My Build - I blame you lot for this....!

[routercnc]

Would gearing them down 3:1 (giving 4mm per turn instead of 12mm, and helping to turn all that inertia) make them more useable?

[HiltonSteve]

The pitch on the screw may not be the only problem, think about the size of the ballnuts. Finding space to fit them in and also making mounts for them could end up more expensive than downgrading to a more usable size like 16mm x 5mm pitch.