Dieter Brehm

Tesla Turbine Machining

Turbine housing that I machined from aluminum

During the second half of 2021, I took a semester-long course called, "Fundamentals of Machine Shop Operations". At Olin, students affectionately abbreviate it to FOMSO. Our teachers Bruce and Nate, shop pros in their own right, taught us from the ground up what we needed to produce accurate, functional parts that met drawing specifications.

If there was one book that I recommend from this experience, it is the machinery's handbook, a near legendary text that prescribes various tables, conversions, and measurements used while doing metal shop work. Below is our class consulting the book on utilizing sine blocks.

our class learning about gauge blocks

We started by hand-filing filing a small cylinder of aluminum into a cube, learning about tolerancing, stroke technique, and squares along the way. Four or so hours later, we had cubes that met the spec!

Mid file of the aluminum cube

Performing this specific and arduous task also had the benefit of teaching us stewardship in the shop as we relentlessly swept and vacuumed tiny aluminum shards everyday, seen in the below photo where everything around me is covered in, "chips".

me, amidst a pile of aluminum chips

We got to experience a variety of shop widgets and equipment, including this tiny set of calipers for getting in tight spaces!

New to me was the whole field of metrology, or, the study of measurement. Standard calipers might be useful to a thousandth of an inch or half a thousandth if you're using top notch ones, but we can use different tools like micrometers to measure up to the tenth of a thousandth of an inch!

tiny calipers

While doing hands on tasks, we also embarked on old and reliable machining texts to give us theoretical context. I thought that they were a pretty dense read, but it was always useful to have a primer on the topics for the following class, and it was interesting to compare the equipment they had back in the day with frankly fantastical digital read outs and laser measuring equipment. That said, check out the flip-clock style indicators on this mill! Wow!

an old milling machine illustration

After the cube, we moved on to new techniques, including sheet metal bending and welding, and reading vernier micrometers that let us read distance measurements of a tenth of a thousandth of an inch without any electricity!

It takes a lot of practice to get used to reading these, but there is a very useful online tool by Eduardo Stefanelli that simulates various micrometers without the need to purchase hundreds of dollars of equipment. Virtual Micrometer (opens new window)

virtual micrometer

For the sheet metal project, we started by laying it all out with a punch and a square. After doing our layout work with dykem layout fluid, we punched the holes with a press and used a sheet metal brake to bend each angle. The break was amazing! It is powered with electromagnets to make it quick and easy to adjust the bends. We tested our sheetmetal widgets against a machined reference jig, and mine passed!

A sheetmetal widget

Once our class got the fundamentals down, we got to work on the big machine tools, namely the lathe and mill. It's said that you could rebuild civilization with just these two tools and a dizzying array of adapters and bits.

A sharp j-type milling machine

We made a, "test piece" that everyone at Olin College needs to make in order to gain regular access to these tools. It's a two part assembly that holds business cards, composed of a threaded shaft and a business card-sized rectangle.

test piece

With those complete, our final test as machinists in this course was to make a "Tesla Turbine". Like other turbines, it takes an input, in this case compressed air, and outputs rotation.

We had to machine surfaces that held bearings to a tolerance of a couple tenths of a thousandth of an inch (+-0.0002!), and utilize many fixtures and set ups to achieve parallel surfaces that would optimize the efficiency of the turbine.

After about 40 hours of machine work on the Mill and Lathe, I finished my turbine! I used a combination of 2 Axis CNC conversational programming and manual operation to make every part on this assembly with the only exception of the o-rings, two bearings, and the screws.

the finished turbine

To test it, we connected it up to the shop air supply and, with a tachometer that measures rotations and a small reflective strip of tape, measured a top speed of 24400-25000 RPM, a success!

the final test, an rpm measurement

©2021 Dieter Brehm. All rights reserved.