Feathers-and-wedges remain the simplest quarrying tool available for the DIY builder. They are easy to use, but there are several factors that play into how successfully the stone will be split.
Hole Size
For smaller sets of feathers-and-wedges, the hole size is what it is; so if you have a 1/2″ set, you need a 1/2″ hole. But for the larger sets, such as sizes 1″ and greater, the hole can be tweaked to adapt to the stone. For example, a 1″ set will typically be used with a 1″ hole for hard stones, such as granite, but for soft stones a 7/8″ hole may be better. The reason for this is that softer stones tend to crush slightly around the feathers-and-wedges as the sets expand, necessitating the slightly smaller hole to compensate.
Hole Spacing
A a broad rule of thumb, the holes for the feathers-and-wedges should be spaced about 6″ apart, though longer distances are acceptable. Obviously, though, if the spacing is too wide, the stone will not split easily if at all. We have also found that using a longer spacing, such as 1′, between the last feather-and-wedge sets and the ends of the stone seems to help in making easier, cleaner cuts in many cases. Tighter spacing can make the stone split easier, but if the feathers-and-wedges are too close together, the surface of the rock may break off, leaving the rest of the stone unsplit.
Hole Depth
The holes should, obviously, be deep enough for the feathers-and-wedges to be inserted all the way with enough clearance for the wedge to be driven all the way down. Deeper holes apparently will help hard stones, such as granite, to split, but in our experiences with limestone, the extra depth seem to result in the stone being more difficult to split. The reason why may be related to the inevitable widening of the top of the hole as a result of the drill being in the stone longer.
Accuracy in Drilling
The holes should ideally be driven straight down into the stone, perpendicular to the desired line of cut. Alternatively, the holes can be angled slightly into the stone, which will aid in the splitting of narrow pieces. The hole should be drilled straight as possible to avoid accidental widening of the hole.
Hammering
The wedges need not be driven in with great amounts of force; in fact, with soft stones, these heavy blows may prove disastrous, resulting in excessive stone crushing around the feathers-and-wedges, resulting in the wedges bottoming out before the stone splits. Even should crushing not occur, heavy blows usually result in the shattering of the surface of the stone around the feathers-and-wedges, not splitting. The exact force to be used depends on the hardness of the stone. Experience is helpful to gauging the correct amount of force to use. Broadly, softer stones need softer blows and harder stones harder blows.
A wooden-handled hammer works best, as the springiness of the wood helps prevent sharp blows that will shatter rather than split the rock. The weight of the head should be about 2 lb or maybe 3 lbs.
Moisture
Stones broadly tend to soften when they are wet and harden when they are dry. This means that wet stones are generally easier to work. But if the stone is already naturally soft, the further softening caused by the damp may make it so that the stone crushes around the feathers-and-wedges before it can split. For this reason, if the stone is very wet, it may become very difficult to split. The end result is that it may be beneficial to delay cutting stone right after a rain event.
Freedom of Movement
The easier the stone can move, the easier it is to split. As a result, make sure the end being split off is free of objects leaning on it, such as other rocks, and is not anchored with dirt or trees against it. Overhanging slabs, for this reason, are the easiest to split, as gravity aids greatly in the work of the feathers and wedges. Just be careful where you are standing when splitting a slab that is not resting securely on the ground!
Stone Arch Bridges 