Step 2: Create the Base
Note: the length will determine how much you can distance the first lens from the slide to allow the 'dot' to expand enough to cover the slide area.
Stiffness is essential. For alignment of the laser is often difficult - unnecessary flex will throw the alignment out too easily.
If using rail, rule a straight line up the centre of the plank, and mount the rail dead centre. You may need to cut the rail in order to fit it on the plank.
If not using a rail, create a centre line very accurately! Any holes drilled must also be very much in line.