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The spark that ignited the idea of making a 3D printed King Midget transmission wasn't mine. Instead the inspiration came from my good friend Ted Richardson. We had just finished a discussion about a KM transmission I had repaired and was showing him something I had made using my new 3D printer. It was a part made for a project I had in mind. However, when Ted suggested making a KM transmission instead I chucked my idea. For after having repaired a few King Midget transmission I thought it would be interesting to make one using a 3D printer. I also thought that having the ability (I am somewhat fluent in using a 3D drawing program) to draw up ideas and make them. I could then do some experimenting that would be easily done. For example I did find another way to not use set screws to hold the driver sprocket of the transmission output shaft.
Youtube has a prolific number of videos on the subject of 3D printing. So there is no need for me to describe how the process works.
I wanted to make the transmission just like they did in the King Midgets Motor manufacturing plant. Breaking down each piece of an assembly to its basic component I made a drawing of that part. In my case I used Autodesk's Fusion 360 CAD software to make the drawings. The next step was to convert the Fusion 360 drawing .stl file to a gcode file which tells the 3D printer what to do. To do this conversion I used Cure to make the prototype transmission and the follow-on units will be with a PrusaSlicer software.
The following pictures show more detail of the process I used.
The 3D parts are not solid but are internally a geometric pattern selected by the maker. Shown is a cross pattern at a density of 20%. The thin outer ring was made to ensure satisfactory extrusion of the filament before making the part.
The prototype parts were made by a Creality CR-10S 3D printer. The only change I made to the printer was to replace the print bed with a 12x12 inch mirror purchased from a local hardware store. Filament adhesion to the mirror was excellent and left a smooth surface on the printed part. The 3D slicing software used was Cura produced by Ultimaker. All of the prototype 3D printed parts were made with a 1.75 mm PLA+3D filament manufactured by eSun.
The combination of the Prusa printer and slicer software has a history of making quality pieces. Other printers for example may or may not have self leveling. This one does have this feature (plus others) as an integral part of the printer and slicer software. To me this is a tool and not a project.
This is the Prusa i3 MK3S+ printing one of the two pieces (part numbers 2-93 and 2-94) required to make the Reverse Sliding Gear Assembly (part number 2-95). The filament , PLA+3D purchased from eSun, is the same as the prototype transmission. Referring to the following illustration pages this is referred to as Ref. no. 20 and 21.
Since I was making this transmission just like the manufacturing plant did I used their part numbers, description and reference numbers. Both of the following illustrations can be found in the 1968 Manual of the model 3 King Midget. In the spreadsheet to track my build I used this information along with my data.
The prototype is pictured next.
Due note that the clear tube (ref. no. 7) was not 3D printed since clear filament isn't available.
Fusion 360 generated a picture of prototype transmission.
Notice the right hand side handle. Turning the handle will show the actual motion of the transmission.
Since it is a plastic like material the motion isn't smooth and somewhat stiff when turning the crank handle. However, the shifting knob does demonstrate forward, neutral and reverse.
I couldn't resist the temptation of showing Sammee. She liked playing with the parts.
The following carousel of pictures shows the collection of parts made for the assembly of several transmissions.
The 1st 3D printed model is done. Next is to add a plaque and paint the base.
Showing the 3D model to a friend at a local car show. That's me on the left.
What interested everyone was what was happening inside the transmission. Very few question about 3D printing but lots of interest in King Midgets.
The base has been primed and is ready to paint a light tan color.
Completed
Plaque frame color represents the serial number of the unit. 1- Brown, 2 - Red, 3 - Orange and 4 - Yellow.
Three close up pictures of the shifting fork, reverse gear and forward sprockets with chain.
With the completion of this fourth 3D printed King Midget transmission marks the end of the project. This fourth one will be shown to the public to not only demonstrate the internal-working of the transmission but tell them about the history of King Midget Motor.
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