I'm posting here rather than at the Rockcliff group because I can attach a picture in this forum.
Have any notes or drawings been posted on the belt drive system? There have been several references to notes, but nothing on the site I can find.
In any case, I am confused as to how the motors and belts would mount to the system. The one picture mounted to a table doesn't really explain it. The first problem I see is that if the belt is fixed and the motor rides with the gantry, won't you end up with a very heavy and unwieldy gantry carrying the weight of four motors and the router?
The second problem is that, unlike screws, the orientation of the motor has to be 90deg from the direction of travel. Will you have to add platforms of some kind?
I've attached a quick sketch of what I mean. You can see that the gantry has four motors on it. Not counting the z-axis (which I assume will just have a screw) the other motors have to be mounted on some kind of flange. Is that stable?
There are a couple of different ways to do your axis movements without having all the motors mounted on the gantry. for instance, you can attach the ends of the belt to the gantry, mount the motor on the end of the frame and drive an axle to the other side to use a two belt setup. The other option would be to use one motor to drive one belt hooked to the middle of the gantry, and hook each end of the belt to the gantry as described before.
Personally, this is the system I would use for two reasons. First is cost, and the second it harmonics the drive shaft would possibly set up. On a machine the size you are thinking about, it might not be a problem, but on my large gantry machine using rack and pinion, the drive shaft betwee the two sides of the machine vibrates quite a bit and the result can be seen in the cut if the material is very hard, too soft, or I move the machine too fast.
Get the basic shape of the machine with the extended axis we spoke about and then send it to me. I'll send it back with my suggestions as models!
No greater love can a man have than this, that he give his life for a friend.