CNC PCB calibration

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seaton
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CNC PCB calibration

Post by seaton » Thu Sep 22, 2016 11:39 pm

more along the lines of Pauls posts but with my CNC for PCB isolation milling.

I finally got the Microscope set up so I could do some measurements of some feeds, speeds and depth of cut calibration cuts using different bits

Bits Im using are 20 Deg Engraving VBit

0.6mm PCB Cutter

0.4 end mill

You can see the quality of cuts vary between the types of cutter, so is a trade of using the Vbit for the very fine work which give a ragged cut as opposed to very clean cuts for the end mill and PCB cutter. (the board is easily cleaned up with fine emery board or wet n dry so is not an issue)

These two images below are for the bit width calibration within the software, i.e. bits are not normally the size they are suppose to be so the diameter is tweaked in the cutting software, when the upper traces = the lower gaps it means that the size in the software is correct. Smallest track size on Left of screen is 1mil (1 thousand of inch) also I don't yet have my stepover dialled in and hence why I have some copper artefacts left because of the difference between the advertised cutter size VS calibrated cutter size.

So with the bit diameter calibrated it is showing me that minimum trace is 1mil and min clearance is 12mil This was done with a 30Deg VBit The calibration test starts at traces 1mil up and increments by 1 up to 25 mil this is done on both Traces and Clearances.

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Feeds, Speeds and Depth settings.

These are calibration cuts at different feeds and depth, ones showing is for 0.050mm depth of cut, again the ragged edge is VBit engraving bit. Measurement ruler is in 0.1mm increments.

So with my 20Deg Vbit I'm getting ~0.2mm width of cut

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Some SMD foot print tests

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Last edited by seaton on Fri Sep 23, 2016 12:32 am, edited 3 times in total.

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seaton
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Re: CNC PCB calibration

Post by seaton » Thu Sep 22, 2016 11:51 pm

Here the same feeds and speeds as above, however are optically zoomed in even closer on the microscope, I love this microscope :) .

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You can see where the last test ended and new bit changed

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seaton
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Re: CNC PCB calibration

Post by seaton » Thu Sep 22, 2016 11:58 pm

Here you can see that the fine tipped V-Bit does not like faster feed speeds as it starts to deflect and not cut properly, sort of bounces over the surface.

20160922-235540-558.png
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At my fasted speed I was testing, not really cutting at all
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Last edited by seaton on Fri Sep 23, 2016 12:31 am, edited 1 time in total.

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seaton
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Re: CNC PCB calibration

Post by seaton » Fri Sep 23, 2016 12:08 am

Results of incorrect feeds for various end mills. I've gone through a few getting this up and running, if you look them side ways they'll break lol

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20Deg V-Bit good tip is 0.1mm this one dropped on floor and now no good.

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seaton
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Re: CNC PCB calibration

Post by seaton » Fri Sep 23, 2016 9:16 am

Here are couple more zoomed out on the feed and speed test pattens based on procedure outlined here http://www.precisebits.com/tutorials/ca ... speeds.htm

I start of at 50mm/min @50um (0.050mm) depth of cut then increase the feed speed by 50mm/min each time up to 400mm/min, then do all again for both 75um depth and again at 100um depth. The Vbit by its nature is affected by depth of cut, while the end mills/cutters are not.

So you can see in the first photo when using the 20Deg Vbit that the lower speeds are good up until 200mm/min after that quality drops off, this is down to tool deflection and is more prevalent in the smaller tools...the bigger bits don't have this problem at the these test speeds

To increase my speeds vs cut quality for the smallest bits I will need to increase my spindle speed, currently my max RPM is 10K on the spindle I have installed atm, however my other one (awaiting new motor) will be capable of 25K rpm so should at least get double the feed rates at the higher RPM.

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parkview
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Re: CNC PCB calibration

Post by parkview » Mon Oct 03, 2016 8:28 am

Your producing some nice clean cuts there. Have you cut out any PCB's yet?

PS. Thats a great link find there. A very interesting read on all the things you have to take into account to cut correctly.

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