First, i am new at this, so this might sound like some dumb questions
First out is the backlash and all thouse bearings. Do i have to use those? Or can i buy a 1 meter long M8 screw and hook the stepper right up to that? Will this be accurate enough? And ofc, strong enough?
Stepper motors... I found this one;
are these strong enough? I am planning to mill in wood, plastic, aluminium, and circut boards...
Thanks for the replys, really need your help
On the other hand, if you are trying to cut a nice circle, for instance, backlash will result in you having a straight cut at one point on each of the four sides. Any time you ask the machine to reverse its direction, there will be a gap where one axis is moving, and the other is not moving, but the software thinks it is.
The purpose of that screw is to push or pull either the table or the gantry. If the screw pushes the gantry, the gantry pushes back against the screw. Something has to resist the movement of the screw. Stepper motors are made to turn, not to be thrust bearings. Could you get away with it? Well, probably, at least for some time. But would you rather buy cheap bearings or expensive stepper motors when the steppers fail from the thrust?
Is the M8 screw accurate enough and strong enough? Well, maybe. If you are successful at keeping the weight of your moving components low, it probably will be strong enough. Will it be accurate enough? Much depends on what you're trying to do with it. If you're cutting out big pieces, it could be accurate enough. If you're cutting out very small pieces, such as watch parts, it most certainly will not be accurate enough.
But accuracy on that screw depends on something preventing that screw from moving along its length, and somewhat limited by the amount of flex the screw allows. Those bearings are there to prevent the screw from moving.
The problem with starting out is that you really have no way of knowing what's going to be important in your machine. Certainly using an M8 screw will allow you to keep the initial price down. After you're up and running, then you'll find out where the shortcomings in your machine are. You then talk to the chief engineer and chief builder (that's you) and see what needs to be improved.