Micro vacuum table for milling PCBs on a CNC router.
This is optimised for making 100x80mm double sided PCBs from 'Eagle free'.
I have been using the A4 mini vacuum table (see Thing this is derived from) for PCB work but found it was too hard to get the Z axis precision needed for reliable fine track engraving. I realised that the acrylic surface was not rigid enough. I also found that the coolant I was using was soaking into the MDF, base causing it to swell.
This micro vacuum table is much more rigid and coolant proof!
The mounting points are designed for a 120mm T-slot table.
I am lucky to have scored a diaphragm vacuum pump which pulls about -0.8 bar. This works beautifully with heaps of suction over this area. You could probably get good results with a vacuum cleaner or similar. The A4 version works happily with a Vax bagless cleaner. I will leave it up to you to figure out the adaptors etc!
Bill of materials:
- Base, CNC cut from 20mm Acrylic / POM / etc
- Top, CNC cut from 6mm aluminium plate
- Push fit pneumatic connector and tube to suit vacuum source. I use 12x8mm tube with a 14" BSP x 12mm push fit connector.
- M4 x 10 machine screws x 9
- 3mm x 5mm alignment pins x 4, cut from piano wire or similar
- 3mm EPDM sponge round seal strip for gasket
Assembly & preparation
- Use silicone sealant between plate and base; screw top firmly to base
- Mount firmly and evenly to CNC bed. I used M8 x 20mm cap screws with my own T-nuts.
- Ideally, use a torque wrench and record torque for future re-mounting.
- Skim the surface to ensure it is flat to the machine's X and Y axis. I used a 6.0mm 2-flute end mill.
- Ideally, use a dial gauge mounted on the spindle to check for flatness in X and Y. I aim for < 0.01mm variation across the board area.
- Cut EPDM to length, use super glue to join the ends and push it into the groove
- Insert the alignment pins into the 4 holes which are +/- 60, 20mm from the centre
- Zero the machine to the bottom left alignment hole which is -50,-40mm from the centre. I use a 3.0mm pin in the collet to check this.
- Advance the machine in X by 100mm and check it matches the bottom right alignment hole. Adjust the position of the table to ensure it is absolutely square, for accurate 2-sided registration.
Using 'pcbgcode' and the supplied Eagle template, top side gcode coordinates start from Eagle 0,0 which corresponds with the bottom left alignment hole in the plate. After flipping the board over, the bottom side gcode coordinates start from 100,0 which corresponds to the bottom right alignment hole, and work negative in X.
- Using some other method of work holding, pre-cut 130x80mm PCB blanks with holes to match the alignment pins; see file 'PCB blank 130x80.dxf'
- Using the Eagle template provided, lay out the PCB and use a suitable gcode generator such as 'pcbgcode'
- Etch the top side
- Flip the board over horizontally; advance the machine by 100mm in X and re-zero
- Etch the bottom side
- Drill, mill etc. Use an air permeable spoil board such as thin MDF or card.