The Tesla Turbine: Discs, Not Blades, Driven by the Boundary Layer

US 1,061,206, 'Turbine', Nikola Tesla. The runner is *"a plurality of flat rigid disks"* keyed to a shaft and spaced by washers, with *"openings"* near the centre for the exhaust. The fluid acts on them through *"adhesion and viscosity"*. The design rule is in plain words: the spacing *"should be the greater, the larger the diameter of the disks, the longer the spiral path of the fluid and the greater its viscosity"*. Tesla drew only a few widely spaced discs *"for the sake of clearness"* — a real runner has many, close together.

Drill out the centres of eight CDs to fit a length of threaded rod as the shaft. Drill six 10 mm exhaust holes round each disc near the centre, all in line. Stack the discs with two thin flat washers between each pair, clamped between nuts. Print a housing that fits round the stack with 1–2 mm clearance, with one tangential inlet at the rim and exhaust ports in the side plates over the disc holes. Run the shaft in two skateboard bearings in the side plates. Balance matters: spin the stack slowly by hand and check it does not wobble before any air goes near it.

Stand the turbine behind a clear guard and wear goggles and ear protection. Connect the air compressor through the regulator to the inlet, starting at 0.5 bar. Read the speed with the tachometer (a strip of reflective tape on the stack) at each pressure, raising it in small steps. **Stop well below 10,000 rpm** — the notebook's rim speeds show why. Then change the gap: rebuild with one washer between discs instead of two and repeat. Compare free-running speed at the same pressure. The gap that works best is close to the notebook's boundary-layer estimate for air.

**US 1,061,206, 'Turbine', Nikola Tesla; original application filed 21 October 1909, divided and this application filed 17 January 1911 (Serial 603,049); patented 6 May 1913.** A companion patent of the same family covered the machine run as a pump. Tesla expected high efficiency and a cheap, rugged machine. In practice the discs flexed at speed, the gaps had to be very fine, and efficiency with steam fell well short of bladed turbines; the bladed Parsons turbine in this catalogue won. Disc pumps survive for abrasive and delicate fluids, where their bladeless shear is gentle. **Honest limits.** Low efficiency at useful power; discs that flex; very close tolerances; and on a CD build, the hazard of a disc bursting.