A Centering Rule





Introduction: A Centering Rule

I wanted a centering rule, and decided to make one from an 18 inch steel rule I own.


  • P-Touch Label Maker
  • Scissors
  • Knife


  • Steel ruler
  • Black on White label tape
  • White on Black label tape
  • Clear packing tape

Step 1: Make Numerals

I am alternating black on white numerals with white on black in order to lessen confusion when using the centering rule. I am making odd number numerals black on white. I am making even number numerals white on black. I left three spaces between each numeral when setting up the label maker. Because it is a centering rule, two of each numeral will be needed, one for the left side and one for the right side of center.

Note: If you do not have a label maker, you can write numerals on a strip of paper with a marker pen and tape or glue the paper strip to the ruler, perhaps even mark them on the ruler itself. You could even print the numerals on a computer.

Step 2: Apply the Numerals

I used a knife point to position the numerals before pressing on each to adhere them to the rule. (You might want to clean the rule of any oils from your skin before applying the numerals.)

This label tape has a slit in the backing paper that runs lengthwise. Simply fold the top half on the printed side toward the bottom half and the backing paper begins to separate. Lift off whichever half you wish. I lifted off the top half and attached the numeral to the knife tip.

Notice that I cut a triangular pointer from some of the scrap tape and applied it at the mid-point of the rule for zero.

Step 3: Remove the Other Half of the Backing Paper

Once the top of each numeral adheres to the rule, flex the numeral in place so the bottom half of the backing paper peels away from the numeral. Remove what is left of the backing paper.

Step 4: Cover With a Protective Layer

I want to protect the numerals from coming off later. In addition the markings on the rule are painted rather than inscribed. I stretched a strip of clear cellophane packing tape over the length of the rule and applied it so there are no trapped air bubbles. Then I used a knife to trim the tape flush with the edges of the rule. As it is, I can continue to use the rule to measure lengths up to 18 inches, or I can use it to find the center of something.

The photo in the Introduction shows the rule in use. You can see the center of the envelope is 2 7/16 inch from either side.



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    Great ible, I never knew of a centering ruler.

    This would have saved me some badly cut lumber due to mental errors.

    Thanks. I do not remember ever seeing one until I saw my son-in-law use one. I find it makes the job easier and less prone to the errors you mention. The purchased variety can be a little expensive, especially compared to the cost of an ordinary ruler you can turn into a centering ruler.

    I hope you don't mind my saying so but you can buy a centering ruler.

    I hope you don't mind me pointing this out, but a vast majority of Instructables could be purchased, isn't this the whole point of this site/community?

    BTW, fantastically simple, yet effective i'ble here Phil. This is one i shall use myself.

    Thank you, Alexandra. As for an Instructable showing how to make something one could buy, there have been times when I needed something, but did not feel I could spare the money to buy it. There are certainly others in that situation right now. Another great thing about Instructables is a project someone else shares may give me the inspiration to adapt part of that project to do something no one has done before.

    My thoughts exactly Phil. If ever I need to buy something, I always check here first to see if there is a cheaper alternative, plus I'm always one to recycle/upcycle before handing my hard earned cash over to big companies.

    Yes, you can. I have not seen them locally, but have seen them on Amazon. Shipping charges apply in addition to the purchase price. Making one from a ruler I already have was a very good solution for me.

    Brilliant idea! Thanks!

    Thank you. I thought about it over several months before I finally came to what I would do.

    I've been meaning to order a centering ruler from Amazon. Glad I haven't. Once again, you've saved me a few bucks with a "why didn't I think of that?" solution, Phil. Thanks!