Part two of part four of the Introduction to Square Rule joinery series
Bringing the concept to the timber
Timbers have needs too!!
Once the reference planes are identified it should be fairly simple to identify them on the timber right? You can just pick any face to be the top reference face right? Well No. Picking the correct surface will make laying out joinery simpler, will make the frame stronger, and ensure that the final frame dimensions match the drawing.
The essential concept here is to properly match the timber’s natural characteristics (both strength and aesthetic traits) to the requirements previously identified. Timbers, all wood really, have natural strength characteristics that are derived from their growing conditions and how the timber was sawn out of the log.
“Reading” the timber; identifying the character and nature of the timber, is an art that takes years of practice, but there are some obvious, and important, characteristics that can observed from the start. For instance many conventional carpenters know the maxim of orienting rafters and joists with “crown up” and the same holds true for timber framing. Crown, bow and twist are all characteristics that are easily identified and should be identified before choosing reference faces. These are just a few characteristics that are observed during a full timber shake out that will be featured in a future post. .
Tying back to the structural requirements discussed in the previous part, we want joists to with their crown up to resist the floor load and so the crown-up surface of the timber becomes its primary reference face. If the joist in question is installed next to a stairwell then there will be another reference plane to consider. Otherwise choosing the secondary reference face will rely on conventions. Similarly when choosing reference faces for a beam in a floor system, we would want to orient the crown up face to be our primary reference face because it supports the joists and the secondary reference face to orient towards any reference planes or conventions identified previously (e.g. exterior walls, interior partitions,etc.).
Some timber structural characteristics to consider
- Location of Knots
- Size of Knots
- Direction of Grain
Considering Seasoning and Noticing Sawing
Another major aspect of the art of timber framing is understanding the effects seasoning has on the future shape of the timber. Where it checks, and how it might move as it dries also plays a role in choosing reference faces. Consider the “rule of thumb” that timbers check to the heart. The closer the heart is to a surface the more it will check on that surface. Knowing this you may choose to place a timber with a heart close to one corner in a corner post location; the sheathing will help minimize the check and checking with not be as visible from the interior. Likewise a timber with a perfectly centered heart is ideally located in a central/unsheathed portion of the frame.
Related to seasoning is sawing. Often the first cut with a band mill is little more “wavy” while the opposing face is perfectly flat. This perfectly flat face would ideally be one of your reference face. Likewise it is not uncommon for two face to be more “square” than the opposing so choosing the “squarer” of the faces will more easily match the perfect timber we hope to work with.
Some sawing characteristics to consider
- Location of heart
- Sawing “dips and humps”
The effects of seasoning and techniques of dealing with them are something that will be explored in greater depth in future posts. The main point is that seasoning and sawing effects will influence which faces are chosen as reference faces. Some minor sawing and seasoning effects can be remedied by re-sawing or “truing” the timber with a beam planer, but severe timber effects such as twist, splits, rot and major crown/bowing likely means culling the timber.
The aesthetic requirements are by far the most arbitrary of the characteristics and due to preceding requirements/considerations may not factor in at all. This selection process falls into the category of “All things being equal” and mostly relies on personal taste; typically the end user. So if the end user prefers knots and no structural requirement dictates that the knots be located one way or the other than by all means choose a reference face to display the natural characteristics in all their glory. Similarly, when a small chunk of wood was dented or removed through handling, you choose to hide it or show it off for a more distressed look and feel.
Some Aesthetic things to consider
- Sawing or handling damage
“…in square rule joinery, the timbers don’t have to be “perfect” the joinery does..”
There is a lot to consider and the first time choosing reference faces it might be overwhelming. The good news is that there are priorities involved and brings us back to the articles first subheading “Focus on what matters and let the rest go”. If one face is out of square don’t choose it as reference face, its un-squareness will be dealt with when the joinery is cut. The lists below are meant as a guide of what to consider first and what to consider last. Through this process some of later steps may be eliminate or irrelevant; e.g. structural integrity is more important than aesthetics.
Reference Planes Prioritized List
- Load bearing surfaces
- Outer Surfaces
- Designated Planes
- Primary Building Components/Openings
- Secondary Building components
Reference Face Hierarchy
- Crown up
- Bow out
- Heart up
- Heart out
- Squarest Faces
- Defects/sawing errors
- Aesthetics choices
Of course the idea only “focus(ing) on what matters” is an oversimplification of the process but most of the time it steers the decision making process forward in a productive way. For instance you will find that crown up usually coincides with the surface closest to the heart which is preferable to have on the upper face to minimize the amount of checking visible. When conflicting problems present themselves like when crown up is the most out-of-square face then there are techniques to address the problem(advanced techniques for dealing these issues will be covered in later posts). The key take away is that we want to best match a timber’s natural characteristics with the role it fulfill within the frame. Remember in square rule joinery, the timbers don’t have to be “perfect” the joinery does.
Now that the reference planes have been identified and we know which faces correspond to which plane we need to begin labeling the timber.