design choices when the budget will not stretch?

[JAZZCNC]

so what decides how you choose the right size motor? i presume weight of what you are driving comes in to it.. does the size/weight of the screw come in to the decision? does the materials to be cut have any sway on it? i also dont understand how the word resolution is used in cnc.. my thoughts are it is similar to a picture where there are so many dot's making curves smoother, does the same thing happen when you lose resolution in cnc? you start to get blocky curves?

Can't really Add more to what Irving already said but I would like to comment on this portion of what Irving said.!

At 600rpm theres going to be relatively little torque available so there is a danger of losing steps... its all a balancing act :)

This comment I don't agree with and is not my experience.? Stepper motors using higher voltage giving best performance will easily work at 600RPM and have a usable amount of torque available, they certainly won't be in danger of losing steps unless cutting really hard and deep or moving/stopping heavy weight around fast.!

Irving's correct that it's a balancing act and very important you consider what you want the machine to do and the feedrates required, then use this information in conjunction with machine data like weight to Accelerate and de-accelerate to aid select correct screw/motor/drive/PSU choice.

All this said when it comes down to it selecting Screw/motor/PSU etc there's only so many options for a given size/style machine doing certain kind of work.? So don't rack your brains trying to figure what's needed just browse the forum's find a similar size and type of machine that looks like it works how you'd like and ask what they use.?

Think you'll find it boils down to only a few options for good quality accurate machine. Like these.!!

Small moving gantry woodworking/plastics only machine: 10mm pitch ballscrews, 1.85Nm, 50V drive, 40-45VPSU
Medium to large moving gantry woodworking/plastics only: 10mm pitch ballscrews 3Nm, 75V drive, 65-70VPSU

Small all round material moving gantry machine: 5mm pitch, 1.85Nm, 50V drive, 40-45VPSU (10mm pitch option costing resolution/torque which is usually preferred for Alu or higher detail work.!)
Medium to large all round moving gantry material: 5mm pitch, 3Nm, 75V drive, 65-70VPSU ( 10mm pitch is high consideration on this larger size machine and the trade off between loss resolution/torque and speed gain can be justified to a degree.?)

Fixed gantry machines can get away with using slightly smaller motors due to less weight being shifted and the fact they tend to be smaller machines anyway because of the room they take up (basicly double the cutting length or width).
Mostly you'll find fixed gantry machines are built for strength and resolution so don't need high feed rates so use high lead screws which give much higher torque.
so.!. . . 5mm pitch/1.85Nm/50vDrive/44-45v is common. With high detail and really low pitch screws then lower powered motors/drives etc can be used.

These examples presume ballscrews and decent supported linear rails if other methods are used then these options could change slightly with chance the motors/drives/psu may need upgrading to over come the higher friction with some methods.?

Then there's the Milling machine/lathe conversions which play to different tunes and very dependent on machine so won't go there.!