CNC and possible PCB application - Page 1
Forum section: electronics / general

author: eurofox
author_rank: Unknown
timestamp: November 05, 2014, 11:37:22 am
content: Hi,I intend to invest in a table type CNC systems for front panel and my aim is to use it as well for PCB prototyping.I want screws on ball bearings, usually this is much more expensive but I think it is the only real option pro precision PCB application.I would like input from people who already use PCB milling and their opinion about this machine, it is in German but google translate will do the jobhttp://www.eurotools24.de/The only part that is missing is the table in aluminium to attach the partsThanks in advance for your input

author: Spikee
author_rank: Frequent Contributor
timestamp: November 07, 2014, 05:13:29 pm
content: It kinda depends what you want to do.For frontpanel engraving and PCB milling the 1000 euro complete 3040/6040 or similar eBay cnc with ballscrews will be OK.Your can but these from UK or DE eBay vendors.If your want to do heavy alu machining something like the FS4MG will fit the Bill. But the price of that ons is around 4200 euro ex. Spindle , Electronics, stepper/servo motors, shipping ...

author: awallin
author_rank: Frequent Contributor
timestamp: November 07, 2014, 06:05:31 pm
content: It's been discussed before, but PCB-milling and general-purpose (front-panel, enclosures, whatever) milling really have quite different requirements.For PCB-milling setting the tool-height is quite critical.The LPKF protomat machines that work quite well have all tools the same length, i.e. they are pushed up inside the collet as far as they go. There is then a collar around the spindle/tool that is pushed into contact with the PCB when the plotter is "pen down". The fine-adjustment is between the height of the spindle and the collar, *not* between the z-axis movement and the PCB-bed.This means the pcb can be slightly bent or at different heights in different places or from run to run, and it still works ok.For PCBs you want really high RPMs, something like 40krpm or 60krpm is typical.For conventional milling 10krpm is already considered quite high speed. One rule of thumb is 6000rpm/diameter, so 1000rpm for a 6mm tool.For PCBs the cutting forces will be minimal, so you will have no problems using properly sized open-loop stepper motors.For general milling the cutting forces are much larger and more variable, so all semi-pro and pro machines use closed-loop servos that can handle high accelerations and variable cutting forces. You *will* get problems with lost steps with a stepper motor system when trying to take heavier cuts in aluminium or even light cuts in steel.PCB milling can be done dry, preferably with a vacuum cleaner nozzle close to the tool to suck away the pcb and copper chips.For milling aluminium or steel you want to use a mist or flood coolant. This is quite messy and most machines have a way to circulate the coolant that flows off the table back to the coolant tank. You want a fully enclosed machine for this.The machine you linked to seems to have dual X axes. Make sure your controller has an idea of how to home this kind of setup safely. You don't want the two motors fighting each other. Some fancy pcb-mill controllers have a web camera and use it for finding where the user has positioned the pcb-blank on the bed. Cheaper models just have alignment-pins in the bed and the pcb-blanks have holes.