by Tom Gaylord
Writing as B.B. Pelletier
Today’s report is written by blog reader New To Old Guns. We met at this year’s Pyramyd Air Cup, where he showed me the items you are about to see. I was impressed, and so was Val Gamerman, the president of Pyramyd Air. He gave his inventions to Val to take back to his office to evaluate, and he and I had already decided that a guest blog would be the right thing for everyone else. So, here we go!
If you’d like to write a guest post for this blog, please email me.
And now, over to you, New To Old Guns.
3D printing to the rescue!
This report covers:
- The Sumatra magazine, the start of it all.
- What is plastic printing?
- How does the printer print?
- Early success: the clip holder
- Iteration is what makes this great!
- Follow on success: belt and gun mounts for the clip holders
- The power of 3D printing
- Other resolved issues with the Sumatra
The Sumatra magazine, the start of it all.
Around 2003, I purchased the Sumatra 2500. It was a beast of a gun compared to anything I’d owned before. I was immediately smitten. But, it wasn’t long after opening the box and starting to use it, I found the first design choice I disagreed with. The clip is little more than a cylinder with 6 slightly tapered tubes and a pair of spring-loaded bearings front and rear providing centering force. There is nothing holding the pellets in the clip! That’s great, in that there is nothing to deform the pellets as they’re loaded and shot, but not so great because you can’t preload clips for field carry. The pellets just fall right out of the clip!
To make matters worse, the muzzle of the gun has to be pointed upwards when loading, so the pellets don’t drop out of the clip then either. But, when the muzzle is upwards, the cocking lever can easily fall from being fully open, and it needs to be fully open to load the clip. The only mode the gun made sense was shooting with a bipod, either from a bench of the ground. Then the bipod would keep the muzzle up a little, and left you with enough hands to load the clip and keep the lever fully open.
That was how I used and enjoyed the gun, usually shooting prone off a bipod. It was a very deliberate, time-consuming affair, taking the 6 shots, open the ammo tin, reload the clip, close the tin, reload the gun, continue. There isn’t really anything wrong with that, but sometimes you just want to have fun banging away, and this was clearly not the gun for those times. If only there was something the loaded clip could be put into, to keep the pellets in!
What is plastic printing?
Plastic printing is a system where an electronically described part is built up out of thin layers of extruded plastic. The parts can be modeled using traditional CAD (Computer Aided Design) software, or with more modern but functionally limited software specifically written for 3D printing. Once the part is modeled, the output is handed off to a piece of software called a “slicer”. It does exactly that, reducing the part into layers of predetermined thickness. Have you ever seen a hard boiled egg slicer, a frame with an array of wires? Think of that, but on its side. And the output is the sliced egg, still all stacked so it still looks like a whole egg. The slicer output file is what is sent to the printer.
A model egg.
A sliced model egg.
The printer itself is little more than a heated extruder head that is movable in 3D space. It receives a steady supply of room temperature plastic filament from a spool and extrudes it out of a very small nozzle. To put some numbers to it, the filament supply is commonly about 1.75mm in diameter, and in my case the nozzle diameter is 0.4mm. That’s quite a bit of reducing!
The extruded head heats the plastic to its melting temperature (that depends on the plastic type, but it’s usually over 205 degrees celsius or 401 degrees F.), and uses the pressure of the fed plastic to push the melted plastic out the nozzle. It can be printed (deposited?) in layer heights ranging from 0.1mm to 0.4mm on my machine, with a default at 0.2mm. That’s 0.0079-inches!
How does the printer print?
Imagine that the object you’re printing is a pyramid, 5 cm tall (that’s almost 2 inches) , 5 cm on each side, and your slicer program is set to make 0.2mm layers. The base layer the printer will print will be a 5x5x0.2mm square (well, technically, a cube). As the print continues, it lays down the next layer of extruded plastic on top of the first. This square will be a little less than 5×5, and now your part is 0.4mm tall. And so the process goes, laying down layer after layer. This part would take 125 successively smaller layers to print.
Early success: the clip holder
The first problem I set out to address was the clip holder. I had in mind a part where one edge copied the outline of the gun where the clip loads, so the pellets wouldn’t have any spaces to fall out. There would also be an internal track that the clip’s bearings would ride in to keep the clip centered. To keep the clip in the holder, I planned a pair of depressions that were deeper than the track, that the bearings would center in. I enlisted the help of a machinist cousin, and in a couple of hours, we had a model. Once my printer arrived, the real fun began!
The clip is in the printed holder.
The holder has been mated to the Sumatra, for loading.
A second view of the clip holder, and how it mates to the gun, preventing pellets from falling out during loading. Just push the clip through the holder and into the Sumatra’s receiver!
Iteration is what makes this process great!
I started using the first prototype, and quickly realized that it could easily be improved on. Adding a lip that would engage the loading slot of the gun would cut down on having to really be attentive when alining the loader with the loading port. An edit to the model added that lip, and now loading became just a wiggle of the holder to make sure the lip was engaged, and a push on the clip. It’s better already!
Here is a side-by-side comparison that shows the added lip.
Follow on success: belt and gun mounts for the clip holders
I printed out a few of the loaders and headed out to the field. It was a little like having a different gun! I could pop the empty mag out, get a loaded holder from my pocket, and load up just like I’d wished. And it could be done with the muzzle pointing downward, which was much more natural. But again, by actually using the parts I’d made, the next iteration became obvious. Why keep fishing into my pocket, when I could make a belt holder for the loaders? So I figured out a tray to capture the clip holder, and tinkered with making various types of belt holders. One holder was intended to be carried on the front or side of my hip, and the other for further around my back. Now I could head out with ammo for 36 shots, ready to go!
The two belt carry designs. The trays are angled on the one intended to be worn on your side, to allow for a comfortable wrist angle. That made a huge difference!
But then came the next question — why reach all the way down to my belt at all, as opposed to keeping the clips on the gun itself? So, I tinkered up and printed couple of refining iterations of gun mounted clip holders. And finally I had what I considered to be a really good product. 18 shots, and my hand never had to move more than a couple of inches from the gun.
Here is the “final” side holder. Final, for now…