http://groups.google.com/group/shapeoko ... 1162e41681?
I happened upon a cnc that does use a belt on the z axis called Zenbot
http://www.zenbotcnc.com/all-products/z ... cnc-router
better pictures from the CNC zone forum
http://www.cnczone.com/forums/pcb_milli ... ne_--.html
and a video of a guy who replaced the z-axis
http://www.youtube.com/watch?v=PJPAA2YzOYk
I am curious how / if this design dealt with some of the disadvantages of using a belt on the z-axis
from the old forum
The issue is about inherent stability. What happens when failure strikes.
In the case of X and Y, nothing much as gravity has no impact on it.
On the case of Z where the whole tool and stage are being held in place
fighting against gravity, the consequences can be problematic.
1. The tool can come crushing down on the piece that you are working as it
now the ability to travel the full length of you Z-axis if power goes off
because you depend on the motor being energized for keeping it locked.
2. Today you can rotate the stepper axis to mechanically to adjust the Z
height - that can only be done electronically if the hold the stage in
place with the belt.
3. The Z-stage rarely moves as much as the X-Y given that the work happens
usually on the X-Y plane - so the characteristic higher speeds that can be
achieved with belts produce no advantage here
4. You are wasting energy by keeping the motors enabled when you don't need
them to be.
Using a screw solves all those issues as the Z-stage is now inherently
stable.
1. On failure it just stays put.
2. Place a wheel on the the axis above the stepper to easily adjust the
Z-height.
3. The screw natural slowness is not detrimental and its resolution
(usually runs opposite to speed) is beneficial to the quality of the work.
4. Save some CO2 (a few grams) by not enabling the steppers unnecessarily.
This is just my opinion based on experience with 3d printers and machines
in general.
Miguel Angelo
