PCB - milling compensation - Page 1
Forum section: electronics / general

author: PODF
author_rank: Contributor
timestamp: June 16, 2015, 01:10:02 pm
content: Hi,I milled myself a PCB. My problem here is that on the left side the traces are very very thin.I think the material is not completly flat and therefore the milling bit is cutting away more copper than it should. It is a V-shaped bit. The deeper it goes, the more it cuts away.Has anyone experience with compensating such unevenness on the pcb? The surface should be very flat, because we milled the ground flat.We tried with screwing down the pcb or even taping it down with doublesided tape.I attach a picture of some traces that get thinner at a certain point.I use G-Code (gerber) for milling. Is there a way that i could measure say 3 to 6 heights on the pcb where the copper starts (i can measure fairly precise, cause i use a closing circuit to auto detect the touch from the milling bit with the pcb-copper) and type these 3 to 6 values in an application that then compensates the whole G-Code file? so my milling would come out perfect?Any ideas?Thanks

author: PODF
author_rank: Contributor
timestamp: June 18, 2015, 10:00:43 am
content: My equipment should be good, I use a CNC-Step High-Z S-720 (http://www.cnc-step.de/en/products/cnc-router-trapezium-spindles.html).It's more the lack of experience I think. Maybe I flattened the bed not right, maybe used wrong tool for flattening, maybe it is not a good PCB, etc.This autoleveling tool sounds great, excactly wat I wanted!The link on the Hackaday article is dead, but I found the software on githubhttps://github.com/Daedelus1982/AutoLevellerI'll give that a try on my next PCB. I hope I get this software to work with my machine.

author: rs20
author_rank: Super Contributor
timestamp: June 18, 2015, 10:05:32 am
content: Already being discussed on this thread:https://www.eevblog.com/forum/blog/eevblog-753-inventables-x-carve-milling-machine-unboxing/msg694996/#msg694996Basically, use your milling machine to mill your work surface to a flat surface. Don't care ifyouthink it's already flat, because what matters is what's flat with respect to the alignment and squareness of the supporting rails of the mill head. Then, use double-sided tape to hold your PCB down. It'll hold it flat with respect to your newly milled, truly flat (from the point of view of the machine) surface. And away you go.(Or, use a mill with a floating head and you don't need to worry.)

author: george graves
author_rank: Super Contributor
timestamp: June 18, 2015, 10:49:13 am
content: Yes any bed shoudl be level - if not, yoru first job is to level it.If your working on a more DIY machine, a touch probe to the z-axis on copper clad is a no-brainer.You have to say what machine/software you are using - or it's just us flying in the blind.

author: BMF
author_rank: Contributor
timestamp: July 09, 2015, 06:36:22 pm
content: Commercial PCB milling machines use a foot that rests on the PCB surface and glides along using air or slippery plastic. This keeps the tool penetration depth constant as the surface height varies. Only when all copper in a very large area is removed does the height change. Some machines use a vacuum platform base that holds the PCB in place. This might help flatten the substrate a little and help if using a fixed Z axis height system. Otherwise you could try using a v-tool to lightly outline the traces and then use an endmill to perform the isolation. The big issue is tool wear and cost. End mils tools don't last as long as v tools, particularly the small end mills. If you are really up for a challenge you could make a small head that contains a high speed motor/spindle that glides along like the commercial units. Your CNC would control X and Y and approx Z. Fine Z would be set by the spindle head. Commercial units also pass vacuum through the head around the tool. This helps cool the tool, clean the path, and maintain an even PCB to foot pressure. You may need to include that too. Just be sure to use a good HEPA filter on the vacuum. You really don't want to breath PCB particles.