Re: Cutting geodes
Consider dopping the geode. Use some dimensional lumber for the dop, to which you secure the geode with some acrylic caulk. Then you clamp the vise on the dop, allowing you to place the stone where and however you need it relative to the blade. I've put a few pictures online to help illustrate the dopping process:
I use this method extensively for slabbing end cuts and rough that is difficult to hold in a vise due to irregular shape, or the need to cut it with a specific orientation relative to the grain of the rock, such as with cats eye.
Usually I cut a flat on the rock first and then glue the dop to the flat. Often the flat is an artifact of first cutting the rock as far as you can in the vise, and the dopping procedure comes into play to recover the remaining rock. In the case of a geode where you can't do that or where cutting a flat for gluing is not otherwise practical, you will need to shape the end of the dop with a saber or band saw, rasp, etc. so you get a good fit of the stone to the dop. You can fill irregularities in the fit with adhesive to some extent, but you need to make the fit of the dop to curved or irregular surfaces reasonable or you may have issues with the adhesive flexing under load as well as taking forever to cure.
One advantage of dopping in conventional slabbing is you can cut up virtually all of the rock in the orientation you want and don't have waste left over in large nub ends that are difficult or impossible to clamp. I have used lumber ranging from a single 1x2 all the way up to several 2x12s bolted together to fabricate dops, depending on the dictates of the rock to be cut.
I have cut smaller dopped rocks the next day after dopping, but its really better to be patient and allow at least several days for the adhesive to cure. The thicker the adhesive in non-conforming fits, the longer it takes to cure and properly bond. The type of acrylic caulk I use (DAP Dynaflex 230) is white out of the tube and clear once cured. I also coat exposed open end grain on the stone side of the dop with a film of adhesive to help prevent it from soaking up oil. If enough oil gets in the wood grain behind the adhesive during the cutting process, the joint can become compromised with a wiggly or detached rock resulting.
You can remove the dop and adhesive after you are finished cutting by soaking in a pail of water. This can take a while for large dops with a lot of adhesive. Removing as much of the dop from the stone as possible by cutting it off with a saw helps to speed this process. A wire brush is helpful in removing the remaining adhesive from the rock.
If you decide to try dopping, I would suggest playing with a couple of smaller pieces first to acquaint yourself with the procedure and technique before you attempt a prized geode. I've dopped a lot of rocks for slabbing so if you have further questions about dopping just ask, and keep on rock'n!
From Bob Keller - November 16, 2007 at 09:29:27