How to hollow stone?

[Julianna]

So that I don't end up breaking another WIP (http://www.sculpture.net/community/showthread.php?t=6032), I thought I would ask if anyone knows what the best method is for hollowing stone.

Basically, I want to turn this into a concave section. I have been chipping away, which is fine, but I'm both wondering if there's a faster way and worried that I'll strike it at the wrong angle at some point and loose the top again.

[Julianna]

Basically, I want to remove this much from the inside...

[bhughes]

If you have an angle grinder you can make parallel cuts across the area just shy of the final depth desired. Then knock of the chunks with a flat chisel. They should break off fairly easy with little force required. Angle your strikes towards the meat of the stone and away from the edge. Then just clean up with a tooth chisel.

[Will]

How about an angle grinder with a zeck wheel or a diamond cup wheel? It's dusty, but much faster. Flapper discs work also. There's little stress to the stone this way.

W~

[grommet]

That seems like it would be an extremely fragile piece-- or is that the intent?

[Cantab]

This looks like alabaster, Julianna. So I wouldn't try to take that much away. The picture in your second post (with line) suggests that you will be liable to fracture the piece. If the other side has more depth, then you might get away with it. Before you try anything at all, hold the alabaster up to the light and look for tiny fractures or linear irregularities in the stone. These are weak points and will come into play when you make the stone very thin.

Angle grinder suggestion: Given the size of the piece, I suspect that you will need smaller discs (4 inch is far too big) and a die grinder to use them in. I have also used shaped carborundum stone attachments in a die grinder to do this work. This is a good option - minimal risk of fracture. This and small discs will do the job. Whatever you do, at this size, avoid trauma.

If you don't wish to go mechanical: I'd now strip away the material with a flat chisel, rather than a claw. (Claws are for punching; flat chisels can be used to strip off stone very gently). Take your time, and work slowly, with a softish support under the piece to absorb the impact of the hits (I use small sandbags). Then cut up pieces of hard carb discs to round out the shape to perfection. It's a couple of hours work this way...

[StevenW]

It's good you use something like a paintbrush to indicate the scale and this looks like a small chunk of rock. I assume you don't have an angle grinder, but they're indispensable. I also assume that like me, your studio space is small and confined, perhaps in the basement? Grinding rock indoors (your house or condo) is not a great idea as the rock dust will go everywhere and get into everything and if you have forced air it will travel throughout the house no matter how airtight you try and make the room. Nonetheless, this is a 2 minute job for one of these:
http://www.toolking.com/makita_9564cv.aspx

I like this model because it's cheap and is variable speed and has a 12 amp motor. I also like the Metabo tools, but their variable speed grinders are more expensive. The 4.5 inch is also small enough that you should be able to handle it easily enough without it overpowering you. The variable speed models are more expensive than your typical Home Depot kind, but you'll find that you need them for a whole host of different reasons, rock hardness being only one. With these types though you want to make sure that if you run it at low speed to run it at high speed for a minute or two before shutting it off. They cool down and eject dust at high speed and burn up faster at low speed.
You can also get a diarex convex diamond shaping wheel for 45 bucks to go with it, I use one that is 20 grit and another that is 100 grit. There's a Granquartz in Toronto I think and they should have them.

http://www.granquartzcanada.com/default.aspx

[Cantab]

I must disagree, Steven. The angle grinder's too big for this job.

[StevenW]

Oh, and seeing Cantabs post, yes he's right. The grinders will eat a small piece of stone like that up for breakfast, but with a 100 grit shaping wheel you can do pretty delicate work and at lower speed (this is why you need a variable speed grinder) it won't bruise or shock the stone unless you press too hard into it. Generally you don't need to press into the stone much at all, just let the grinder do the work.

[Julianna]

The angle grinder probably won't be the best option because, as Steven noticed, I'm working in a basement. Although I've got air purifiers all over, I don't think the place could sustain that much dust being created.

grommet: Yes, it's meant to be very fragile. But not TOO fragile ;)

Cantab: Thanks for the reminder about finding the fractures. I have exceeded the file attachment size for this post (should have made those first three smaller!), but there is a fracture diagonally across the back. That's why I wasn't too comfortable with doing much more work using a chisel.

Ideally, I'd just go at it with a dremel outdoors. I had briefly considered using a rasp, but I know I'd have to go through about three before I got it down far enough. Moving to Australia where there isn't winter also crossed my mind, teehee.

I think I'll go downstairs to stare at it and hope for inspiration...

[tonofelephant]

Juliana,

Do you have an electric drill with some concrete bits? If so I have a possible way to speed up your production.

The object is to drill a series of holes in a line (think of a groove like an angle grinder would do for you). Then drill several series or lines of holes. With your flat chisel and hammer you can then remove the stone remaining between the drilled grooves that you put in the stone.

After first using a small drill bit move to a larger drill bit. This will help connect the holes and make it easy to remove the waste stone.

To make sure that you do not go to deep, first mark the drill bit with masking tape for how deep you are going to drill. This will allow you to get the same depth hole every time. Also learn from my mistake. Go a little bit shallower than the finished edge - like 3/16" to 1/4". this gives you some screw-up room. Also prevents chisels beeing thrown across the room after the stone breaks badly from drilling to far.

This is procedure can be a bit nerve wracking but it does work. Better than working away at the stone with hammer and chisel or nibbling at it with a riffler.

Carl

[dondougan]

Julianna,

Given that you can't make a big dusty mess, Carl's suggestion of the bored holes is what I'd do.
Also given that it is alabaster you are working, I'd be tempted to use sharp steel twist drill bits at relatively slow rpm rather than regular carbide-tipped masonry bits.

One advantage to regular twist bits is they are relatively sharp all along the flute, and this means you can lean the drill from side-to-side when depth is reached and enlarge the holes to tapered slots which makes the waste easier to remove than the waste from just straight holes. Anything that reduces the need to create trauma with hammer & chisel is a good thing. In fact, to clean-up the waste a razor-sharp flat or round-nose chisel I'd suggest using a wood or plastic carver's mallet rather than a hammer.

For powertool shaping rotary rasps or burrs in a drill will work, but they tend to load-up very quickly in alabaster. I have hollowed-out functional vases and ikebana containers in soapstone and limestone (though never alabaster, as it is water-soluble) with high-speed steel cove router-bits (1-1/2" diameter - chucked-up in a drill rather than a router) following a pilot hole with the center nub. To smooth the bottom of the hole(s) you can use the cove bit after cutting-off the center nub with your Dremel tool.

Hand tools only? For what it is worth the ancient Egyptians made small-necked hollow vases from alabaster with bronze cutting 'wires' on a rotary tool to enlarge the drilled centerhole. Though the wire method wouldn't work with your big broad concavity, it suggests the scraping action could be employed -- what about a woodworkers' scorp or inshave? Perhaps modified more as a scraping tool rather than cutting/slicing (teethcut into the edge with Dremel tool?). I have an antique barking-spud which could probably be used to scrape the kind of concavity you contemplate. Alabaster is soft. Think creatively is my tool-using motto.

Don

www.dondougan.com

[Will]

Such great advice from everyone.I face some of these same issues everyday in the class room. As a Labtech/TA, I have to help the other students find resolution to these same problems. I will take this information into the studio and share them.

Julianna, I look forward to seeing the outcome.

W~

[GlennT]

Continuing on the drilling idea, I have a few bits that are for machining metal. I don't know what they are called, but they are constructed like a two twist drill bits in line 180 degrees apart from each other, with a thicker smooth shaft in the middle for the drill chuck to hold. Rather than having pointed tips, the tips are flat but retain the sharp cutting grooves that form the shafts. So if these bits are in a drill press which locks at a specific depth, you can then move the piece that you are working on and use the sides of the drill bit to cut horizontally into the material after you have drilled your vertical hole. It is similar to what Dondugan mentioned with a regular drill bit, ecept that you can move it around a lot further to remove as much material as you want.

I have used these on wood and metal, not stone. It requires holding the material very firmly and not forcing too much removal of material at a time, so as to maintain control of the piece. You don't want the bit to grab the material out of your hand and spin around like a propellor and zooming off into outer space, not that that has ever happened to me!:eek::p:o

[desertrock]

I would use this convex diamond shaping wheel on an angle grinder at low speed (1000 RPM). Use the 100 grit which will give very little vibration to the piece. Support the piece in a cradle of sand bags. The dust should be minimal and considering the softness of the alabaster you'll have your piece hollowed out in about 10 minutes. You'll use this tool a lot once you try it, and it will last for 20 or 30 sculptures (maybe more) of alabaster.
The link below shows this $30 tool. Buy it with the mounting hub for 5/8-11 threads to fit a standard angle grinder.

http://www.granitecitytool.com/showitem.cfm?itemnum=1513&catnum=14&pcatnum=91&mcatnum=92

Mark

[dondougan]

Glenn,

The bits are machinist's milling cutters. What you describe is exacly what they are made for -- and of course the milling machines use clamps or vise jaws to keep the whole cut very precise. I use something similar with my drill press and move the stone under the fixed-height of the rotating (carbide) bur (along the lines of a pin-router). Using a tool like that freehand takes a deft touch, plenty of appropriate safety gear, and a certain degree of self-confidence coupled with a savvy common-sense awareness of what will happen if(when) something goes wrong . . . i.e. make sure that propeller travels in a trajectory AWAY from soft flesh rather than towards.

The carbide burs (such as I use) are intended for high speed application in a die-grinder, and at high-speeds kick up a good bit of dust. Since Julianna was not too keen on dust I was trying to suggest slower rpm tools to keep the dust down. If a drill press is available I'd say use the milling cutters at a slower rpm.

More than one way to skin a cat . . .
Don

[Julianna]

Thanks for all the suggestions, guys!

After much thought, I've decided to pursue the hole-drilling option, but use a rotary tool instead of a drill. With the size of the sculpture and the tools, I think that one will be best for precision/control.

What I plan to do is mark the drill bit, drill a hole in the centre, then drill toward it from all sides. I don't think that area can handle much more shock, so this looks like it'll be a very slow process.

I'll post pictures once I have some.

[Blacksun]

pick up a quality half-round wood rasp at any hardware store and rasp away.... The orange alabaster you're cutting will shape rapidly with that tool.

[Julianna]

Thanks for the tip. I've been filing down other parts of the sculpture, and I think you're right. It's just a matter of finding a rasp with the appropriate shape.

Incase anyone is wondering, I haven't attempted that yet. I'm working on refining the rest of the sculpture to get the flow of the curves right before I work on that part.

[marblecutter]

My simple suggestion based on the photograph and the delicacy of the stone. Finish the outside as you intend to, then after a day of rest and a warm cup of tea, find a box larger than the stone. Pour plaster of Paris in the box and sink the sculpture as deep as possible and let it dry at the preferred angle without covering the area that will be carved away. When it is dry you will have a strong rectangular support for the delicate piece so you can carve out the core. You may wax the stone first to keep it from absorbing water from the plaster, or wrap it in thin plastic. Now you can easily drill and cut. Don't use the three or four-tooth chisel for that purpose as is indicated on the marks that I see. Use the a single point starting from a drilled hole in the center and work your way around it slowly and keep your tool sharp.

[StevenW]

That's a great idea Marblecutter.

[Julianna]

Now we're talking! And it gives me a chance to play with plaster of Paris!

If only my cold would go away so I could actually do some sculpting...

[marblecutter]

Julianna,
I have not been productive as well. Not because of a cold which would have been more welcoming, but a toothache. Because of the infection, the gum is swollen and the tooth can not be pulled until the antibiotics kill the germs. This is the season when people get sick and must refrain from work. It is nature and the body's way of taking its own break.
We must reluctantly succumb.

[Randa350]

Try Fibromyagia and sculpture....like living with the flu everyday. lol. Marble and Julianne, hope you guys are both feeling better soon. I can't wait to see the finished piece! This looks like it is going to be awesome.

[marblecutter]

Tooth ache went away after one month of pain and the final removal of the tooth. Two down and 30 more to go. "God takes us away" one piece at a time until the heart stops. Sometimes one is taken "whole".
Fybromiagia! I learn something new and feel that I suffer from the symptoms. Sculpture must be the activity that keeps us ticking until the clock of life winds down.

[Merlion]

Cldue, apparently your dentist also knows how to hollow, by removing your tooth.

Actually dentists are also trained on plaster casts, precision grinding and sculpting (of teeth).

[marblecutter]

The tooth was not hurting but had a metallic filing which was removed and replaced with a compound resin. Apparently a bacteria was trapped in the nerve and caused an infection. The new dentist is only specialized in pulling and would not let me keep the tooth which they claimed will be used for medical school studies. It is a big business with everyone on the planet having +- 32 teeth that sooner or later will need some form of work.
A friend who does bronze animal sculptures, trades his work with a dentist. I have never tried this type of bartering system. There is an Island where people used large stone discs as currency. The value was based on size and quality of the stone. In my country Haiti, the Gourd was once traded as currency. Paper money is still called Gourde. In 1972 when I left for the United States, 5 Gourdes were the equivalent of one U.S. dollar.
The Art of Selling. The dentist sells to me the anesthesia, the comfort and convenience of the office... and the expertise in the use of a pair of pliers.
How many dentists are equally happy with a piece of art, a sculpture, as I am in the absence of the pain that made me wish as did my brother with brain tumor for a lethal injection?
There was a mobile sculpture hanging from the ceiling of the dentist's office. The only art in the entire 4 story building. It was made of four geometric styrofoam shapes colored in fluorescent paint. They hung from sticks and strings and turned with the breeze of the ventilation in random directions. This piece of art diverted my mind only momentarily from the succeeding activity while the anesthesia took its effect. Across the street where mammograms are done for predominantly women, stands a sculpture that I made in 1992. It was donated by a patron who survived breast cancer. How many people I wonder, find comfort in the sculpture as they stare at it in the waiting room?
I have another sculpture called Family of Man. It is in a hospital on the other side of town. A friend of mine told me that she enjoyed looking at it while her husband was dying of cancer. Many people who work in that very hospital have never paid notice.
The pleasure I derive in creating sculpture is in the visual effect that it has on the viewer as well as the tactile if they care and and are bold enough to touch it.
What good is money when life loses its meaning in grief and pain?
Art is as powerful as medication - but the former is most readily cast aside and taken for granted and is regarded as being trivial and unnecessary - by some people who may find comfort in the hollow of a stone.

[Julianna]

After much contemplation, I decided to take the safest (and probably one of the slower) route and simply use a rotary tool on the stone. The stone just doesn't feel like it can take any more impact, and the space is too awkward for either an angle grinder or a hand rasp.

Here's a picture of the progress so far (not much to see, really).

[steponmebbbboom]

Julianna, at this point i would recommend irrigating the piece with cold water in combination with the rotary tool and a rasp bit, doing this will have two benefits: it will carry away swarf and prevent dust and clogging of the bit, as well as cooling the surface of the piece so as to avoid fractures. you will find using a low speed with the die grinder and irrigation will allow you to be more aggressive with the bit and spraying water will be minimal.

i have found dremel tools to be completely useless for all but the most delicate work because it has absolutely no torque. you can rev it up to thirty grand and stall it to zero almost immediately as soon as you put any pressure on the work. i would recommend a heavy duty 1/4" electric die grinder from a contractor supply store. two grinders that come to mind are the makita 906H and the Hitachi GP2. the makita turns at 30K just like your dremel but get this the motor is 3 amps vs. 1A or less for a dremel. you should find it locally for about $220. the hitachi has a 4.7 amp motor and costs about $200. the speed is non-adjustable and it will not last as long as the makita. but for what you are using it for either of these units will more than suit your needs and the icing on the cake is that with much less rotating mass and small bits you wont suffer nearly as much vibration as you would with open shoe grinders, PLUS the noise level will be so low you may find you no longer need hearing protection.

to use them wet you will need to use the water sparingly, collect all water in a basin possibly using a recirculating pump or empty the catch basin frequently, USE A GFCI OUTLET and ensure the ground fork of all plugs and receptacles are functioning correctly. never let water accumulate on the ground and never immerse the tool in water. if the grinder gets wet, shut it down. however i think youll find the absence of dust, increased bit life, lower noise levels and increased versatility of the big amp die grinder will be worth the increased set-up time. ive ground stone and glass dry and wet, and the wet method is easier on me and my work. dont forget to turn the rpm down if you can so it doesnt sling water everywhere; you wont need to go fast anyway with a good rasp and good irrigation.

heres a couple pictures, the green one is the hitachi. as i said the hitachi's speed is non-adjustable; my foggy recollection of using the mak is that it does have a variable speed but the mfr product description does not specify. it should be easy enough to fabricate a lexan shield to keep slung water from flying everywhere in the worst case.

[racine]

is Merlion a dentist too? one way occurred to me, might save some effort. paint the outer form with water soluble paint, red for example then bore a 1'' hole in the centre to the center of the stone. place a fused dynamite stick into this hole and centralise. light fuse, run away....intermission. [falling roof tiles].. now all the bits left over with red paint on reassemble. you can use children to do this as they like puzzles and come cheap, you can use stone filler* to stick and homogenise the new wonderful shell, almost like the original, voila!

* however i like sticky tape as it comes in different colours.

[racine]

seriously what about getting serious and splashing out on an air compressor, that way with the variable speed grinders and die cutters you can run water over the job or immerse a bit more. no dust, less damage. electrics away from job. revolution.

[Blacksun]

WHOA! Do not use water / immerse it in water/ wash it with water while carving.....when carving the orange alabaster..... The stone is far too fragile, unlike the marble and harder stones..... you will wind up with a broken mushy mess..... Kind of like carving a plaster block. Carve it dry or say goodbye to your sculpture.

When it's done, of course polish it with water, but never use water during the actual shaping!

[steponmebbbboom]

huh.

i did not consider that alabaster posed a specific risk to wet grinding. it seems to work quite well on other materials ive worked with.

if that is the case, i retract. the high powered die grinders may still be worth looking into, though. good luck and let us know how it turns out

[StevenW]

Depends on the kind of alabaster and at what stage you are at really... I agree the orange is a bit too soft already to handle water and generally I don't use any water on stone to begin with, dry is best for me. The alabaster I dig up myself would surely turn to mud as it is not the purest stuff to begin with (It's very beautiful nonetheless)... Die grinders and angle grinders and rasping by hand are all the same thing with different pressures and speeds. If one is careful enough with an angle grinder or die grinder and it is a variable speed model it should not present too much of a problem taking down even a small amount.. Don't be scared, if it breaks make another one and learn what kind of tolerance the rock has for the future. Being too timid with rock is as bad or worse than being too rough.

[Julianna]

Thanks for all the suggestions. The rotary tool is actually fine for alabaster. I have it set at a very low speed, but I do notice it stalling when I press too hard. It's all a matter of finding the right balance between speed, precision and control. When it comes down to it, I would much rather spend more time getting it done right.

http://www.unitedmedia.com/comics/dilbert/archive/images/dilbert2008031349276.jpg

[StevenW]

Ha, that's cute.. Variable speed tools are great.. Just make sure when running them at low speeds for any length of time that when you're done you crank up the speed to max and let the tool run by itself for a minute to cool down. Running rotary tools on low speeds cooks the motors on them generally as they are air cooled and rely on high speed to keep them cooler and dust free.