Re: EVO Filter construction

Paul G8AQA

Very sad you don't have any BA taps and dies. I have 0BA to at least 12BA with nuts and screws to suit.
Paul G8AQA

On 30/01/2021 16:27, Neil Smith G4DBN wrote:

After Andy mentioned this type of filter some time last year, I had a go at making some. Because of my metalbashing addition and for general bling (and maybe performance), I made the tuning screws from Tellurium Copper, with knurled heads for easy finger-tweaking.  I might still have a few of the tuning screws kicking about if anyone wants some to try.  I cut the threads deliberately oversize to improve the fit, and made slightly thicker than standard brass locknuts, although the pic shows a stainless one.  I also made up some solder-in threaded collars to give a longer thread engagement, but that is more faff than just drilling and tapping the holes.  I used a thread-rolling tap rather than a normal cutting tap for the copper waveguide.  Whether they work any better than brass screws, I didn't have the energy left to investigate, but I had a pile of machine-shop fun, and that's an end in itself. These are M3 x 0.5 with 9mm head and 2.3mm plain shaft.  I also did some M4/M5 and giant ones which were extra-fine M8 x 0.5 threads and some teensy ones with M2 x 0.35 threads.  BA would actually be a better choice because of the thread angle, but I don't own any BA taps/dies.  Using a tapered split collet worked OK at 4mm, but it was getting tricky at smaller diameters.  It was a fun way to idle away some time on a summer afternoon.

Neil G4DBN

On Sat, 30 Jan 2021 at 10:30, John Fell <john.g0api@...> wrote:
"Evanescent filters are so easy to throw together, and drilling too many tapped holes while just playing around .... ".

This from Mr "I don't do mechanical things "   LOL.


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