Montoya Stone Carving

Montoya Sculpture & Supply has been serving stone carvers and sculptors since 1973. We stock Italian and domestic hand and power tools for stone carving along with tons and tons of soapstone, alabaster, wonderstone, marble and limestone. Located in West Palm Beach, Florida. Please visit my website for tools and supplies.

Thursday, May 05, 2005


Lets look into the basics of setting up for and using air tools for stone carving. Its pretty simple and you will enjoy the ease and speed with which you will be able to remove stone. You need a compressor and some air tools..

The Compressor- this part of your setup is used to compress the air to drive your air tools. A gas or electric motor is used to compress the air into the metal tank to be distributed through the hose to your tools. Most of the time its best to use an electric motor because you just plug it into the outlet. The electric motor compressor allows you to use this equipment in confined spaces like garages and sheds where you don’t want gas fumes from a gas motor to build up. Just in case- gas fumes contain CO2 (carbon dioxide) and prolonged exposure to carbon dioxide build up in confined spaces will kill. Of course larger electric units have different electrical needs and may need to be hard wired. Gas units can be handy if you are in an area that does not have electric readily available.

In selecting a compressor, it is important to select a large enough tank and motor. You can get into a lot of technical details here but in general you will need a 20 gallon air tank with a motor that can produce at least 3 CFM (Cubic Feet per Minute). Motors that can produce this can be as small as 1.5 hp (horse power). The 3 CFM should be produced at 90 psi (pounds per square inch) . The larger the motor the longer service life and higher psi. In general the higher the horse power the higher the cost of the unit. I like the portable wheel mounted units for ease of moving. Of course your compressor unit needs to include couplings and hose.

A few other items to be aware of;
-the metal tanks that store the compressed air will build up water due to the compression of the air. The tank needs to have a valve to drain the water.
-it’s a good idea if your motor has a oil sight glass so you can check on the oil level inside the motor.
-look for a unit with a good belt guard to protect against accidents.
-if you are going to be using your unit with a buddy using it at the same time, remember that higher operating pressures allow multiple operations simultaneously.
-there are many different types of connectors. I recommend the “M” or Industrial connector

There are three main air tools you want to be able to use with the compressor: the air blower, the ¼” pneumatic dia grinder and the pneumatic hammer. The air blower is an inexpensive little attachment used for blowing dust off of your cloths, out of your hair and out of tool housings.

The 1/4” pneumatic dia grinder is a rotary tool. The air entering the tool spins the inner turbine at between 12,000 and 35,000 RPMs (Revolutions per Minute). This is the tool your compressor is sized to fit. It has the highest air demand. It uses an average of 3 CFM (Cubic Feet per Minute). It eats up air fast. Be sure to select this tool with a lower or equal CFM rating than your compressor is capable of generating or else your motor will stay on all the time trying to compress the air while your tool is eating it up out the other end.

Select a dia grinder that is between 20,000 and 25,000 RPMs due to the safety ratings of most of the attachments available for these tools. Most have a lock–off trigger (you have to flip something to squeeze the trigger) and the trigger is variable speed (the harder you press the trigger the higher to the maximum rated RPMs you will go). You can also control the speed with the psi pressure valve. Generally they run at between 60 and 90 psi. These tools come in front and rear exhaust models. The front exhaust blows air over your work surface and the rear exhaust blow it to the back. Each has an advantage and oddly the rear exhaust seems to be most popular. This tool is rather easy to find at your local super mega hardware store starting as low as $15. A vaiant of this tool is one with the business end at a 90 degree angle from the tool. This would be a tool for a special application which you probably would not need in your initial tool set up. There are also long shaft versions which give you another 6”-8” of reach should you be carving deep into a stone. The pneumatic dia grinder has an advantage with the number of attachments available for it.

The attachments available for the pneumatic dia grinder include;
-reduction collet (1/8”) allows you to use attachments with smaller shanks. Standard shank size for this tool is ¼ inch.
-carbide burrs used to shape and bore
-mounted grinding wheels in different shapes and sizes
-cut-off wheels for shaping and cutting up to 2” into the stone. These are often diamond coated.
-rotary chisels are triangular shaped burrs in different sizes and shapes. When spinning at 25,000 RPMs they are like an aggressive chisel that digs into the stone and leaves a fairly smooth surface.
-flap wheels are small drums that have many small square sheets of sand paper attached to it. They come in different sand paper grits and are made to wear down as they spin to expose fresh grit. They are rated up to 25,000 RPMs and make fast work of sanding the stone surface..
-polishing attachments include cloth wheels and goblets which you use to polish and shine the surface of the stone. Spin the cloth wheel or goblet into an alabaster or marble compound and apply it to the surface to create a high polish.


This tool is probably the main reason you are looking at the purchase of a compressor set up. They are great tools with a simple operating system. They are basically a cylinder inside a container, and as the cylinder goes back and forth it hits the shaft of the chisel. Lets say you could hit your chisel with your hand held hammer about 30 times a minute, compare that to 350 times per minute with a pneumatic hammer and you get an idea of how fast you will be carving stone. And now assume you could keep up that rate with your hand held hammer, and you really understand how much stone you will move.

There are different sizes and shapes of pneumatic hammers. With a pneumatic hammer you do not so much push the hammer as GUIDE it. Air Hammers come in different sizes, weights, shapes and noise level, depending on manufacturer. They are all of high quality and are built to take a beating, Standard chisel shaft is 12mm (1/2”) and is interchangeable between makers. Use steel chisels on soapstone and alabaster and carbide tools on marble and granite. In selecting the tool you will want to consider the type of work you are doing, and how long you will be holding the tool. The larger the tool the heavier it will be. In the Cuturi line the “V” hammer is a favorite and weighs 1.54lb (.7kg), the larger is a “T” and it weighs 3.3lb (1.5kg). This tool, depending on size, will consume less than 1.5 CFM, compared to 3 CFM for the dia grinder.

A few other things related to air hammers. Always operate within the recommended pressures (60 to 90 psi). Start your session and end it with a few drops of air tool oil. A few drops during the work session is a good idea. Failure to oil the tool will result in damage and if not oiled at the end of the session can lead to seizing and possible formation of rust if there is moisture in the tank or air line. Keep the connectors at the intake of the air hammer and hose clean because this is the easiest way to introduce sand and dust into the tool. Sand and dust in the tool is bad. This can cause the tool to seize up.

Between the air hammer connector and the air hose you can add some handy attachments. One attachment is the in-line blower which makes it easy and fast to blow off your working surface with out having to disconnect the air hammer and connect a separate blower. You just reach back along your hose and press the little button and instant blower air. Another attachment is a small in-line pressure regulating valve making it easy to adjust air flow. Another attachment is a swivel. The swivel allows the hose to drop down so that the angle of the air tool is not holding the hose up. This takes some of the pressure off while guiding the tool. These attachments can be added separately or all together. They generally will all fit within about an 8” length depending on the manufacturer of the attachment.

Always wear safety equipment, particularly eye and ear protection. Damage to human ears begins at 85 db and the air hammer usually runs below this threshold. But air dia grinders run in above 85 db and its so simple to protect your ears by reducing the db level with a set of rubber/plastic ear plugs. After a few hours of guiding the air hammer around the stone (time flies when you are having fun) your hands may feel tingly from the vibration. Vibration absorbing gloves will help reduce this. For more on safety read Technical Bulletin #6 “Safety for the Stone Carver”.

If you have the space for a compressor you will really enjoy having the option of using air tools. Air tools are simple to use and save time. When using air tools it’s a good idea to have a plan of attack for your stone and mark cut and shave lines on the stone. Air tools make fairly fast work of the stone. You need to be aware of where you are going when using your air tools because you are going to get there fast.