I tried autoleveler and concluded (maybe wrongly) that the PCB board high spots were the result of very minor warpage, not inconsistencies in the materials’ thickness. As a result, I reasoned, when the autoleveler measures the height, it does so without the benefit of any pressure (mere electrical contact triggers height measurement), but when cutting, a little pressure will force the PCB’s high spots down, with the result that they are not fully cut in those areas. To remedy that problem, I bought a thick piece of Plexiglas, a vacuum pump and other materials to make my own vacuum board, but then realized that I could get good results, cutting not more than 0.10 mm in two passes of 0.05mm each, by simply leveling my MDF in advance of a days’ cutting. (I don’t know if it moisture or thermal expansion/contraction, or otherwise, but I find that more than after a few days, the MDF takes on a warp of up to 0.10mm. )
I would be very interested to see others’ vacuum boards. I saw Peter’s earlier comment about success with his vacuum board (table) and his good results cutting 0.2mm -- he must have meant 0.20 mm, right? Because 0.2mm is 4 passes at 0.05, and I typically need only 1 pass, and rarely more than two. Am I missing something here? The boards I am cutting are usually 4”x6”, and are much more problematic than 2”x3”.
From: firstname.lastname@example.org [mailto:email@example.com] On Behalf Of Bernardc
Sent: Monday, August 20, 2018 10:41 AM
Subject: Re: [pcbgcode] Can only get a single isolation pass around tracks
Assume that you not use SMD on your PCB as etching with 0.9 mm….
Autoleveler is perfect to correct the copper default. I use 2 flutes V type 60° dia 0.127 mm with 0.05 mm depth and it is not necessary to make further pass. Mini = 0.0254, Max = 0.762, Step = 0.0508, Feedrate = 400, Turn = 12000 T/mn. I can etch for SSOP. (The problem remains welding ;-)..)
De : firstname.lastname@example.org [mailto:email@example.com]
De la part de Rick Obel
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.
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.