Tesla Turbine - Part 2

Photos and drawings by Author

Runner Shaft Hub

This part needs to be made before any more operations on the disks are performed. Begin with some 2.500" diameter (or larger) aluminum stock. Using a cutoff tool, turn a section down to something over 1.000" diameter and wide enough that a normal lathe tool can be used (Photo 33). Turn this part around, put it back in the lathe, then turn the inner diameter to 1.000". Use a left-handed tool to face the inner edge (Photo 34). Center drill, drill, and ream the central 0.375" hole (Photos 35 and 36). Part off leaving a 0.125" thickness of the 1.000" diameter portion (Photo 37).

Now we'll move to the rotary table. After centering the table under the spindle, clamp the runner shaft hub to the table as seen in Photo 38 and center it. Move the mill table left by 1.000" and drill six No. 29 holes spaced 60° apart (Photo 39). Tap these holes 8-32.

Runner Disk Central Holes

Now we'll do some more operations on the runner disks. Clamp the aluminum block in the mill vise. Attach the top four disks to the block (not the end disk!). Center the 1.000" hole under the spindle (Photo 40). Use a boring tool to widen the hole a bit less than the required 2.750" diameter (Photo 41).

Runner Disk Final Operations

True up the runner shaft hub in the four-jaw chuck (Photo 42). Bolt all five disks to the shaft hub, and bolt all the disks together with the bolt circles drilled and tapped previously. At this point, mark the position of each disk so they can all be reassembled in the same orientation later on. Turn down the outer edge of all the disks to the final diameter of 7.000" (Photo 43). Remove the top four disks, again noting their positions. Put them back on after spacing them from the end disk with 0.031" thick washers (Photo 44). Bore out the central holes in the top four disks to their final diameter of 2.750" (Photo 45).

Runner Disk Assembly

Start with the runner exhaust end disk. Place a 0.5" long 8-32 flathead screw in each of the 18 holes and place upside down on a flat surface. Place a 0.031" thick No. 8 washer over each screw. Place one of the 0.050" thick disks over the screw/washer combination. In similar fashion, build up the remaining two 0.050" thick disks (Photo 46). Finally, put on the runner shaft end disk and tighten all 18 screws into the holes tapped in this disk. Remember to keep all the disks aligned as you marked them when doing the final turning! The assembled disk stack should look like Photo 47.

Runner Shaft Hub Continued

Now we'll drill the remaining four No. 19 holes. Clamp in the mill vise. Drill four No. 19 holes spaced 0.375" from the center portion. Follow each hole with a 0.250" drill to a depth of 0.250" (Photo 48).

Bearing Frame

The bearing frame is made from 0.500" thick aluminum stock 4.000" wide. Begin by cutting and milling two pieces 6.750" long and two pieces 4.500" long. On both of the 6.750" pieces, mill the 0.500" wide by 0.250" deep slot as shown on the drawing, followed by the 0.500" wide by 0.250" deep cut on the end (Photo 49). Drill and countersink the six No. 19 holes, three in each slot (Photos 50 and 51). In one of the 6.750" pieces, drill the two 0.375" holes. These will be used to mount the runner casing to the bearing frame (Photo 52).

Now drill the six No. 29 holes, three in each end, in the top and bottom pieces, as seen in (Photo 53). Tap these holes 8-32. Put the bearing frame together as seen in Photo 60.

What follows is a fairly detailed description of drilling the two 0.750" diameter holes used for the bearing cups. The problem I had was how to drill two holes 5" apart when the spindle of my mill didn't have that much travel. Begin as seen in Photo 54. Using your 0.750" drill bit, adjust the height of the mill head so the tip of the drill would almost touch the highest portion of the bearing frame. Now put in the drill chuck. Locate the hole with an edge finder and clamp the mill table in position. Remove the uppermost piece of the bearing frame. Using a 0.500" collet and a 0.500" shank drill, install the bit as shown in Photo 55. Re-attach the uppermost piece of the bearing frame. If all is well, the tip of the bit will be in the correct position and will almost be touching the bearing frame (Photo 56). Drill through. Photo 57 shows my mill spindle at its maximum extension - not far enough to drill the second hole. Back the spindle up, loosen the collet, and extend the shank of the drill bit out as far as you can and still leave enough for the collet to hold onto (Photo 58). Now, drill the second hole through.

Remove the bearing frame and take it apart. Make sure to mark each piece so they may be re-assembled in the same orientation. Drill the 0.750" hole for the tachometer connector (Photo 59). From this hole, locate and drill the four No. 33 holes for the connector mounting screws (Photo 60). Finally, drill the two No. 19 holes used for mounting the valve body (Photo 61). Note this photo also shows how the tachometer connector is mounted.

We will work on the shaft and bearing cups in the next issue.

Errata from the Author

On page 21 of the September/October 2001 issue, mu is equal to 1.79 X 10^-5 Ns/m2. Somehow the mu (μ) didn't get printed. Issue 16 of the TEBA news, from which I got this formula, describes mu as "the dynamic viscosity of the fluid," and then further states the fluid is air and the value for mu is 1.79 x 10^-5 Ns/m2.

(The omission was an electronic error and I apologize for any inconvenience - Ed.)