Tips and news

Air Hammer Usage

Air hammers are a major investment. However, they increase speed to about 6 to 7,000 blows/minute. Still you stay in touch with the stone meaning that you do not lose control; stay “spiritually” connected. We prefer these cylinder air hammers (Cuturi and Trow and Holden) as they have very few parts and are therefore very reliable. (see the notes on air compressors)

Power Tools

The most important tool are the basic hand chisels, a 1.5# hammer and a rasp. The first power tool should be an angle grinder (7.5 amps or more) and a diamond blade (or a Dremel if working very small). The next step is a big but wonderful one: an air compressor. This will open up the world of lighter but more powerful tools.
A portable compressor should be rated for at least 4.6 cfm at 90 psi (30 gallons). This will run an air hammer. To drive an air grinder you need a larger stationary machine that preferably has at least 12 cfm at 90 psi. If you use the portable compressor, there is nothing wrong with getting an electric die grinder that uses 1/4” shaft tools.

Blade types

Use the right diamond blade for the stone and tool. Sintered blades are great for alabaster, limestone and very hard marbles. They are the most durable but are not god for soft or medium marbles. Electroplated blades are for alabaster and marble and cut the fastest. Vacuum brazed diamonds are the most versatile for alabaster, limestone and marble. Since the diamonds are partially melted into the metal they have good longevity but are a little slower.

Blade safety

First, those black abrasive blades are dangerous – my commentary. Diamond blades are wonderfully fast, long lasting and safe if used wisely. Use no more than a 5” blade on a 4” angle grinder (<12,001rpm). A larger angle grinder (<8001rpm) takes up to a 7” blade and a body grinder (<6001rpm) is needed for a 9” blade. The best blades have hubs or flanges so they screw onto the arbor of the grinder. Make sure the blade is firmly on the arbor of the grinder, connected by almost all the screw threads.. Regularly check the tightness of the screws of the hub. Never twist the blade during the cutting process and avoid putting the blade all the way into the stone; leave at least ¼” space to the hub. Call us to get the best blade for the stone you are taming.

Safety

All the stones sold from 2sculpt are safe: no asbestos, arsenic, radioactivity or trans-fats. Still you should always wear a paper mask and safety glasses. If you are using power tools and therefore creating a lot of dust you need ear protection and should have on a respirator. Whereas a paper mask catches about 40% of the dust, a double respirator labeled as P100 will provide about 99% protection. Gel bicycle gloves without the fingers are my favorite for vibration.
Drilling basics
If a stone is strong – like limestone, larger marble blocks – they can be drilled with a masonry bit and a hammer drill. If the stone is fractious or thin it would be wiser to use an abrading bit: a diamond core drill. The vacuum brazed of these can be run dry while the sintered ones run wet. You can use a water feed polisher or put a dam of clay or tape around the hole-to-be and fill it with water. Start the drill at an angle and slowly work it into position (1500 to 4000 rpm). (Never wear gloves on the hand on the core drill as it can get stuck in the rotating shaft.)

What’s So Hard?

When choosing a stone for sculpting we must consider its consistency (how fragile it may be), its patterning (how busy it is) and its workability (its hardness). The MOH scale is a quickly accelerating rating of stone from “1” for soapstone to “10” for diamonds. Other factors such as molecular structure can also affect hardness. Here is a rough guide of our most commonly used stones:

1 Soapstone
1.5 Alabaster
2 Limestone and Steatite
3 Softer Marbles and Travertines
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6 Granite and Basalt

Some of us like the harder stones. We get sharper lines, more exacting cuts and beautiful finishes. With the right tools we can cut, chisel and polish with reasonable effort.

The Mounting Process—Summarized

• Get a flat and level surface to work upon
• Determine sculpture position; secure and hold it
• Mark bottom level line
• Cut bottom; check for flatness (might use a tile)
• On larger bases, cut out center of the bottom to make flattening easier
• Determine hole location in sculpture bottom (find center with a pebble)
• Drill hole with hammer or core drill (consider the bedding plane)
• Determine hole in base: mark sculpture footprint on the base or cut out a template (cardboard or masonite); mark “up”
• Drill base
• Decide on pins: stainless steel or turning pin: gluing one or both sides or using threaded connectors. Consider the ultimate weight of the piece.
• Put non-scratch feet base or adjustable feet on larger pedestal
• Proudly display sculpture

Sanding Tips

I use the first two grits of sandpaper dry and the rest wet. I wash off the stone between grits and allow it to dry for inspection before continuing. Use an old sheet of 1000 grit sandpaper for a few minutes between grits to bring out missed scratches.
Half your sanding time is on the first grit—getting out those deep scratches. Then the next grit might be 1/4 your time and so on. The last grit is a “breeze.” Scratches hold light. Get them out and the stone glistens.
Aluminum oxide vs. silicon carbide vs diamonds
Sandpaper and grinding tools made with aluminum oxide (AO) do not work well with stone. The grains quickly round out and stop cutting. Silicon carbide (SC) grains develop new sharp edges as they wear so they are the stone cutting choice – unless you have the diamond option. Diamond tools last longer and cut up to 20X faster than SC.

Chemistry of Finishing
Sand, sand, sand. The more scratches removed the deeper the color and the more gloss. If you “finish” sanding then wet the stone it might look much better. You can continue sanding to get more scratches out or apply a coat of color enhancer. The silicon in the enhancer seals those micro-scratches. Wax is a nice top coat for protection and a smooth feel. Buff the wax by hand or with a tool to heat the wax into the stone. Black wax enhances very dark stones. Outdoor sculptures can be left alone or protected with a breathable sealer like Limestone & Marble Protector. Water must be able to leave the surface.