Probably a Stupid Question.

[Ger21]

Two motors are used to keep the gantry square, and make it more rigid, not to provide twice the power.
If you drive a gantry with a single screw in the center, it likely will exhibit racking when cutting at the ends of the gantry

[Electroconducive]

Two motors are used to keep the gantry square, and make it more rigid, not to provide twice the power.
If you drive a gantry with a single screw in the center, it likely will exhibit racking when cutting at the ends of the gantry

Sorry, I should have been clearer. I was thinking of using the servo with two ball screws either side connected with a timing belt. The machine is too large for a single central ball screw.

[m_c]

There is no reason why you can't mix and match steppers and servos on different axes.

You still want to avoid any unnecessary weight though.

[Electroconducive]

Thanks m_c

I'm finding it hard to keep the weight down with an epoxy granite filled steel gantry of a suitably rigid shape.

I'm probably over compensating quite a bit. I'm going to try and bring the weight down.

I'm also failing to understand how to calculate which motor I'll need for a given linear system.

I'm basing the servo on Boyan's massive purple machine. Which I believe used a 400w servo for a 120kg gantry.

[Ger21]

Weight is not an issue, as long as you have the power to move it.
We're looking at a new industrial router that weighs about 4-5 tons, and rapids at 96m/min.

There's no reason to fill the gantry beam with epoxy granite imo. A steel beam with a 10-12mm wall thickness is plenty strong enough, if you add some internal bracing.