Dopping to Finish Back of Stone

[GKJdesigns]

When I first started cutting I tried wax and didn't like it at all. And except for larger stones, I dop with super glue and use 1/8" brass rod rather than dowel or nails. (I cut opal, so a large stone for me is anything near or over 15 mm.)

Once the top and sides of an opal are finished, and after removing it from the brass rod, I finish the bottom off differently. If its a large stone I'll now use PVA glue (Elmer's) and a dowel. Most are not large, of course. If the dome is low or flat, I *might* use brass rod again. But usually I use a dowel with... (drum roll) ...hot glue. Yes, a hot glue gun. It takes a little practice to use well (what doesn'?!), but it's faster than wax, or at least I am.

With the back finished off the opal goes into the freezer for about 20-30 minutes. Then, unlike wax, after removal from the freezer only a small percentage fall off the dop. I generally have to work them off with a fingernail and often need to scrape glue residue off the face. It all comes off but, being anxious and lazy at this point, it would be nice if they more or less fell or popped off as with wax.

So I was wondering if anyone has any other techniques or options that might be viable and maybe easier.

With this team, we have to cut to Ben Stein: "Anyone? Anyone?"

[StoneTemple]

Ben Stein?
Gary, I might recommend giving the wax another try.
A retired cutter shared this tip with me that he learned from cutters in Thailand.
Have your stone on a flat surface with the side to be dopped face up, hold the dopstick with wax on it about an inch above the stone, with your other hand, light a disposable lighter and place the flame directly on the stone with the top of the flame heating the dop wax, only takes a few seconds. Ususally about the time the wax starts to drip (or catch fire :D ) it's ready to place on the heated stone. If you need to adjust the stone position just hold it it the tip of the flame again and adjust as necessary.
I've used this technique for many years and have even used it carefully with small opals, but would hesitate using it with any opal over a few mm's.
The advantage with the wax is it only takes a few minutes in the freezer for them to fall off and remenants can be scraped off with your fingernail.
The other dopping compound I use is superglue but don't like the long wait for removal via acetone.
HTH
Mark

[GKJdesigns]

Thanks for jumping in, Mark, and thanks for sharing the wax dopping technique. I have thought many times about giving it another try. Your way sounds quick and clean. That's worth trying. I'll have to buy some wax again! Do you use green?

Do you use brass rod or a nail for the dop when you use superglue? If you are using metal you can stop using acetone. Using one of the cheap butane torches you can get in any hardware store, I heat the rod about 1/2 inch from the stone while rotating the rod in my right hand. After a few seconds, I gently grab the the stone with the thumb and index finger of my left hand and give it a slight pull. If it isn't ready to come off I just heat for a couple more seconds until it comes off easily with little or no force. Then a few strokes on lap or fine sandpaper removes the residue.

You have very nice stones in your shop! Very creative shapes.

The Ben Stein reference is from Ferris Bueller's Day Off - remember the economics teacher who put his students to sleep? Stone Cutters is a little sleepy, too. But you woke up! :)

Gary

[GKJdesigns]

Here's a postscript on hot glue.

I put an opal (dopped with hot glue) into the freezer this morning after finishing the back. And then I forgot about it until just a few minutes ago. So it's been in there for about 8 hours, not 20-30 minutes. I removed it, grabbed the opal with my free hand and pulled with a twisting action. The opal came almost completely free with no real force. The edges of the hot glue shattered like glass. There was a little residue but it came off very easily with a fingernail.

Hah! I wasn't keeping them in long enough to reach the temperature of the freezer. A couple of hours should be more than adequate. Maybe I don;t need wax...

Gary

[StoneTemple]

Hi Gary

The hot glue sounds pretty slick too. Thanks for the butane tip. Actually my last batch of stones I popped from the brass dops using a razorblade. I had polished the back sides first, then superglued to the dops, preformed rounds using a friends faceting machine, then finished them, get this, by chucking the dops up in my electric drill, (SAFETY WARNING READ NEXT POST!!!) firing up the Nova wheels and giving them a quick spin through the grits, rotating the drill to spin the stone surface opposite the wheel direction, I can quickly shape the profile on a 280 grit, clean up on a 600, a quick pass on the 1200 then 3000. After that I match the direction of rotation and move to hte leather pad w cerium, thus converting my 1725 rpm disc to a much lower speed for polishing. I have no idea what the resultant rpm is but it's probably closer to what is typically recommended for polishing.
Anyway, these were all produced with this method very quickly.
http://www.flickr.com/photos/stonetemplelapidary/8514037831/in/photostream

Mark

[StoneTemple]

DANGER!!! DON'T TRY THIS AT HOME

Ok, ok, so the previously mentioned method is not without it's electrical shock hazard. There is a bit of water that splashes on my drill, which is double insulated, I am aware of the potential danger here but the water on the drill has been minimal. But, to help prolong my life I have purchased an air compressor and pnuematic drill to eliminate any risk of electrical shock.
I was going to get a cordless drill, but wanted a short right angle head to get different angle approaches to the wheels that aren't possible with the usual hand drill shape and the battery operated right angle drills I looked at seemed rather large and bulky. I just recieved the pnuematic drill in the mail yesterday, so I'll see if it's small size will be as effective as I imagine.
Mark

[GKJdesigns]

Superglue - I use Loctite 454 for dopping, a gel superglue that is excellent for rough, uneven, or porous materials. It is amazing glue for dopping.

To flatten the "back" of a piece of rough opal I use a 360 grit diamond disc. I don't bother to go any finer because very often the profile of the stone can change as the opal is cut. In that case I end up changing the plane of the back. I do like to finish backs at 600, though.

Locktite 454 works great on flat surfaces ground with grits up to 600. I've tried it with stones and brass dops polished with 1200 and 1500. While for superglue you might expect that the flatter and smoother the better, but at those grits 454 fails for me. I can get through only a few wheels before the stone falls off. Though it does happen, it's unusual for that to happen for surfaces prepared with coarser grits. 454 seems to like surface defects!

The best deal is the 20 gram tube. The best deal on that is from this guy on eBay: http://www.ebay.com/itm/LOCTITE-Instant-Adhesive-Cyanoacrylate-Super-Glue-ALL-/360485950460?pt=LH_De...

If your more comfortable with Amazon, here is the best deal there: http://www.amazon.com/Loctite-Prism-Surface-Insensitive-Adh/dp/B0001A3HRW/ref=sr_1_4?s=industrial&ie...

Be sure to squeeze from the tail of the tube and to keep the nozzle clean. This stuff doesn't seem to dry up and clog like standard superglues, but you might at some point need to clear the tip with a needle. Keeping it refrigerated extends its life, but I don't bother. It just lasts and lasts.

Just a satisfied customer,
Gary

[StoneTemple]

I had found a 4 gram bottle of Loctite Ultra Gel Control from the local Winco for a few bucks, probably not the most economical way to purchase but when I found my old superglue tubes had solidified this was "super" convenient.
Hmm, not sure I'm going to use that air tool, it's much louder than I had anticipated. Wouldn't be an issue except I'm living in a duplex and the neighbors are almost always home. Looks like the cordless drill will be my modus operandi.

[GKJdesigns]

Yeah, that gel superglue is good stuff.

I'm anxious to hear how your cordless drill works out, Mark. Every time I find the color in an opal almost demands a round cut I cringe. If i was a faceter it would be easy, but I just wing it on the wheels. And, of course, the slightest deviation from round is immediately noticeable to the eye - but often not caught until I'm two wheels past 600! It's not so noticeable once bezel-set, though. :)

[Former_Member]

Mark, great pointer. And written very well.
Encouragement and sharing is half the battle for newbie cutter and polishers.

[StoneTemple]

Thanks Mickey
Nike's slogan Just Do It! should be the mantra of anyone wanting to get into a craft, there's no better way to learn IMO. Sure, read up from some authorities on the subject (the old books on lapidary from the 50's and 60's still apply today though some of the tooling has improved (diamond wheels can't ne beat), ask questions if you need, but learn from doing.

[Former_Member]

Some of my best info has come from old hobby books. The guys at the club have also been helpful with assisting me at different junctures of my rock work.

Tutorials online work for some techniques, being able to watch and learn by doing.

[StoneTemple]

Hey Gary
So I got a cordless drill for the rounds but the rpm's (900) are a little slow. The low rpm's can contribute to bounce of the stone against the wheels, particularly if the stone is not perfectly round to begin with.
Will look for a higher rpm drill next.

[GKJdesigns]

I wonder if a faster drill would be significantly better, Mark. The stone would still bounce to some degree. I think the main problem is that the drill is handheld. All it takes is one little bounce to set up some reinforcing bouncing/vibration and i think that would ensure that the stone would be out of round.

There might be a way to modify the cab rest that comes with a Genie. I'm thinking of some sort of bushings (brass nuts? Miniature bearings?) that could be mounted on the cab rest. Then insert the brass dop and chuck it in the drill. Your free hand could then hold the cab rest steady while the drill turns. That would do a lot to minimize or possibly eliminate bouncing.

You've got me thinking. I never use the cab rest that came with my Pixie. Hmmm... ...maybe another new product? ;o)

[StoneTemple]

Well, when using the plug in drill, if I got a little bouncing going on I could crank up the rpms and it would go away. I did let one cab go with it and got somewhat of an oval out of it. :)
My cabbing unit is an old Fran-Tom that I've stuffed 4 of the large Nova wheels into. I've thought about adding a steady rest to it that I could mount various fixtures to, maybe a crude faceting jig of some type. Also something like a small arbor that could be set to different angles, perhaps with a keyless chuck on the wheel end and a small shaft that could be inserted into a Foredom handpiece.
Anyway, past my bedtime. Must sleep...

[GKJdesigns]

I think that you're onto something with the rpm, Mark.

Running your drill at an rpm that is an even multiple or fraction of the rpm of your wheels could contribute to the bouncing. For example, if the drill and wheel rpm are equal, then the stone and the wheel would always make contact at the same points. If one rpm is twice the other, identical contact would occur half as often but still enough to cause bounce due to edge roughness of the stone. The wheel must contribute to some degree as well because it sure can't be perfectly round. I would think that varying the speed of your drill as you cut would also improve the results.

I had never heard of a Fran-Tom unit. I found this link on the Rock Tumbling Hobby site where someone was modifying one similar to yours:
http://andy321.proboards.com/index.cgi?board=tips&action=display&thread=38900&page=1

Making jigs, fixtures, and modifying tools always eat into my time! But I enjoy doing that as much as cutting or making jewelry.

[StoneTemple]

That's the machine I have, but I still have the saw on mine. Like I said, I've got 4 of the 8" novas in it, I've redrilled the holes in the top and relocated and added water drip valves.
When I bought it I needed to have a new shaft made as the original was bent and caused the saw blade to wobble badly.
I then replaced the two stone wheels with diamond. A plated steel100 grit and 280 grit and a 600 and 1200 grit nova wheels, I added a flex-o-disc on the end with a leather pad and used mainly cerium oxide, but sometimes aluminum oxide for harder stones.
The problem for me was the steel plated wheels wore out too fast and they're expensive.
I finally made my own flat lap on the cheap by putting a shaft adapter on an electric motor, mounting that in some angle iron and using a cut down plastic bucket for a splash guard. Thin 8" diamond discs are cheap compared to wheels, I now use 100 grit flat laps for shaping, and have 4 Novas in the FranTom unit, a 280, 600, 1200 and 3000.
Works great!

[StoneTemple]

Actually I need to build a new flat lap, I've gone through a couple iterations of my homemade jobs, all the pressure is right on the motor shaft and they eventually die. They're usually good for a few years though. Next one will have a belt driven shaft mounted disc, should last me forever. Until then I have use of a faceting machine which is a great flat lap not to mention the faceting head.

[GKJdesigns]

You'll have to post some pictures, Mark! Maybe start a new thread, too, describing how you made it.

Where do you buy your 8" diamond discs?

[StoneTemple]

I buy the discs where ever I find them cheap, numerous ebay sellers, Kingsley North, etc.
You need a base lap wether it's diamond plated or just a plain lap. Then I use the thin top discs, they sometimes come with a sticky back but I don't bother with that. I think I probably get as much use out of a $25 8" 100 grit lap as I do out of a wheel costing 6 times as much and I can change it in a minute as opposed to taking nearly an hour to disassemble my machine to replace a wheel.
I will post pics once I get around to building a new flat lap, I just have no incentive to do so with the faceting machine in my possession. :D

[Former_Member]

Just a little add on dopping..Funny when setting up a large volume cutting setup..I once cut several thousand cabs a day. My biggest challenge was dopping. I used several techniques depending on material..I cut many plastic and stabilized stones so could not use solvents to release the stone. I also used many materials for dops..tried every thing from phenolic fiberglass to brass to wood to plexiglass and each had its place. this was on the auto cabbing machines..but I would think on the opal to polish the back..use wood dops and white glue.when done put in warm water and it melts off..could not be easier...but the glue will only hold for a small time after exposed to water. I used white glue on my ultrasonic cut small turquoise cabs to grind the dome and then finish in a tumbler..I did thousands a day with that setup..much time was saved using the water melting glue..now there are several white glues and I had access to the formulators in the lab at Borden..they told me the school glue is the most water soluble and was developed for the kids to wash out of their clothes and melts the best..white glue second and then the yellow wood glues..
Have fun
Jim

[Former_Member]

I've thought of using white glue, but I guess I don't have the patience for it. I use gel type super glue and standard wooden dowels. I find the gel holds much better in this scenario than the regular liquid super glue. Then to release the stone I soak in acetone for a couple hours. I don't work with any stabilized materials so I guess that's why I can get away with this method.

Gary, how long do you have to wait for the white glue to dry before you can start cutting?

[GKJdesigns]

Hi, Philip - I use Elmer's Carpenter's Interior Wood Glue or Titebond II, but not for finishing backs, just for the original dop for larger stones. I've not tried plain old white glue but I think it would work fine. Before putting it to the wheels I coat the glue and a portion of the dowel with nail polish to make it waterproof. I'm leery of the school glue that Jim used but it may be OK if given the nail polish coat.

Just to be safe I always allow the glue to dry overnight. So I often glue in the evening knowing that I'll be ready to go anytime the next day. That helps me somewhat to deal with my lack of patience.

I dislike soaking stones in acetone to remove superglue and of course can't do that with doublets. The acetone gets funky with the dissolved glue and I worry about leaving a coating on the stone as it evaporates. I also try to avoid the fumes as much as possible, too. Part of my problem is I seem to always be looking for a suitable container (unbreakable with excellent sealing) for a small amount that would make it easy to fish a stone out really fast.