Arch profile making

Measure.

Measure the opening where the arch is to span and mark it on a stiff board like plywood or MDF.
Measure up 200mm or so, the measurement isnt all that important, this will sit inside the opening the arch has to span and stops the arch profile from moving sideways as you lay over it. see arches
The rise in this example is 200mm from the springing point. see glossary



The example above is of an arch profile which is a fairly flat, you can make them any shape you want.

For a semi circle arch mark the centre of the opening size at the bottom of the plywood and use a radius lath with a pencil to mark out.

Mark out.

Use a small thin sheet, mdf or similar is good as it is really flexible and less likely to break when bent.

Nail

The nails were used to sit the flexible board against leaving you free to mark out.

Gauge

Mark the gauge over the profile before you cut out the arch, this will give you time to redraw the arch and make it work gauge across the top.


When you are happy that it is all going to work with regard to height, gauge, width etc, cut out with a jigsaw, you are going to need two pieces, nail them together before cutting out this will ensure they are both the same size.

When you have the two arch profiles cut out nail spacing blocks between the two, make sure they are square to each other.
For a single skin arch the two profiles nailed together should measure 100mm thick overall, for a double skin arch 200mm.