Splitting igneous Basalt using wedges and shims.

Quoted text begins.I hear what you are saying about "not enough wedges"
I'll get some more and try again.
Are the spacings correct?
End of quote.

Sam,

Bill is correct, more w/s are needed. The spacing is OK, but you would need the
same number of w/s on the other side of the boulder, as well as another two in
the top. Make sure that the holes are drilled deeper than the length of the w/s
so that the wedge is clear of the bottom of the hole. If the w/s are a bit of a
sloppy fit in the hole, you can add shims (I use 1/8" x 20mm brass strip) to
tighten things up a bit.

Some tips:

Place some packing (timber, steel bar or something) directly under and along the
splitting line, this will cause the stone to overhang at least one side, using
gravity to help pull the stone apart. Some wedges loosely placed under the
overhang will help to control the falling rock when it does split.

When you see a crack opening up near a w/s, stop tapping there and concentrate
on the ones that ping with the highest pitch.

When all the w/s are tightly wedged, walk away for a bit and let the crack
develop slowly. Pour water on the w/s and drill holes, the capillary action of
the water will assist with the opening of the crack.

Simon