You know, now that I think about it, when I first got mine hooked up it was also all over the place too. When I pulled it apart it seemed 2 things were going against repeatability. I found the grease was substantially increasing the amount of force required to trigger the probe. The other issue was alignment of the ball contact PCB. I did the loosen the PCB screws and let things settle into their happy place and removed the grease and used a product called ACF-50.
We use that stuff in avionics and essentially every electrical connector in the airplanes we work on. It’s an oxidation and corrosion protectant as well as a light lubricant. We apply it to aircraft structures also. Its primary purpose is corrosion protection and its used in very sensitive electronic components. Everything from de-ice valves and pneumatic switches prone to water ingress and freezing at altitude, AOA sensors, torque transducers, to panel screws to prevent corrosion and galling.
Took my probe apart this weekend to try and troubleshoot. Appears to be mechanical inconsistency on my end like you are suggesting. I would dial the probe in, test and the tip would run out again. I tried leaving the adjustment screws tight, dialing it in then loosening them, dialing it in then tightening the cap screws. No matter what I did it would be inconsistent after pushing the tip every time and I had a really hard time getting the tip to settle back in to where I dialed it in the first time.
Did your modifications keep the probe consistent in the long run? Any pictures to show how much you polished the cups or how much stronger a spring you used?
Id have to take it apart but i Just polished it enough that it was smooth to the touch with a dremel and used a longer spring of the same diameter that i had in a box of assorted chinesium springs. I really do believe the thing that made the biggest difference was the wire extensions. I was having the same issues you are talking about where you’d zero it manually, then if you touched the probe it was no longer concentric, I haven’t had those issues since then. The X axis ball screw just pooped the bed so i may have time to take the probe apart again and take some pictures
Took the probe apart again tonight. I have to say Thirdwings approach is more professional, but this was quick and free. I just stripped as much insulation off the red wire as possible to give it more flex. Since it ties the board to the probe tip, I believe this is just a ground and the insulation is kind of unnecessary anyway? It cannot short on anything that it already is touching, the probe tip is connected to the body via the spring so figured I’d give it a shot. After stripping what I could reach, I reassembled.
Then I followed the Langmuir guide and loosened the screws holding the ball contacts and resnugged. After dialing it in, the probe repeated multiple times, enough that I was satisfied. Will see how it holds up in the long run.
I can’t wait I really need one.