Extruding/ Cutting from mid-plane

As a new user I can’t upload a short video clip so I hope the image and my description help explain this issue accurately…

I have extruded a flat ring, 3mm thick, 200mm outer diameter, 190mm inner diameter (imagine a giant 1euro coin but with the centre disc missing), on the front plane.
Using the centre point of this ring, I create a plane perpendicular to the ring, so that the plane dissects the ring (think of it as a plane offset from the top plane by 100mm). On this plane, I sketch a circle that is 5mm smaller than the diameter of the outer edge of the original ring. My intention is to cut a small slot / keyway of 2mm through the ring, at its middle, using this perpendicular sketch.

Going back to an almost front plane view, I highlight this sketch and pull it upwards by 1mm, cutting away (subtracting) a slot from upper half of the original ring. That’s what I want, well, half of what I want….

Since Shapr3D doesn’t have a ‘from mid-plane’ function, and considering I want this to be a 2mm keyway, symmetric by 1mm from either side of the middle of the disc, I assume I’d then need to re-highlight the sketch and drag it downwards by 1mm, subtracting material from the lower half of the ring and leaving me with a 2mm total slot removed from the disc.

However, this will not work. Using the mode select icon, I try ‘new body’, it adds a new 1mm disc perpendicular to the ring, but using ‘subtract’ it will not subtract from the ring. The program stalls for a second as if it is working on it, but nothing changes. I tried swapping the order of which way I pull the sketch and it will subtract in either direction, but not both, as in, I can only subtract in one direction and do nothing in the other.

This seems like a very basic thing to achieve and I’m pretty sure the approach logic is sound but it won’t work. A ‘from mid-plane’ function would do this no problem. Despite it being a bit annoying / cumbersome (requiring the extra steps of replicating what a ‘from mid-plane’ would achieve, by repeating the cut/extrude on the other side of the plane) I can live with not having it, but now this as really confused me.

Any help would be great, thank you!

Can you draw what you are trying to achieve with pen and paper - this doesn’t sound like it should be tricky but I am not sure I fully get what you are trying to achieve.

Thanks for your reply @Jagey . I can’t just now, but basically the image I’ve attached is exactly what I want to achieve. Except, that is only a cut/ subtract above the blue sketch of 1mm. I want to then do the same below the blue highlighted sketch, but if you see the blue arrows highlighted, with the dimension of -1mm beside it, that’s me trying to ‘pull’ down an extrude/ cut, but it just stays as is, nothing happens?

not sure I got your dimensions but I did this below by hiding the ring, then extruding the perpendicular disc by 2mm up then moving it 1mm down then unhiding the ring and subtracting the disc from it. This gives a 2mm x 2mm notch on both sides of the ring and, of course, there’s a very slight curvature on the inner faces due to the circularity of the disc edge.


@Jagey Yes, that is exactly what I am wanting to achieve, including the curvature inside the slots. Thanks for your time and thinking of that work around, I’ll probably use it! Doesn’t it seem strange though, that you’d to do all of that, just to achieve what should technically be possible with a cut/ subtract body in on direction and then the other, as I was trying? Or even better, a ‘from mid-plane’ command…

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