New to mach3 i have a 4x8 router table. The first cut cycle cuts perfect depth and when the machine cycles to (next cut same tool) the g code has the same Z movement but it plunges into the stock over an inch and breaks the bit. I use bobcad to generate g codes and an industrial cnc router table. I do have a uc100 controller on windows 10. Any tips would be great!

Sounds like you Z axis could be missing steps on the rapid upward (+Z) movement.

Try halving the Z axis Velocity and Acceleration settings in motor tuning and save the changes. If this makes any difference then experiment with your Z axis motor tuning settings until it performs correctly.

Tweakie.