2019-05-07

PCB Milling bits

I have been playing with milling PCBs, and the issue is working out what bit to to use for milling PCBs.

The CNC 3018 I got comes with some fine tipped bits, they are cheap, and sharp..,


They are indeed pointy. If you try milling, they break, as they seem to in a slight breeze. They may have uses for wood or something, but for PCB they do not.

Broken bit

Even broken, they have some use, but the width depends on where they broke. And you have to start the cut again once it breaks. Bugger.

Flat end mill

You can get flat end mill bits...


These are not bad, but as you can see, the end is quite long. This is a 0.5mm diameter bit, which is still quite chunky, but it can cut the copper off a board.

The problem is they snap, and do so easily. It is a tad obvious from the design. So not so good.

What they do work really well for is drilling a hole and moving around to make a larger hole. All of the holes I make are done with this 0.5mm bit.

Bigger bit

I also have a 1mm version...


This is something I use for cutting the PCB outline. Works well.

Cutting the board.

What I found works well is a wider bit...


The issue here is depth control. At 45 degrees it means cutting down an extra 0.05mm means an extra 0.1mm width.

The trick is Z axis levelling, which bCNC can do. I added to my CNC 3018...



I initially tried to connect the wires to "Z" on the controller, but missed and was connected to next pins which are "A5", but it seems they worked and "Z" (I assumed Z end stop) did not work. The bCNC code just worked (with "A5"), and did auto levelling. Wow.


End result is I can cut tracks between 0.1" pitch pins!

I have been getting good at single sided designs with no links, but this makes it that bit easier.


P.S. Designs and code on GitHub... @aaisp giving back to open source.

It is funny how old-school lead(+silver) solder is easier to use...


5 comments:

  1. Yeah the lead free stuff sucks. Melts at a higher temperature so my cheaper iron struggles, it doesn't play nice when repairing previously leaded solder joints, it doesn't flow the same as leaded, it cracks under thermal cycling/stress as it's more brittle, the list goes on.

    Lead free solder is one of the main reason modern electronics fail (in all cases where fucking them is a short spell in an oven to reflow). Can't help but think all the added ewaste from prematurely failing electronics far outweighs the benefits of switching away from lead..

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  2. Sorry, I'm possibly being thick, but can I have a tiny bit more detail on the levelling?

    Wires from A5 to the (metal) workpiece, and the spindle/motor, and when there is electrical contact between the two the zeroing is complete?

    I think Candle also supports this on Windows.

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    Replies
    1. I am using bCNC on a Mac. It has an auto-level feature which probes the board in several places doing exactly that, and adjusts the Z accordingly.

      Delete
    2. Thanks, I'll try it!

      I got my 3018 pro from aliexpress as it was cheapest, but there is a company called Sainsmart who seem to have an updated version:

      https://www.sainsmart.com/collections/cnc/cnc-router

      This one has autolevelling and limit switches and stuff so I knew it was possible!!

      I've been using Artcam for designs and it supports multiple tools, so I've been doing most of the work with a 2mm bit before using one of the (fragile) 0.5mm ones.

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  3. Your bit breaking problem is probably due to incorrect feed/speed, depth of cut or chip clearance.

    When I built my own CNC Mill, I went through loads of bits until I learnt to use the correct settings and sorted out an air blast to clear chips. Copper is sticky and really does need good chip evacuation to avoid recutting work hardened chips.

    There are loads of online speed/feed calculators which might help. FWIW, I use GWizard (more settings that you can shake a stick at including the cutter geometry) which ISTR has a free trial period so you could use that to get things in the right ball park.

    ReplyDelete

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