Recent Blogs
Spring Cyclograph: Adjustable Drawing Rule, Animation and Polar-Curve Calculator
See how a spring cyclograph forms a curved drawing edge with end clamps and a center screw. Explore a separate exponential-spiral calculator.
Spherometer Mechanism Explained: How It Works, Parts, Diagram, Formula and Uses
A spherometer measures the radius of curvature of lenses, mirrors, and curved surfaces. Used by opticians and machinists for sub-micron accuracy.
Self-registering Barometer Mechanism Explained: How a Barograph Records Atmospheric Pressure
How a self-registering barometer works, with formulas, a worked meteorological example, and tradeoffs vs aneroid and digital pressure loggers.
Section Liner Mechanism: How the Pawl-and-Rack Indexing Works, Parts, Uses, and Hatching Formula
Section Liner explained — how draughtsmen use this drawing tool to hatch parallel section lines fast and consistently in mechanical and architectural drafting work.
Roller Parallel Ruler Mechanism Explained: How It Works, Parts, Diagram and Marine Navigation Uses
How a Roller Parallel Ruler works, the geometry behind its tracking accuracy, and why marine navigators still use it on paper charts today.
Reflecting Drawing Board Mechanism: How It Works, Optical Diagram, Parts and Uses Explained
Explore a reflecting drawing board with a flat mirror at 45 degrees. Calculate virtual image size and alignment with the paper from three dimensions.
Omni-Telemeter and Odontograph: Two Hiscox Devices
Explore Hiscox's optical omni-telemeter and separate odontograph. Compare gear pitch-circle radii from tooth counts and diametral pitch.
Great-Curve Delineator: Arc Radius and Rise Calculator | FIRGELLI
Explore a constant-angle circular arc. Calculate radius, sagitta, rail angle and apex-rise change from chord length and half central angle.
Trammel for Drawing Ellipses: Semi-axes and Slider Span
Explore two sliders in perpendicular tracks. Convert ellipse diameters into semi-axes and ideal slider spans, with hardware clearance and fabrication tolerances excluded.
Tracing Bar: Guides, Pivots and Entered-value Comparisons
Explore how guides and pivots constrain a tracing bar. Add entered offsets, scale a length and convert units; the calculator does not solve the traced...
Parabola Scriber: Exact Taut-String Station Geometry
Explore a taut-string parabola scriber. Calculate curve depth and equal focus/directrix distances at a selected station within the entered aperture.
Lazy-tongs Pantograph Mechanism: How It Works, Parts, Scale Formula & Engraving Uses Explained
How a lazy-tongs pantograph copies and scales drawings using crossed extensible links. Used in drafting, sign-making, and engraving since the 1600s.
Geared Ellipsograph: Cardan-Circle Geometry Calculator | FIRGELLI
Explore an ideal 2:1 rolling-circle ellipsograph. Adjust ring pitch diameter and pen offset to calculate ellipse semi-axes, area and eccentricity.
Ellipsograph Turntable Mechanism: How It Works, Parts, Formula and Diagram Explained
Explore an extended-arm ellipsograph and compare guide clearance with load-scaled measured deflection. The ideal ellipse is separate from the fit comparison.
Eidograph Mechanism Explained: Parallel-Bar Drawing Copier, How It Works, Parts, Formula, Diagram
See how an eidograph’s equal pulleys, parallel arms and matched fulcrum position produce a scaled drawing. Compare copy length and area ratios.
Cyclograph: Three-Rule Circular Arc Mechanism and Coordinate Calculator
See a three-rule cyclograph draw a circular arc using two fixed guide pins. Calculate radius, arc length and pencil coordinates from chord spacing and rise.
Conchoid Delineator Mechanism: How It Works, Parts, Diagram, and Uses in Drafting
Explore a conchoid drawing instrument. Adjust the rail distance, stylus offset and arm angle to calculate coordinates on either curve branch.
Three-part Parallel Ruler: Arm-length Mismatch Comparison
Explore the equal-arm parallel-ruler arrangement and compare three entered length mismatches. Percentages are dimensional comparisons, not angular-error predictions.