While the weather was somewhat inclement over the last few days, I used the time to make a couple of centre finding jigs/devices. They are basically just cut, drilled and screwed together so I won't go into the construction details as it's really basic. The only thing I will say is that all the holes have to be drilled very accurately, or the devices won't work properly. The first is a small one, made of oak, a strip of 3mm aluminium, two bolts and some small bearings. It will draw a centre line down the middle of any piece of wood that will fit between the bearings.
The jig is placed on the wood with the bearings on either side and twisted until they contact the sides. When moved along the wood, it will draw a line exactly in the centre.
The second one is based on the priciples of a parallelogram, and is for use on larger pieces of timber. It's made from 15mm square aluminium tube and 19mm aluminium strip. Again, it is placed over the wood and the sides squeezed until they contact either side. When slid along, it draws the centre line. It can also be used to mark out a mortice (or tenon) by scribing along the outer edges of the central bar. By using different width central bars (this one is 6mm), different sized mor*tices can be marked out.
Drawing a centre line.
Marking out a mortice.