This is an experimental model of a “Curved Cornett” from the 1981 book The Amateur Wind Instrument Maker, by Trevor Robinson.

There's a lot of details missing from the very rough drawing of this cornett. I used pixel estimation to estimate where the holes were located, and other base measurements that were not provided. 

I copied the page from this book, which I believe is fair use. I have added a significant amount of extra work in order to make this into a proper 3d model. 

I do not know the provenance of Trevor's model came from, as he didn't cite where he got his research. 

I am calling this an experimental model, since the mouthpiece is questionable. I'm not a great brasswind player, and can't tell if it's me, the model, or both.

FreeCAD and STLs are both provided.

Resin printing orientation: Align vertically, 80deg instead of 90., with heavy supports. Once printed, you will have to epoxy together. There are octagonal sections that fit loosely. Use quick setting binary epoxy on both sides of joint and hold in place. 

If you wish to change direction of bend, you can mirror the parts in the slicer.