Hello everyone. This week I am going to get into machining the flywheels. I have been looking forward to testing the capacity of my new lathe and these wheels are going to fit the bill just fine. Not only are they large (over 8” in diameter) but they are fairly heavy. Just the perfect challenge for my new machines ;0)
The first order of business is to inspect the wheel castings. It is important to determine which wheel will be on what side of the engine and what side will be facing out. This decision will be based on how concentric the casting halves are to each other. If the mold halves that made these wheels were out of alignment during casting it will show up when they are spinning (of course this will only be visible on the unmachined portions of the wheel). The best way to see if the casting halves are aligned is to spin them on the lathe. I can “see” the misalignment much better as the wheel spins so I mounted each wheel on the lathe and looked at them from all angles. Just as I suspected one of the wheels was misaligned and a determination was made to put that wheel on the “pulley” side of the engine. This will somewhat “hide” the wobble of the casting making for a more concentric look when spinning. I identified the outsides of the wheels respectively and started getting to work on truing the “governor” wheel in the lathe’s chuck. I used a dial indicator on the inside of the wheel (both sides) to get the best average measurement to ensure the best plane of rotation. The alignment was verified by spinning up the wheel for a visual inspection as well.
The next step was to bore the 1/2” hole for the crankshaft. I used a 15/32” drill bit to bore the initial hole for the wheel as seen below. You will notice the use of the tool bit to steady the drill.
I could now use a boring bar to widen the hole to 1/2”.
I was very careful when approaching the final dimension and made .001” deep passes as to not overbore the wheel. I used the crankshaft to verify the fit was correct before moving on (not shown).
The next step was to face the inside hub where the governor arm bracket will mount. I measured the thickness of the spokes (about .410”) to determine the center of the wheel and used that measurement to gauge the depth of the cut. I came up with .245” from the face of the spokes to make my face.
I used compound rest’s indicator dial to measure off .245” and started cutting the face...
To make the transition from the rough casting to the hub I decided to cut a radius in the corner with a custom ground tool bit as seen below. I used an 1/8” radius cut and took it down to a hub diameter of about 1.162” diameter.
At this point I decided to use an turning arbor to finish the rest of the machining processes. The turning arbor will act like the crankshaft and ensure that when the flywheel is tightened down on the crankshaft it will spin true without any wobble. To do this I must broach the keyway and install the set screws. On my 6CI steam engine build I used an unconventional way of cutting the keyway in my flywheel. This time I plan on using an 1/8” keyway broach (seen below) to cut the keyway which should be a good learning experience.
I set the wheel up in my arbor press and greased the broach for a first pass.
I aligned the bushing with the spoke as seen below...
The first pass went fairly well with moderate pressure. You can see the shavings below.
I added the second pass shim to the bushing and made my second pass...
The keyway was now cut and looked pretty good :0)
At this point I decided to bore the “pulley” wheel as well. Since the “pulley” side wheel had the imperfection of the casting halves I decided to center the outside half so it would appear to spin true. This was done by offsetting the center of the wheel with a four-jaw chuck so that the outside face was concentric with the axis of the wheel. This step is really not necessary although I am certain it will look much better than the two halves wobbling about :0P
Here is a picture of me having fun with my new lathe ;0)
I cut the same 1/8” radius on the hub as before leaving a 1.162” diameter. I also faced the outside of the hub to .483” from the outside of the spokes (.688” from center of the wheel).
Since I was in the boring process I decided to bore the pulley at this time as well...
I used the keyway broach to cut both the pulley and the “pulley” flywheel at this time (flywheel not shown).
I decided that I would machine the outside of the pulley first to get a feel for how the lathe would do with turning larger radius parts. This will require me to install the set screw to tighten the wheel to the turning arbor so I drilled and tapped a 8-32 hole in the wheel as shown.
Now I must make my turning arbor. I cut a 5.5” long piece of 1/2” tool steel rod (not included in the materials kit) and then cut a 3” long keyway in it much like the ones made in the crankshaft. I then drilled a centering hole in one end to be used with a live center on the tail stock of the lathe.
I cut and installed a piece of 1/8” keystock into the arbor.
I mounted the pulley on the arbor and cut an 1/8” radius about a 1/4” into the hub as shown (done on both sides of the pulley). This will help the pulley casting to appear to run true when spinning later on. I also plan on polishing the hubs much like I did on my 6CI kit.
I now extended the turning arbor out of the chuck and used my live center to support the end of the shaft. This will provide an axial reference for the bore of the hub to ride on and should ensure that the pulley will run true when spinning on the crankshaft later on. I installed the pulley on the arbor and tightened the set screw as it would be during final installation.
I began to turn down the outer diameter of the wheel at this point.
I turned the wheel at about 250 RPM using .005” per revolution feed for this process. The final outer dimension was cut to 3.050” in diameter.
I faced off the two outer edges for a final width of 1.3”.
The pulley is designed to be beveled to properly track a belt so I decided to modify the design a bit to allow for a three segmented surface in lieu of a roof-shaped design. This was done by scribing the wheel at .525” from the outer edges and cutting a 3° taper to these lines.
I set up my compound rest so that it was 3° as seen below...
I now was able to cut the taper in the wheel just up to my scribed lines.
I used some 320 grit sand paper followed by some metal polish to finish off the surface.
I used the Dremel tool to blend in the radius on the hub at this point.
Finally I sanded and polished the hubs to finish the pulley.
I am happy with the outcome so far and expect to finish the flywheels very shortly. Please join me again for the next episode to see what happens next ;0)
