The inner spoke thickness is 0 and the outer spoke thickness is 0. This is a 4-hole web cutout. Use an inner hole angle of to have a 3-hole web cutout.
This is a straight spoke flyweel. The rotary table must be rotated 0 (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.
This is a curved spoke flywheel and a fixture must be built to mill the curved spokes. This fixture must offset the center of the flywheel 0 from the center of the RT. Construction and use of the fixture is explained below.
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 relative angles of the spokes, but it should be noted that often moving from one position to another will span this angle increment. The spoke angles shown in this table are simply based on the number of spokes. They are always very large multiples of degrees and easy to dial on any RT.
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 degrees for each. Return the RT back to 0 degrees when done.
These holes will be drilled at an offset from the center of the flywheel by shifting the center of the rotary table in X or Y. These holes can be any reasonable size for a pin to mate with a corresponding hole that will be drilled in the fixture. Thus, a standard rod size may be preferred.
The location pin hole angles are listed. Advancing from hole to hole is done by rotating the RT degrees for each. Return the RT back to 0 degrees when done.
Cutting straight spokes requires shifting the RT under the mill and applying a rotation so that a side of a spoke may be cut along the X axis of the mill. The following instructions provide the procedure and precise settings to do this for this particular flywheel. When all is set up properly, a side of a spoke can be milled by lowering the mill cutter into an inner hole and cutting along X until the corresponding outer hole is reached. The flywheel will be rotated 0 to the next spoke and repeated until a side of all spokes has been cut. Then a new setup is made for the other side of the spoke, and this is repeated for the remainder of the spokes.
The following figures will be referenced in the step-by-step instructions that follow.
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 for Step 1.
Now rotate the RT exactly 0 (0) degrees clockwise, which is a setting specific to this particular flywheel design. See the figure for this clockwise rotation for Step 2 and observe that this rotation brings the cut line (shown in red) in parallel with the X axis (up/down).
Now Y needs to be offset by 0 to account for the spoke thickness. See the figure 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 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 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 and make the final finish pass at the exact offset. This offset should precisely cut from the edge of the inner hole to the edge of the outer hole.
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 degree rotation from the current cut for this flywheel design. Don't change other settings, except jog the Y for the rough cut vs. the finish cut as was done for spoke 1. Repeat until all the right sides of the spokes are cut.
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 (0) degrees. Now the right side of the end mill should be in line to make this cut, except that the 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 away 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 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 and make the final finish pass at the exact offset. Repeat until all the left sides of the spokes are cut.
Cutting curved spokes requires the construction of a fixture to hold the flywheel in position so the RT may be used to sweep out the arc to be cut by the mill on the left (outside) and right (inside) of each spoke. The fixture positions the flywheel by the center hub hole and a location pin hole drilled earlier in each waste area of the web cutout.
Note that the flywheel may be removed from the RT at this time. It may be useful to experiment with the flywheel blank in order to create a fixture of a size that fits well on the RT.
The fixture is a metal plate. The thickness of the plate doesn't particularly matter unless the flywheel is offset off the edge of the RT in which case the fixture must be rigid enough to support the cutting operation. If the entire assembly rests on the RT, the main concern is that holes in the plate be reasonable enough to locate pins. Sheet metal probably won't do.
The following figures show the fixture layout and how the fixture will be placed under the flywheel for a cutting operation.
Relative positions for the locations in the fixture layout are provided in this table. It can be seen that these are all relative to point A so they will need to be shifted inland onto the fixture plate.
Point A is the center of the flywheel and point B is for a location pin to align the flywheel on the fixture for accurate clamping. The fixture in the diagram is shown with a width of 0, a height of 0, and the relative position of point A is offset (0,0) from the lower left corner. The fixture plate can vary considerably from these dimensions as long as the flywheel can be supported and clamped. Note that if the flywheel is not hanging off the edge of the flywheel, shims the thickness of the plate can be used for clamping to allow a narrower/shorter plate to be used.
Points C and D will be used as centering points for the fixture+flywheel to be centered on the RT. Keep this in mind when laying out the size of the fixture. These points will be centered on the RT, so the flywheel could be hanging off the edge of a small RT. Points C and D might simply be punched so the fixture can be centered and clamped to the RT at one of the points. Alternatively, these might be holes that fit an alignment fitting that fits in the center of the RT. Note that these points may be close together.
Note that many holes have already been drilled in the flywheel, and these might be leveraged for clamping. Simply create the fixture with pins installed at points A and B such that the flywheel fits without play. Once the flywheel is positioned, the holes can be transfered to the fixture plate with center punches. They may be drilled and tapped for clamping bolts if the fixture plate is of a substantial thickness.
One final note on the fixture is that the cutting operations shouldn't cut into the fixture plate, so it may be reused for other purposes, including as a fixture plate for other flywheels. The point locations will differ for different designs, but they might be shifted to avoid interference with previously drilled holes.
Center the RT under the mill head. Now center point D of the fixture plate onto the center of the RT and clamp the fixture leaving room to allow the flywheel to be later placed without removing all the clamps. This could be done with a minimal set of clamps because the flywheel will eventually be clamped down and this should provide more cutting support. For now leave the flywheel off. The RT will be rotated for cuts so the RT need not be zeroed nor does the fixture need to be aligned along X or Y. Angle readings won't be used.
Next, shift the RT in X to account for the cutting radius of 0 less half the cutting diameter of the end mill. Place the flywheel hub on the pin at point A on the fixture and with the first spoke's location pin hole over the location pin at point B. Clamp the flywheel. Without running the mill, verify it can plunge into the inner hole and sweep to the outer hole.
For the cut, shift the RT a tiny bit more in X away from the spoke edge. Now run the mill using the RT to sweep out the cut. This could be performed in multiple depth passes depending on the capability of the mill. Finally, shift the RT back to the exact radius, still accounting for half the cutting diameter, and run the final pass. It should intersect the inner and outer hole edges perfectly.
To do this, leave the RT position as-is. Unclamp the flywheel being very careful not to disturb the centered position of the fixture on the RT. This means at least one clamp must be holding it down unless another method has been arranged to keep it centered. Carefully lift the flyweel off pins A and B, rotate it to the next spoke position, drop it back on pins A and B in this position, and clamp it down again. Now it should be ready for the next spoke cut. Without powering the mill, check that this is true.
Now, as before, shift the mill slightly away from the spoke in X and make the rough cut using multiple passes to get to depth. Then shift the mill back to the correct X and make the final pass. Repeat this procedure for the right side of all the spokes.
As before, place the flywheel on the fixture and clamp it down. Without power, make sure the mill will correctly sweep out the outside edge of the spoke and connects correctly with the inside edges of the inner/outer spoke holes. Once this looks correct, move it out a little more for the rough passes and make the cut. Return to the correct radius, still accounting for half the cutting radius and make the final pass. Repeat this for each spoke.
The difficult part is done!
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.