Tesla Turbine - Part 5

Photos and drawings by Author

Valve Body

Begin with a block of aluminum 1.500" X 1.500" X 2.500". Drill a 0.250" diameter hole centered in the 1.500" square all the way through. Widen the hole with a 0.438" drill to a depth of 0.750" from the point where the flutes of the drill bit just touch the edge of the 0.250" hole. Turn the block over and, with a 0.339" (R) diameter drill, repeat this process (Photo 124). Tap the 0.339" diameter end to 1/8-NPT (Photo 125) and tap the 0.438" diameter end to 1/4-NPT. Turn the block on its side and drill through with a 0.875" drill (Photo 126). Position the block as shown on Photo 127, drill the two No. 29 holes to a depth of 0.500" then tap 8-32. Locate and drill the No. 43 hole on one side of the block only, as seen in Photo 128, and tap 4-40. Note there are three extra holes shown in the photo. They were drilled for a valve design that I didn't use so don't worry about them.

Valve Slug

Start this part with some 1.00" diameter brass rod. Turn down to a diameter of 0.875" for a distance of 1.500" (Photo 129). This should he a running fit in the 0.875" hole in the valve body. Clamp the valve slug in a V-block and center it under the spindle as shown in Photo 130. Drill the two No. 43 holes to a depth of 0.500" and tap 4-40 (Photo 131). Transfer the part back to the lathe, part off (Photo 132), and face off the end. Leave a 0.063" long portion of the 1.00" diameter. Put screws in the previously drilled and tapped holes and use these to align the slug as shown while clamping the valve slug back in the mill (Photo 133). Drill a 0.250" hole through also seen in the photo.

Valve Actuator

This part is made in a similar manner to the tachometer sensor wheel. Using a cutoff tool, turn about 0.75" of 2" diameter aluminum stock to a diameter of 0.875". Turn the outer portion, at the headstock end, to a diameter of 1.438" (Photo 134). Face off the inner edge with a left-hand tool (Photo 135) and then face off the outer surface until the 1.438" diameter portion is 0.250" thick. Transfer the part to the mill after centering the rotary table under the spindle. Clamp and center up the valve actuator (Photo 136). Rotate the table to its 0° position then drill the two No. 33 holes (Photo 137) to a depth of at least 0.625". Center up under the spindle again. Install a 0.250" end mill and then move the table left until the mill clears the actuator. Lower the spindle and move the table right until the mill just touches the edge of the actuator. Cut in by 0.250". Lock the mill table, then rotate the rotary table clockwise by 37°, cutting the actuator as shown in Photo 138. Note the position of the two No. 33 holes. Transfer the actuator back to the lathe and part off (Photo 139). Turn over and face off the end (Photo 140). Using screws inserted into the No. 33 holes, transfer back to the mill and clamp as shown in Photo 141. Drill a No. 29 hole 0.250" deep then counterbore with a 0.250" end mill and tap 8-32.

Valve Actuator Stop

This part is a bushing made from 0.250" diameter brass rod. Drill a central hole with a No. 33 drill (Photo 142), then part off (Photo 143).

Valve Handle

The valve handle is a simple piece of brass rod 0.250" diameter. Turn down 0.250" of the end to a diameter of 0.166" and thread 8-32 (Photo 144).

Valve Assembly

Photo 145 shows the assembly of all the valve pieces.

Final Assembly

Photo 146 shows the ten-tooth belt pulley mounted on the end of the shaft. This is the pulley called out in the purchased parts list. You, however, may choose to use a different method to extract the power generated by the turbine. Install the valve assembly to the top plate of the bearing frame such that the 1/4-NPT hole is facing the same edge as the nozzle. Install a 1/4-NPT male to 3/8" compression adapter. Use 3/8" thin-wall tubing (the kind you can get at most hobby stores) along with a pair of 90° 3/8" sweat fittings to make the connection between the valve assembly and nozzle. This may be seen in the September-October 2001 cover photo. Put on the brass cover plate using 8-32 cap head screws.

Now the assembly becomes somewhat up to you. I chose to have the turbine drive a generator since I had an old 115V DC permanent magnet gear-motor. I removed the gear head and made a new bearing for the output end from a block of brass. I affixed another pulley on the shaft (first a 20 tooth, then later I switched to a 10 tooth for more output voltage). I made a bracket for the motor and attached the bracket to the bearing frame. This set up may be seen in Photos 147 and 148. Since the motor I used is probably not going to be like anything you have, I'm leaving the details of what your turbine drives and how you do it up to you.

Tachometer

Photo 149 shows the tachometer circuit I built. This is also the same tach circuit used in my Terry Turbine, published previously in Live Steam. The picture and schematics are provided as an example as there are many ways this could be done. This circuit uses an LM2907 frequency-to-voltage converter. This device takes the pulses produced by the optical sensor on the turbine and turns them into a varying voltage. The digital panel meter then reads the voltage. The circuit produces 1V at 10,000 rpm. The panel meter can read a maximum of 1.999V so the maximum speed it could read would be 19,990 rpm. The numbers on the panel meter represent RPM x 10 so when it displays 800, the speed is 8000 RPM.

Operation

Photo 150 shows the Prony brake setup I mentioned at the beginning of the article. It is a simple clamp on a smooth brass cylinder mounted on the shaft. The end of the rod presses on a postage scale. Since the length of the rod is known, it's an easy matter to calculate the torque in ft-lbs. The block is clamped tight, giving the zero speed torque as seen in the photo.
Loosening the clamp allows the rotor to speed up. This worked fairly well until the speed got above 6000 rpm, then it became difficult to get a good reading - I needed more hands than I had to try and hold on to everything. Still, even this crude setup gave me an idea of how much power the turbine produced. In Photo 151, you can see the results of trying to operate a 40W light bulb. Photo 152 is a little more quantitative. First of all, notice that I've switched to the smaller, 10-tooth pulley on the generator. I found that I had enough torque to do this and I got a lot more voltage out of the generator. Here I'm lighting a 15W compact fluorescent bulb with 130.2V produced at a speed of 8140 rpm. Note that I used a DC permanent magnet motor so the power produced is 130VDC. If you use a compact fluorescent with electronic ballast, DC works just as well as AC. However, a fluorescent lamp with an inductive balance will most definitely not work on DC!

I hope you enjoy building this as much as I did. The most satisfying part is seeing light bulbs glowing at full brightness with all the power being generated by the turbine. The output power can be used to run all kinds of things, or you may choose to build the turbine just for its own sake. Have fun!