Loss in Converting Logs into Sawn Timber.

Progress, Volume XIV, Issue 5, 1 January 1919, Page 410

Loss in Converting Logs into Sawn Timber.

By Joseph Butler, Managing Director Kauri Timber Company, Ltd. In order to ascertain whether a sawmiller conducts his business on efficient lines it is necessary to adopt some fairly accurate system of determining the loss entailed in converting logs into sawn timber. The object of this paper is to endeavour to get New Zealand sawmillers to standardise a system which, if inaugurated, would be of value to the trade by not only arriving at a fairly accurate system in each individual sawmillers’ case, but of having a value by way of comparison with other sawmillers’ returns, and by this means locate where a saving could be effected.

It would seem that the first thing to standardise would be the system of measurement, Unfortunately, custom dominates the different districts, but this could be overcome by measuring the logs in the customary way, and in such cases, where necessary, of making another measurement for the standardised way. In New Zealand, the Railways (for purposes of carrying) and the Northern millers (for purpose of contracting and buying) have adopted Hoppus' tables as the basis of measurement. Other districts adopt other methods, some the square of the quarter girth at the small end, some a square inscribed on the small end, some by the mill's output, &c. This differentiation destroys all chance of making universal comparisons.

'ln America they have generally adopted Boyle's scale, which closely approximates Hoppus', with the exception that it gives a slightly less measurement for smaller logs.

As Hoppus' is used by the Railways, and is also recognised by a large section of sawmillers who purchase logs, it would seem that this measurement would be the one most easily adopted.

Hoppus' measure is inaccurate so far as a log is concerned, but. accurate when applied to squared timber having equal sides. Any deviation from this shape produces an inaccuracy, and in the case of a perfectly round log it becomes the difference between 3.1416 Hoppus measure and 4 actual measure; therefore, on a perfectly round log Hoppus gives 100 ft. instead of 127.315 actual.

Owing to the non-symmetrical form of logs there in no way of accurately measuring their contents by a tape measure. The only reliable way would be measuring the displacement of water caused by the total submergence of the log, and this is not practicable.

The system of weighing in the logs, and weighing out the timber and the slabs separately, might be accurate enough and would give the loss by slabs and sawdust, which is quite a desirable return, but the cost of weighing machinery and weighing would swallow up the advantage of the

return. Apart from this, the different specific gravity of the different parts of the logs . would render the return more or less inaccurate. ; ' . \ Having determined that Hoppus is the recognised measurement for logs, there still remain a number of uncontrollable factors that destroy the accuracy of log measure. These are roughly: (1) size, (2) shape, (3) known and unknown defects, (4) size of timber required. (1) Starting with logs at 12ft. centre girth, an allowance of 1 per cent, on every foot less in girth to 6ft., and from below 6ft. an allowance of 2 per cent, should be allowed off Hoppus measure. For over 12ft. girth, logs should be taken at net measure. There is no mathematical precision in this.

If the quantity of sawdust and the quantity of timber can be ascertained, then the quantity of slabs is also obtainable, always assuming the logmeasure is accurate. Some time ago, in order to ascertain what would be a fair deduction for sawdust, the writer obtained the kerfs from nine different mills. These kerfs were on short pieces of wood sawn in a few inches and withdrawn. For the purpose of determining the width of the kerf a gauge was made by cutting longitudinally an ordinary draughtmam's scale of one-tenth of an inch, at a taper of one in ten. The graduations on the scale then read as .01, so that by. inserting the point of the gauge into the kerf as far as it would go the width could be read on the scale in lOOths:

Each inch inserted would read as .1. By this

(2) Shape.—A sectional' measurement of the many-shaped logs would make any calculation covering it too complex to be of use, therefore it will have to be assumed that shapes average themselves out. (3) Defects. —An allowance for defects involves an opinion, and opinions are of varying quantity. It will therefore have to be assumed that a fair adjustment takes place.. (4) Size of Timber Required.—This is a factor that in assessing loss in conversion has not been taken into consideration by millers, and although present market conditions absorb the contents of the log, still the mill cutting large sizes is at an advantage over the mill cutting small sizes so far as loss in sawing is concerned, and the miller who calculates timber produced under one inch in thickness as one inch also arrives at a result which varies in accordance with the proportion of timber under one inch produced. '

means a much more accurate measurement could be ascertained than by the ordinary method of laying a rule across the top and guessing to the nearest thirty-second of an inch. It was surprising to find the variation of width of kerf. Breakdown saws, including band-saws, varied from ,130 to .400 of an inch. Travelling bench saws, including band-saws, from .130 to .287 of an inch. Drag or breast bench saws from .160 to .225 of an inch. Gang saws showed the slight variation of .140 to .150 of an inch, due to all the saws being the same gauge, the variation being caused by more or hss set of the saw. Splitting saws, including band-saws, from .080 to .135 of an inch. Small drag saws from .130 to .270 of an inch. (To be continued.)