Tap, Stud, Nut, and Cap

 I had ordered 1.25 inch threaded rods for the studs.  Once I got them I realized that the pilot holes needed to be a little deeper.  Then there was another crossroad, cut the rods, or deepen the holes.  At this point I had already tapped fourteen holes.  So, well, the easiest rework was to make the holes deeper which was cutting aluminum.  Otherwise I would have been cutting twenty four steel rods.  Also, I am thinking I want more steel content around the periphery of the rotor for a little flywheel effect.

When I first cut the pilot holes around the periphery I made them 800 mils (0.8 inch) deep.  Then, after picking, and buying the threaded rods I realized that the pilot holes needed to be right at 1 inch.  So I have to rearrange the Mini Mill to do radial indexing again, and align the rotor to make all the pilot holes 200 mils deeper.  This went fairly quickly because I had already set up this operation.  After making the pilot holes deeper, I could tap all the holes deeper, then install the hardware.  I did have the issue of drilling holes that were already tapped.  This did work well because the original pilot holes are still there, and the threads are cut into the walls of the pilot holes, so you just have to be careful to run the drill bit between the existing threads, and not chew on the walls of the pilot holes.

The last task on the rotor was to increase the size of the center hole so that I can mount the rotor on the arbor that I will use to hold the rotor on the motor.  I have used this center hole as a center in all the machining processes.  So I want to change the size of this hole without affecting the position in the X, and Y axes.  The right thing to do would be to put the rotor on a lathe, spin the part, and use the center chuck to hold a drill bit to bore out the center hole.  So, instead, I used drill bits on the drill press to do this.  I didn't firmly clamp the part so that the drill bit could center itself in the hole.  Then used a series of bits to increase the size of the hole incrementally.  So, in about six steps I increased the size of the hole from around 230 mils to 375 mils.  Then gave it a test fit on the arbor.

The completed rotor weighs 22 ounces, which is heavier than I thought it would be.  I've also been thinking about things like the flywheel effect, and the gyroscopic effect.  When I spin it the torque effect from the spinning rotor will drag the frame in the same direction.  So, having mounted it, and spun it a little, like five minutes ago, it does seem to be reasonably balanced to spin at low speeds.  As the speed goes up, it does vibrate a little more, so when I start finishing the part I'll pay more attention to the balance on the rotor.

So, now I need to start thinking about fabricating the stator which is the collector for the system.  Yeah!  It Spins...

CEG Rotor

 OK, I finally have the major cuts done on the CEG Rotor.  This includes the radial cut where I made the round shape of the rotor, and the peripheral holes for the electrodes.  The Rotor is four inches in diameter, and a half inch thick.  Then there are the holes around the periphery which are pilot holes for 1/4-20 screws.  There are 24 pilot holes spaced 15 degrees apart, at the four inch diameter of the Rotor.  At this point it is a rough cut piece.  There are more operations to perform.

Now take a look at the drawing.  The outer diameter of the cut is the same, and the 24 pilot holes are there.  But the drawing has more features that haven't been machined into the part yet.  There are chamfers around the edge of the Rotor on both the top, and bottom sides.  The center hole is a larger diameter.  The tooling holes are not in the drawing.  The pilot holes are the same diameter, but both the drawing, and the part do not have the 1/4-20 threads.

So, yeah, there is more work to be done in the machine shop.  The center hole was first used to align the part to the center pin on the Rotary Table.  When I finish the machine operations that use the Rotary Table I will increase the size of the center hole to 0.375" to fit the Arbor I picked to hold the Rotor in the assembly.  Also, I will need to tap the pilot holes for 1/4-20 screws in order to hold the electrodes.

Here I have revised the CEG Rotor drawing a little.  I changed the Chamfers to make the angle a little steeper.  The Tooling Holes have been added.  The change in the Chamfers is to accommodate the tooling holes.  We want some nice flat, level areas where the clamping screws are holding the part in case there is some reason I want to put it on the Rotary Table again.

Radial Indexing

 The next cut that I need to make on the New Rotor are the radial holes around the periphery of the Rotor.  When I was cutting the radius of the Rotor I was using the Rotary Table as a Rotary Chuck, the idea being the Rotary Chuck holds, and turns the part while the Mill is cutting around the periphery.  In that configuration the Rotary Table was horizontal.

Now I want to Drill Holes from the periphery of the Rotor toward the center of the Rotor.  In this configuration the Rotary Table has to be mounted vertically on the Machine Table, and the machine will be drilling holes into the Rotor in the Z axis.  So, we are still dealing with the three axes of alignment, and a rotary axis.  This time we want X, Y, and rotary axes of movement clamped while we do a Drill operation in the Z axis.  Then I'll loosen the clamp on the rotary axis, move the rotary axis 15 degrees, clamp the rotary axis again, and do another drill operation.

The first obstacle is the Rotor itself.  The Rotor's diameter, four inches, is a little longer than the distance between the center of the Rotary Table, and the vertical mounting surface of the Rotary Table.  This means the Rotor protrudes past the mounting surface of the Rotary Table by about 275 mils. and we need a short riser to get the Rotor above the surface of the machine table.  We need to freely rotate the Rotor around the axis of the Rotary Table to make the peripheral holes.  Also, we need to assemble the Rotary Table assembly on the Drill Press Machine Table, and not on the Milling Table.  When the Milling Table is on the Drill Press there is insufficient vertical clearance to make these peripheral cuts.

Here I have used a 0.375 inch Aluminum plate to be the short riser to get the periphery of the Rotor off the machine table.  The mounting screws are countersinked into the short riser plate so the short riser plate can sit flat on the machine table.  Then I can slide the Rotary Table assembly around the machine table for the X, and Y axes alignment.  There are two C-Clamps that secure the Rotary Table assembly to the machine table once it is aligned.  I have scratched a line around the periphery of the Rotor to indicate the center of the periphery of the Rotor.  I also have some lines on the face of the Rotor which will help with the X, and Y axes alignment.  I used a framing square, the center of the Rotary Table, the Drill bit, and the center line of the periphery of the Rotor to perform the X, and Y axes of alignment of the Rotary Table assembly to the Machine Table, and the Drill.  Blarg...  Thatz a mouthful...

 There is a compass around the edge of the Rotary Table.  Once I had the X, and Y axes alignment locked I rotated the Rotary Table to 0 degrees.  I spent a considerable about of time scrutinizing the X/Y alignment, Rotary Alignment, and depth of cut before I felt confident to make a cut.  The more time you spend fabricating a part, the more valuable it becomes.  As its value increases you feel compelled to overthink each following cut, and don't want to make any mistakes.  This is where it ceases to be a part, and becomes an investment.  Any mistakes could lead to considerable rework, or even scrapping this part, and starting again.

I have made five holes so far, and my process seems to be working well.  At this point I'm going to take a break, and think through this again.  I'll make some measurements on the holes I have cut, and look at the consistency of the cuts.  At first glance it looks like it is going well...

Full Circle

 This was a very aggressive cut for my Mini Mill.  I was hanging over the limits, and had a couple incidents where this became obvious.  The Chuck is held to the Quill with a Morse Taper.  This is the way that Drill Presses typically hold the Chuck.  It is perfectly OK when you are drilling, down cutting into the material, because the force applied to the Quill, Morse Taper, Chuck, and Bit is downward.  This keeps the Morse Taper thoroughly seated, and locked.  You will never have a problem drilling.

I call this thing a Mini Mill.  OK, there in lies the problem.  I'm milling, side cutting, with no downward force.  The force applied to the cut is from the side, and is a cutting action so this force is cyclic causing vibration.  This applies the force through the Bit, into the Chuck, on up to the Morse Taper, and into the Quill causing the entire machine to vibrate with this sideways force.  Drill presses are not meant to do this.  Some would say this type of cutting is not possible, and you will never get a good cut.  I'm going to say that is wrong.  You can use you drill press as a Mill when you keep everything tight, don't over load the machine, and make relatively small cuts that don't create excessive vibrations.  The depth of the cut is relative to the amount of vibration you get, and the tool will let you know when you are cutting too deep.

In the first incident the Chuck came off the Morse Taper while I was cutting.  The Chuck stopped spinning, and I had to abort the cut.  There was no adverse effect because when the Chuck is disconnected from the Morse Taper it will stop spinning.  In the second incident the Morse Taper came out of the Quill.  In this case the Mill continued to spin, and I kept cutting, but the cut was going deeper as I went around the radius of the part.  The amount of vibration, and noise that the machine was making increased.  I noticed it visually, and then immediately aborted the cut.  This did have an effect, but that effect was the cut got deeper, and didn't affect the radius of the cut.  If anything it caused the Mill to move away from the radius of the cut.

This is the Mini Mill configured to cut the radius of this part.  There are a lot of things that I can improve on this machine.  I noticed that the X Axis will move with vibration, and I had to work around that issue.  It would be nice to have clamps that hold the axes that don't move with a cut.  There is not depth hold on the Z Axis, really another clamp, but with this cut I was holding the Z Axis with one hand, while doing the part feed with the other hand.  It does have a depth limit, but not a hold at depth clamp, and that would be handy, LOL!  Milling machines have a screw that goes through the Quill, Morse Taper, and Chuck which holds the rotating assembly together vertically, and that, also, would have been very handy.  Then there are the bearings that the Quill is riding on.  In a Drill Press these bearings are meant to handle a downward force.  With a Milling Machine these bearings are capable of handling downward, and side loaded forces.  I think what I am telling myself here is this I need a Milling Machine...  and a Lathe...