After following the build instructions, I ended up with the two springs on the pick-up tube just barely touching the bearing between them. In operation, this means the tube rests with about 1.5mm of compression on the top spring and a corresponding gap to the bottom spring.
This works fine, but it feels like way too much force during probing. I hope I have that term right - I mean the operation that presses the nozzle down against something until the limit switch trips.
Given the various notes about potential damage to LEDs from compression, and the potential damage to the tapes under components, and a general desire to be gentle when touching various things under the nozzle, is there value in increasing the spring tension in the up direction? I know JuKu has mentioned that he doesn't use the springs at all, just the weight of the tube. Is this a good starting point? Is there a guide on how much pressure we should aim for? Is there a too high or too low?
I guess I could measure with some kitchen scales and compare?