This is a remix of the very nice design you can find on Github [1].
The internal central table is removed to have a free area.

Sadly, it is not customizable and will leave you with some limitations of the coil turns and diameter. I have used a different wire than described there and could fit this many turns:
x - 120 turns, y = 80 turns, z = 30 turns @ 0.4mm copper wire.

[1] https://github.com/tarciszera/3D-Helmholtz-Coil-Simulator/blob/master/README.md