Direct drive verse gear reduction

[ed vitanovec]

I have been looking at a CNC routers with gear drives and have a question. They offer direct drive and 3:1 gear reduction, what are the pros and cons of each type?
Thanks! Ed

[Neal Schlee]

I have been looking at a CNC routers with gear drives and have a question. They offer direct drive and 3:1 gear reduction, what are the pros and cons of each type?
Thanks! Ed

3:1 gear or belt reduction allows for a better matched torque curve to the motor, you generally see this setup on the smaller size 23 motors.

Neal

[George Carlson]

I think there's more to it. I'm not sure why a builder would offer the two options unless there was also a difference in the axis drive mechanics. Direct drive is common in systems using ball lead screws. The pitch of the lead screw provides the reduction needed for tourque. In a rack/pinion system, reduction is needed to develope the tourque required to move the axis. Generally, direct drive lead screws have almost no backlash, so they are very precise. Reduction systems produce backlash, but it's hard to beat a rack/pinion system for speed.

[Gene Crain]

resolution also comes into play

[james mcgrew]

George is right on this one !!

[Neal Schlee]

resolution also comes into play

This is true, whatever the ratio is (1:3) or (3:1) you'll decrease or increase the motor steps by that amount.
For example, you can use a less expensive size 23 micro stepper motor (with a micro stepping driver), these are generally high rpm but not very torquey at the higher rpm and with the desired ratio bring the output rpm down and multiply the torque and still get a relatively good resolution. Then you'll need to also take into account your final drive pitch, whether it's rack & pinion or lead screw to get to where you need to be.

I've got a Multicam Plus 44 that is driven this way and the size 23 steppers with transmissions and R&P drive it nicely and thats with 2 Z's and 5.5hp Perske's that weigh 30 lbs. each. It's not a speed demon but does max out at approx. 200 IPM with decent cut resolution.


Neal