Timber splices join two member segments using geometry and connections selected for a particular structural and conservation context. This calculator draws an illustrative splayed scarf and reports dimensions only; it does not assess fit, capacity or repair suitability.
Timber Splicing Interactive Calculator
Set a bolt diameter, displayed hole oversize, member depth, illustrative splice-length factor and slope ratio. Results are drawing dimensions only.
Equation Used
- Dimensions are nominal and shown in one two-dimensional section.
- Hole diameter equals entered bolt diameter plus entered diametral oversize.
- Illustrative splice length is the entered factor times member depth.
- The splayed face is represented by a straight right-triangle hypotenuse.
- Loads, species, grade, moisture movement, defects, net section, fastener capacity, bearing, splitting, bending, shear, stability, connections and code compliance are omitted.
Timber-splice Drawing Geometry
Historic-building guidance notes that repair joints must suit how the structural member works and that several scarf forms are used. New Forest National Park guidance describes repair scarfs at about three times member depth while emphasizing preservation of sound historic fabric.
The diagram is an illustrative splayed scarf with a separately displayed bolt and hole. It is not a standard connection detail.
What This Calculator Does
The tool adds selected diametral oversize to bolt diameter, multiplies member depth by a user-entered splice-length factor, and resolves a displayed 1:n slope into run and face length.
It does not decide which splice belongs in a beam, post, plate, sill, roof or conservation repair.
Displayed Dimensions
illustrative splice length = k h
slope run = n h
displayed face length = sqrt(h squared + run squared)
The 1:n relation is a drawing slope only. No force path or capacity is inferred.
Worked Display Example
For a 19 mm bolt, 1.2 mm displayed oversize, 300 mm member depth, length factor 3 and slope 1:6, the hole diameter is 20.2 mm, illustrative splice length is 900 mm, slope run is 1800 mm and displayed face length is about 1824.8 mm.
Assumptions and Limits
- Standards context: the cited NDS provision specifies bolt holes 1/32 to 1/16 inch larger than bolt diameter and requires alignment, washers and other installation provisions.
- Calculated: nominal display dimensions only.
- Not calculated: joint type selection, fit acceptance, moisture compatibility, loads, species, grade, defects, bearing, fastener yield modes, net section, splitting, bending, shear, tension, compression, stability, creep, durability, fire, repair sequence, inspection or code compliance.
Frequently Asked Questions
Is 1.5 mm a universal hole-clearance rule?
No. The cited NDS bolt provision gives a range and other jurisdictions, fasteners and specifications may differ.
Is three times depth always the correct scarf length?
No. Three times depth is an editable illustration drawn from the cited conservation guidance. A suitable repair detail depends on the member, loads, condition and project requirements.
Does a longer slope guarantee more capacity?
No capacity relation is modeled.
Does the calculator assess face gaps or moisture?
No.
Does it choose a repair joint?
No.
Can it approve structural work?
No.
References
- American Wood Council, 2018 NDS Chapter 12, section 12.1.3: bolt-hole and installation provisions, including 1/32 to 1/16 inch diametral oversize.
- New Forest National Park Authority, Timber Frames and Roofs: conservation context, scarf-joint forms and approximate repair-scarf length guidance.
- USDA Forest Products Laboratory, Wood Handbook, Chapter 8: wood-fastening behavior and connection-design context.
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