Pump Flywheel

Pump flywheel

Modeling in O scale and in the middle of making a small oil engine I needed a flywheel. The problem was that it needed to be 3/4″ dia (that’s 3ft in O scale) .. and for the life of me .. I couldn’t find anything. I ended up scratch-building the darn thing and this is how I did it.

Parts – HO Driver

I finally got a set of old HO locomotive drivers from my buddy Gary. They were a brass tire with a plastic center pressed in. I popped the rim off .. filed the flange off and I ended up with a ring that measured .750″x.110″. That scaled to 3ft x 5-1/4″ in O scale. Great. The only problem was that there was knurling on the inner surface of the ring. I fixed that by super-gluing a strip of .020″ styrene over the knurling. That accomplished two things .. 1) Hid the knurling and 2) supplied a place for the styrene arms to adhere to.

Sketchup drawing

First thing I did was draw the center of my flywheel in Sketchup. In the drawing below I drew a circle .640″ dia. That’s the inside measurement of the rim (with the styrene strip). I made the arms from .022″ x .066″ styrene strip so I drew these in. The hub I made from 1.8″ tubing .. drew that .. and finally indicated the 3/16″ dia reinforcing ring.

parts

Here’s all the bits cut out. You can see the brass tire with the styrene strip cemented on the inside.

Evergreen styrene tubing telescopes – odd numbered sizes of round tubing telescope into next odd numbered size – even numbered sizes of round tubing telescope into the next even numbered size. That’s why I used the 3/16″ tubing. I cut these .020″ wide. They will reinforce where the arms cement to the 1/8″ hub. The 1/8″ hub is in two parts – one is .125″ long and one .145″ long. Finally, the .022″ x .066″ strips.

work surface

Moving the camera back a bit and you can see the set-up. I glued the Sketchup printout to my marble work surface (nice and flat). I used the glue stick to do that.

Note: My “marble work surface” is a single marble floor tile that I got from Lowes. A couple of dollars at best and you have a perfectly flat work surface.

gluing up

I first used the school glue-stick again and glued the 1/8″ x .145″ hub to the center of the drawing. I used this length simply because I wanted the hub to stick out 1/8″ on either side of the flywheel. The .140″ is simply that 1/8″ + the thickness of the arms. The strips of styrene that make up the arms are simply glued to the 1/8″ hub. A small round-file stroked across the ends makes them fit. I used the Tenax for cement. Let that set up a few minutes and dropped the 3/16″ ring over the hub and cemented everything well.

Finishing up

I used a razor-blade to snip off the arms even with that .640″ circle on the paper and then when it had dried, popped it all loose. Flipping the center over I added the other 1/8″ tubing (.125″ long) centered on the assembly and then dropped the other 3/16″ ring over the hub and snuggled up against the arms and cemented everything well.

Finished

Finished flywheel .. mounted on my scratch built steam pump. I created this for my pump house. All that work and you can’t see it except by twisting yourself into a pretzel.