I find that my MDF bed plate has about 10 to 20 thou error over surface and I want to mill PCB tracks onto a 1.6mm FR4 copper board which are normally only .007 thou deep so I want someway of milling in Mach3 an area for board to fit, I thought of using Fusion360 and sketch a flat surface of the size i need and then extrude to so 0.01" and then offset "Z" axis so I just cut a 0.025 thou area in this bed, Unless there is another way would appreciate any help

Regards John

Hi,
you can and will need to surface the MDF. A simple surfacing Gcode file will do that, I think one of Mach3 Wizards will do it, even a rectangular pocket wizard
would work.

What you really want to look at is a software utility called Autoleveller.

http://www.autoleveller.co.uk/

Craig

I looked at that already and downloaded the file but couldn't work out how I use, Do I mill a 1mm area then input the Gcode of the board I want to mill and then click create gcode and it modify s the code after it probes the board.

Tried using a gcode from another page and it stops in Mach3 on a text line (.../Program Files (86x)/EAGLE-6.3.0/pcb-gcode.ulp) which I presume is the gcode I picked but it seems different to the .tap file prior to loading Gcode into Mach3.

Is there a youtube video to point me in the right direction

Regards John

Hi,
my personal experience is that prior to using Autoleveller I could get only fair results even after surfacing the spoil board, and even then only on smallish
through hole boards and that was with a lot of cutter wear.

With Autoleveller I don't bother surfacing the spoil board and I can do surface mount boards down to TSSO (0.2mm clearance between pads) no problems and one cutter lasts
hours and hours.

You need to go back and have another look at it. Do yourself a favour, the free version works but the subscription version (20 GBP) generates a probe file and is much
easier to use and understand. If you're serious about making PCBs this is the way to go.

Craig

Hi,
if you are convinced you need a flat surface then use the rectangular pocketing Wizard that ships with Mach3. It will generate Gcode
to cut a pocket, the base of which will be flat.

I would not recommend holding the PCB blank down with clamps or screws around the periphery, it distorts the blank and all that effort you put into getting a flat surface
to work from is in vain. I would use double sided tape. Note also that fiberglass PCB blank board almost always has some warp or bow in it, usually not more than 10 thou
over several inches but its enough to cause problems when isolation routing. Double sided tape can help pull that bow/warp out of the board.

With Autoleveller I don't bother machining the spoil board flat, the probing and subsequent Z axis Gcode optimization obviates the need for it.

Craig

I use the "Surfacing with tool down in Y" wizard and a 1 1/2" surfacing bit to face my spoil board

Hi,
does it work sufficiently well that the PCBs come out OK?

Craig

I haven't been milling PCBs but I have been doing some very shallow engravings in thin brass and they work out great, also using a vac table. That Autoleveller software looks pretty great I'd like to try it out. Mostly I work in wood so it doesn't apply much.

Hi,
yes Autoleveller is useful if you are trying to get something 'dead flat' like a PCB where 1/2 a thousandth of an inch out of true plane will have unacceptable results.

Craig

I'd just write it by hand, but then I write everything by hand.