Saturday, July 12, 2014

Things the Prekies Apparently Don't Know

I did this full scale layout exercise with the prekies last week and for the first time since implementing it the whole thing went over fairly poorly.  I'm not 100% sure what the problem was, but I did observe there are three things they absolutely don't know...

To lay out a long straight line you use a chalk line.

A fairly rudimentary carpentry tool, chalk lines are excellent for establishing a straight line.  The "chalk box" stores a reel of string and a reservoir of chalk.  As you withdraw the string it gets saturated with chalk and then you pull the string tight and snap it on the surface you want to mark.  You get a fairly decent mark to follow.  I've seen folks use chalk lines out to 50 feet.

To construct a perpendicular line you can use three tape measures and a 3-4-5 right triangle.

Pretty much always the next step after establishing a straight line will be establishing a perpendicular line.  There are lots of sketchy ways to do this, but using a 3-4-5 right triangle is pretty bulletproof and conveniently scalable.  Best circumstance need three people and three tapes, but with a little back and forth it can be done with three tapes and one person.  The best part is that there's no projection involved - no "eyeballing."  If you select a measurement multiple of 5 longer than you need then your layout will be within your construction.

To lay out large arcs and circles you use trammel points.

Trammel points have taken a bit of a hit in my world with the introduction of affordable large scale output - to say nothing of the explosion of CNC fabrication.  But if you need a large scale compass for layout trammel points are the way to go.  I've used these for shop and theatre layout, for big and little projects, for arcs, circles, and even in a modified way for ellipses.  Before online shopping this was a fairly difficult item do find in a "theatre duty" grade.  Nowadays though they are easily available online.

I am certain I knew about chalk lines and about 3-4-5 triangle layout when I was in high school.  Trammel points I might not have learned about until college.  So I guess that they didn't have all these tools in their bag might not be totally unexpected - but still a little disappointing (especially seeing as how classes in the past have had them).  Anyway, I think I have a lesson plan for Tuesday.

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