Ein Modell kann durch folgende Schritte zurecht geschnitten werden.

While working on models there are often cases where the geometry of the model needs to be removed or otherwise modified. There are multiple options, explained here from most simple to most complex.

1) Cutting

In this case, the object we are working with has bolt holes on the right side, which we don't want since it increases vertex count and shading issues caused by the holes.

To make a straight cut, we need to enter isometric view mode.

A cut can only be made in edit mode (to enter and exit press the tab key, or the dropdown on the top left). Press the K key to use the cut tool and then C to make the cut through the whole object. Click to start the cut, and click again to end, then Enter to confirm the cut action.

To select vertices through the entire model, use X-ray mode (see arrow top right), then use box select to choose all the geometry on the side that is to be deleted.

Select the vertices on the edge (still in x-ray mode)

Switch the transform orientation to Cursor. This will cause scaling to use the cursor as the reference point for this operation. (ensure the cursor is in the world center by using Shift-S → curso to world center)

With vertices on the deleted side selected, press the S key to scale, then the X,Y or Z key to lock to the axis to be scaled upon, then press 0. This scales all vertices to zero on the world origin, which was selected in the last step.

Return to object mode (tab or top left menu), and with the object still selected, click on the modifier tab (the wrench on the right tool panel), then click „add modifier“, and choose the mirror modifier.

Make certain that only one axis is selected. This will mirror the selected object which uses the same origin as the last steps as the point of mirroring.

Apply the modifier

Enter edit mode and x-ray mode, then select the edge loop created in the middle from the mirror operation, and press X to dissolve it.

2) Replacing surfaces

In some cases, it's quicker to simply replace a face that has unwanted geometry.

In this example, there is a hole through the box which is not needed.

Switching to edit mode (tab or drop-down menu on the top left), choose face select (3 key or the 3 icons top left), simply select the faces around the hole.

With faces selected, press the X key and choose „delete faces“

The faces are gone, but now the hole itself remains.

Select these faces in the same way (or use loop select)

Switch to edge select (the 2 key or click on the icon on the top left) and select edges accross from one another. (Note: the hole on the other side is ignored for the sake of brevity)

With both edges selected, press the F key to fill the gap with a new face.

To ensure the new face is facing the correct way, select face orientation from the drop down menu (see the arrow). Blue should be facing outwards, red inwards.