I have used a knife to cut tracks but I find it difficult to control and avoid nearby tracks or components. I found this and thought it was a very good idea - I haven't tried it yet!

From: https://electronics.stackexchange.com/questions/677894/how-do-i-cut-a-trace
A scalpel/xacto blade (preferably new, fresh and sharp) can be used in a drill-like motion to cut the trace, rather than a cutting motion. Place the tip of the blade on the trace, press down lightly and twist the knife. The tip will dig in and cut the trace. Be careful not to go too deep on multi-layer boards!
Compared to a cutting motion, this technique means there's less chance of slipping and cutting adjacent traces and it also makes the break wider.

 

I find that tracks are easier to cut if you heat the board first with the hot-air tool.

 

Why are you doing this the hard way? Seriously. DO NOT cut FR-4 PCBs. They are Fiberglass, and you WILL inhale the dust unless you wear respiratory. Anybody who does not wear something like this and cuts, saws, snips FR-4 boards is an idiot. If you don't want the PCB maker to cut the boards, put a white silkscreen box around each one and USE A SMALL SHEET METAL BREAK. To cut them. Not expensive, no dusst, perfectly crisp, clean edges.

Let's say you have a small, 2-layer PCB with all 4 layers of silkscreen & solder mask. The absolute BEST deal I've found is from a China board maker called PCBWAY.COM. I've used them for years without a single problem, and they DON'T CHARGE FOR ANYTHING other than the PCB itself. No setup, No screen charge, No silkscreen r solder mask charges. You can get boards in just about any color you want.

Example. 2-Layer PCB, solder Mask + 4 SILKSCREEN LAYERS:

Let them panelize it however they like, and add a break-out rail, so you can snap the boards apart.
Allow there to possibly be a bad PCB on the panel (I've never received a bad one). If not, they charge 30% more on the job.

Five 1.5"x1.5" such boards will run: $3.01ea. If you add 30% to job, it's $4.50 extra & not worth it- that covers S&H.
S&H using GLOBAL DIRECT SHIPPING takes 2-6 days, and only costs: $4.21.

Your total cost for 5 PCBs is: $19.27 / 5 = $3.85ea.

Upload your gerber file to them from any PCB software, and their quote is instant. Takes them 24-hours to make the boards, 2-6 days to ship, and voila. REAL PCBs.

 

TS wants to cut a PCB trace for trouble shooting purposes only, not for fabricating a PCB.

 

TS wants to cut a PCB trace for trouble shooting purposes only, not for fabricating a PCB.

Perhaps @BobaMosfet has never made an error on a board and had to made a blue wire bodge?

 

Perhaps @BobaMosfet has never made an error on a board and had to made a blue wire bodge?

Exactly what I'm trying to do!

 

Cutting a copper trace on an FR4 PCB, or even on a paper/phenolic PCB, is not to be done in one brute-force pass!! THAT will ALWAYS lead to grief. The tool that I have found works best is, indeed, an Exacto knife with a slightly modified blade profile..
That is, an angled, pointed blade with the tip of the pint worn off and then resharpened to a flat, not tapered, cutting edge, so that it is a "chisel-tip" about one-millimeter, (0.05 inch) across. For very close traces, narrower than that . This very short, straight cutting edge is then applied straight toward the PCB to press a groove into the trace to be cut.
But before proceeding farther, back off and verify it is the correct trace being cut. THEN put the end of the blade back into the formed groove, and press in a bit while adding a very slight twisting motion back and forth a few degrees. Then pull out the knife and examine carefully. To widen the gap in the trace, gently pry up one end of the cut trace using the Exacto blade in the groove.

The benefit of this method is that to undo the cut just push the ends back to each other and add a bit of solder bridge,

 

Perhaps @BobaMosfet has never made an error on a board and had to made a blue wire bodge?

Correct- never have

 

Exactly what I'm trying to do!

Fair enough. But why cut a groove? In every commercial fix I've seen like that, they just use a jumper soldered between 2 vias.

 

Correct- never have

Can't have designed many boards, then.

 

Fair enough. But why cut a groove? In every commercial fix I've seen like that, they just use a jumper soldered between 2 vias.

Because sometimes traces don't go to the expected place. Well duh.

 

But @BobaMosfet is correct. Cutting FR4 boards with a saw is nasty business. Both to your lungs and to the saw.

Best method to cut pcbs apart is with a tile shear, a sheet metal shear or a heavy-duty paper cutter..... although these may not work well for their intended purpose after slicing up pcbs.

 

Fair enough. But why cut a groove? In every commercial fix I've seen like that, they just use a jumper soldered between 2 vias.

That adds a connection and presumes the existence of suitable vias. It is no use if there is an unwanted connecting track.

 

I can not imagine "cutting a groove" in a PCB as a means of breaking a trace. The method I described works very well and is quite suitable for even closely spaced traces. In addition, I HAVE SEEN actual grooves cut, bit not ever with a high speed rotary tool. An exacto knife blade or a steel scribe is all it takes.

 

I haven't tried it yet!

I have now! I got a scalpel handle which is cylindrical and makes twiddling the blade round easy.
It works a treat and is completely controllable.

 

I once tried a scalpel and not only are they much more expensive, the blades that I got were not heavy-duty like the cheaper EXACTO blades.
But certainly yours is much easier to control safely and cut only where you intended to cut.