Foolent Derarn

Foolent Derarn is the precision workbench app built for bell founders, bell restorers, and church bell maintenance teams. Whether you are truing a medieval tower bell or tuning a new casting fresh from the pit, every calculation, cut plan, and foundry record lives in one place. At the heart of the app is the Shave Studio, a real-time coupling simulator that models how removing metal from any of five internal zones — Crown, Shoulder, Waist, Soundbow, and Lip — shifts all five acoustic partials simultaneously. Set your depths in millimetres, watch Nominal, Quint, Tierce, Prime, and Hum move in real time, and know before you touch the lathe whether your plan will bring the bell into true. The live verdict tells you exactly how many cents of deviation remain and whether the bell is ready to sign off. When your cuts are planned, generate a Cut Plan in one tap: an ordered sequence of lathe passes, each specifying zone, depth, and the correct tool, ticked off pass by pass as you work. The Zone Pins screen lets you photograph the inside wall of the bell and place depth pins on each zone, feeding the pass order directly from the metal. When the last pass is complete, sign the docket and export a permanent tuning record — rendered as a facsimile foundry receipt with a full before-and-after partial table — straight to your photo library. Track every bell in a ring on the Peal Board, consult the illustrated Shelf for nine bell forms, ten bench tools, and six clapper types, and choose from four historic tuning standards from A=440 down to A=415. Foolent Derarn works entirely offline with no account and no sign-in required.