I've built other guns of this type using different sizes of PVC pipe and firing pins. If you are in the US, two common sizes of pipe work well with the 1/2-inch thick foam are 2-inch diameter "schedule 40" PVC pipe for the barrel tube and 1-inch "IPS" PVC pipe for the axle tube. This size will fit as many as twenty-four 3/16-inch diameter firing pins or eighteen 1/4-inch dia. pins. (cont.)
The firing pins themselves are made from 3/16-inch dowel rod. The pins are about 3/8-inch in length. This is the minimum length that will allow enough of the pins to protrude on the outside of the barrel tube so that rubber bands can be hooked over them. If pipe material with a greater wall thickness were used to make the barrel tube, the length of the pins might need to be increased. The velcro disks are glued to the bottom of the pins with a flexible polyurethane adhessive. (cont.)
The disks on the bases of the firing pins are made from the "hook" side of hook-and-loop two-part fastening tape. Velcro is just a brand name for this material. I used piece of 1/4-inch thin-walled brass tubing spinning in the drill press to cut the individual disks from the tape. I chose to use Velcro to help insure that the foam compression pad didn't slide inside the barrel tube, but a different material could probably be substitutes. (cont.)
The foam is held in place inside the barrel tube by friction with the inside of the tube and by the velcro disks on the bases of the forty "firing pins". There's no glue, so the pad can easily be removed. The trick to building this type of mechanism is to find a combination of thickness of foam material and pipe diameters such that there is enough friction that the barrel assembly stays joined to the axle tube, but not so tight a fit that it is difficult to manually rotate or slide it.
The sponge material comes from 1/2-inch-thick closed-cell foam camping pad material that I purchased at Recreational Equipment Inc. in the US. I'm not sure if it is a product they currently carry. A sacrificial paper template was applied to the barrel tube with markings for all the holes. 3/16-inch holes are drilled for the forty firing pins at one end and the loading tabs at the other end, and 3/4-inch holes are drilled to make the honey comb pattern along the length of the tube (cont.)
The barrel tube is made of a 13-inch length of 3-1/2-inch diameter PVC pipe. It is not the kind of PVC that is common in the US today. It has a slightly thinner wall than currently manufactured PVC. I bought the pipe at a reclaimed building supply store years ago. The axle tube that slides inside the barrel tube is made of common "2-inch" PVC, which has an actual outside diameter of 2-1/2 inches.
I mount a section of dowel in a drill press then cut it using one of those electrical multi-tool crimper/strippers. As the dowel spins, I close the tool around the dowel at one of the stripping holes which simultaneously cuts the dowel and puts the angled tip on it. I use a little depth-guage cup attached to the underside of the tool with magnets to get consistent length of each firing pin. With each cut, a firing pin is severed from the dowel and the next one has it's tip shaped (continued).
The grip is made of 3/4-inch-thick birch plywood. I'm not sure how to measure the height of the grip. The shape and size can be whatever you like. The important thing is that the trigger ring is positioned correctly relative to the axle tube, so that it fully depresses the firing pins but does not make too tight a fit for the barrel tube to be rotated easily.
For comparison, the TwistMek-40 uses older non-standard thinner-walled "3-inch" pipe for the barrel tube and modern 2-inch schedule 40 pipe for the axle tube. If building a gun with either combination of pipe sizes, it works well to make the trigger ring (the short section of pipe that depresses the firing pins) out of the 1-inch IPS PVC pipe.
Noticed this gun sort of shoots from one side, instead of down the sights. would it be possible to rotate the position of the deflection groove (in the deflection tube) to compensate? I would understand if a bit of re-thinking for the trigger slide assembly might be necessary.
Thanks for the info.What type of sponge you are using for this gun?And the end of the barrel tube,how you make it into slot?I noticed there are many holes on the barrel tube,is it original one or you drill it yourself?Thanks.
Yes, new designs appear all the time! There a lot of innovators in Japan and other parts of Asia, as well as in the West. Recently, I've gotten a lot of video views from Vietnam and Brazil, so I'm interested to see if we eventually get some new designs from those countries. My main focus for my designs continues to be true full-auto mechanisms--rapid-fire driven by energy from the rubber band ammo itself. Over the next year or two I hope to unveil a couple more mechanisms along that line.
I've been watching your videos and they're all amazing. Anyways I have a suggestion for updating this model which you might have thought of long ago: Adding some kind of Gatling-like lever to rotate the barrel would make this model a bit easier to use and aid for a more constant shooting. This might not be worth making though, considering the RotaryMek's system which seems much simpler than making some gears and a lever to add to this model.
Yes, a more complex driving system could be designed for a gun with this type of mechanism, but I probably won't be pursuing that, since there are other mechanisms that are better suited.
(continued) In between cuttings, I hold a bit of sandpaper under the spinning tip to smooth the shape. To complete the firing pins, I glue a small disk of "hook" side velcro to the base of the pin using Seamgrip adheasive. The velcro disk is slightly larger diameter than the fining pin/hole, so it keeps the pin from falling out of its hole in the barrel tube. The velcro also helps keep the blue foam compression pad stationary relative to the barrel tube when it is slid on the axle tube (cont)
Thanks for all your information.Since this is your product,I would like to have your permission first before I try to build one for my personal entertainment only.Is it okay?
(cont.) Finally, I soak the completed pins in some hot wax so as to give them a bit of moisture protection. To keep the mechanism running smooth (firing pins depress and rebound easily), I also apply a bit of wax to the tips of the pins periodically.
Yes. There seems to currently be a lot of interest in this design in Brazil, so I'm waiting to see if maybe somebody there comes up with a motorized version.
Hey man I ,love your guns and was inspired by your approach and have been building guns my self but I can't figure out how to make the ring that holds the rubber bands and how to find the center and make bigger so I can add more rubber bands, could you help me?
The rubber bands are loaded on to the barrel tube, which is made from 3" Schedule 40 PVC pipe. Small dowel firing pins sit in holes at the rear of the barrel tube and the rear ends of the rubber bands are hooked over the firing pins. A template is used to mark the locations for the firing pin holes in the pipe, and the holes are drilled on a drill press, with a fence on the drill press table to help with aligning the pipe for each hole. If you want to make a gun of this type with a larger barrel tube, you'll need to first determine what pipe size to use and find a corresponding smaller pipe size to use as the axle tube on the gun's frame. You'll also need to find suitably dense foam sheet to use as the compression pad gasket between the tubes. The fit of one tube inside the other with the foam needs to be snug, but not so snug that the outer tube (barrel tube) can't be rotated relative to the inner tube. For the width of the template for the firing pin holes, you'll need to calculate the circumference of the barrel tube and then determine the necessary spacing for the firing pins.
Thank you but I was referring to your other video where you build a semi auto rubber band pistol how do you design and build and find the center of the gears
Roboman Robinson I use CAD software and a basic understanding of geometry in the design process. The video describes the building process. Not sure what you mean by "find the center" of the gears.
