The largest CNC machine we make at this time (12/04/2015) is the GreenBull 6'x12' model. This model has 2 options for Z-axis travel.
The short-z option has a total Z travel of 5.75 inches. From that you would subtract the length of the end mill used and the thickness of the spoil board to determine the maximum material thickness. (Example: If the end mill extends 1.25" from the collet and the spoil board is .75", then the material could be up to 5.75 - 1.25 - 0.75 = 3.75 inches in thickness). This is good for most sheet-type materials.
The long-z option, used mainly for large 3D carvings, requires a custom frame and allows for up to 36" of travel.
The tolerance of our machines, like any machine, depends on several variables. The major variables include the manufacturing tolerance, the type of machine control used, the precision of assembly, the thoroughness of maintenance, and the initial and ongoing calibration of the machine. Because we sell kits only most of these variables are outside our control. Therefore, we are hesitant to guarantee a certain level of tolerance for an end user. However, in our experience, tolerances of .001" are readily achievable with our machines.
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What tolerance can I expect from your largest cnc machine and the laser cutter? Also, what depth can I get on the z axis?