My interpretation of your results is that with the closer plate-spacing you were able to get the same (or greater) capacitance using smaller plates, and that with smaller plates there's less conductor loss, as the current flowing over the plates just has a shorter distance to cover. Less loss in conductors, better Q. The different washer material could also be contributing better conductance, though that effect gets mixed in with the fact that the washers are thinner, once again shortening the distance that the current over them has to cover. You clearly had to do some long, careful work to produce these devices and measurements. Thank you for sharing the results with the rest of us.

The three-level hierarchy qrp-gaijin described (Post, Comment, Reply) is something I've seen on other forums where it is perhaps better suited than it is for TRB. On NextDoor, for instance, many posts get 100 comments/replies, and the comments/replies there are so short that you can often see 15 or so on the screen at once. The Replies are visually "nested" by indenting them just below their parent Comments; this makes them easy to follow, and can be especially helpful for posts that get small contributions from many, many people. In contrast, TRB posts more often get something like 10-20 comments/replies, and each of these tends to be longer and carry much more information. The possibility of seeing all of them on a single screen, nested into a visible outline, is pretty much gone -- and might not have added much value to these discussions anyway. As it is now, the three-level multithreading adds some confusion when you read through a post for the first time. If Wix has a global switch for disabling the Reply feature on future posts (without losing any of the Replies on existing posts), I think that would improve readability and logical flow. It would become a two-level hierarchy with a single chronological order, much like the old TRB, and if you want your comment to make reference to another's, you could accomplish that just by pasting in a snippet of their text. Of course, each of us could just refrain from using the Reply button, too. I have learned my lesson now after having littered Greg's post on variable caps. Many thanks to Larry for setting this place up! Casper

Nice work, both in the construction and in the testing! Speculating on what factors might be limiting Q now, Dielectric losses: 1) There might be an opportunity in using thinner sheets of HDPE, if you can find them and have the hours to cut them again. 8mm probably won't be very different from 10mm, though. 2) What material are the blue vane-spacers made of? The vanes they're in contact with should all be at or near the same potential, so maybe less opportunity there, but worth considering. Conductor losses: 1) The washers separating the vanes on the shaft. What are they made of? Is it possible that they were shipped with a thin coating of oil that could be removed by bathing/spraying with carburetor cleaner or acetone before assembly? 2) Wiper. I didn't notice from the photo how the rotor gets connected to the outside circuit, but there might be some losses there. Casper

Those milky-white bases look more like polyethylene (which would be great!). The acrylic available near me is usually clear, because it looks nice that way and acrylic allows it.

Acrylic can look very cool -- no question -- but if you want this capacitor to be part of a high-Q tuned circuit, you could consider plastics having a lower "dielectric loss" than acrylic, such as polyethylene or polystyrene. Lossier materials like acrylic (aka Plexiglass, Lucite, ...) tend to cause a "dulling" of your tuning. Ben Tongue's old site had some exploration of insulating materials and their effects on Q. Jim Kearman made a copy available: http://kearman.com/bentongue/xtalset/24Cmnts/24Cmnts.html As I understand it, the farther away these lossy materials are from an electric field, the less difference they make. But bringing them in closer, as in the supports of a tuning cap, will likely mean a performance hit. Cheers, Casper

I have gotten some good caps from Oren Elliott Products: https://www.orenelliottproducts.com/product-category/air-variable-capacitors/ Some of their models (the ones ending in "P") come with a 6:1 planetary reduction drive built in, which can be very handy for a receiver or tuned loop -- the half-turn movement of the plates gets spread out over 3 full turns of the knob. When I last ordered, many of their S2 caps also came with optional trimmers; it's a good idea to email them to check / specify which options you prefer (and which ones happen to be in stock in hobbyist quantities). From their product listing you can see that the prices drop sharply if you can buy at least 2 units, and even more sharply if you can spring for 5 (but that's a lot of projects for me). Cheers. Casper