I have been thinking about my decision to use a 1/4-20 threaded rod to drive the axis instead of an acme screw. The answer is the typical engineering answer: “trade-offs”.
The primary goal of my HobbyCNC plans is to provide a functioning 3-axis router, with reasonable performance, using common materials, within the budget of a hobbyist. This build will provide an excellent foundation for learning the spectrum from design through machining.
1/4-20 ‘all thread’ threaded rod
On the positive side – it is inexpensive and readily available (at least in the U.S.). I’m sure metric versions are easily available outside the US.
On the negative side – it takes 20 turns to move one inch. This means a big sacrifice in axis movement speed. I reliably get 30 ipm. I haven’t tried to push it, but I have reached 48 ips, but not in production. Also, if you get past 3 feet (approx 1 meter) or you get the speed up too high, this thin rod can ‘whip’ and create an unpleasant knocking sound.
FWIW, I use 1/4-20 drive screws on my machine. Works great for wood, plastic, PC board isolation routing and engraving aluminum.
On the positive side – typically larger diameter (less/no whipping), high accuracy, precision machined, fancy ball-bearing nuts available. Also fewer threads-per-inch you can get much faster axis movement!
The downside: Cost. These are at least an order of magnitude more expensive. Like $100 per axis instead of $10. (prices vary widely, don’t nit-pick me).
If you want to go with Acme screws, please do. If your primary focus is to learn and experience machining on a budget, stick with the 1/4-20.