Lets say I want a board that is 100mm by 100mm. On the edge cuts layer I add lines to define my border. The lines have a width of 0.05 mm. It appears edge cuts layer is using the ‘outside’ of the line to define the edge of the board resulting in a board that is greater then 100x100mm.
Is there a way to tell the edge cuts layer to user the ‘middle’ of the line width? How do I create a board that is exactly 100x100mm?
My searching for this issue has failed me, so I’m asking. Thanks.
It’s a question you should ask the board manufacturer.
Can you really notice a difference of 50 µm given the milling process to cut the board? It’s in the region of the width of a human hair (an imprecise 17 to 181 µm apparentlly). 
If you’re talking about the values reported by the board statistics dialog, that’s a bug that should be fixed in the current version 8.0.6.
FWIW department:
I just checked at JLCPCB. They are inexpensive so I assume that they are not the most precise. Their dimension accuracy is given as (copy-pasted):
±0.1mm(Precision) and ±0.2mm(Regular) for CNC routing, and ±0.4mm for V-scoring
And they give their best price for a 100 mm square (maximum) 2 layer board. I ordered such a board with them. Edge cuts layer showed 100 mm square. I have not measured it but they did not charge me for going over the size…
I believe they use 101.6 mm as that’s 4 ancient inches. But I usually stop at 99.06.
No, it’s a matter of convention or de facto standard. The middle of the line is used as the edge. Please show the exact problem and give KiCad version info.
±0.2mm is pretty much the standard tolerance for every PCB manufacturer that I have ever used.
I’m 99% sure that my PCB manufacturer uses middle of lines at edge.cuts.
When I add round hole using edge.cuts its size is also defined by middle of circle line, I think.
They do, the centre line is the path the CNC follows.
The point of drawing a thicker edge-cut in the GERBER, and the design, is to cater for the router bit diameter, and tolerance
Thanks, I appreciate the discussion. I was pulling my hair out trying to figure out what was going on. From your feedback, and further playing around, this may just be an issue with the PCBWAY plugin, which appears to be adding the line width to the overall size of the board. (I’m still learning all of this)
Why does this matter?
If you go to pcbway and do a quick quote for 100x100mm board it will say $5. If you increase the size to 100.01x100.01mm it will give you a quote like $28. A big jump for an inconsequential size change. I could see that the additional dimension was coming from the line width. If I change the line width, I would see that change in the size reported to pcbway.
Creating a gerber file outside of the plugin appears to be working as I would expect it to, so I will avoid the plugin.
Again, thanks for the discussion.
10 in 110 can be more important than 01 after dot.
The first dimension is 10% over the threshold. You should also let the software detect the size from the gerbers, that’s the best guide.
Sorry, that was a typo–fixed. Should read 100.01x100.01. The only change is after the decimal.
Just as a matter of interest, JLC allows up to 4 ancient inches = 101.6 mm. Seems that PCBWay is strictly metric.
I just drew a rectangle on Edge.Cuts from (50, 50) to (150, 150), and KiCad reports the board size as 1e4 square millimeters. I had even set the line width to 1mm but it does not fool KiCad.
It’s not KiCad’s responsibility how 3rd parties interpret line width, and you should also not assume all PCB manufacturers do this in the same way. I once read through Aisler’s specification, and they do something weird with this line width. As far as I can remember, they even treat it differently, depending on how wide the lines are, but I can’t recall further details.
I’m not sure if changing Edge.Cuts line width isn’t the way to increase the clearance from edge to copper not changing the edges itself.
If you Uncheck (see screenshot #1), then you get a Line based on the Line Setting (and, of course, can change it afterwards)…
Screenshot #2 shows the line set to 0.001mm and then Imported into Kicad with manually setting set to 0.001mm
#1
#2
Results In PCB (imported DXF) see thin Grey line (grey because it’s properties panel is open. Otherwise, it would be Yellow, per that Layer’s color.
Final Comparison: Two lines in PCB, settings Unchecked. Thus, both lines are at 0.001mm width (instead of at the Checked width)… Shown below in Yellow (imported into Margin layer)
No not anymore. A few KiCad versions ago (V5 or so, don’t know when it changed) lines on Edge.Cuts were treated as copper tracks when calculating edge clearance for zones, but this has changed. Now it is an explicit clearance set in: PCB Editor / File / Board Setup / Design Rules / Constraints / Copper to edge clearance
In early KiCad V8 versions, this was set to 0mm, which is very bad for production (this can and will create shorts in multi layer PCB’s during production) The defaults have changed, I think it’s now 0.5mm, but if your setup is still from the early days of V8, then the default for new projects may still be zero.
