My very basic circle and square gcode seems scaled

[mudmin]

I bought a cnc and I literally just want to cut circles and squares on little plastic enclosures.  I'm really trying to avoid learning a full cad software to do something so basic. Inkscape is perfect...except that everything is scaled.  Thanks in advance for reading this far and any help you can give!

Here's the problem:
1. Draw a rectangle. If I need 100mm x 60mm, I have to draw it 98x58 because the gcode it generates cuts on the outside of the line. That's not bad, but circles are an even bigger problem.
2. If I do a 10mm circle, the circle winds up cutting out like 23mm with a 2mm bit. It's a perfect circle, the scaling is weird.  If I draw a 2mm circle, I get 5.5 mm.

Here's what I'm doing:
1. Draw my shape to the exact measurements.
2. Path -> Object to path
3. Extensions->gcodetools->orientation points - set depth etc.
4. Extensions->gcodetools->pathtogcode
5. Make sure my tool diameter, feeds, and speeds are right.

I get an exact, perfect cut of what I drew, on my 3040 Chinese CNC, but things are scaled. Squares by the size of the bit.  Circles seem to be actually scaled.  What I THINK I need is to know how to tell it to cut inside the line instead of outside, but I really don't know what I'm talking about.

[brynn]

When you cut the square, do you use a 2 mm bit?  Because that would explain the 2 mm discrepancy that you see.

If you're using the Gcodetools extensions, there's a setting for the size and type of tool.  You need to use the Tools Library extension to set it.

As far as I understand, you have to use them in this order:

Orientation Points
Tools Library
Path to Gcode

I'm not sure what could be going wrong with the circles.  If using the Tools Library extension doesn't fix it, please share your SVG file with us.

[mudmin]

I do use a 2mm bit and I tell it that it's 2mm and I can correct for that in the drawing (although cutting "inside" the line would be better.  Circles, I don't really understand what it's doing. It almost seems scaled.  Again, is there a way to specify which side of the line it cuts on?  Seems like it has to be possible.

[brynn]

As far as I know, these Gcodetools extensions don't have such an option.  However, I'm not intimately familiar with them.  It's possible there's something for that, and I've just never seen it.

However, if you didn't use Tools Library, you didn't use it properly.  I think there's a chance that setting the correct tool and width, using Tools Library, might fix both problems.  It probably will fix the problem with the rectangles, and then you don't have to make any correction.  I'm not sure if it will fix the problem with the circles, but it might.  Unfortunately, since I don't have any cutters, I can't really test it myself.

Try setting the tools, using the extensions in the order I explained above, and see what happens.  If that doesn't fix both problems, let us know, and we can investigate further.

If it doesn't fix the circle problem, please share your SVG file with us.

[mudmin]

Thank you. I figured out the circle problem.  It was actually two problems.  Circles are the right size, plus the diameter of the tools now.  I will look at the tools menu and see if I can figure anything out. Thank you!

[mudmin]

Try setting the tools, using the extensions in the order I explained above, and see what happens.  If that doesn't fix both problems, let us know, and we can investigate further.

Whether I use the default tool it automatically puts in (with adjusted settings)
https://i.imgur.com/BYKgb8C.png

Or I make my own tool in the tools library
https://i.imgur.com/hPJKXCf.png

The hole comes out the same size

[brynn]

Glad you figured it out!