[Bob La Londe]

Ok... I picked up a little router recently. It claimed some stupidly fast rapids for its size and build. Amazingly it can do them on X and Y as long as nobody opens the shop door and changes the air presure in the shop suddenly. LOL. Seriously its lamely underpowered. Has a Nema 17 on the Z that even with the light weight handpiece they setup as a spindle struggles when going up. I suppose with a different controller and different power supply it might be better, but it came home to me how lame it was when I blew a fuse. The power supply, spindle and controller all run through a 2 amp fuse.

So... I am borrowing the motors and controller of one of my other machines to see if I can't get a little better performance out of it. I don't have (or want to have) any other NEMA 17 steppers besides that one that was on the Z so I have to modify that axis atleast for a Nema 23 motor. They have the Z axis motor hanging down behind the gantry driving the Z ballscrew with a belt and pulley setup. If it was a gear reduction I would understand that given the dinky motor, but its a straight one to one. I can modify the mount easy enough to use the same pulley and mount the motor in a similar manner, but I could just as easily use some spacers and mount motor above the end of the screw with a helical coupler making a direct connection.

Other than the fact that the machine will be taller is there any reason to put the stepper motor behind the gantry using the belt drive as opposed to directly over the screw using a helical coupler? The Y & X on this machine both use direct helical couplers.

Both of my little desk top mills have the Z stepper right up on top directly connected with a helical coupler to the Z screw and they work just fine.

[CarveOne]

Three reasons that I can think of:

1. Need to use gear reduction to increase torque.
2. Can't make motor mounts accurate enough to prevent shaft/coupler/shaft misalignment when the screws are tightened, common problem if they only have a few hand tools to build with. Probably the reason 1:1 is used.
3. Just because they want to do something different. (kewl factor).

[louieatienza]

Bob, it could also to be to provide better weight distribution. Gives the machine a cleaner look. And you can swap out the pulleys to change performance. Belts alo more forgiving of misalignment and better damping of vibrations/resonance than couplers. Two pulleys and a belt can even be cheaper solution than some helical couplers.

[Bob La Londe]

I had not considered weight distribution. Makes sense though. I'll plan on putting the larger stepper in about the same place since I am also going to be installing heavier spindle too.

[CarveOne]

Louie makes a good point, and I had forgotten that one. I've seen admonitions about belt stretch causing backlash. I really don't see that as much of a problem with good quality short 1/2" or wider belts, possibly with internal Kevlar reinforcing strands.