I recommend doing your initial calibration without material, and then doing the calibration project once you have it dialed in. I designed the project to be indicative of lost steps and calibration errors under load, but the default values provided by Easel usually need to be tweaked slightly for the individual machine.
If you have a dial indicator, you can attach it to your spindle mount and calibrate the Z axis using it. I showed how to do that near the end of my video on calibration, in this thread: X-Carve Maintenance/Troubleshooting Videos - Add Your Own!
What is your current steps/mm setting for your Z axis, and what type of lead screw do you have (M8 or ACME)? You can look at the Machine Inspector in Easel to find the setting, and if you post it here we can tell you whether it’s roughly accurate or not.