Tell Model-2 Air Pistol - Repaired using 3D Printer.
With thanks to Harry for these pics and description.
My Great Uncle died recently and he left me this Tell II air pistol. These guns were manufactured in Germany between 1927 and 1935. As you can see its rusty and in bad shape, so I decided to give it a little TLC. When I received it it was unfortunately not working as a small lever in the handle that locks the barrel in position had broken. This meant that all the air pushed by the spring was simply escaping out the back of barrel and not firing the pellet. Ill show you how I gave this little gun a nice clean and fixed it through the magic of rapid prototyping made possible by 3D printing.
Here is the pistol stripped into its component parts. The huge ass spring runs the entire length of the barrel. This is thought to be the smallest spring loaded air gun ever made and the engineering that makes it work is quite incredible! As you can see its incredibly rusty and needs a good clean! I bathed it in warm water with a little washing up liquid then used a scourer on the rusty bits and a pipe cleaner to reach the inside. Its not pictured but there was actual moss living in the handle!
here is the latch that broke. that bit on the left is supposed to come round into a hook but the top of the hook sheared off. Never fear, 3d printing is here!
A wonderful human being over at www.airgunforum.co.uk named ccdjg sent me this scan of the original patent application for the gun, showing the part I was looking for in its unbroken form! From this I was able to produce the above trace (with the help of my lovely GF who showed me how to use GIMP properly), which I then turned into a 3D Model and printed.
here is a picture of V1.0 next to the original piece. This version was slightly too big and didnt fit in the gun properly, but luckily these parts are so tiny it took little time to print a new smaller one. (These latches took around half and hour each to print).
here is V2.0 on the printer and next to the original part. As you can see it is slightly smaller and the hook at the top has been flattened as I was worried there was a clearance issue with the barrel. This version was nearly there. The only issue was the hook was slightly too high and held the barrel ever so slightly open. No matter! back to the printer I go!!
Here is the 3D STL file of the final design, V2.5. This version wasn't worthy of being V3 as it was simply a minor adjustment of V2.0. I moved the hook area down slightly which had the added advantage of thickening that top section so hopefully it wont shear off again!
It works! V2.5 fitted perfectly into the mechanism and locks the barrel nicely against the back plate, allowing it to fire once more /images/happy.gif" height="14" width="14" alt="happy.gif"> I will be sending the CAD model to a CNC mill at some point to get the part made out of something stronger than PLA, but until then it seems to work like a charm. Here are some shots of the final gun after cleaning.
YouTube video of a Tell Model 2
With thanks to Steve for this video.
Nickel-plated Tell 2
With thanks to Baz