at this point, aluminum hammers rode on a brass rod, with a pair of aluminum "spurs" sitting inside the receiver where it might be possible to link them to the trigger (this turned out to be a stretch goal that was way waaaaay too stretchy).
Since we also had never clarified if these were cased grenades or caseless rockets, whether they had a rim or extractor groove, or whatever, I made some arbitrary cool-looking claw hardware on the inner face. If we didn't like it, we could always cut it off.
We decided it was worth it to have moving parts. 3d printing couldn't provide the necessary strength alone, not and stay under budget, so the evolving design used metal stock and plumbing parts as a sturdy skeleton, with 3d printings to carry the higher levels of external detail.
Many of the mechanical details simply had to be worked out in situ. Because of the lead time for 3d printing (at least 10 working days from completed and accepted model), I just had to count on building the actual working parts while the 3d parts were in production, and hope I could cut and glue them to fit them in place when they arrived. More or less, this is what happened.
DESIGN:
The first pass was a massing study; I modeled up the various shapes using primitives (boxes and spheres) in order to get a sense of what looked right. One of the first problems was that the centerline of each barrel lined up with the wall of the tube that ran into the butt stock. That meant the assembly basically "hung out" the sides.
As I developed concepts with the client with a lot of back-and-forth emails, we went back and forth on the concept of exposed hammers. We finally went with them, although they are not strictly period, as by the time we finally decided the 3d order had already been sent. Conceptually, at this point, aluminum hammers rode on a brass rod, with a pair of aluminum "spurs" sitting inside the receiver where it might be possible to link them to the trigger (this turned out to be a stretch goal that was way waaaaay too stretchy).
Since we also had never clarified if these were cased grenades or caseless rockets, whether they had a rim or extractor groove, or whatever, I made some arbitrary cool-looking claw hardware on the inner face. If we didn't like it, we could always cut it off.
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Thanks