How to carve small, "deep" stone bowls?

November 10, 2021 2:16 PM

I want to make rough, ~3.5" diameter, flat-bottomed, non-angle-grinder bowls in stone. They need much steeper inner bowl sides than a 4.5" angle grinder can do. How? Dremels seem slow and non-ideal. I've bought inexpensive bowls like this from import stores in the past. How do they do it?

I want to carve small, controlled, bowl-like items to use in (fairly large) terrarium water features. Every tutorial I can find carves bowls using an angle grinder, which makes shallow arcs in the stone.

Why not use a dremel tool? The Dremel tool I have, at least, isn't ideal. I've tried drilling stone with it in the past, and it was slow going, partly because it seemed to want to go too _fast_. Also it doesn't have a lot of power (this was corded), and seemed kind of lightweight.

I'm not necessarily carving very hard stone, but I'd like to have that as an option -- I'm still exploring what kind of stones to use.

Is there a router-bit-like thing I can use? Should I use a diamond hole saw / drill bit with a drill?

I'm open to hand carving methods or power tool methods.

These don't have to look refined or polished, but I do need to avoid leaving sharp points or edges.

(I already think I have the technology to make holes, lips/pour spouts, etc., but the bowl/water containing parts of these fountain features I can't figure out).

Current idea is to use a ~2" diamond hole saw, maybe making multiple cuts, then use a chisel to break out the individual sections inside the cuts. I'd like more precision, speed, and control than this though.

Examples of stone items that have similar proportions to what I want:

bowl
bowl
bowl
bowl
bowl

What I already know how to do but _don't_ want:

not interested
not interested

posted by amtho to Grab Bag (17 answers total)

I'd envision something more like a lathe.
posted by primethyme at 2:24 PM on November 10, 2021 [1 favorite]

Response by poster: Oh, I see, that makes a lot of sense. It might be how it's normally done.

If possible, I would love an alternative solution that
a) would allow me to make non-circular shapes, and
b) is less expensive and space-consuming than buying a lathe...

I was hoping for a hand tool... but I'll totally understand if it doesn't exist :(
posted by amtho at 2:32 PM on November 10, 2021

I know I've seen some marble carving being done with a hand sized air chisel or air file on the history channel or a history youtube somewhere. Maybe that would fit?
posted by Horkus at 3:03 PM on November 10, 2021

Best answer: A Dremel is a small and low powered version of a die grinder. So a proper die grinder and appropriate bits would probably do it
posted by RustyBrooks at 3:17 PM on November 10, 2021 [1 favorite]

(I've only used air powered die grinders but presumably electric ones exist)
posted by RustyBrooks at 3:17 PM on November 10, 2021

Electric (both battery and mains powered) exist. I've used several different plug in Makitas and they've seemed to be decent kit.
posted by Mitheral at 4:59 PM on November 10, 2021

I’ve seen hollow diamond bits that drill a donut-shaped hole with an attachment for coolant flow. You could drill holes, break off the cores, and then you’d have a lot less stone to grind off. Just a thought—I am not a stone-carver.
posted by Gilgamesh's Chauffeur at 5:14 PM on November 10, 2021

Fix your stone to a turntable ,fix your Drexel on the end af a long hinge as to steady the tool at an angle to the rotating work , find and enlarge the center I like using a diamond ball 5/16 . This takes time ,and coolant , the tool category at sciplusdotcom may be helpful . Once the opening is large enough agentle rotational motion with a diamond hole saw enlarge and deepen the hole.
posted by hortense at 5:27 PM on November 10, 2021

Best answer: When I saw people doing this commercially in a low capital environment, they used diamond hole saws and hammer drills to rough out little blanks, with some hand chiseling to knock the bigger chunks out, then followed up with a variety of die grinder tools. So exactly along the lines of your initial thought process. It's fairly labor intensive but you can carve out whatever you like. A die grinder, suitable hammer drill, and a few bits will run you a few hundred US. The pneumatic grinders are more compact and I find them easier to use, but inexpensive electric ones will do the job if you're short a suitable air compressor.
posted by jellywerker at 5:29 PM on November 10, 2021

Response by poster: jellywerker: Does the diamond hole saw have to be used in a hammer drill, or are those two separate steps you're describing?
posted by amtho at 5:56 PM on November 10, 2021

Those are two separate steps, but you can get drills that have both operation modes.

Diamond hole saws cut/grind, so you just need to spin them, hammer drill bits work with a fracturing action, so hammer mode will save you much frustration.

Good luck!
posted by jellywerker at 3:25 AM on November 11, 2021

Given the resulting thickness (or rather lack of it) of the bowl wall I would not use a hammer drill as there's a fair chance of shattering the bowl once you get it close enough to finished. Also, hole saws tend not to be particularly suited to a drill's hammer action.

What I would do is use a drill press with a hole saw fitted. Those can be used not unlike a lathe while keeping the object stationary, which IMHO would be a good thing if the object you're working on is badly clampable. Drill presses are way cheaper than a lathe sized for working on items the size you mention, take less space (I've got a large, freestanding one, and the floor area it takes is maybe 50x50cm, yours can well be a tabletop one) and hardly needs the training to operate one safely that a lathe requires. And after drilling out the bowl core you fit an appropriately-sized grinding ball (HSS or carborundum) to smooth out the rough shape.
posted by Stoneshop at 5:15 AM on November 11, 2021

Response by poster: Hmmm... what about a drill press with a [does this exist] large rasp fitted?
posted by amtho at 6:04 AM on November 11, 2021

They make grinding stones in different shapes to fit angle grinders. I’m not sure how well they would hold up to stone.

https://www.grainger.com/product/2D917

Or get a more powerful end grinder with a carbide bit. Think professional Dremel tool.

https://www.grainger.com/product/MONSTER-Cylinder-Bur-SC-22YA87
posted by ohjonboy at 6:17 AM on November 11, 2021

Hmmm... what about a drill press with a [does this exist] large rasp fitted?

That sounds like an accident waiting to happen. You'd have to simultaneously steady and maneuver the stone while at the same time raising/lowering the drill bit/rasp.
posted by Thorzdad at 6:35 AM on November 11, 2021

Stoneshop: to clarify, the hammer drill was used for initial roughing to get a pocket started.
posted by jellywerker at 11:59 AM on November 11, 2021

Drills, and drill presses particularly, are designed specifically to withstand axial loads. That is, the type of load encountered as you press the tip of a drill bit down into the material to be drilled. Transverse or lateral loads, like you'd get when trying to use a drill press like a vertical milling machine (say, plunging an endmill into the workpiece, and then moving the workpiece around to remove material) will generate forces that the tool is not designed for. In all likelihood, you'll quickly wear out the bushings or bearings in the drill motor, introducing wobble, and reduce what was once an accurate drilling machine into a wobbly piece of benchtop art.

Since it was mentioned, a router has a variety of bits available in different profiles and sizes, upcut and downcut, but with a bowl diameter of ~3.5", this is smaller than the bases of most routers and you'd have nothing to steady it on. You could possibly do this with a router mounted to a table, but you'd better have some really creative workholding jig for that, and ugh even typing this my brain is going NO THIS IS A REALLY BAD IDEA JUST STOP.

For such a (relatively) small piece, I'd go with, or at least start with, a good die grinder. Good, secure workholding is going to be important, and for me, building the perfect jig for a project is at least half the fun. Diamond cutting tools are nice and work very well for stone, but they're expensive and often aren't available in as many profiles as tools made from other materials, like tungsten carbide (which was pretty much the standard for industrial stonecutting, before diamond tools became cheap enough to be mass-market.)

Always assume that the workpiece WILL break at some point, whether from strain or an inherent flaw or weakness in the material, and consider where's the tool going to go when it does? And of course, wear proper PPE like a respirator, gloves, and eye protection, at all times.
posted by xedrik at 2:03 PM on November 11, 2021