Flywheel builder v2.0
The inner spoke thickness is 0.360 and the outer spoke
thickness is 0.212.
This is a 4-hole web cutout. Use an inner hole angle of 36.0 to have a 3-hole web cutout.
This is a straight spoke flyweel. The rotary table must be rotated 4.6
(4°36'0'')
degrees clockwise to bring the spoke edge parallel to the mill axis. The table must be offset by
x=0.220 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 [undefined obj element curveRadius:length]
from the center of the RT. Construction and use of the fixture is explained below.
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.
These instructions will assume "up" along the X dimension, so on a typical mill the flywheel will be oriented so
that up/down when the RT is zeroed is along the X axis.
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.
Table 1: Spoke angles
| Spoke | Angle |
|---|
| 1 | 0.0 |
| 2 | 72.0 |
| 3 | 144.0 |
| 4 | 216.0 |
| 5 | 288.0 |
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 inner holes for the cutouts.
- Drill the leftmost inner holes for the cutouts.
- Drill the rightmost inner holes for the cutouts.
- Drill the leftmost outer holes for the web cutouts.
- Drill the rightmost outer holes for the web cutouts.
- Drill a hole in the waste of each web cutout for a location pin for curved spoke cuts.
- 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
Setup
Several of the operations will be performed on the RT while the flywheel is centered under the mill.
Center the RT under the mill. Center and clamp the flywheel on the RT.
The clamps must not obstruct drilling and cutting operations, so look carefully at the outer hole positions.
None of the spoke cutting operations require high precision, so it is reasonable to consider moving a clamp provided
the flywheel remains well clamped by two or more other clamps when this is done.
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 0.375 diameter. These holes will be drilled
at an offset 0.625 from the center of the flywheel by
shifting the center of the rotary table in X or Y.
This is a 3-hole web cutout, so there is only one hole to drill on the clockwise side of each spoke.
The angle is listed for each spoke.
This is a 4-hole web cutout, so 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 right hole for each spoke first,
and then go around again drilling the left.
Advancing from hole to hole in this manner is done by rotating the RT 72.0 degrees for each.
Return the RT back to 0 degrees when done.
Table 2: Inner hole angles
| Spoke | Angle |
|---|
| 1 | 36.0 (36°0'0'') |
| 2 | 108.0 (108°0'0'') |
| 3 | 180.0 (180°0'0'') |
| 4 | 252.0 (252°0'0'') |
| 5 | 324.0 (324°0'0'') |
Drill the Outer Holes
The outer holes are 0.188 diameter. These holes will be drilled
at an offset 1.438 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 72.0 degrees for each.
Return the RT back to 0 degrees when done.
Table 3: Outer hole angles
| Spoke | Angle |
|---|
| 1 | 8.0 (8°0'0'') | 64.0 (64°0'0'') |
| 2 | 80.0 (80°0'0'') | 136.0 (136°0'0'') |
| 3 | 152.0 (152°0'0'') | 208.0 (208°0'0'') |
| 4 | 224.0 (224°0'0'') | 280.0 (280°0'0'') |
| 5 | 296.0 (296°0'0'') | 352.0 (352°0'0'') |
Drill Curved-spoke Index Location Holes
The spoke cutting for curved spokes will eventually require the flywheel be clamped on a fixture (not yet -- keep it centered).
The flywheel will be located in position on this fixture by the center hub hole and the location pin
holes that are drilled in this step. These index location holes are drilled in the
waste material of the web and are drilled in a manner similar to the inner and outer holes.
These holes will be drilled at an offset [undefined obj element locationPinDistance:length]
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 72.0 degrees for each.
Return the RT back to 0 degrees when done.
Table 4: Location Pin angles
| Spoke | Angle |
|---|
The Spoke Cutting
At this 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 the easiest operation,
use an end mill smaller than the smallest hole diameter of inside/outside holes.
The mill will cut from an inner hole to the corresponding outer hole. A larger end mill may be used
with care if a hole is particularly small, but some cleanup filing or finishing with a small end
mill will be required to finish each cut.
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 72.0 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.
Cut the right side of the first spoke
The following figures will be referenced in the step-by-step instructions that follow.
Step 1: initial setup
Step 2: rotate for cut
Step 3: shift sideways
Step 4: adjust for endmill
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 4.6
(4°36'0'')
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 0.220 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.
Cut the right side of the rest of the spokes
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
72.0 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.
Cut the left side of the spokes
Now the left side of each spoke must be cut. Return the RT back to zero.
Now back up the RT by advancing clockwise 355.4
(355°24'0'') 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 0.220 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 cutting fixture
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.
Fixture Layout
Fixture Position for Cut
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.
Table 5: Fixture layout locations
| Point | X | Y |
|---|
| A | [undefined obj element fixtureA.x:length] | [undefined obj element fixtureA.y:length] |
| B | [undefined obj element fixtureB.x:length] | [undefined obj element fixtureB.y:length] |
| C | [undefined obj element fixtureC.x:length] | [undefined obj element fixtureC.y:length] |
| D | [undefined obj element fixtureD.x:length] | [undefined obj element fixtureD.y:length] |
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
[undefined obj element fixtureSize.x:length], a height of [undefined obj element fixtureSize.y:length],
and the relative position of point A is offset
([undefined obj element fixtureOffset.x:length],[undefined obj element fixtureOffset.x:length]) 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.
Cut the right side of the first curved spoke
An arc radius of
[undefined obj element curveRadius:length] will be used for cutting all the spokes.
This same arc radius is used for both the right and left sides of the spokes, but the center point on the fixture
will be different. The right cut will cut the line as shown in the following figure.
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 [undefined obj element curveRadius:length]
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.
Cut the right side of the rest of the curved spokes
Now that the right side (inside) of the first spoke is cut, the right sides of the rest of the spokes need to be cut.
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.
Cut the left side of the curved spokes
The left (outer) sides of each spoke are cut in a similar manner to the right side. To prepare for this, unclamp the
fixture from the RT and now center point
C on the RT. To do this, re-center the RT under the mill head, center and
clamp the fixture on point
C, and then move the RT along X for the
[undefined obj element curveRadius:length]
radius. This time
it must be increased by half the cutter radius so the cutter cuts on the inside of the arc.
The left cut is shown in the following figure.
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!
Finishing the Web
This is a 3-hole web cutout, so only the outer arc of the web needs to be cut. The inner hole already drilled forms the inner arc.
This is a 4-hole web cutout, so the inner arc of the web needs to be cut.
Return the RT so that it and the flywheel are centered under the mill.
The inner arc is at 0.438.
This is the inner hole center distance of 0.625
less the radius of the inner hole which is 0.188.
Offset X (or Y) by this amount as well as an additional distance to account for the end mill radius.
Make the cut for each web being very careful NOT to cut through a spoke!
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
1.532 from the flywheel center.
This is the outer hole center distance of 1.438 plus
the radius of the outer hole which is 0.094.
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.