Before we discuss conversion methods further, stability needs to be considered. It
will come as no surprise that timber is a commodity that changes shape and size quite
appreciably, due mainly to the changes in moisture content. Most changes will have
occurred in the drying processes carried out by the timber processor but will still
continue, though by smaller amounts, once it arrives in the workshop. Changes will
also continue into its final location, especially if destined for our modern centrally
heated homes. Release of in built tensions when cutting, or planing, to a smaller
size can also be a problem.
Movement can occur:- 1. Along the length of the board (up and down the trunk). 2.
Between the annual rings. and 3. Along the annual rings (around the trunk). When
the timber is acquired from the merchant, that is after the initial drying out has
taken place, changes in length will be very small and can be ignored. Whilst condition
two will result in some change it is very much less that that due to condition three.
SK. 1 shows three typical end grain formations. The board shown in "A" will change
just a little in width due to the very small changes between growth rings and whilst
there will be a potentially greater change along the growth rings the amount will
be very small due to it being relatively thin. Board "C" on the other hand will change
appreciably in width and very little in thickness. Therefore, for stability, and
other reasons as will be explained, boards as in "A" are preferred, but are much
more expensive due to more work being involved in the conversion.
Also in the case of board "C" the board will be prone to "cup" due to the difference
in growth line lengths and can also "twist" and "bow" along the length.
After cutting, boards will be air and often kiln dried also. Do though ensure you
purchase kiln dried timber. Air drying is a slow process with 1 year per 1" thickness
being a quoted time and even then having a much higher moisture content than kiln
Conversion methods (continued)
There are two methods (with variations) of cutting the felled log "quarter sawn"
(SK. 2) and "through and through" (SK. 3). Whilst there are advantages of stability
with "quarter sawn" boards that conform to SK. 1a, it can be seen that there is an
appreciable amount of scrap. This, together with what is a more complex operation,
makes the boards more expensive, as a result, "quarter sawn" boards are not so readily
The method shown in SK. 3 is known as "through and through" being a relatively simple
operation with wastage minimal. It will produce boards of types "a" "b" and "c" though
only the centre board or two will truly conform to a "quarter sawn" board. The converter,
may chose to leave this in with the rest in which case you may find a board or two
like this available.