Arch Template Generator | Nicholas Fury Batson

This tool runs entirely in your browser with JavaScript. Please enable JavaScript to use it, or grab the original Python generators from the source repository.

Units

Cylinder

Outside diameter (optional)

What it is: the outside diameter of the round form, across the full circle. Optional, used only for the end-view diagram and to estimate wall thickness. How to measure: across the outside at its widest point, through the center, or divide the outside circumference by pi.

Inside diameter

What it is: the inside diameter of the opening, across the full circle. This is the main input, it sets the size of the arch template. How to measure: across the opening at its widest point, through the center.

Segment width (informational)

What it is: the width of the board or segment the trim will cover. Informational only, it does not change the template; it just helps you sanity-check the build. How to measure: the face width of a single board.

Inward overhang (trim past the ID)

What it is: how far the trim extends inward past the opening, toward the center. Larger values leave a bigger lip over the edge. Typical value: about 0.25 inch, or 0 for trim flush with the opening.

Trim widths

Widths

What it is: the radial width of the trim band, from its inner edge to its outer edge. Add several to compare options; each gets its own printable template. The selected radio marks which width the diagrams and cut planning focus on. How to measure: the width of the trim stock you will cut the arch from.

The selected width is the one shown in the diagrams and cut planning.

Canopy (optional, end-view diagram only)

Canopy end-to-end

What it is: the full end-to-end width of an outer cover or canopy that sits over the opening. Optional, used only by the end-view diagram to check clearance. How to measure: across the cover at its full span.

Center to canopy underside

What it is: the vertical distance from the center of the circle up to the underside (inner face) of the outer cover. Positions the cover in the end-view diagram. How to measure: from the centerline up to the inner top surface.

Center to canopy top

What it is: the vertical distance from the center of the circle up to the top (outer face) of the outer cover. How to measure: from the centerline up to the outermost top surface.

Cut planning (optional, cut from boards)

Board width

What it is: the usable width of the boards you will cut segments from. This caps how large each arch segment can be. How to measure: the actual width of your stock (a nominal 1x12 is about 11.25 inches).

Board length (for board count)

What it is: the length of each board, used to estimate how many boards you need. How to measure: the length of the stock you plan to buy (for example 96 inches for an 8-foot board).

Strength vs. joints

What it is: the trade-off between fewer joints (larger, weaker segments with more short grain at the tips) and more joints (smaller, stronger segments). Balanced is a good default.

Download PDFs

Paper

Print Letter size at 100% scale (not “fit to page”). On every sheet, verify the 1″ calibration box with a ruler before tracing.

How it works

1. Enter your measurements

Type decimals (82.375) or fractions (82-3/8). The preview and computed geometry update live as you type.

2. Download & print

The trim template tiles a full-scale half-ring across Letter pages. The end-view diagram is a 2-page reference drawing. Everything is generated locally, nothing leaves your device.

3. Assemble & trace

Trim each sheet on the dashed border, tape them together using the red registration crosshairs, lay the template on your stock, and trace the cut lines.

The geometry began as a pair of Python generators; this page is a faithful client-side port. Source on GitHub.