Why use electric tools? For me I find it easier to do certain jobs and faster. Also you can achieve finesse when you are only taking off a small amount, and can really chomp away at the stone when necessary. Admittedly, you can’t always get the same type of finish that a hammer and chisel can produce, so I accept this limitation. Having been trained in stone carving with a hammer and chisel, I only use a chisel occasionally now, and don’t worry about this, though some would see this as sacrilege!!!
David Newman 16/10/2017
When I first started using electric tools I used them in my garden, generating a large amount of dust. I can see now that this is unreasonable , unless you live a long way from your neighbours!
The marking of the work is important as inside a mask you need to be able to see the Cutting/ sanding line clearly. The best solution I have found is a black indelible marker pen such as the Edding 750 marker.
Cables should be watched carefully and routed to the nearest socket and one should avoid walking on them as this weakens the outer covering. I have managed to cut a cable once with a grinder, so it is best to always be fully aware of where the cable is.
Stone can be graded according to hardness and the Mohs Scale is very useful. For example the quartzite that I am currently working has a hardness rating of 7 , 10 being the hardness of a diamond, so it is very hard. This is very useful in assessing which diamond tools to use, as general purpose diamond tools used on quartzite are relatively quickly worn out.
- Calcite (most marbles)
- Orthoclase , Feldspar (granite)
- Quartz (granite)
- Corundum ( ie ruby)
When I first started using a hammer and chisel to carve stone, a mask such as the Scott Profile 60 was adequate as the amount of dust was not vaste with the worst of the dust forming on sweeping up at the end. However, the use of electric stone caving tools is a different matter altogether as the dust produced can be so bad that you can hardly see in front of you . I looked into background removal of dust from a studio and the price of even a basic machine was at least several thousand pounds. In the end I bought a Makita 447M dust extractor unit that can be connected to an angle grinder or grinder to pick up some of the dust at source. This considerably reduced the dust but not totally stopped it. I knew that the simple masks were inadequate as the dust was getting inside them, probably because with a beard it is impossible to create a seal. I decided to buy a Spirit SX Powered Air Purifying Respirator (PAPR in short) , where a stream of air is filtered and constantly fed into the mask . The mask I bought had ear protection, a visor , helmet and air filters. The advantages of PAPR are : that the unit is light so one is unhindered to walk around, battery power pulls the air through the filter so there is no additional resistance to breathing to the wearer, since the air is fresh breathing is free even under physical exertion, the constant airflow can provide cooling to the wearer, and loose fitting headgear options provide respiratory protection without the need for a tight face seal. The extra polythene temporary film over the visor was not so good as it reduced visibility so I stopped using these. There is no condensation in these helmets and with having a beard I could never achieve a good seal on the old masks. The battery is rechargeable and the Spirit unit has warnings when the battery is low , if the airflow is inadequate, or the filter needs replacing. I understood that glasses could not be worn inside the helmet , but though it’s a tight fit I can manage to see ok with my glasses on from within the helmet. My helmet has material edges to fit to the face , though it is possible to use a helmet with padding to fit the face and a chin seal.
Some stones, such as quartzite can only be worked with electric apparatus as the force of a chisel can break it into layers. I find that electric grinders and sanders can achieve very fine working of curves , especially if one is working to a set design, and the work is not experimental. Having had no instruction in this side of stone carving it has all been trial and error for me. The staff at Stonetools (Tunbridge Wells) have also been very helpful in advising which tools would work best for me.
I soon learnt that any diamond drill must be water cooled to last any length of time . In some of my long Purbeck limestone sculptures I made a reservoir of clay at the top of the sculpture to be drilled , then filled this with water to cool the bit. Recently, with having to drill flat paddlestones of quartzite, I put the stones in a plastic bowl of water to provide the cooling. Stonetools on their website have a lot of useful information, including the optimum speeds of drill rotation for different stones and drill size. Fortunately the floor standing pillar drill that I have, has a drill speed indicator and a continuous range of drill speeds available. Drilling hard materials needs patience as it is best to apply only gentle pressure. The pressure applied should not significantly slow the drill speed from the set speed. Too much pressure will strip the diamonds off the lowest part of the core drill and make it useless.
Duct extraction guards are available for many angle grinders, and do greatly reduce the dust , and you can even get them for 230mm angle grinders, but you have to hunt around as they are rarities.
As regards sanding with diamond pads , this is usually done at a slow speed of say 1500-2000rpm, whereas many grinders work best at much higher speeds , such as. 6800rpm or higher.
This is where a sander/ grinder such as the Makita 9565CVL is invaluable as you can use it’s variable speed control for different types of working. Although the general purpose diamond pads work well on most stone, when you are using the hardest of stone like quartz or granite , then special granite pads should be used, as the ordinary pads don’t last 2 minutes with these stones. Pieces of stone should be regularly cleared from the floor, as tripping on this waste could be potentially very dangerous.
The grinding wheels come in all shapes and sizes, and some are more aggressive than others. The Grinding Wheel Turbo Convex was very useful in making the curved pieces in the Torsion Series.
Angle grinders of all the pieces of equipment need very careful handling. Using an under powered grinder on a very hard rock is slow and difficult. It is best to have a powerful angle grinder and the most appropriate cutting blade for the stone. Angle grinders are potentially lethal tools ,so in my opinion should be held very firmly , and the case of my large Makita sander/grinder, I hold the body as well. I think that all stone , unless it is so heavy that it is guaranteed not to move should be fixed to the bench with a clamp. The woodworking type clamps work well. Probably the most dangerous manoeuvre is cutting a curved groove in hard stone. This should be done cautiously .Preferably, a strengthened grinder blade such as the Vanity Teardrop should be used on curved slots. The 230 mm grinder is very heavy, and the current it takes on start up is high so may trip the trip switch on start-up. As it is so heavy, you should position yourself, or the stone so that the working position is comfortable , and frequent rest taken. Some blades ( such as the Stonetools Blade All Stone VTS Reinforced) have side reinforcements which will keep the blade cutting freely, even if the blade is twisted in the slot during cutting. If a segment of angle grinder blade comes off this may well be due to excessive twisting , the material moving during cutting , or incorrect blade for the material.Any broken blade must be replaced with a new one. Pieces of rag , or any loose clothing should be removed from the area of cutting tools, polishers and drills.
I find that with the dust around , the threads of polishing pads and drills easily become locked up tight. I use car grease that can be bought from a garage to prevent this. Dust does get into these electric tools and all efforts should be made to clean them. The manufacturers advise that the dust be blown out with compressed air. I find that a vacuum nozzle is better than nothing applied to all the air vents of the tools. It is pretty certain that if you use the tools regularly , the day will come when they stop working. This does not necessarily have to be a serious problem. The brushes will wear quickly with regular use and will need replacing. The brushes for any model can usually be bought online , and can be replaced without expert knowledge. All that has to be done is that the spade connection has to be removed for both brushes and the spring unit is pulled up to remove the remains of the brush unit. The new brush is placed in situ and the spring allowed to press the brush down against the commutator.
There is quite a lot of vibration associated with grinding , and although they sell a handle that is supposed to minimise this, I am dubious about it’s benefit. I would advise that a variety of tasks be done in a day to avoid the adverse effects of excessive vibration on the fingers while constantly in one position.
Silicosis is a long term occupational lung disease caused by inhaling large amounts of crystalline silica dust , usually over many years. Usually exposure is required for 10-20 years , though it can rarely occur after a few months of very heavy exposure. The condition is ultimately fatal due to respiratory failure.
Different Types of stone have different percentages of silica in them:
- Sandstone and Quartzite. 70-90%
- Slate. Up to 40 %
- Granite. Up to 30%
- Limestone and marble Up to 2 %
The health and safety executive are not only concerned about avoidance of breathing in stone dust In the studio but they are also keen that none on the stone dust gets carried indoors to be breathed whenever it becomes disturbed. They advise changing of overalls outside and then showering on going indoors.
With all the advantages of electric tools I would add that it is very easy to take too much stone off with an angle grinder say. This can be avoided if some margin is allowed for further working with a grinder, and also the use of cut lines on the stone showing the projected line of cut for a whole plane can help to prevent some costly mistakes!
Another tip when making complicated designs, is not to try to do the whole design in one stage, but break it up into stages of refining in order to keep the basic shape, and work on different aspects in the separate stages. Lifting of heavy stones needs some attention. Sack trucks have their place up to about 150 Kg weight.
Above this lifting trolleys are very useful indeed and you can work on them as well. Lifting trolleys are available up to 500kg or even 1000kg (1 tonne).
A pulley system in the studio is very useful, which can be used above a lifting trolley. The chain type with a lifting capacity of a tonne is ideal for heavy sculptures, especially if there is a strong beam available in the studio.
I have a mains off switch at the entrance to my studio in case of any emergency. This is recommended.
Do enjoy using and getting to know your electric tools, and make safety a priority.
David Newman (October 2016)
References Stonetools Ltd (Tunbridge Wells) www.stonetools.co.uk (lots of advice re tools and drill/ cutting speeds, and purchase of many of the items mentioned above)
Health and Safety Executive. www.hse.gov.uk/pubns/indg463.pdf.
Mohs’ Hardness Scale. geology.com/minerals/Mohs-hardness-scale.shtml