Different types of rulers and straightedges serve specific functions in instrument building. Below are the essential varieties used by luthiers:
Precision Steel Rulers
- Best for: General measuring tasks, layout work, and marking.
- Features:
- Typically made of stainless steel for durability and accuracy.
- Available in various lengths (6″, 12″, 24″, and 36″).
- Marked with both metric (millimeters) and imperial (inches) scales.
- Uses in Luthiery:
- Measuring body dimensions, scale length, and fretboard widths.
- Marking bridge locations and nut slot spacing.
- Ensuring consistent placement of sound holes and bracing.
Notched Straightedges
- Best for: Checking the straightness of fretboards and necks.
- Features:
- Notches correspond to the positions of the frets, allowing direct contact with the fingerboard surface.
- Available for different scale lengths (e.g., 24.75″, 25.5″, 34″ for bass).
- Uses in Luthiery:
- Checking the neck relief without the influence of frets.
- Identifying high or low spots in the fingerboard before fretting.
- Assisting in fretboard leveling preparation.
Full-Length Precision Straightedges
- Best for: Assessing the flatness of surfaces and components.
- Features:
- Typically made of anodized aluminum or stainless steel.
- Edge is precision-ground for a perfectly straight reference.
- Available in various lengths (e.g., 12″, 18″, 24″).
- Uses in Luthiery:
- Checking the flatness of the neck and fretboard.
- Aligning bridges and saddles.
- Ensuring a level work surface for gluing and assembly.
Fret Rocker
- Best for: Detecting uneven frets.
- Features:
- Small, flat-edged tool with three or four different-length edges.
- Typically made of stainless steel or aluminum.
- Uses in Luthiery:
- Placed across three frets at a time to detect rocking motion, which indicates an uneven fret.
- Helps identify high or low frets before leveling.
Centering Rulers (Double-Scale Rulers)
- Best for: Ensuring symmetrical layouts.
- Features:
- Markings radiate outward from the center, making it easy to find midpoints.
- Uses in Luthiery:
- Centering bridges, rosettes, and neck joints.
- Aligning headstock designs symmetrically.
Applications of Rulers & Straightedges in Luthiery
Measuring Scale Length & Bridge Placement
The scale length of an instrument (the vibrating length of the string) must be measured precisely. A steel ruler helps determine the exact bridge placement, ensuring proper intonation and playability.
Fretboard & Neck Leveling
- A notched straightedge allows luthiers to check the true flatness of the fretboard before fretting.
- A full-length straightedge ensures that the neck is level and properly adjusted before fretwork begins.
Checking and Leveling Frets
- A fret rocker helps detect uneven frets that can cause buzzing.
- A straightedge ensures that all frets are level before final dressing and polishing.
Aligning the Neck and Body
During assembly, rulers and straightedges help verify that the neck is properly aligned with the body and bridge. This is crucial to avoid issues with string action and intonation.
Bridge and Saddle Setup
A straightedge is used to verify saddle height and ensure that string action is correct across the fretboard. It also helps check for any unwanted neck angle issues.
Ensuring Symmetry in Design
A centering ruler aids in aligning headstock shapes, bracing layouts, and rosette placement for a balanced and professional appearance.
Choosing the Right Rulers & Straightedges for Luthiery
When selecting rulers and straightedges, consider the following factors:
- Material: Stainless steel or anodized aluminum is preferred for durability and accuracy. Avoid plastic rulers, as they can warp over time.
- Markings: Clear, etched markings (rather than printed) ensure longevity and precision.
- Flatness & Accuracy: High-quality straightedges should be machined to a high degree of flatness (typically within ±0.001″ over their length).
- Length: Choose different lengths for various tasks—longer rulers for body layouts, shorter rulers for nut and saddle work.
Maintenance & Best Practices
- Store straightedges properly: Hang them or store them flat to prevent bending.
- Keep them clean: Wipe down rulers and straightedges to remove dust, glue, or debris.
- Avoid dropping them: Even a small dent or bend can compromise accuracy.
- Verify accuracy periodically: Use a known flat surface (such as a precision granite slab) to check for warping.