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I have an arduino powered CNC machine with the Protoneer v3.00 shield. I have a probe setup for auto levelling which works correctly, I get a depth map for the board.

But the issue is that this depth map is created to the point at which the bit touches the board, but the board has some flex in it such that it is raised above the table in the centre. This therefore means that when it comes to milling, any flex in the board gets pushed down by the bit before any milling occurs and so the depth map is not correct as it has not taken account of this.

I realise therefore I need to ensure the board is firmly clamped to the table at all points and so I think a vacuum table is the best option. I have found one which is 210mm x 120mm and has a 10mm x 10mm grid for the vacuum holes (vacuumtablesuk SEAL2 VT2012).

I will be needing to clamp standard FR4 fibreglass PCB board, and I am wondering what vacuum pump would be suitable? I am lost as to how to choose a vacuum pump so any advice and links to suitable pumps would be greatly appreciated!

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    $\begingroup$ Welcome to Engineering.SE James! This is a very detailed in-depth question that is well suited for this site. However, if you're looking at simple in-depth guide for selecting vacuums and fluid dynamics, a few other related questions might be able to help. For example, engineering.stackexchange.com/questions/14604/… has some general guides. However, I think you have enough information here for a full scope answer, just need time until someone can process it all. $\endgroup$ – Mark Apr 6 '17 at 17:17
  • $\begingroup$ Do you mean milling the paths, as in DIY small volume PCB production, or milling technical gaps in the PCB (holes for screws, cutting PCB to shape of enclosure, gaps for larger elements to fit through) ? For the former, a vacuum table might be an overkill; use a firm machining table and good clamps. $\endgroup$ – SF. Sep 4 '17 at 11:01
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I would recommend a slightly less technical approach and use double sided sticky tape. It's wonderful stuff, and you can get what's called removable tape. Probably makes it a bit easier, but you can always use a heat gun /hair dryer to warm the PCB and lift it.

It should have enough gooey shear strength to resist the slight lateral milling forces, especially if you get enough of it down. Clean up with solvents.

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I would recommend starting with a wet/dry vacuum (shop-vac). They pull a fairly stong vacuum and have a high flowrate that will be forgiving for misalignment and leaks.

The down side is these vacuum cleaners is that they typically have a low dutycycle and are not designed to run for 8 hours straight. You may run into reliability problems depending on the quality of vacuum cleaner and how hard you push it. But regardless this is a very low cost way to test your design.

Once you have it working you can measure the pressure with a u-tube manometer and the flowrate by placing a trashbag of known volume over the exhaust and timing its fill time with a stopwatch. With those two values you can select an efficient and effective vacuum blower for your application.

Motorized Impeller

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