Very sad you don't have any BA taps and dies. I
have 0BA to at least 12BA with nuts and screws to suit.
On 30/01/2021 16:27, Neil Smith G4DBN
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.
filters are so easy to throw together, and drilling too
many tapped holes while just playing around .... ".
Mr "I don't do mechanical things " LOL.