Subtract works differently depending on how it's created

Very much a beginner question here. Haven’t used any CAD programs in ages.

I’m trying something quite simple - to push a hole through two parts of a shape.

So I’m trying to create the hole by creating a circle on one plane, pushing it through, creating a group, and then subtracting it.

This works fine if the original circle is created freehand. But if it uses any guide points, or even snaps to a size (1mm radius), it never quite works and the original shape is no longer a solid.

Really no idea what’s going on here.

When you mention 1mm radius it gives a big clue to the problem. SU has a line segment tolerance of around 1mm, when you go below that faces fail to form. You need to work at a larger scale and scale down when finished. Tiny faces can exist but they are difficult to create.

Also, to create the shape above it’s easier to push the shapes through raw geometry and intersect the faces to remove what you don’t want. Then make the result a group.

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Thanks for the advice on the general method of intersecting the faces - that worked well in general.

However, I did still sometimes have some issues even when I made it bigger (8 times bigger in fact). When it didn’t work properly, I just ended up using a guide point to make the two holes separately.

It is not unusual to have to scale up by 100 or even 1000 to make small geometry issues go away. 8 may not be enough.