Making precision oval iris plates without CNC machining is HARD. Especially if you don't have a good precision boring head for your mill. Here's how you can make a ludicrously over-engineered fixture for manual lathes to make arbitrary-sized oval iris plates for very high-performance Microwave Waveguide Antennas.
The shape I'm making isn't strictly a mathematical oval, it's a STADIUM, with two parallel sides and semi-circular ends. The thickness, length and width of the iris determines how the iris plate transforms the waveguide mode and impedance and allows matching between rectangular and round guides for example.
If the diameter of the holes is a standard reamer size, it's possible to make this purely on a mill, but I'm making lots of different sized iris plates, so tooling gets expensive very rapidly. you can use a rotary table, but you have to slide the workpiece along to re-centre the second hole, and work-holding gets challenging.
This isn't the best way to do this by any means, but it was a lot of fun making the dovetail slide. Simplest alternative of course is to make a simple fixture without a slider and use a boring head on the mill to machine the two holes after drilling them close to size, then finish the sides.
Nowhere near as much pointless over-engineering fun though!
An even simpler cheat is to make an iris with four radiused corners. You can make that using a single end-mill, but chatter is always a problem in the corners if you are using a manual mill. It's trivial on a CNC mill or Wire-EDM machine of course.
AIMEE my snarky but hyper-intelligent sidekick makes "helpful" comments about my oversights and shortcomings as usual. After all, there are plenty to go at.
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00:00 Why are we here?
04:24 Mandrel slider
09:28 Mount
11:39 Haimer self-destruct
13:40 Slitting Saw
16:42 Relief and alignment bore
23:42 First Trial Iris