At first I tried using CDs because of their large surface areas, but they didn’t hold up too well under the milling machine. I also had a stack of platters from old and defective hard drives, but I didn’t know if the smaller diameter disks would work as well.
One problem I ran into is that some newer hard drives use ceramic disks instead of metal. They’re still coated with metal, but they’re thinner and a couple platters shattered when I tried to machine them:
My original plan for the center hole pattern had small holes (for threaded rods and washers for spacers), as well as large holes (for air vents).
The second set of platters had radial arcs cut in them such that the inside edge of the radial cutout is close to the outside diameter of the spacers that I removed from the hard drive assemblies.
The hard drive platters were stacked and clamped to a rotary table between two sheets of scrap aluminium but the top disk (above picture) still took some extra damage. The rest of the platters look much better though (see the complete rotor assembly below).
I decided to be lazy and use the spacers that were between the platters in the original hard drive assemblies rather than machine my own. This increased distance (roughly .05″ instead of .012″) may lead to turblent flow rather than laminar flow but will be close enough for this project.
With the turbine platters and spacers complete, I turned a shaft from round stock. The inside diameter of both the platters and spacers is .98″ which is the diameter of the thick section in the middle. I left the whole length at .98″ until I knew the width of the chamber and the inside diameter of the bearings. The wide part is 1.77″ long which fits inside the 2″ thick acrylic chamber.
The collars are essentially wider versions of the platter spacers. The inside diameter has to fit on the shaft, but they can’t be too tall so they block the ventilation holes in the disks. Also, they can’t be too wide or they will take up too much horizontal space inside the chamber. I made each collar .3″ which is enough space for a #10-32 set screw to hold them (and everything else) in place.
The bearings and brass fittings were the only new parts in this project (everything else was reused from scrap materials). These metric bearings were pulled from a box of old and used bearings and I had to machine the shaft and side panels to fit them.
There are eleven platters and ten spacers held together by the two collars. The hard drive platters are hard to keep clean so I wore gloves when assembling the rotor. There should be a fair amount of pressure between the two collars or the disks will rotate about the shaft instead of with it.
The main chamber is an acrylic block machined down to 4.75″ x 4.75″ x 2″. The square block was mounted in a 4-jaw lathe chuck, drilled, and then bored out. The final cutout is about .07″ larger than the disks. The air inlet is taped for a 1/4″ pipe thread and all of the other holes are taped for 1/4-20 socket head cap screws.
The side panels are .47″ thick acrylic and have untaped .25″ holes for alignment to the main chamber. The center hole is .6″ with a .280″ deep counterbore for the bearing. The bearings are metric so I used the 4-jaw chuck and boring bar again to try for a press fit into the side panel. However, I made the counterbore a few thousandths too big which allows the bearing to rotate in the side panel.
Many other Tesla Turbines that I’ve seen online have larger ventilation holes in the sides. I was going to cut the same radial pattern from the disks in the side panels, but I decided that wasn’t necessary after a trial run with just the .6″ hole.
The two brass fixtures are a 5/16 – 45 tube union (picture 5), and a 1/4 tube, 1/4 pipe hose barb (picture 6).
The original AutoCAD .dwg file is available here.
Above sections last updated 11.Nov.2005.
I couldn’t have done this without help and I would like to thank: Peter Federighi (for giving me the original idea), my boss John Davis (for going on vacation and leaving me to my own amusement), and Ron Musgrave and Mike Vinton in the Physics Department Instrument Shop (for all their patience and expertise).
Please send any questions or comments to me at firstname.lastname@example.org.