The density of materials can be given in pounds/cubic-foot, or kilograms/cubic-meter, but it is often expressed in terms of specific gravity, which is the factor by which a volume of the material is heavier or lighter than the same volume of water. This is handy, and particularly so when using metric measure, because the metric system uses water as the reference density for weight, with one cubic centimeter of water weighting one gram, one liter weighing a kilogram, and one cubic meter, weighing one metric ton. (A metric ton is 2,200 pounds, vs. 2,000 for an customary ton (cwt) in the US.) The specific gravity of the carvable stone ranges from about 2.4 to 3.0, i.e., a given volume of stone weighs a little less than three times as much as the same volume of water. Some stones are a little lighter, some a little heavier, and they vary even with categories, but you will not be far off if you estimate most stone, e.g., marble, limestone, and granite, at 2.7, and the iron rich, mafic stones, such as basalt and diabase, at 3.0. Water (and therefore, a person30) has a density of about 62 pounds per square foot, versus about 2.7 x 62 = 170 pounds per cubic-foot for stone.
Using these facts, it is easy to estimate the weight of any rectangular block stone. The volume of a rectangular block of stone is length time width time height. If you measure in inches, you can convert to cubic feet by dividing this by the number of cubic inches in a cubic foot, 1,728, then multiply by the weight per cubic foot. If all you have is the specific gravity, multiply the volume in cubic feet, times 62, times the specific gravity.
A useful trick for smaller irregular stones is to compare it to a volume of water. For instance, a piece of stone the size of a gallon plastic jug of water will weigh about 8 * 3 = 24 pounds. If it's the size a five pound roast beef, call it fifteen pounds. A cubic meter of stone will weigh about three times as much as a cubic meter of water--about 6,600 pounds, or three metric tons.
Even a small piece for a bust, say, three cubic feet, will thus weigh about 510 pounds. How does an artist handle masses like that without a crew? It's actually not hard, with some lumber and a few basic tools. This section will give you a basic bag of tricks that can be used in many situations. Just remember Murphy's Law: "If something can go wrong, then sooner or later it will go wrong," and don't be under or between heavy things when it does.
If you have a strong floor, moving blocks of up to a ton or two around the room is easy, even when working alone. You need a crowbar, some pipes, and some scrap lumber. The process is illustrated below
A block on rollers can only get away from you for at most half its length, at which point the front will tip and wedge itself against the floor. The other pipe will be at the tipping point, so it's easy to tip it back up. You can limit the motion of the stone by putting either the crow bar or a piece of two-by-four against the floor at a sharp angle in front of the stone. With this technique you can control even a multi-ton stone.
You can easily punch a crowbar through the planks of a wood floor, even if the floor as a whole is plenty strong enough to hold the stone. If you working on a wooden floor, use a wooden plank to lever on. It should be perpendicular to the joists (which are usually at right angles to the direction of the floor boards) and long enough to span two of them.
If there is uncertainty that the floor is strong enough, a standard engineering manual (any library will have one) will give you the bearing strength of the floor based on the size of the joists, the distance they span, and their distance apart. If you are on a first floor, temporary columns from the basement floor to mid-span can to strengthen the floor enormously. Tubular steel columns with screws that allow them to extend to the exact height needed can be had at any lumber yard. Steel is only worth it for permanent installation; if it's just temporary, you can use 2x4's or 4x4's. You can cut a piece the width and depth of the joist out of a 4x4 and nail it to the joist, or you can use one 2x4 directly beneath the joist, with a longer one fastened to it, and to the side of the joist. Either makes a very strong post. Use a construction screw or a 10d nail every six inches to fasten the 2x4's together, plus two or three through the longer 2x4 and into the joist. If the post is not quite long enough, snug it up by driving two roofing shingles under it, from opposite sides, to wedge it more tightly. Another thing that makes a floor stronger is "bridging" between the joists. Bridging keeps joist under load from twisting, making them stronger. This should already be present, but if it is not, you can either buy and install ready-made steel bridging at the lumber yard, or simply fasten a 2x4 spanning across the joists from the underside, and screw it to each joist with three heavy construction screws.
Another consideration on a wooden floor is the strength of the flooring between the joists. For heavy stones, you should working with two-by lumber, perpendicular to the joists, under the load.
Now that you've got the block where you want it, you will want to lift it to a convenient height for working. The process is illustrated below.
If you only need to lift a block a little, use the technique described above to lift it onto wooden blocks instead of pipes. Two-by-fours or four-by-fours can be laid across each other several layers deep. Toe nail the supporting lumber together for safety, so it won't shift when you move or turn the stone. A bed of 4x4's is good up to a foot or so. Rough 6x6 or 8x8 shoring lumber is good for higher platforms, and very cheap.
If you want to get onto a higher bench than that, the following technique can be useful. You need a pair of heavy timbers to use as a ramp--old floor joists are great for this. The stiffness of wooden board is proportional to the width multiplied by the cube of its thickness, so thicker is a lot better. One plank probably isn't wide enough to use as a ramp, so fasten two together side-by-side by screwing wide pieces of plywood or strong lumber to the back. The two planks don't have to be touching-- you can space them apart for greater stability.
One trick for getting the stone up the ramp is illustrated above. You roll the stone up a ladder of blocks spaced so that as the stone rolls over a block, it is close to it's tipping point just as the leading edge touches the ramp. Try this out on with the planks flat on the ground before trying it on a ramp.
Whenever you're using a ramp, be very sure it is fastened securely to the trestle or work surface you intend to place the stone on, and be sure the entire construct is secure and immovable. Placing the trestle against the wall is ideal. Fasten the ramp the trestle or work surface with the soft iron strapping sold for hanging plumbing pipes. The strap is one inch wide, and comes in a roll, pre-perforated for bolts or screws. Screw it to the ramp and the table with construction screws or nail it with concrete-form nails (they have double heads to make them easy to pull out again when the form is dismantled.) This is not shown in the illustration.
If the block is too big to roll by hand, or does not have a square cross section, a come-along or block-and-tackle can be used to drag the block up the ramp by brute force. If the stone is not not too heavy, you can wrap the chains directly around the block on all sides, like tying a package, hook the come-along to the chains, and just drag it up the ramp right on the chains. Chain can be connected temporarily using carriage bolts, nuts, and heavy gauge washers. Use the bolts that are at least as thick as the links.
A steel eye ring attached to the wall several feet above the workbench surface is a great permanent feature for the studio. If it's anchored with expanding anchors, it has to be placed so that the direction of pull on it will not be close to straight out, but at least partly from the side. The ring in my studio is attached to a 3/4 inch threaded rod that sticks out two inches, and extends through the wall, so that it cannot be loosen or be pulled out from any direction.
For heavier blocks, you can make a temporary sled to drag it up the ramp on. If you can find a shipping pallet of the right size, you can just nail a piece of plywood to the bottom. Rub bar soap or bees wax on the bottom to grease it. Lash the block to the skid with rope or chain, and attach the winch hook directly to the lashing.
Be sure the work surface and the ramp are strong enough and cannot be pulled over. You can reinforce them with temporary 2x4 reinforcement if necessary.
This traditional rig, seen below is useful for directly lifting moderate loads. It's a system of rope and pulleys that gives you mechanical advantage by exchanging distance for force. A rope over a single pulley gives no mechanical advantage, just a more convenient orientation of the lifting force. The block and tackle employs many loops of a single rope to draw two sets of pulleys together. To draw the pulleys together one unit of distance, you must pull one unit of rope for each of the lengths of rope that connect the pulleys, thereby increasing the pulling force in proportion.
A block-and-tackle is elegant, but they are cumbersome to operate and much more expensive than the alternative, a chain fall, but you might get one cheaply on craigslist or at a yard sale.
A chain fall,illustrated below is similar to a block and tackle, but it works with chain instead of rope, and uses gearing, rather than pulleys to obtain mechanical advantage. They are typically hung up high, either rigged to roll along a beam or simply hung on a hook. They are rated at anywhere from five hundred pounds to several tons.
An extendable chain with a hook on the end hangs down from the metal block that houses the gearing. A manually operated chain fall has a second loop of chain that the operator pulls on to turn the gears. By pulling the loop of chain in one direction or the other, the hook can be slowly raised or lowered. They are also available with electric or pneumatic power instead of the loop of chain.
Unless your chain fall is mounted on rollers from an I-beam, you'll only be able to use it to lift stones onto and off of dollies and other rolling platforms.
Make sure the attachment is solid--a loop of chain around an existing beam is good. Fasten the loop of chain with appropriately sized bolt and washers. For heavy lifting, overhead beams can be temporarily shored with a metal columns or four-by-fours. And once again, stay back. Don't be anywhere where you can be hit by either the stone or the chainfall if something breaks.
In the studio you can use them for dragging stones around the floor or up and down ramps, or for lifting stone directly onto a platform. Be very careful when using one to lift, because it's inherently hard to operate from a safe position. You need to be safely above the level of the stone. Also, be aware that the maximum rated load for lifting will be lower than for pulling. A two-ton come-along costs about forty or fifty dollars.
An engine hoist, show below is a small, lightweight hoist used by mechanics to lift engines from automobiles.
Depending on the model, they're good for up to two tons and usually operate hydraulically. They have a lift a hook suspended from the end of an arm that's long enough to reach to the center of the engine compartment--plenty of distance to place a fairly large work block on a supporting structure. They have long feet to slide under the car or bench to keep the base beneath the hook. A new two-ton engine pulling crane costs about four hundred dollars, but you can often find them used on craigslist.com or eBay.
A hydraulic work stand is a fantastic studio accessory. The stand shown below will lift a thousand pounds to a working height of up to 36 inches.
Prices for lift tables vary wildly for some reason. The one shown sells for three hundred dollars online. Very similar tables with the same rated capacity sell for as much as twenty-five hundred dollars.
A lazy Susan turntable with bearings is ok for modeling in clay, but it isn't good for carving stone. You really don't want hundreds of pounds of stone moving too freely; it's dangerous and it makes it hard to work.
A better solution is to set the block on a round or octagonal piece of plywood, instead of directly on the bare bench. For up to a few hundred pounds, this will reduce the friction enough that you can shift the stone by hand. Soaping the bench top, or rubbing bee's wax on it first will reduce the friction further. Formica, melamine, or masonite, laminated to the side facing the bench, reduces the friction much further, but be careful, as it can reduce the friction to to the point of being dangerous.
A large screw or lag bolt, through the center of the plywood and into the bench will constrain the motion to rotation, making it much safer. A C-clamp can be used to lock the turntable in position while you are working.
Cradles, an example for small pieces is shown above, are good for holding work in the right position. This one has plank sides and hardwood slats, make working on pieces at odd angles easier. Two-by-ten fir or pine off-cuts make good sides. Great stock for slats can be had from the discarded futon bed frames that people are always throwing out.
For larger pieces, nail a cradele together out of 2x3 hemlock or fir. If the front edge projects downward half an inch or so, it can be allowed to hang over the front of the work bench to prevent the workpiece from sliding to the back of the bench.
Alternatively, pairs of holes drilled on each side to allow 1/2" bolts to drop through will allow any of the sides to catch the front of the bench.
Sand bags are useful for blocking up a piece in progress. For small bags, sections of the legs from old blue-jeans can be sewn into sacks. Lumber yards sell sand in fifty-pound plastic fiber sacks that are sturdy enough to use as is if you need bigger bags. These are the same kind of bags used to make temporary flood walls. The same bags are usually sold empty as well, for about a dollar apiece, and are good for smaller sizes. The soft iron wire used for tying concrete reinforcing rods is the best thing for tying them closed.
Sometimes there is no good way to lift a heavy stone down from a truck bed. Perhaps there was a loading dock or forklift where you picked it up, and now you have a thousand pound block in the truck with no way to get it off. Simply pushing it off the back of the truck is not out of the question, if you pad the landing. In quarries, piles of dirt or sand are used to catch the huge blocks as they are split from the living rock. If you do have to drop a stone off the back of a truck, you can similarly cushion the landing with a wooden pallet or other old junk.
Block the pallet up well off the ground with a couple of 2x4's or 4x4's laid flat under two outer edges, to give it room to flex on impact. Arrange it so the pallet or pallets are supported from the ends of the main structural members, and the weight will land across them, so there will be lots of flex. The wood will probably break--that's fine, the bending and breaking soak up the energy of impact. If the stone is very heavy or will drop far, use two pallets, with spacing between them as well as on the ground. You can also lay a thick stack of corrugated cardboard on top to further cushion it.
You can also make a landing pad with several inches of flattened corrugated cardboard boxes, or other crushable material, laid directly on the concrete, with a piece of plywood on top to spread the weight, and prevent the impact scattering the padding, or the stone penetrating to the concrete. Several styrofoam swimming pool noodles in a tic-tac-toe grid, with a piece of plywood on top, can absorb a very large impact.
Beware of padding that can bounce, such as tires--padding that crushes is safer, both when you drop, and later when you take the stone off the padding.
With everyone well back, tie a rope around the block, and if possible, fix the end to something solid, then drive the truck away. Moving the truck, rather than the stone, is safer for the truck, as the truck is farther from the impact, and the rope helps to control any tendency to roll twoard the vehicle. The stone can roll, and wood can fly, so stay well back.
Also, be very careful of uncontrolled tipping or rolling of the stone when getting it down from the landing pad. Only drop stones that have a compact shape. Long pieces and slabs can snap even if they are quite thick.