When is a two-foot rule not a two-foot rule?

[Herv Peairs]

I had an interesting surprise this morning. I measured twice, but with different rules, and the same distance yielded different measurements. This caused some head-scratching. It turns out that one of the rules, a "two-foot" Starrett I picked up a few months ago at a tool meet, is a shrink rule (the clue being the small type that says "SHRINK 1-8' TO FT."). This particular shrink rule adds an 1/8" per foot, and is thus 24 1/4" long. Google taught me that these were intended for use by pattern makers when making molds for cast iron, which shrinks an 1/8" per foot when it cools. Fortunately, I've not gotten myself into too much trouble with it.

I suppose everyone knew about these but me.

Herv

[Timothy Thorpe Allen]

I picked one of those up (a pattern-maker's shrink rule) at a tool sale, but the seller stopped me (apparently it was obvious to him that I didn't know what it really was....).

I have since made a shrink rule for my wife, a potter, who's clay shrinks on average about 12% overall from thrown form on the wheel to coming out of the glaze kiln firing....

[Jim Koepke]

During my days as a printer one of the shop rules was to use the same tape measure for all measurements on any one job. Tape measures often did not agree with each other, especially if from different makers. Small differences, but they could add up to make a larger difference.

One of my four fold rulers is used all the time and many of the lines have been redrawn with a fine Sharpie. It is used more like a story stick than for precision measurement.

BTW, my thought at first reading the title of of this thread, "When is a two-foot rule not a two-foot rule?" was to say, "when it is a protractor."

Stanley Rule Protractor Angles & Distance.jpg

This comes in handy at times.

Almost forgot to mention Dutch rulers. At one time their inch was a different size than the inch we use. Some of their old rulers and tape measures are different.

jtk

[Andrew Seemann]

You see shrink rules on eBay every once in a while at good price, Starretts even. The good price is probably because not many people have a lot of use for them

An oddball home made ruler I have (made by me) is a keyboard ruler. It measures in natural key head widths for keyboard instruments with a 6 1/4 octave span. They look like inches but are a little short.

[Prashun Patel]

I think the shrink rules are the exception, not the rule.

[Mark Hennebury]

I don't use a rule, as a rule.
I require military precision in my shop, and will only use digital calipers... as a general rule of course.

[Tony Zona]

I think the shrink rules are the exception, not the rule.

Shame on you.

[steven c newman]

So was the French rulers....before they went metric....

[David Eisenhauer]

Tweak the meds a little Mark, please.

[Normand Leblanc]

I own on of those shrink ruler, it's a Rabone 18 with 4 different scales. I use it a lot like a straight edge.

IMG_6241.jpgIMG_6242.jpgIMG_6911.jpg

[Mike Hutchison]

Had not heard of shrink rule that I can remember;
maybe I can claim somebody put one on my bench the next time
I make a bad measurement/layout mark.
Jim K. I printed out that table; don't know if I'll ever use it per se since I have
metal and plastic protractors, but it is interesting none the less.

[Jim Koepke]

Jim K. I printed out that table; don't know if I'll ever use it per se since I have
metal and plastic protractors, but it is interesting none the less.

It comes in handy measuring something when away from my protractors and being able to work it out. It is just another tool in the ol' quiver.
If one can measure out 12" a four fold ruler isn't necessary.

jtk

[John Stevens]

Very interesting! Thanks all.

—John

[steven c newman]

Have to watch out...sometimes you will get a 6' Mason's folding rule, instead....

Spent $2 this morning. Rule was intact....one side was the "normal" markings.....with "Lufkin Modular Rule".....other faces were for laying out brick and block spacings....

[Tom Bussey]

There are all different sizes of shrink rules. And wooden patterns are only so good for so many pours I was told about 25 but I am no expert.. There is also wood pattern makers and metal pattern makers. Lets say a company wants engine block castings. The wood pattern maker would make a pattern for the metal pattern maker so shrink needs to be incorporated in but the metal patter has to have shrink incorporated in because the shrink factor for the metal pattern to the casting applies. So the wood pattern maker has to allow for both shrinks

Also any type of plastic also has its own shrink factor, so the shrink factor also applies to plastic mold production. and Die casting also has to have shrink factored in. Iron, brass, aluminum, plastic, to name a few all have their own shrink factor. A 2% shrink factor is usually applied in blow molding or vacuum forming which is basically a 1/8th shrink per foot.