My approach is very similar to Sam’s, but three differences that I believe help:
1. Immediately before cutting a PCB, I pre-level my sacrifice board, which is MDF. I believe that the MDF warps over time, even though I rarely remove it, or even adjust it.
2. I don’t use angled bits (sorry I don’t know the correct terminology). Instead, I find that conventional end mills produce a cleaner, more consistent cut. I am still experimenting with diameters, but find 0.6mm breaks easily, while 0.9 is unnecessarily wide. Lately, I have been using 0.7mm but will focus on 0.8 next.
3. If the incomplete etching (is that the right word?) is localized, I will re-run just those areas at a deeper depth.
Rarely do I need three passes, and a second pass is only required about half the time.
From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of sdmonaco via Groups.Io
Sent: Monday, August 20, 2018 7:56 AM
Subject: Re: [pcbgcode] Can only get a single isolation pass around tracks
You might try my single pass etch approach, which I now use for all of my boards. I setup pcb-gcode to do a singe pass etch for all traces and shapes. After completion, I inspect the board without removing it from the fixture. If I see any areas with incomplete etching, I lower my z-axis zero point by 2 mils and re-etch the board with the same gcode file. I continue with this until I have a nicely etched PCB which usually only takes about 1 to 3 passes. This approach also corrects most leveling issues as well. I try to keep my trace widths over 12 mils because each pass will shrink your trace width by about 1 mill for a 30 degree spade bit.