Tesla Turbine – Rotor Design

A Tesla turbine is a bladeless turbine that uses a series of closely spaced smooth edged disks that are mounted on a bearing supported axle. The disks also have holes drilled in the face of the disk. The series of disks are enclosed in a circular housing. The housing has either a single nozzle or multiple nozzles that are aimed at a tangent to the edge of the disks.

Air or another fluid is forced through the nozzle and impinges on the edge of the disks allowing the disks to absorb energy from the fluid flow through adhesion and causing the disks to rotate. The fluid flow spirals around the edge of the disks and is eventually exhausted through the holes in the side of the disks and ultimately exits through holes in the side of the housing.

ROTOR DISK CONSTRUCTION

Although the rotor disks on a Tesla turbine are generally made from thin material, I thought I would experiment with something thicker and add a series of micro grooves on the edge instead. Since I had some 1/8 inch plexiglass on hand, I decided to use that.

I started construction by using my PCB layout software (DipTrace) to create a full scale disk template that outlined the outer diameter of the disk, the center hole location, and the location of the four exhaust holes in the side of the disk. I printed out five copies of the template since I was going to make a five disk rotor.

I used a plastic scoring tool to cut out five 2.125 inch squares of 1/8 inch plexiglass and then used rubber cement to attach the templates to the plexiglass squares.

Next, the four 0.250 inch exhaust holes and the 0.375 inch center hole were drilled in each disk separately. Each hole was first located using a number one center drill.

Note: Both drill bits were modified for use on plastic.

How to modify a drill bit for plastic

Each disk was then cut out using a scroll saw and the edges were carefully sanded on a disk sander just to the template line.

In order to ensure that the outer edge of all five disks were concentric to the center hole, I lathe turned a arbor from 0.5 inch aluminum hex stock. The five disks were installed on the arbor and turned to a outer diameter of 2.0 inches. Note: It is possible to eliminate the use of the arbor and turn the outer disk diameter with the disks mounted on the rotor axle.

ROTOR AXLE

The axle was turned from a 3.0 inch length of 0.375 inch aluminum type 6061 rod. The plan was to use two axle bearings with a inner diameter of 0.25 inches to support the rotor and therefore each end of the axle was turned down slightly under size to a diameter of 0.247 inches for a length of 1.0 inch.

In order for the disks to fit properly on the axle shaft, it was necessary to also turn a few thousandths from the area where the disks would be located. Since I had to remove the axle from the three jaw chuck in order to turn each bearing shaft, I used a dial test indicator to indicate the axle each time it was reinstalled to ensure that the machined areas were concentric with each other.

The axle was then threaded on each end using a 0.375 inch x 24 TPI threading die over a length of about 0.25 inches. Two 0.375 inch x 24 TPI hex jam nuts will then be used to secure the disks together.

Next the rotor was assembled using nylon washers between each rotor disk and also underneath each hex jam nut. The exhaust holes were alternated in an offset pattern and the nuts were then securely tightened making sure the disks were centered on the axle.

Since my efforts at threading the axle by hand was not perfect, I noticed a slight wobble in the rotor disks when the completed assembly was spun. I solved this by first marking the relationship between the jam nut and axle on each end. I then disassembled the disk and by machining one end at a time, I placed the jam nut on the axle and lightly faced the inside of the nut until it was perfectly perpendicular to the centerline of the axle.

Finally, the rotor was reassembled and was installed on the lathe and the rotor disks were turned to final diameter of 1.90 inches.

This completes the construction of the rotor.

 

ROTOR TEMPLATE WITH DRILLED AND SANDED DISK

ROTOR TEMPLATE WITH DRILLED AND SANDED DISK

 

ROTOR AXLE

ROTOR AXLE

 

MACHINED ROTOR COMPONENTS

MACHINED ROTOR COMPONENTS

 

COMPLETED ROTOR

COMPLETED ROTOR

 

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