Hi guys. There's been some renewed interest in an old thread about finding the centre of a circle. Here's a recipe for a simple tool to do it - other tools are available:
Here's what you need:
A simple 90 x 45 x 45 deg set square available in almost any cheap geometry set and a couple of strips of plasticard.
Mark the centre of the long side of the set square by either measuring an angle of 45deg in the 90deg corner using the protractor or a rule to measure the length and halve it.
Take your two strips of plastic and glue them to the set square leaving a gap just wide enough for your modelling knife blade. You can just fix one strip in place to use as a guide for your blade, but two strips makes sure it doesn't slip.
I've not trimmed the ends of the strips - I'm waiting for the glue to set - but that's it. Finished.
To use it, place the disc you need to find the centre of in the hole in the middle of the set square. If your disc doesn't fit, get a bigger set square.
Make sure it's pushed tight into the 90deg corner and use your knife to lightly mark a line using the slot between the plastic strips. Rotate the disk about a quarter of a turn, push it tight into the corner again and mark another line.
Where the lines cross is the centre of the disc.
Ta da!!
Here's what you need:
A simple 90 x 45 x 45 deg set square available in almost any cheap geometry set and a couple of strips of plasticard.
Mark the centre of the long side of the set square by either measuring an angle of 45deg in the 90deg corner using the protractor or a rule to measure the length and halve it.
Take your two strips of plastic and glue them to the set square leaving a gap just wide enough for your modelling knife blade. You can just fix one strip in place to use as a guide for your blade, but two strips makes sure it doesn't slip.
I've not trimmed the ends of the strips - I'm waiting for the glue to set - but that's it. Finished.
To use it, place the disc you need to find the centre of in the hole in the middle of the set square. If your disc doesn't fit, get a bigger set square.
Make sure it's pushed tight into the 90deg corner and use your knife to lightly mark a line using the slot between the plastic strips. Rotate the disk about a quarter of a turn, push it tight into the corner again and mark another line.
Where the lines cross is the centre of the disc.
Ta da!!