Measure for measure: notions of accuracy

Detail of Woodpeckers Posi-Lock T-Square

Words and photos: Raf Nathan 

What is accurate? Often we use our tools and machines and assume they are accurate and set correctly. You assume your ruler is correct and that your tape measure reads the same measurements as your ruler, which is usually not the case. If you use the same ruler right through a job then the measurements will be consistent throughout. If you are passing measurements to other makers for cutting lists or parts, or buying cutters of a certain diameter, you need rulers that have standardised measurements, so it’s essential to get quality tools.

Systems of measurement have developed from as far back as the Egyptian cubit, a unit based on relative lengths of the human forearm and digits. The Romans took it a step further, adding units based on the foot and the ‘stride’. In the middle ages, Edward II defined an inch as three barleycorns and added standards for feet, perches and acres. In the 1800s the French Academy of Sciences developed standards based on the size of the Earth. The ‘metre’ was one ten-millionth of the length of the meridian arc from the equator to the north pole, passing of course through Paris. The current international standard for the metric system is the International System of Units (or SI). This now defines a metre as 1⁄299792458 of the distance light travels in a second.

From right to left: the unbranded special and Torquata equivalents, along with the original Woodpeckers tool.

Translating those systems into tools is not straightforward, however. Making accurate rulers and tapes is not easy. Compare your rulers and tapes because there can often be a variance of up to 0.5mm or more over a 300mm span. The secret in making a ruler is to have the zero point and the one millimetre mark perfect. This will depend on the operator of the router, laser or etching equipment aligning everything perfectly.

For quite a few years under the name Interwood I designed and had made some wood measuring tools. My summation of that time is that it is extremely difficult to get measuring tools made. Farming out the making sounds simple, but you have to seek out fine toolmakers able to work to strict tolerances, so that 0mm is always 0mm.

The Woodpeckers ruler is consistent with my reference Starrett ruler.

In that time, I had a large batch of my Super-Squares made by Woodpeckers in Ohio, America. They are masters of making woodwork measuring tools and have been for 35 years. The company has a really strong perfectionist trait, ideal for making rulers. Their secret is to have all the toolmaking in-house. The routing, engraving and assembly is all under the one roof, so they have total control over the whole making process.

Woodpeckers tools are not cheap and they mainly supply to their huge North American market, hence metric tools are not a large part of their range. They make rulers, T-square, bevels, squares, drilling guides and tables, router lifts and even clamps. They also run one-time tools in a limited batch and then discontinue the line.

They say imitation is high flattery and so it is with copies of their tools. As better lasers and CNC routers have emerged there are quite a few Chinese and Taiwanese toolmakers producing what I call copies of the Woodpeckers tools. I found a few look-alikes of their Posi-Lock T-Squares for sale on the internet and bought an unbranded tool for $16.48. In comparison, the Woodpeckers tool is a one-timer and when available sold for $245. I also trialed a similar Torquata tool at $60, engraved with the identical model number to the original.

There is a large groove machined in the middle with small holes at 1mm increments for placing a fine pencil.

Posi-lock T-squares

The original Woodpeckers tool has a 15mm thick solid aluminium head routed to accept the laser cut stainless steel ruler. This version has a 24" long ruler, more than enough for most workshop operations. The angle is changed by loosening a knob and clicking the protractor across into pre- set angles 20–90°.

The ruler has laser-cut indents at inch and 1/8" increments to position a pencil or scribe to mark parallel distances from an edge. The Woodpeckers angle setting is very crisp. The protractor head has precision drilled holes at set angles that click onto a spring loaded pin. A knurled knob locks the angle. The Torquata uses a similar system. It has a 9mm thick aluminium head again machined out to house the beam. On this, the ruler is 2mm aluminium and 300mm long. It is well made.

The unbranded tool has a thin plastic body with a stainless steel ruler and like the others clicks into angle pre-sets. It’s not very good and I can’t recommend it.

I thought it a little bit academic as to whether these squares would read correctly over the distance of the ruler given that the ruler/protractor moves. I checked them for 90° and 45° as best I could with my reference squares. The Woodpeckers and the Torquata squares were quite accurate so at around $60, the Torquata is a good buy.

The Woodpeckers original alongside the $38 Hanghaijia internet special.

T-Squares

Woodpeckers have a range of T-squares and these have been very well copied. Their main models are in imperial for their home market with only a 600mm metric version available, hence the attraction of copies. I noticed various different copies available varying in price from $38–200. The Woodpeckers is $253 and is a large and impressive tool. The head is machined from 12.75mm thick aluminium with a 6.25mm thick and 57mm wide ruler. The ruler is beautifully machined to sit in the head and locks in place with six allen screws.

The ruler is angled on the edges to improve marking measurements and there is a deep groove in the middle
of the ruler with machined holes to position a fine pencil and use it to scribe a parallel line. These holes are at 1mm increments with 5mm holes set for the 32mm cabinetmaking system.

The Hanghaijia tool I bought was $38 with a 300mm ruler sitting in a 14.8mm thick machined head. The ruler is a hefty 8.5mm thick and locks down with four allen screws and is very well made.