That file predates the Z-Plus which is limited in how deeply it can move/cut.
Some folks have found a three-layered system a good approach:
- bottom: original MDF baseplate (sealed with spar urethane or lacquer) with some holes and threaded inserts installed from underneath for adding threaded inserts to secure
- middle: a threaded insert board larger than the working area by the reach of a clamp which has holes in that border area which match up with the threaded insert holes in the bottom layer to secure it, a grid of holes in the working area field for threaded inserts installed for workholding, and additional holes with threaded inserts to secure — discussion of bootstrapping this at: Notes on rapid positions and wasteboard leveling
- top: a spoilboard the size of the supported working area plus the diameter of the endmill used for surfacing along X, and endmill radius along Y, (with a matching radius at the back corner) which has holes in it to match the threaded insert board for workholding purposes (these may be drilled at need) and holes to secure it to the threaded insert middle layer