Can someone point me in the right direction on how to calibrate the z-axis movement. I have a c-beam type setup and the z-axis is physically moving a lot more than g-control thinks it is. Nearly had a heart attack when I tried to cut the proper sled and smoke started belching from the wood 
You need to change the pitch setting for your z-axis in GC (not sure how this works in webcontrol). The way you describe it, it is different than the 8mm default and you are moving it more than intended.
Search for z-axis pitch and you should stumble across somebody explaining how to.
Thank you - searching now!
from one of the discussions:
For anyone that has a similar question, in ground control, under the settings tab, you can simply click on z-axis pitch and change it to whatever. Thanks MetalMaslow!
You need to count the starts on your lead screw and multiply it by the pitch of the threads to get the proper value (lead) to insert in ground control. If you have an official C-beam, then you have 4 starts and the pitch is 2mm, thus the lead (amount of movement with 1 full rotation) is 8mm.
Edit: if you are using a pulley to drive the leadscrew from the motor, unless the pulleys are the same size, you will need to do additional math to calculate what distance the router mount is traveling with a full rotation of the motor. Or you can measure it manually.