Recommended Slab Thickness For Cabs

I usually cut and cab rock slabs at about a 1/4" thickness.... Montana moss agate I go to 3/16th....

Yeah, 1/4" or a hair thinner. Anything thicker and you're spending hours grinding it down, unless you are purposefully making a really high dome (like for a cat's eye effect).

So I checked the thicknesses of the slabs and about a third are 7/32", which is fine for what we are doing. Could a "proper" cab be made with material so thin?

Al

When I have rough cut slabs for people who cab, the typical request is 1/4 inch unless they have a particular project in mind. When looking at complete rocks before cutting, I have seen guys use a finger to estimate how many slabs they think they can get from a particular rock. That kind-of takes into account the waste from the blade they are using and of course they know the size of their fingers. I have never seen anybody take out a tape measure. I also find it funny when a big finger guy tries to tell me that he can get x quantity of slices as part of the buyer's negotiation to underestimate expectations.

The real reason for this comment is your earlier statement that you looked at length x width of a particular slab. FYI - The best guy that I met did not focus on that. Instead, he looked at each individual slab with an eye to what parts he would later cut that would be exceedingly interesting. He had a great eye to find that one magical section to cab. Food for thought

I completely get that and while we did a little of that this is mostly an experiment to get our feet wet. It really is fun trying to find the best picture/scene/pattern in a given slab.

Thanks, Al

Good info as i was thinking thicker must be better (to a certain extent) but was not considering how much extra work it is and the toll it takes on the machines.

Al

Exactly. The old-timers knew this, and slabs as thick as some "prefer" these days just were seldom done for cab stock 40+ years ago. Around 4.5 - 5.5 mm (3/8" - 7/32") is what I recall being most common. Then everybody started grinding on ganged wheels. Sure, thicker slabs allow more room for material that has lots of flaws and pits (sometimes you can grind through them, sometimes you just uncover more) or for wasteful technique (i.e., using the coarse grinding wheels - or any grinding - anywhere near what will be the top of the cab, resulting in deep scratch marks that take a lot of extra sanding to remove), but plenty of fine cabs were cut back then from that thinner stock with domes, back bevel chamfer and even double-sided/domed pieces.

As said, cat's eye, star and extremely large cabochons beyond 30x40 can sometimes require more thickness, as can carving stock or pieces being used for non-wearable jewelry lapidary projects. Tight-patterned stones that can yield smaller cabs (for things like rings, brooches, small pendants or side stones) can be cut from much thinner slabs, as can more expensive varieties where grinding off any more than necessary is an indulgent, but useless, waste. IMO thin/low domes are easier to set and less liable to coming loose in things like rings (I've seen high-dome bullet cabs that people insist on putting in rings where it doesn't take much side pressure to lever them out of high bezels).

On the other hand, some jewelry, other work and stone types (e.g., translucent stones with interesting inclusions) look far better and are more comfortably worn when cut even thinner than 5 mm. There is no one-size-fits-all thickness. I've seen far more gems ruined by being cut too thick than too thin (plume, sagenite, triple-flow, turtleback, iris, etc. that look exceedingly dull set beside slabs/cabs from the same material that were thinly cut), aside from the wasted material. Depends what stone you are cutting and for what purpose it is going to be used.

We spent a good chunk of the day playing with the pendants we cut. Previously A.J. was just rounding the edges on each piece leaving the faces flat, figured that by the time they got out of the tumbler these would be more than adequate for his fair. After reading the replies here we wanted to see if we could put domes on them. To a newbie looking at a thin piece of stone it seemed that there was no way to get a rounded surface, but I'll be damned if we didn't do just that. We are just using a bench grinder (they will be tumbled later) now so these will definitely not be as refined as what gets posted here all of the time but it has been a great learning experience. Gotta say it was pretty addicting- I did the small ones as I didn't want him getting caught up in the grinder, have the burn marks to prove it.

Thanks for the help!

Al

I hear you about the bench grinder. I have a pretty nice variable speed grinder that I can dial in so as to minimize the heat buildup in the stone. It also has dust collection ports built in and is currently hooked up to one of my shop vacs with a very good filter. That in conjunction with continually dipping them in water to be able to see the rocks better has made for a pretty decent setup. To tell the truth, doing this with my son keeps me very honest when it comes to safety.

All of that being said this is a temporary setup as I see us getting into cabbing properly, there is far too much inspiration on this site and we want to get in on the action! At that point the grinder setup will probably just be used for preshaping tumbles. Have even thought about hooking it up to my woodworking dust collector as that has some serious pull, although it might suck the rocks right out of our hands. 

Pics will be forthcoming, they are next in line for the vibe. Probably be done two weeks from now.

Thanks, Al