Coaster template
Set marble count, coaster size, edge clearance, and demon-core seat size/depth. Print a 1:1 plan for cutting and drilling, plus a section of the shallow spherical carve.
Preview — plan shows cut outline, marble seats (dashed), and demon-core carve. Section shows the shallow spherical seat with nested demi-spheres (large lower + smaller upper). Print at 100% scale.