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[montanajohn]

  I am looking for advice on what methods/equipment you all are using to grind and polish faces on larger specimen rocks.  I have been using the richardson high speed sander but it does have drawbacks as it polishes only the face and will chip edges and the face as well.  8" expanding drum hasn't worked well for me either but I'm probably doing something wrong.  Any advice would be appreciated, thank you

[55fossil]

    Yep, Richardson's sander is not the best for cabbing. It sure is great for T-eggs and other things though.  The Expando drums are my go to for large cabochons. You need to make choices based on room and budget. Those really big diamond units are great too.
    Expando drums with silicon carbide belts can fit every budget and size. I have a variable speed two drum unit with a water feed. Quick and easy to change belts. Also, the water drains so you have fresh water at all times. Much safer as you are not tossing waste water with silica into the air and your lungs. Still need to wear a mask for safety. But cutting with clean water is tops. Belt selection is crucial. It is cheap to have a huge a selection of belts from 60 grit to as fine as you want.  I had a friend who ran a single drum unit with water feed and he cut great cabs on it, any size you wanted.
      I also have a diamond genie that I love for small to medium cab cutting. But cutting large cabs can have it drawbacks like when your big cab catches the edge of another wheel and leaves a big gouge. It recycles the water so you need to change it frequently. Thinking about hooking up a water feed to it and a drain????? 
     You did not say what type of setup you have for your expando unit.  Show a picture or give a description and maybe someone here can help you become a pro at using it.

[montanajohn]

  What I'm looking for is advice on large specimen's, with say, 4' to 10' faces, rather than cabs.  I have a genie, and an old frantom set up with 8" 60 100 and 200 hard wheels, but none of these will work on large faces.  I have tried an 8" expanding drum but am not knowledgeable about the belts and have created more scratches than polishes.  If you could advise on belts, or are there other methods?  Used to see something called a bull wheel advertised but don't know anything about them.  I have a pretty good pile of stuff I bought that didn't work.....
Thanks

[vitzitziltecpatl]

Something like the unit in the following link would be good if you can get a decent scratch free pre-polish.

https://richardsonrockranch.com/lapidary-equipment/

A wet sander/polisher like those used on countertops might be a good option, too.

[55fossil]

   BELTS:   Silicon carbide belts run wet are the gold standard to many lapidaries. While there are basic standards such as starting with 100 grit and progressing through 800 grit and then polish the cabochon. This does not apply to every type of jasper or agate, etc.  Soft stones, hard stones and then the tricky stones that have mixed hardness all require a different technique.
     Things to consider when using silicon carbide belts: You can use too much water and the stone never seems to cut. Too little water and the stone burns or chips. You need to check the stone as you polish and look for the scratches left from each polish stage. Pressure: Same as water, too much pressure and you leave scratches or burn the stone, too little and you never seem to advance the cutting and polishing. Dry sanding is okay. Use a face mask, gentle force and go slow. Wet cutting is slower at first but can be faster once you learn a good technique.
     Some people seem to have a natural gift at cutting stones. Practice is the best teacher for most of us.  Practice on stones you do not treasure until you develop some decent skills.  There are some books that can teach you the basics but a club full of lapidaries or good friend can be much quicker. You will need to develop a technique that works for you.....
      Then there are the little tricks. Many cutters like to use a really worn 100 grit belt to get a blistering polish. Often this is run dry with very light pressure on the stone. I like to use a 100 grit diamond wheel to do my rough shaping and then switch to SC belts. A wet diamond wheel cuts so fast and no burnt or chipped stones.
   There are a lot of helper techniques for beginners. Draw lines on the preform so you can see how you are progressing as you cut. Start at the outside and work in on domed stones. Too many to list...

Google, read, repeat. Then practice, practice and more practice........  good luck

[montanajohn]

Thank you for the good information.  I am confused some on these sc belts though, as when I went from a 320 to a 600 I got pretty deep scratches, which only came out with a 200.  And you are saying a 100 for a polish?  So if I went to straight diamond belts would that help, and what grit sequence?  Is the 8" expanding drum still the best route?  I've made thousands of cabs over 20+ years  with diamond wheels but am stumped on these large faces.
 I appreciate your help

[gunsil]

I have never polished large faces of specimens, but my friend who does so uses a flat lap. Sounds like that is what you need. 55fossil, you seem to keep referring to cab work while montanajohn wants to do large flat surfaces, much larger than any cabs, and cab machines and equipment will not suffice. A 15" vibrating flat lap will make perfectly polished specimen faces up to 12" across.

[irockhound]

Just to add a note.  Depending on the size of "large", you can buy 6 and 8" no hole flat lap disks that have a 1/4" threaded stud out the back just like the polishing wheel for the Genie and Titan. This allows you to have a full 6" or 8" surface grind on your Cab machine or facet machine.  Obviously if large is over that size the various flat laps like the vibrating and reciprocal allow you to do much larger.

[55fossil]

    Montanajohn said he is polishing faces on larger specimen. I assumed he is putting a rounded face on them although a flat face is okay as well. Either way, he asked about 8 inch expando drum polishing so that is where I went with my answers. If he is only polishing flat faces it needs to be mentioned. I would definitely use flat laps or even recommend the Richardson's high speed sander like the one I use. Great machine that will burn and chip rocks, shred your hands and cover you in rock dust if you are not careful. And it is fast too.

     Belt Sequence:  Start low, say 60 or 100 grit for hard surface, possibly 220 for softer. Continue with higher griot in sequence. I did not say to polish with 100 grit, but you can polish with a worn 100 grit. You need to practice, practice and practice to learn what works with your equipment and techniques and the type of stones you have. Even the experts chip and burn a stone now and then. Try searching the data base here for previous discussions on polishing. There are so many possibilities to cover. It is tough now with this Covid crap. I learned a ton at the Gresham, Oregon rock club from people who showed me techniques and different machines. Then I practiced cutting scraps from the waste cans. A lot of scraps...... 

[montanajohn]

  Thank you all for the the good information.  This is mostly agates, usually Montana, pieces for presentation.  There are no rock clubs in 200 miles and no lapidaries I know of so the answers need to come from here, which they do, there are a lot of knowledgable people on this site.  I'll gather this up, sit down. shut up. go to work.
Thanks again, all of you

[Felicia]

There are 12" no hole flat laps available.  Glass artists use them, but the wheels are the same kind of diamond, co$t more, of course. Not big enough, I guess for the 10" ( that's " not ', right?) Vibrating laps available in large sizes, again, $.

[montanajohn]

Thanks Felicia, and I have tried vibratory flat laps in the past, probably should again, but they require patience which I was not blessed with any of...

[vitzitziltecpatl]

Montanajohn - You and I were blessed with similar amounts of patience.

That's probably why I thought of polishers for countertops. Would be easy to grind concave areas into a face until one got used to the feel of the tool, but should reduce the type of scratching you've been experiencing using other methods.

Would be quicker, too.

Good luck with whatever method you decide on.

[montanajohn]

  I do need to ask one more thing...
have any of you used the wet belt sanders, like the covington, with a large belt area to work on?
Worthwhile investment or just more stuff?

[vitzitziltecpatl]

If it has a large enough belt area to avoid scratches from the belt edges, it would be the best solution.

No swirl marks to worry about. Same as sanding on a wheel except for the stone being stationary instead of the "wheel".

You might still want the Richardson's Buffer for final polish. The domed padding under the leather is great for large surfaces. We have one of those. I just made a second head for ours to use with a different compound. I have not used the large wet belt sander.