Freesteel Blog » Some circuit board cutting

Some circuit board cutting

Monday, November 23rd, 2015 at 8:16 pm Written by:

Let’s start with the most important circuit board I’ve milled in the last few days.

It’s the last one I did — and it should have been my first.

But we’re lazy at doing the necessary cutting trials, aren’t we?

There had been flaws in the circuits I had machined. In particular, some contours had not quite been fully cut leaving a little join of copper that I had to break with a scalpel. Also, some cuts were much cleaner than others.

Until I did these experiments I thought that uncut material would be at the ends of a cut, possibly due to a tool deflecting back from the cutting forces. And I imagined that the messier lines were because I was in a hurry and cutting too fast.

The truth was the exact opposite of what I thought.

The square cuts in batches 7 and 8 are cut in the direction of bottom left to top right with the top right ones done first.

Batch 7 had the tracks extended because I was looking to counter the tool deflections, which didn’t exist.

Batch 8 shows what’s really going on. In areas where the cutting is too light the tool can drag along the surface for a distance before it bites.

The pairs in batch 9 are done with two diverging cuts above and two converging cuts below. The upper ones exhibit gaps.

The roughness of the cut edges are all due to the feedrate and spindle speed.

Batch 3 was done at 3000rpm and feedrates of F600 (metres per second?) and is horrible.

Batch 5 is at 8000rpm with F50 in first column, F150 in second column and F450 in fifth column. It gets better the faster you go. Batch 6 extends the increasing feedrates, but was at 16000rpm. Batch 2 is same as batch 5 but also with 16000rpm.

Batches 1 and 4 are likewise F50 on the left stepping up in increments of F100 going to the right and shows that a minimum feedrate is required to make it nice.

Now that I know the parameters for what potentially makes a good cut, I should be able to make a single test piece of copper where it carves out the numbers of the feed and speed conditions in a big array that I can nail to the wall.

Anyways, to make sure I am isolating the tracks properly, I now machine an extra millimeter around every contour. Also, it’s necessary to probe the copper and adjust for it’s not quite flatness (a feature I saw in the chilipeppr system). Neither of these features are available in flatcam, so I have scavenged its gerber-loading code and made my own set of tools.

Here’s a vid of the process on a simple circuit.

Then I got a very ambitious job and I spent the whole of Friday doing a really complex circuit as part of the machine upgrade:
I’ve super-imposed the back and the front sides of this monumental piece that was off the edge of my capabilities. I did it with one gouge, a lot of messed up drill holes, but made it for the last post.

I was too stressed to get any documentation, beyond this one picture. The big holes are for the location pins when flipping it over, so it was a good idea to squeeze one right in the middle along the reflection line.

That’s it for now, until the next circuit job shows up. Or I should get back to some brass machining if I intend to make any truly unwanted Xmas presents for any friends.

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