Content moved to my web page: Autoleveller
Shimming the Spider
I use Lovejoy spider couplings between my steppers and the drive screws. When last I used auto levelling, I noticed the Z axis stepper was making fine adjustments, but there was too much play between the couplers, and most of that fine movement was lost. I carefully trimmed a strip of aluminum from a soda can and carefully wrapped it around the rubber coupling spider. You can see a bit of this shim in the video below. No play in the coupling. Here is a short video of the Z-axis in action during board milling. I was surprised how much it moves!
FWIW, here is a photo of one half of the coupler (the threaded rod is 1/4-20). For reference are the original spiders I used from Jameco. I actually had no problem with them, I just "felt better" with the big, beefy, professional spiders!
Anti backlash nuts
Here is the outcome. This is consistent across the entire board. Although not a complex design, it was demanding and a sufficient test. Here is a 20x magnified shot of a 9mil trace. This run my tool was too deep, it should have been 16 mils wide. I still have the old habit of routing deeper to avoid 'air milling'. Next board I'll back out the tool 1 mil.
What I am looking at is the consistency of the trace width. Horizontal, vertical and diagonal the width is spot-on. also, the lines are very straight edged.
PCB Milling tip
I covered the copper with a good layer of WD40 before milling. This made a HUGE positive difference. The edges of the copper were milled very clean, just a light once-over with a ScotchBright pad was all it took.
|Click for larger image|
Here is the same magnification on a different board, cut earlier, without the mods and without WD40. This image is after sanding with 120 grit paper!