Boxwood was a popular choice of material for rulers since the 18th century, the fine grain of the wood preventing splintering and allowing a smooth finish. Today we are looking at an example of a 1918 dated engineer’s ruler:
This ruler has a number of scales on it and is marked with the /|\ mark indicating government ownership and a date of 1918:
One end of the ruler indicates that this is an ‘engine divided’ scale:
Whilst the other has the ruler number ‘5A’. The ruler would have been part of a set of different scaled rulers, each with their own numerical designation:
Making a ruler was an involved process, as outlined in this description from Howley Tools:
Stages in the manufacturing process
Preparing the slats or sticks
Boxwood logs were first cut into short lengths of ten or seven inches and quartered, then cut down further into slats using a fine saw to give a smooth cut and minimise waste. These slats were then dried to reduce the moisture content of the wood to around 9%.
The surface of the assembled rule was then smoothed to make it flat on both faces ready for the lines to be marked on. This was achieved using a file by men known as ‘filers-up’, and sometimes using specialist rule maker’s planes. The edges of the rules were also straightened at this stage in the same way or bevelled or sloping/shaped edges added. In the 1900s this was done using a cutting machine.
Finishing – Dividing or Marking
Before they were marked the assembled rules were rubbed with Shellac (a type of varnish). This was used so that the marking process would not raise the grain of the wood and the blacking used to fill the markings did not stain the rest of the rule. The rule was then divided – i.e. the line of measurement (or other line/scale) was marked onto it. It was placed in a jig known as a dividing board, next to a pattern or ‘master’ for the particular rule being made. The dividing lines were then drawn into the boxwood using a square and scribing knife. The worker lined up the square against
the pattern by eye and drew in each division. A skilled worker could mark a 2ft, 4-fold rule in a couple of minutes with this equipment.
Next the gauge line – the horizontal line running just above one or both edges of a rule was scribed or drawn in using a type of woodworkers marking gauge. This line acted as a guide for the user to show the 1/8” and 1/4” marks. These lines were later put on by a gauge machine, with two cutting knives and a moving carriage.
Finally, figures (numbers), tables and any lettering were marked onto the rule using a mark punch and hammer along with the maker’s and/or retailer’s name. Each number would be marked in turn, i.e. all the 1’s on all the rule, then all the 2’s and so on.
The marker used the same hammer (often made in the same works) with all the different punches, and from experience knew how much pressure to apply to ensure that every figure was exactly the same depth on the finished rule. Later belt-driven punching machines were used for all but special rules. These had cradles which held the stamps /mark punches and punched the figures for an eighteen -inch length in one operation.
The finishing room was often called the Rushing Shop. Here the rules were first wiped with Shellac and all the lines and numerals were then filled with blacking which was rubbed on with a rag, piece of cloth. The blacking was usually a mixture of charcoal dust, whitening (powdered chalk/calcium carbonate), tallow and oil (linseed or other). The excess blacking was cleaned off originally with rushes (hence the name of the Shop) and later by rubbing the rule in a box of sawdust. No particular drying time was needed for the blacking. The rules were finally hand polished. Different manufacturers at different time periods varied the finishing process, varnishing, polishing, and rushing a different number of times before and after blacking and changed the recipe for the blacking and varnish.
‘Engine divided’ would that denote the markings were put on by machine and advertised as such implying a more accurate measurement than by hand ?
Or is that a particular type of scale for a particular usage ?
I remember using triangular cross-sectioned plastic drafting rulers for six possible scales on each.
It might be easier to just click a tab on the screen today but it’s hard holding the monitor still enough to scribe lines on the piece you’re working on when making a scale model 😉