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I am a raw beginner at FreeCAD and 3D draughting. Watched some tutorials and designed 2-3 simple items. Aiming to use it for 3D printing.

My question relates to 2D sketching. As I understand the workflow, one draws 2D items that one can then extrude, cut etc. So one picks the drawing axes (eg X and Y), and the sketch is then at Z axis zero. After extruding, one can place another sketch on a face for further extruding etc.

But the sketch is always at relative Z/3rd axis zero.

Consider a fairly large block extruded 10 mm thick. Say I want (example only, never mind why) to cut a 20 mm disk from the interior, 3 mm deep, 5 mm from the bottom surface therefore 2 mm from the top.

If I place a sketch on the top surface, make a 20 mm circle and use that to cut a hole, the cut will always start at the top surface - but I want it to start 2 mm down. I.e. it seems to me I need to be able to offset the sketch from local Z/3rd axis zero, in this case to -2 mm.

Can one do that, or have I missed the point somewhere?

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  • $\begingroup$ so you want to set an offset of -2... Do you use StekchUp or FreeCAD? $\endgroup$ – Trish Oct 9 '20 at 20:47
  • $\begingroup$ FreeCAD, but maybe the answer below is what I need, thanks. $\endgroup$ – nmw01223 Oct 11 '20 at 4:17
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This answer assumes you're working in the Part Design workbench.

So you want to adjust the starting height of a pad or pocket. There are two ways I can think of to do this easily.

  1. Adjust the Z attachment value of the sketch to lower the sketch below the surface.
  2. Use the "two dimensions" option in the pad/pocket operation and set the second value negative.

By the way, it is highly suggested not to attach a sketch to a surface. The current development version (0.19) and previous versions have an issue ("topographical naming") where editing a previous feature can change the internal name of a face causing the attachment to break. There is a solution under development but it doesn't loom like it will get in earlier than 0.20. You should instead simply adjust the Z attachment value to match the face you want.

Also, there is a very active (and very helpful) forum here. I'd suggest asking further FreeCAD questions there.

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  • $\begingroup$ Thanks, really helpful. Very much a beginner, didn't realise one can jus create a new sketch without attaching it to s face. I have noticed strange happenings when I've gone back to make changes, so maybe I have seen this issue. I'll try the forum. $\endgroup$ – nmw01223 Oct 11 '20 at 4:18
  • $\begingroup$ This actually answers some questions I was having too. Especially that topographical naming issue. Now I can fix my broken models without having to start over. $\endgroup$ – RDragonrydr Oct 12 '20 at 21:17

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