Carving Obsidian with Power

Trapper John · Jul 4, 2019

Although I've seen several videos showing the results of carving obsidian with a variety of rotary tools, I've never communicated with anyone who has habitually - and successfully - done so. Consequently I'm turning to this forum to see if anyone else has experiences to share.

I can help keep conversation focused by sharing this background:

• I am an experienced power carver. I have worked in a variety of softwood, as well as in soapstone and pipestone. I've carved waterfowl, songbirds, grizzly bears, and pipes.
• Sorry, I have not taken any pics of my work. It is "okay" at best.
• I am well acquainted with a variety of tools and burrs. I would be interested in discussing bits and burrs used by others in carving this stone.
• I understand the characteristics of obsidian. I know it is "glass," that it shatters readily in a conchoidal fracture, and it is very, very sharp. It registers 5-5.5 on the hardness scale.
• I always wear safety gear when carving. This includes gloves, ear protection, a respirator, and full face protection.

I hope this helps to profile me as well as to give some idea about my experience level. What I would like to attempt to carve is a seated, howling wolf about 5 to 7 inches tall. In fact, we obtained a good amount of obsidian from Glass Butte after a recent field trip to Eastern Oregon. Now I'm looking for input from those of you who may have thoughts about and familiarity with this material.

What do you think?

hvacker · Jul 4, 2019

I'm sure you know what ever tool used, it has to be harder than what is being carved. Corundum, carbide, diamond.
I've seen bits for cutting small holes tiles that might work. Harbor Freight has some cheap enough to try. I think they are carbide.
A flat lap with diamond dust cuts most anything with flat features. I've done rough shapes with my diamond wheel 10" saw.
I'd like to see the work.

Trapper John · Jul 4, 2019

Hvacker, I do indeed plan on watching my burr choice. I've read, for example, that diamond burrs will "scratch" obsidian. While this may be quite true application of finer and finer sanding should polish out the scratching.

I will happily share the results of my efforts as I proceed. Being that it is summer and I spend more time collecting than carving this time of year, the actual work may proceed in fits and starts. I just hope this thread doesn't die out first!

Trapper John · Jul 4, 2019

Here's a quick update to my initial post.

Knowing that I started this, I had a hard time restraining myself so I took one rotary tool to a small scrap of obsidian to satisfy my initial curiousity. I've taken a few pics which will probably get posted tomorrow. Here's my "methodology" to this point.

Tools used

1. Dremel 4000 with a diamond ball bit. Cut a grove quickly and cleanly.
2. Same tool with diamond cutting wheel. Cut a small segment nicely.
3. Speed as set at 15,000 and 20,000 rpms. Faster is better based upon results to this point.

Comment
Since I cut close to a conchoidal fracture the material did break off close to the original fracture line. Memo to Self: Use unblemished rock first. Cut into block shape with a cutoff wheel . . . Perhaps an angle grinder with a diamond wheel. Proceed to carve as usual. Problems may occur along fracture lines and with impurities in the rock itself.

Next Steps
Previous observations were correct; diamond burrs cut but scratch. No attempt was made to polish and hopefully those of you into lapidary will have some thoughts on the flaps and wheels that may help here. I have seen some examples of relief carving on obsidian and it appears that detail can be preserved and polished. I am not troubled at all by the need to proceed carefully and slowly.
Also, I do have a microcarving tool that is a bit more sensitive to speed and may not heat up as fast as the Dremel.

I'll try to post pics tomorrow as previously noted. It's either going to work - or not!

galenrog · Jul 4, 2019

What are you using as a coolant and lubricant? I prefer water, but some carvers prefer various cutting oils.

Trapper John · Jul 5, 2019

H2O for me as well. I used oil on larger material, as in slab saw cutting, back when I first started playing with rocks. With smaller rotary tools a quick dip has worked on softer material but you raise a good point. I will have to consider a drip source before too long.

ToddsPoint · Jul 6, 2019

I've never carved obsidian, but have carved lots of other stone. I use a Dremel rotary with 1/8" and 1/16" shaft diamond burrs and a water drip. The small burrs are okay for small objects, but carving your wolf would take too long with the little burs. An angle grinder with a diamond wheel (which I have two of) would be too much for the obsidian and it would destroy it. So, you need diamond burrs in a rotary tool that are bigger than the 1/8" shaft Dremel burrs. You need a Foredom tool with flex shaft that take larger diamond burrs than the Dremel. Here's a couple of pics of stuff I carved with diamond tools. My DeWalt angle grinder w/diamond wheel (called a "V-crack tool" or "crack chaser") mounted on a Black & Decker work mate vise. With this setup, I can turn any rock in the world to dust.

The trilobite is Mook jasper from OZ. Duck is rutilated quartz, source unknown. Pendant is heated Kaolin flint from So. IL. Bear is red granite from local glacial till. Sphinx is dendritic steatite from Montana. Bear and Sphinx are both pipes. Gary

fuss · Jul 6, 2019

Nice Gary, that an 11 amp grinder?

Trapper John · Jul 6, 2019

Gary, that's beautiful work. It reminds me to start taking pictures of what I've carved.

Your.comments on burr size are much appreciated. I agree that it will be hard going with 1/8" burrs. Fortunately I have a Foredom/flexshaft setup, as well as microtool availability so bit sizes, hp, and rpm are pretty well covered. I also have a Dewalt angle grinder. I obtained plans for a grinder stand from a fellow on YouTube that has to be finished, so equipment-wise I feel ready. Assorted files, riflers, and other diamond cutting devices are also on my bench.

Basically I'm all dressed up and ready to go. The exception is larger burrs for the Foredom. Here I am less sure of myself, simply because the catalogs are full of choices and I am short on experience with harder material. Any suggestions here? That question applies to the angle grinder as well.

ToddsPoint · Jul 7, 2019

Trapper John said:
Gary, that's beautiful work. It reminds me to start taking pictures of what I've carved.

Your.comments on burr size are much appreciated. I agree that it will be hard going with 1/8" burrs. Fortunately I have a Foredom/flexshaft setup, as well as microtool availability so bit sizes, hp, and rpm are pretty well covered. I also have a Dewalt angle grinder. I obtained plans for a grinder stand from a fellow on YouTube that has to be finished, so equipment-wise I feel ready. Assorted files, riflers, and other diamond cutting devices are also on my bench.

Basically I'm all dressed up and ready to go. The exception is larger burrs for the Foredom. Here I am less sure of myself, simply because the catalogs are full of choices and I am short on experience with harder material. Any suggestions here? That question applies to the angle grinder as well.

I'd say buy an assortment of diamond burrs for your Foredom. Round ball and football shape are useful. Buy several shapes and try them. The most useful shapes will become obvious. Post some pics of your attempts at the obsidian. I'm sure you know to wear a mask when grinding that stuff. Gary

ToddsPoint · Jul 7, 2019

fuss said:
Nice Gary, that an 11 amp grinder?

I'll have to check. It's a DeWalt but nothing special. They last a couple of years and the bearing eventually go. Gary

Trapper John · Jul 7, 2019

Gary (and others), do you have a few manufacturers/brands to suggest? In the past I've experimented with diamond sets available online for less than $20 and I've planned on finding out what seems to work best and then to upgrade. Spending $30 each per bur may be justified in the long run but for this dust-and-chips maker it's a bit too early for that! As you pointed out shank size is a key consideration and it seems to me that plating quality adds yet one more variable to the equation.

ToddsPoint · Jul 8, 2019

Trapper John said:
Gary (and others), do you have a few manufacturers/brands to suggest? In the past I've experimented with diamond sets available online for less than $20 and I've planned on finding out what seems to work best and then to upgrade. Spending $30 each per bur may be justified in the long run but for this dust-and-chips maker it's a bit too early for that! As you pointed out shank size is a key consideration and it seems to me that plating quality adds yet one more variable to the equation.

I'd start out with the least expensive China burrs and see how they do. I've had good luck with Chinese diamond tools. Another source I use is Texas Diamond Tool Co. Much higher prices there. Gary

hvacker · Jul 9, 2019

I once worked in machine factories. Cutting fluids were used instead of plain water. Even though metal was what was being cut I use the fluid because it makes water wetter. It's a 20% emulsion of the fluid and water but it can be diluted to what ever I want. I believe it helps with the cuts and helps preserve the cutting edge. I buy it at NAPA.
Oil can penetrate soft rock and stain it. Turquoise for example. Oils also don't carry away heat as effectively as a water based fluid.
I don't think I'd use fluid with a peanut grinder. Unless I needed a bath.

Trapper John · Jul 17, 2019

Here are two pics representing my "experiments" with obsidian. I worked with the material as follows:

1. Obsidian source was the Glass Butte area in Oregon. Sample was selected chiefly for size and apparent lack of fissures, etc.
2. Rock was cut with a Dewalt angle grinder using a 4 1/2" diamond blade.
3. Carving tool was a Dremel 4000 using balled shaped diamond burs of indeterminate grit and size.
4. No attempt was made to refine dimensions or shape. The key question was to determine how the rock would handle rough carving.
5. No attempt was made to polish the rock.

Observations

1. Initial Cut
* Tear-out was observed on the initial diamond cut. (Note pic #2 where the "edge" cut is shown.) Entry and exit points of the blade are clearly defined. I believe the fixed speed (11,000 rpm) of the grinder coupled with the thick kerf of the diamond blade contributed to this annoying but thus far insignificant problem.

* I think I will try to find a thinner diamond blade for my grinder. Alternatively, a tile cutter may prove to be adequate for my slab thickess, which will ultimately be <= 30cm.

2. Object Shape
* The "spiral" was cut without regard to final dimension or appearance. I focused on determining how easily the obsidian carved a spiral shape. I also wanted to judge depth of cut and surface appearance. This is an experiment, not an attempt at laying out a proper ammonite.

3. Next Steps
* Polishing Experiments - the objective being to obtain the characterisitc gloss of fractured obsidian. I will start on the edges and experiment with different tools and grits. I'll then attempt to polish the 'carved" surface.
* I also have a Foredom Flexshaft and "H" series handpiece. Unfortunately the brushes needed replacement and are on order, so I can't report on the benefit of the higher hp which is quite a bit greater than the Dremel.
* Bear in mind that I am trying to learn what experienced Lapidaries already know! Any comments, advice, or additional referals to reference material will be gladly accepted!