Regardless of the material you work with, INCRA Rules will make you more accurate and that translates in to better, faster jobs. Click image to enlarge

INCRA Rules

When only exact is “close enough”

Text, photos and video by Tom Hintz

Posted – 9-24-2012

No matter what you are building, creating a precise layout is the only way the project can turn out straight and square. Every time you settle for “close enough” even small errors begin to accumulate and by the time you finish the total error can be disturbing in its scale. I have been using INCRA Rules for years on the woodworking side as well as in my metalworking. In that time I have found that they have a very real impact on virtually any project that requires measuring which of course is everything this side of making a mud pie.

The Basics

INCRA Rules are available in a wide range of configurations that should cover any job you have. These high-tech measuring tools feature stainless steel blades that are tough and resistant to a bunch of the things we often have in a metal shop. The real secret (parts of which are very well kept) is the way INCRA marks the scales. 

The sophisticated process used by INCRA results in extreme accuracy, including these perforations down to 100th of an inch! Click image to enlarge

With traditional measuring instruments you simply align a pencil or scribe with number or line on that device to make a mark. If you need a long line you may try to maintain the alignment with that line or number as you slide the instrument along an edge on the workpiece. INCRA Rules do have numbers and lines but they also incorporate very precise, 5mm holes or slots that capture and guide the pencil or scribe with a sharp point. That point size may sound familiar because it is common to many mechanical pencils, scribes and even regular pencils sharpened to a fine point. Even when making a single dimple or dot-type marking, the holes in the INCRA Rules insure that you are in the exact spot for that dimension. Eliminating the wander that inevitably develops when trying to follow the edge of a common square or rule can have dramatic impacts on the accuracy of your work and the final product.

I have found the accuracy and consistency of the INCRA Rules to be a huge help when doing things like clamping up pieces for welding. Having such precise layout lines all but insures perfect alignment of the pieces after welding or after drilling and bolting it in place. That assumes that you actually set the piece in the layout lines you made so accurately.

Sophisticated Accuracy

With all of this accuracy hinging on the numbers, holes and slots getting them in exactly the right place on the instrument is crucial. To do that INCRA uses a Photochemical Etching manufacturing process that uses glass phototools along with a chemical etching spray bath to create both the perforations and numerals and lines. Along the way INCRA developed proprietary manufacturing control techniques that make their remarkable accuracy possible. The result is dead-on accurate measuring tools that are as easy to read as they are to use.

Configurations

INCRA Rules are available in a wide range of configurations and sizes. Regardless of the job at hand you should be able to find an INCRA Rule that fits your needs. The models shown in this review represent some of the more common but follow the link at the end of this review to see all of the variations of the INCRA Rules that are offered.

The T-Rules (left) have an edge guide that allows making perfectly straight, dead-on layout marks. the Bend Rule (right) has slots that run around the 90-degree corner to perfect alignment on both faces. Click images to enlarge

One of my favorite INCRA Rules is the T-Rules (T-square) because of their versatility in the shop. This is an especially handy tool when layout lines parallel to a straight edge are needed. I don’t think that there is a more accurate or easier way to make those lines than with an INCRA T-Rule. The T-Rules are available in 6”, 12” & 18” lengths with fractional markings. They are also available in 150mm and 300mm metric versions. INCRA also offers a “Tiny Rule” that is only 3”-long and two Professional T-Rules with even more sophisticated resolutions in 6” and 12” lengths.

The Bend Rule has been a lifesaver for me more than once. This is essentially a plain (OK, plain for INCRA) straight rule that has been precisely bent 90-degrees on the long centerline. If you have ever tried to draw very precise layout marks around a square corner you know how easy it is to be pretty close and how hard it is to be dead on. The INCRA Bend Rule has a set of their ultra-precise slots that run around the 90-degree corner. If you can’t draw an exact layout line around the corner with an INCRA Bend Rule you just are not paying attention. The Bend Rules are available in 6”, 12” and 18” standard versions and 150mm and 300mm metric models.

INCRA Rules are also available in a 12”-long Centering model. The Centering Rule is also available in a 300mm version. This rule stars with 0 in the center and their normal ultra-precise markings and perforations working outward in 1/32” graduations. The Centering Rule also has a protractor set of grooves at the center point in 5-degree intervals. I have found the Centering Rule to be especially handy when I absolutely need to locate a piece in the center of something else. I actually found that you might have to make your center layout a bit larger than you need. I recently wanted to set a ¼”-thick plate on the centerline of a 4”-wide strip of steel. I centered the rule and marked off a ¼”-wide layout line only to find that because the steel was actually ¼”-wide it covered the layout lines. I had to go back and draw the center layout lines 1/64th” wider so I could set the piece between them. It came out perfect.

You can also get Protractor Rules in 6” and 160mm versions. These rules have the same ultra-accurate perforations in a 180-degree arc in ½-degree graduations. The graduations are marked with 0 in the center and another row with 90-degrees at the center. All of the protractor markings point towards a center hole located above the guide bar so you can mark that point as well. It also has a centering 6-1/2” scale along the straight bottom edge.

The Centering Rule (left) has markings working out from the center. It also has this protractor section at the center that gives it even more utility in the shop. The Protractor Rule (right) has full markings every 1/2"-degree plus a centerpoint where all those markings meet! Click images to enlarge

INCRA Rules are available individually or in many packaged sets. To see the full line of INCRA Rules see the link near the end of this review.

In the Shop

Taking advantage of the INCRA Rules precision is easy, thanks again to the holes and slots. However, you do have to pay attention to which opening you place the pencil or scribe. We want and need the fine resolution but that means that there are lots of holes and slots available for error if you are not looking at what you are doing. I know someone will email me saying this is the fault of INCRA’s design but it’s not. I have made this mistake myself but realized that I am the dumb one in that situation. With resolutions down to 100ths of an inch it is worth the effort of actually looking at what you are doing.

I have found the flexibility of the INCRA Rules (not the Bend Rule naturally) can work in our favor when the surface being marked is something other than flat. Even these thin stainless steel bodies can’t conform to dramatic profiles but for many round and curved forms, the INCRA Rules are just as easy to use on these curved surfaces as they are on flat material and you are not sacrificing any accuracy.

The only thing that really takes getting used to with the INCRA Rules is the extreme precision. You are liable to discover that you may have been making concessions with your old measuring and marking tools and unconsciously may try to do the same with your new INCRA Rules. Habits like always cheating to one side of pencil line just will not work with INCRA Rules. Once I got familiar with using the INCRA Rules I could not go back. I quickly grew accustomed to marking everything dead on and the only time that really works is with INCRA Rules. The consistency of the captured pencil or scribe meant that the old ways of measuring and layout just did not get it any more for me.

Conclusions

If you are serious about being as accurate as possible with your layout and marking you really need to check out the INCRA Rules. I don’t know of anything that is as precise as the INCRA Rules this side of a true laser system. The ability to employ this level of accuracy with hand tools in a normal shop is remarkable and will benefit your work in no small way.

The INCRA Rules vary in price by their size and configuration. A 6” Marking Rule costs $13.95 (9-23-2010), an 18” T-Rule is $46.95 and a 12” Bend Rule goes for $25.95. Check the link below to see the full line including sets and their prices.

INCRA Rules are not cheap but the quality of the materials and workmanship mean that they are a one-time purchase. I figure that the stock I can save with such precise layout along with not needing extra “do-over” material will add up to savings that exceed the cost of the INCRA Rules before very long at all. If your shop is at all active, your INCRA Rules will be free before you know it.

See all of the INCRA Rules configurations on Incramentaltools.com - Click Here

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