A number of stem or log attributes are recognised and/or measured during log-making (bucking of logs within a stem). One of these is a “spike knot”.
Spikes knots are the result of acutely angled branches. So in essence they are just a normal branch which has formed on a steep angle in terms of the stem. They can effect log and end-product value, and quality and in particular make material unsuitable for peeling or some sawn products. This is due to the increase in the knot area ratio (horizontal area of the knot when sliced as part of a piece of lumber or veneer) )that the knot will occupy in the final product.
Common Methods Throughout The Industry
There are a number of different methods in New Zealand for measuring “spike knots” in log products. This article aim to summarise a few of these to help produces of log specifications to understand why it is important to make note which method should be used.
Examples of specifications seen in the industry can be confusing to a log-maker, such as these noted below which have been extracted from company specifications across the country for a medium diameter structural sawlog grade:
- length of knot + branch entry point > 2.5 x knot width (grade constraint Spikes < D/6 to max 6cm)
- Spike knots must not exceed 2x knot width or 10cm (either condition)
- Max 10cm – measured hard knot lengthwise along the axis
- Max 10cm with a a max of 4 spike knots in any non-stop 6m of log length
- Spike knots not permitted
- Max 7cm – all knots measured hard knot lengthwise along the axis
- Length of hard knot <2x knot width to max 14cm
- Max 6cm (no real definition here ?)
- Measure as normal branch
- Length of hard knot >1.5 X knot width to max 10cm
- Top of knot to branch entry point < 16cm
So from this you can see where confusion arises. It is important that suppliers, logmakers, customers and log quality assuance staff are all aligned to the meaning of each of these types of descriptions given in log specifications.
The point at which a normal knot (branch) becomes a spike knot should be well defined in a company or customer log attribute defintion. A logmaker can then easily just look at all knots as normal, until this definition is reached. Once this definition is reached then a maximum tolerance value can be used to define spike knot size for each individual log grade.
It should be noted that some log grades measure all knots lengthwise and in this case spike knot defects can be ingored and all knots just treated as the same.
Step 1 – Differienate a Normal Knot from a Spike Knot
A spike knot is often referred to as an acutely angled branch, with an angle of 20 degrees or less. As branch angle is hard to measure once the branch as been trimmed flush with the stem. A more practical method is to measure the oval shape of the flushed trimmed branch (length vs width), as the steeper the angle the longer the length of the flush trimmed oval.
A common system as noted in the “FITEC Best Practice Guidelines for Manual Log Making and Processing” is measure the length of the hard knot parallel to the axis (C). This must be less than the “specified tolerance value” times the width of the hard knot (A).
Step 2 – Define A Spike Knot Constraint for an Individual Log Grade
Now that a spike knot is defined as being present a logmaker can then just apply the log grade specification for spike knots. This might be a max width, length of the knot, or just no spikes knots allowed.
There are 4 common ways to state the tolerance for spike knots within a individual log grade specification are:
1. Specified value to max hard knot width (A) eg. <2x, to max 6cm hard knot width (A)
2. Specified value to max hard knot length (C) eg. <2x, to max 14cm hard knot length (C)
3. Not Allowed
4. Treat as normal knot as all knots measured lengthwise.