Posted by Rado (18.104.22.168)
In Reply to: Re: Dimension for arch template needed posted by ken
Er, how long is the string... this is how I do it to get the string just right long between 3 points (2x arch sides and 1x arch height points):
1. On an old board make a long straight base line.
2. On this base line mark the arch width two side points.
3. Set the exact center in the base line between these to points.
4. From this center point draw 90 degrees line upwards (appr. of the arch rise length.)
5. Mark the desired arch height point on this 90 deg. line.
6. Take a string with pencil on one end and point the pencil on the 90 deg. Line arch rise/top mark.
7. Hold the string straight directly below and along the 90 deg. line.
8. Hold the pencil straight and move it towards to one side making provisional radius until the base line is reached.
9. A: if you end up too far from the arch side point (on inside), just hold the string a bit lower so the string is a little longer and do it ones more.
B: on other hand, if you draw the arch line too wide then shorten the string a bit.
C: this takes 1 minute to tune the arch radius precisely.
10. Draw the arch line from one arch side to the other trough the top arch side point. Now you can start to place bricks along the arch line.
*** You can always decide to add extra brick(s) into the arch making it elliptical and keeping the existing arch rise height just the same; simply by starting to push arch bricks on each side outwards while keeping first brick on both sides on the total arch width mark. Cut the template out slowly pushing the saw blade along-licking the line and on outside of the line, it is easy really (saw blade is about 1mm thick if you wanted to have the template absolutely precise e.g. for the oven firebrick arches ;o)