A Tool Within a Tool

Use Your Wooden Folding Extension Ruler as a Slide Rule; It’s a Nice Trick to Know 

By Corporal Willy, March 6^th 2010

      I hope there are not too many people out there in the world like me.   I will clarify that by saying, when it comes to doing some mental math that is.  I never got those special sets of Algorithmic Genes issued to me when I came to be.  So over the years I learned how to cheat.  I use paper and pencil or fingers and toes if I have nothing else.  I always envied those that could do some pretty involved calculations in their heads.  When I was working as a construction electrician, fractions were a constant threat and rather than taking a chance I would work them out with pencils and paper to make sure.  Also, for an electrician to use a metal tape measure it was pretty dangerous when working around electrical apparatus, so wooden folding rulers only were on the tool list.  I guess it is pretty obvious to mention that, but what isn’t so obvious is a very special attribute that the Wooden Folding Extension Ruler has, that most people don’t realize.  It was my construction partner John that showed me this cute trick while I was laying out the bending marks on a five inch galvanized pipe.   Those marks that I was laying out were for the Developed Area (bending area) on the pipe.  My partner was scraping the ice and snow off of the pipe before we put it into the very big hydraulic bending machine.   There are tons of pressure needed to bend these large pipe sizes into 90 degree bends, offsets and kicks.   You don’t want to make mistakes here; it is both expensive for the boss and can be very dangerous if you do not know what you are doing.  Every year electricians get hurt using this equipment

      Okay let’s look at the screen shot of just the first segment of a wooden folding extension ruler down below that I did in SolidWorks.  The center metal slide out extension is good up to six inches here even though it measures 7 inches.   This extension on the ruler is mostly used to do inside measurements, when by unfolding another section would then make it too long.   Do you have one of these?

In the next screen shot we are going to take a mixed number of inches and a fractional part of an inch and subtract another inch and a fractional number from that.  Here goes nothing and I hope you understand my dialogue here in describing this procedure.  Using the metal center slide we move it to an alignment position where the three and three sixteenths of an inch will be subtracted by the “subtrahend” or bottom edge of the two and a half inch mark.  This bottom edge mark would be the subtracting number.  Then what is sticking out on the extended end beyond the ruler is what is left over or your answer in this case which is eleven sixteenths.

You want to do another one?  Sure hope I’m not losing any one here with my explanation, but not everyone is an engineer or other technically trained person that is going to be reading this article.  Okay then, how about this one which might be a little easier to understand.  Again using the Center Metal Slide, you have a measurement of five and a quarter inches that you align with the number you are taking away or subtracting from it by using the bottom edge which in this case it will be the three inch mark.    Yup, you got the correct answer that is sticking out the end and it is the same number you just did in your head.  Even I got that one.   It is much trickier when it comes to all those little sixteenth thingies but just as accurate.  Good eyes are important here for accuracy.   If you do not have them then this method probably will not help you very much.

One more for the road, okay?  We have six inches on the Center Metal Slide and we want to subtract two and eleven sixteenths from that number.  Align those two measurements up to one another and the answer is to the left side waiting for you to read it.   I hope this was helpful to some of you out there.