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INCRA RulesFoolproof, innovative precision from INCRAText & Photos by Tom Hintz Precise layout is crucial to how a project turns out. The accuracy of woodworking machinery is of little consequence if the layout markings are not placed accurately. Regardless of how simple or complicated a design is, woodworkers need the most precise measuring and marking tools possible to do the job right. The INCRA tools reviewed in this story are part of a complete line of uniquely designed, super accurate measuring and layout tools that make woodworkers of all experience levels more accurate and consistent. The INCRA tools are also extremely durable, fast and easy to use. Initial ImpressionsThe INCRA line of marking tools is impressive in terms of materials and manufacturing. Everything about the INCRA marking and measuring is first rate. All of the edges, including those around the fine slots and holes are very clean and burr-free. That allows the tools to slide easily on the material being marked without snagging or marring the surface. It is obvious that INCRA takes pride in producing top quality tools with unequalled accuracy and insures that by refusing to fudge on the manufacturing budget. All of the INCRA marking and layout tools are manufactured in the U.S.A., not farmed out to overseas factories. Proprietary Manufacturing Processes
The blades on INCRA marking tools are made from stainless steel, a material that is very durable and does not corrode. At only 0.010"-thick, the blades are very flexible, making layouts on curved or even circular work pieces easy and very accurate. Sophisticated proprietary manufacturing processes developed by INCRA hold tolerances to a remarkable + /- 0.0005"! These remarkably tight tolerances are key to the INCRA design. Insuring that the slots and holes fit the mechanical pencil lead properly eliminates even small user-induced errors. These same processes allow INCRA to create multiple scales that are very easy to read thanks to their clarity and a special matte surface that enhances their visibility. What makes INCRA marking tools truly unique are the slots and holes at all graduations. The slots are sized to restrict a pencil lead so it can do nothing but produce a fine line precisely centered on the selected graduation. This eliminates the deviations even slightly dull or leaning pencils create along the edges of traditional measuring and marking devices. The slots and holes are designed to fit a standard 0.5mm mechanical pencil lead but a sharp common pencil will also fit. In fact, if your pencil is a little dull, insert the tip into a slot and spin it a few times to sharpen it to fit! The innovative design of the slots and holes insure computer accurate layout lines that are somewhere between difficult to impossible to equal with virtually any other layout tool or technique. Precision Guide Bars
Some of the INCRA marking tools are equipped with guide bars that allow the user to precisely register a line along or from the edge of a work piece. The guide bars are made from a special aluminum extrusion with a lip along one edge that indexes the blade exactly 90-degrees to its length. The removable guide bars are fastened to the blades with finger-tightened knobs. Being able to reposition or remove the guide bars allows using the blades for tasks such as setting router bit heights or interior flat work. Marking Rule
Both long edges have holes every 1/32". Straddling the long centerline of the rule are a pair of slotted scales, one spaced at 1/16" and the other at 1/32". The "0" end of the rules have half slots cut in them that insures the base line is also dead on rather than spaced a pencil lead width out as is the case when using a normal rule. The flexibility of the INCRA rules means they can be easily used on curved or even circular stock. Because sets of scale holes are perfectly aligned along the length of the rules, they can be used as a compass. Using the INCRA rules in this mode is extremely fast, dead-on accurate and far easier than trying to adjust and use a normal compass. T-Rules
Once you use an INCRA T-Rule, traditional sliding-blade squares will be a thing of the past. The INCRA T-Rule have all the same features as the marking rules but have an indexing guide bar affixed to one end that keeps the rule perfectly square to the edge of the work piece. The INCRA T-Rule have one non-perforated edge with 1/64" graduations that can be used as a plain square. The other long edge has holes at all 1/32" graduations. Along the center are two lines of slots, one graduated at 1/16", the other at 1/32". There is also a 1/64" scale consisting of four rows of holes arranged at an angle because there would be no separation between them in a single line. The array of marking holes and slots eliminates adjusting the length of the blade as with a combination square. Simply insert the pencil in the appropriate hole and draw a line precisely where you want it. This also means multiple lines from the same edge are drawn far quicker with absolute accuracy because it does not have to be re-set. Just move the pencil to the scale hole at the next dimension wanted and draw the line. The end of the INCRA T-Rule has a non-perforated 1/32" scale. Bend Rules
The INCRA Bend Rules solve two of the more frustrating marking problems in woodworking. Drawing marks on or near the edge of a board and transferring a line around the edge. Both are difficult to do accurately with traditional marking tools. The INCRA Bend Rule has a 90-degree fold along its length with slots at all 1/16" graduations that also wrap around the bend. This makes wrapping a line around an edge very easy and dead-on accurate because nothing has to be moved or re-set. The INCRA Bend Rules have holes along both edges at all 1/32" graduations. To accommodate varying stock widths, the bend is actually slightly off center, yielding a 7/8" and ¾"-wide surface. With two surfaces against the wood, the INCRA Bend Rule is very easy to hold in place with no slipping or rocking. The "0" end features half-slots cut into the edge for precise base markings. The right edge has holes at 1/32" graduations that can be used to draw lines along the length of the edge by simply sliding the rule along it. Laying out hinge mortises has never been easier or more accurate. The triangular shape of the INCRA Bend Rule is great for measuring drawings. Just lay the INCRA Bend Rule in position and the markings are at the drawing surface, eliminating parallax. INCRA Bend Rules are available in 6", 12" and 18" lengths in both standard and metric versions. Protractor Rule
At 6 ½"-long and 3 7/8"-tall, the INCRA Protractor Rule fits nearly any job very well. It has a 7"-long guide bar that keeps it square to the work piece. A full 180-degree range is featured with long slots every 5-degrees, short slots every 1-degree and holes every ½-degree. Slots and holes are also provided at 22.5 and 67.5-degrees to either side of zero. Horizontal and vertical "sight windows" at the center make aligning it with markings on a board without the guide bar fast and very accurate. The holes and slots in the angle scales all key off a center hole located at the inboard edge of the indexing bar which places it precisely at the edge of the wood. The center hole also aligns with the sight windows. A 6 ½"-long centering scale with holes every 1/32" runs along the bottom edge. This bottom scale can also be used as a super accurate compass by placing a fine awl in the "0" hole and the pencil in any of the 1/32" graduations to draw circles faster and more accurately than ever. In addition to marking extremely accurate angles, the array of slots and holes make it simple to identify an existing angle. Centering Rule
The INCRA Centering Rule has 1/32" scales along the top and bottom edges with holes at each graduation. Both ends have half holes for making accurate marks there. Both scales start at "0" at the center and work out to the ends making it simple to find the center of a work piece. Just align the same number at each edge of the wood and the "0" mark is exactly centered. The fine 1/32" graduations make this a very accurate and fast process. The top and bottom scales can also be used as a compass by inserting a sharp awl in the "0" hole and the pencil at the desired graduation. At the center of the INCRA Centering Rule is a 180-degree protractor feature with slots every 5-degrees. A horizontal and vertical "sight window" at the center of the angle slots makes aligning that feature with an existing mark simple and accurate. In The ShopUsing the INCRA marking rules couldn't be easier. In fact, when I started using them for this review I had one of those, "Why didn't somebody think of this sooner" moments. Once you see how the INCRA rules work, the concept is deceptively simple. However, manufacturing these features to the necessary tolerances is obviously no small task.
The key to the INCRA rules is the sizing and location of the slots and holes. The fit between the rule and pencil lead means layout lines are drawn properly or not at all. Because the slots and holes are precisely centered on the graduation, the line drawn through them is also exactly centered on that graduation, not next to it like with traditional marking tools. This eliminates a common and consistent error of more common marking tools that can grow quickly if the pencil is not very sharp. The slots and holes make it all but impossible to draw a crooked or misplaced line. Holding the pencil in the slot or hole also prevents deflections caused by the point catching the grain of the wood. Using the Centering or Marking Rule as a compass is remarkably simple and precise. Keep in mind that by inserting the pivot point at one end, extremely accurate circles with a diameter double the rule length are easy to draw. The precision of the holes makes drawing circles far more accurate than trying to set a compass to a scale and then spinning the line on the work piece. The flexibility of the INCRA rules is very handy when working with curved or round objects but also makes holding them securely on any irregular surface just as easy. The result is layout lines are far more accurate in virtually every situation. ConclusionsIn the INCRA promotional video, the narrator says that their rule design is the first major improvement to rules since measuring began. While that is certainly a lofty claim, I have to agree. The design of the INCRA Rules is ingenious and works as advertised in all situations I have been able to create. The ease of use with the INCRA rules is remarkable in itself. It is not often that a tool design can improve your woodworking, save time and simplify a task all at the same time. The INCRA Rules are also virtually foolproof to use. The only way to make a mistake is to insert the pencil in the wrong hole or slot. The clarity of the markings, made easier to see by the matte finish means this kind of mistake is all on you, not the rule! Adding a set of INCRA Rules to your shop is an investment that will pay dividends with every project. Do you have a comment about this page? - Email Me!
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