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(Last updated 19/6/00)
CALCARC
Calcarc was created when I was building my pergola. I wanted to cut some arches
out of the bottom of the rafter-y things on the top. Trouble was my $40 jigsaw had
a tough enough job cutting through the 1 inch thich wood, and I was wanting it to
be accurate enough that the parallel arches formed a rippling frame for the
horticultural vista beyond... and in the end it was truely a site to behold.
Now to create shallow flowing curves is not something you can do by sight
easily. I ended up creating a huge 10 meter or so compass by fixing a piece of
string to a post. I knew the linear length the arc (between the supporting timber
that the rafters sat on) and I knew the Height of the arc (I made this 2/5 the
height of the Rafter-y timber so as not to weaken it too much but still get a
noticable curve).
Armed with this information I had to figure out exactly the distance the
wood had to be from the strings pivot. A bit of trigonometry and some C programming
later I came out with CALCARC.EXE a command line driven program that calculates it all
for you. (although it didn't calculate the stretch in the string which at that
length can be an appreciable amount of the arc height when your walking from one end
of the rafter to another!...a newton meter soon fixed that by ensuring I was providing
the same pull throughout the excercise. I also switched to very thick nylon
weedeater line to reduce the stretching somewhat )
Calcarc can be run from your MSDOS prompt. You'll get simple help (as below) if you type calcarc
[enter] with no parameters
Example of calcarc with no parameters
C:\>calcarc
Error Error Error ERROR!!! invalid parameters
==============================================================
|| calcarc Height Length Copyright HR Frazer 1996||
|| e.g. calcarc 60 1310 ||
|| gives the Radius of circle to produce this ( =3605.208 )||
==============================================================
Example of calcarc with parameters
C:\>calcarc 60 1231
=====================================================
|| CalcArc Copyright HR Frazer 1996 ||
=====================================================
Arc of Height 60.000 and Length 1231.000
requires a Radius of 3187.002
Peaking at half length ( = 615.500 )
Download calcarc.c source code