Flywheel builder v1.3

The inner spoke thickness is 0 and the outer spoke thickness is 0. Use an inner hole angle of to have a 3-hole web cutout.

The rotary table must be rotated 0 degrees clockwise to bring the spoke edge parallel to the mill axis. The table must be offset by x=0 plus half the cutter diameter. See the step-by-step instructions below to build this particular flywheel design.

Fabrication of this Flywheel

This generated guide provides instructions for cutting out the web in the flywheel design shown above. This guide does not cover details of the Z dimension. It is expected the flywheel will initially be turned on the lathe. Face the flywheel on both sides. Bore the axle hole, which could be smaller than the final hole if the flywheel must be fitted to a mandrel or fitted for a guide for centering on the rotary table (RT). Trepan the flywheel. i.e., turn the webs in preparation for the cutout procedure below. The flywheel can return to the lathe after performing the web cutouts if desired.

Orientation

Note that the angles for the flywheel are dimensioned such that 0 degrees is pointing "up." When the flywheel is centered on an RT on the mill, this "up" direction could be aligned with either the Y axis or the X axis. Which axis is used does really matter, so the instructions from here on will be vague about this. There may be a slight advantage to using X as cutting operation may be easier to see.

In these instructions spokes are numbered from 1, which is the spoke facing "up," and they go around in a clockwise direction. In general the web cutouts will be performed in a clockwise direction for this reason. If for some reason your rotary table works better counterclockwise, there is no reason that can't be done. Just be consistent to avoid backlash and, more importantly, confusion.

Here are the spoke angles for this particular flywheel design. Cuts will not be performed directly along these angles as these identify the centerlines of the spokes, but it should be noted that often moving from one position to another will span this angle increment. Hint: the angles are greatly simplified if they are a multiple of the turn of a crank on the RT. This may be something like 4 degrees. The design of the flywheel can usually be tweaked so this is the case, and working the RT becomes much easier.

Finally, note that degrees are shown rounded to tenths. A tenth of a degree is 6 minutes, 0 seconds. This should be accurate enough for flywheel web cutouts.

**Table 1: Spoke angles**
Spoke	Angle

Order of Operations

There are many ways to cut out the webs of the flywheel, but this ordering works well and is what will be described here. As mentioned earlier, it is assumed the flywheel has been faced and trepanned on the lathe, and a center bore has been made, whether sized for the final axle or not, so that the flywheel webs can be cut. The center hole will be the key datum from which measurements will be made.

Drill the leftmost inner holes for the cutouts.
Drill the rightmost inner holes for the cutouts (if there are any -- 3-hole cutouts are common).
Drill the leftmost outer holes for the web cutouts.
Drill the rightmost outer holes for the web cutouts.
Cut the right (clockwise) side of each spoke.
Cut the left side of each spoke.
Cut the outer arc of the web cutout.
Cut the inner arc if it is a 4-hole cutout.

Setup

Center and clamp the flywheel on the RT. The clamps must not obstruct drilling and cutting operations. Center the RT under the mill. Zero the RT and mark the flywheel so it is obvious where the 0 (spoke #1) is located. Many operations will reset to this position as their first step.

Drill the Inner Holes

The inner holes for this flywheel design are 0 diameter. These holes will be drilled at an offset 0 from the center of the flywheel by shifting the center of the rotary table in X or Y. Advancing from hole to hole in this manner is done by rotating the RT 0 degrees for each. Return the RT back to 0 degrees when done.

**Table 2: Inner hole angles**
Spoke	Angle

Drill the Outer Holes

The outer holes are 0 diameter. These holes will be drilled at an offset 0 from the center of the flywheel by shifting the center of the rotary table in X or Y. Use care to reset the distance from the center as the RT was offset for the previous drilling of inner holes. It may be best to re-center the RT and adjust the offset from there to avoid error.

There are two holes to drill on the clockwise side of each spoke. The angles are listed. It is less error prone to drill the left hole for each spoke first, and then go around again drilling the right. Advancing from hole to hole in this manner is done by rotating the RT 0 degrees for each. Return the RT back to 0 degrees when done.

**Table 3: Outer hole angles**
Spoke	Angle

The Spoke Cutting

At the point the "corners" of the web cutouts have been defined with drilled holes. Now the sides of the web cutouts along the spoke edges will be milled. For best results, use an end mill equal to or smaller than the smallest hole diameter. The mill will cut from an inner hole to the corresponding outer hole.

To position for this cut, start with spoke number 1 by ensuring the RT is centered on the mill and returned to the zero position. See the figure below for Step 1. Now rotate the RT exactly 0 degrees clockwise, which is a setting specific to this particular flywheel design. See the figure below for this clockwise rotation for Step 2. The cut on the left side of the end mill should now be in line to make this cut, except that the X or Y needs to be offset by 0 to account for the spoke thickness. See the figure below for this sideways shift in Step 3. Again, this offset is specific to this flywheel design. This offset must be further increased by half the diameter (radius) of the end mill being used to cut the spoke. See the figure below for the end mill radius shift in Step 4. Don't forget to account for the cutter diameter!

Before cutting, lower the mill head without plunging into either hole and verify the cutter will cut from the left side of the inner hole to the left side of the outer hole. If all looks good, note the current Y (or X) position and slightly increase the distance. Now the cut can be made, potentially in multiple depth passes depending on the capability of the mill. Once it is completely cut through, reset Y (or X) and make the final finish pass at the exact offset.

This cut the right side of spoke number 1. Now use the RT to rotate past spoke number 2 and do the same cut to the right of that spoke. This will be a simple 0 rotation from the current cut for this flywheel design. Don't change other settings, except jog the Y (or X) for the rough cut vs. the finish cut. Repeat until all the right sides of the spokes are cut.

Step 1: initial setup

Step 2: rotate for cut

Step 3: shift sideways

Step 4: adjust for endmill

Now the left side of each spoke must be cut. Return the RT back to zero. Now back up the RT by advancing clockwise 0 degrees. Now the right side of the end mill should be in line to make this cut, except that the X or Y needs to be offset the other way by 0 to account for the spoke thickness. And again, account for the end mill diameter by adjusting further for half the cutter diameter.

As before, lower the mill head without plunging into either hole and verify the cutter will cut from the right side of the inner hole to the right side of the outer hole. If all looks good, note the current Y (or X) position and slightly increase the distance. Now the cut can be made, potentially in multiple depth passes depending on the capability of the mill. Once it is completely cut through, reset Y (or X) and make the final finish pass at the exact offset. Repeat until all the left sides of the spokes are cut.

The difficult part is done!

Finishing the Web

Finish by cutting the outer arc. Return the RT so that it and the flywheel are centered under the mill. The outer arc of the web is at 0 from the flywheel center. This is the outer hole center distance of 0 plus the radius of the outer hole which is 0. Offset X (or Y) by this amount, but reduced to account for the end mill radius. Make the cut for each web being very careful NOT to cut through a spoke!

That's it. The flywheel may be removed from the RT and cleaned up with files or further lathe operations.

Flywheel diameter		Rim Thickness
Hub diameter		Shaft diameter
Inner hole diameter		Outer hole diameter
Inner hole distance		Outer hole distance
Inner hole angle		Outer hole angle