Sharpening CNC tool bits

Recently I was routing a small PCB on the 3040 CNC router I purchased a few months back.  There are lots of reasons folks buy into this technology. Mine was that to prototype any sort of electronics, I had reverted to using veroboard (circa 1970 technology) ... not only is it hard to get it is expensive to boot.

Exhibit 1

Realising that the world had moved on in the past forty years .... I still did not fancy messing around with a potpourri of chemicals , including some previous bad experiences with Ferric Chloride..

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Ferric Chloride is still a commonly used chemical to etch PCBs... interestingly if you experiment with it .. you'll find that it generates some heat along the way.. but if you give it some heat the reaction is accelerated massively ... HOWEVER I don't recommend the following action . On one occasion I decided that a little heat would help ... Unfortunately using a large coffee jar on top of an electric  heating element loaded with a PCB masked blank, and 1-2 litres of Ferric Chloride, the jar cracked , and Ferric Chloride spewed all over the electric heater, then subsequently the bench, then the concrete floor.... suffice to say the mess was permanent.. hard to explain to ones parents  at the time .. and still vivid..

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Using a CNC router is to cut PCB's is not an entirely straight forward process, (much more on this subject later), however it can be done ... with useful results, and I'm sure that once proficient it will be an entirely suitable prototyping approach ..

Last week I proceeded to cut a small single sided PCB to support a monostable which drives a pendulum. The board is small 40mm x 80mm and only has 20 components, though some high voltages and currents. I had spent many hours trying different track sizes, and tool bit sizes attempting to get a set of workable trade-offs

On one attempt however I selected a tool-bit that normally would not have gone back into the toolbox .. the results were awful to say the least Exhibit 2

Cleaning off the swarf revealed the magnitude of the calamity. All the edges were rough to touch, the track sixes were uneven. Looking at the tracks through the microscope reveals a lot about the mess that was created

Exhibit 3 & 4

And it was all over the board, not just one location, it got worse as you zoomed in

Exhibit 5 & 6

Disappointed doesn't describe the feeling at this point ... this is step 6 or 7 of a 9 step process. The result was a mess and unusable.. ! Still waiting for an Ebay shipment of new tools, this was my last 30 degree conical 3.175mm tool bit. (1/8th inch)

Carbide CNC tool bits have two ground cutting surfaces to provide relief in the cutting action, that is an edge and a relief to clear the chips. Even the smallest toolbits (0.1mm and 10 degrees), are sharpened in this way. These toolbits are so small as to be able to pierce your skin, and not even feel the 'prick'

Exhibit 7

Notice the ground edge even at 0.1mm. The guilty tool bit in our case looked much less tidy ...A quick examination of the tool bit revealed  a lot ... and still being in the trial and error stage with CNC, it is  probably better explained as ERROR and TRIAL ...

Exhibit 8

Notice the top edge, with two major chips plus many minor ones, AND the the somewhat less than conical end point...  (exhibit 8). You could barely feel these failures, let alone see them .... However I attempted to use the microscope, and to sharpening stone to see if I could improve things..... (never tried to sharpen carbide previously).

Attempting to keep the angles the same, and improve the tip, checking every few stokes I 'wiped' the tool over the fine side of the stone thus ...

Exhibit 9

Exhibit 9 & 10

Whilst it is difficult to keep the same precision angles, but with care you can approximate the factory grind. Checking every few strokes on the stone.. I was satisified with the results

Exhibit 11 & 12

Notice most of the edge is cleaned up , and the point now has real shape, if not conical, at least not jagged ...

And so what about results, well they speak for themselves, resetting the X0 and Y0 points and running the job again with the refurbished tool bit ... see for your self ....

Exhibit 13 & 14

Lots to observe here, sharp edges, rounded corners , uniform cuts all with a refurbished tool that cost less than 50c of Ebay. So if you are stuck, have a go.. tidy up your tool bits, and resist the first course of action to throw them in the bin when they become dulled by the FR4 or break (as they do in my company) due to inexperience (or incompetence ..)

All up a great result, and worth a try ..

Stay safe ... Peter