About modeling method of counterbore hole on the bottom side.

If counterbore holes for nuts and bolts are provided on the bottom side, printing tends to be disturbed. Also, it is not practical to use support pillars because they are too narrow.

The modeling methods described here solve that.

As an example, we will model counterbore holes and through holes for M3 nuts and screws.

1. Make a counterbore hole to fill the nut.
For the time being, let's set the diameter of the inscribed circle to 5.6 mm and the depth to 2.5 mm.

2. Make a hexagonal through hole for the screw to pass through.
For the time being, let's set the diameter of the inscribed circle to 3.3 mm.
The key to this method is not to make this hole circular.

3. Based on the bottom surface of the counterbore hole for the nut, draw the same straight line as one of the hexagonal sides of the screw hole to make an equilateral triangle.
Then, rotate and copy the equilateral triangle as shown in the figure.

4. Cut the body with three equilateral triangles. The cutting depth should be the same as the thickness of one layer of 3D printing.

5. In the case of counterbore holes for nuts, the corners will be rounded and it will be difficult for the nuts to enter, so provide a small groove to prevent this.

The recommended groove width is 0.1 mm.

That's all there is to it.

Finally, take a look at the slices.
You can see that there is always a foundation at the start and end of the bridge, and that the bridge is always in a straight line.

The counterbore holes for bolts are simpler.
Please refer to the attached model.

This is the end of the explanation of this method.