Greg Tidwell
off to a rocking start
Member since August 2016
Posts: 5 
|
Post by Greg Tidwell on May 30, 2017 12:20:18 GMT -5
Hi all,
Sorry if there is another thread on this. I searched and found nothing, but wasn't confident that I searched all the right terms. Please give a link if this has been done to death.
I am a novice stonecutter. Well, maybe intermediate. I've been at it for several years now. But I have never been able to figure out how to get softer materials into perfectly round cabochons. It seems that they frequently are a bit lopsided. I was wondering if there are any tips, tricks, approaches, et al that I am not aware of. So, how do you guys get perfectly round cabochons?
Thanks! |
|
|
|
Post by Drummond Island Rocks on May 30, 2017 12:43:14 GMT -5
Hi all,
Sorry if there is another thread on this. I searched and found nothing, but wasn't confident that I searched all the right terms. Please give a link if this has been done to death.
I am a novice stonecutter. Well, maybe intermediate. I've been at it for several years now. But I have never been able to figure out how to get softer materials into perfectly round cabochons. It seems that they frequently are a bit lopsided. I was wondering if there are any tips, tricks, approaches, et al that I am not aware of. So, how do you guys get perfectly round cabochons?
Thanks! Most fool proof way is to use a diamond core drill to make your preforms then just cab the dome. www.kingsleynorth.com/skshop/product.php?id=46592&catID=1179The I.D. of the bit will be the O.D. of your cabochon  Chuck |
|
gemfeller
Cave Dweller 
Member since June 2011
Posts: 4,063
|
Post by gemfeller on May 30, 2017 12:44:57 GMT -5
What kind of grinding/sanding machine are you using? Does it have a cab rest? If it does, using the cab rest to grind exactly to the outline is one way to accomplish accurate rounds. It can also establish whatever angle of girdle you want.
Other methods include using a rotary device like a Foredom to spin the preform against the grinding wheel; using an automatic preformer, available on some machines; free-wheeling faceting machines; drilling round cores and slabbing them into perfect rounds etc.
You can grind very accurate rounds free-hand if you're patient and careful. I built an arm-rest in front of my Genie so I can lean my forearms on it go allow maximum control. I'm sure you'll get other answers but those are the ones I'm familiar with.
|
|
bsky4463
fully equipped rock polisher
Member since September 2013
Posts: 1,696
|
Post by bsky4463 on May 30, 2017 12:46:06 GMT -5
Use a diamond hole saw or ..... rough cut preform circle as close as you can, attach to dop that fits into a drill or rotary tool (foredom), chuck the dop in the tool, hold perform perpendicular to wheels or lap, with both spinning you will get the perfect circle. Use plenty of PPE and stand off to the side, sometimes the cabs peel off the dop and go flying. Good luck. Cheers
|
|
|
|
Post by Lapidaryrough / Jack Cole on May 30, 2017 13:37:04 GMT -5
Preform + small gas engine valve stem + drill on GFCI. or battery drill. i use diamond 8'' & 8'' silica.
And i use old valves from my 202 heads
Nice way to do sheen obsidian
|
|
hh5
starting to spend too much on rocks
Member since January 2012
Posts: 136
|
Post by hh5 on Jun 5, 2017 15:45:30 GMT -5
Thanks for the tips, still trying to get a uniform round.
|
|
jeannie
spending too much on rocks
Member since January 2017
Posts: 266 
|
Post by jeannie on Jun 6, 2017 9:42:18 GMT -5
I draw concentric circles around what I want to be the center point of my circle, and then go very slow to shape it so that those circles disappear, one at a time, in a very uniform way. I love circles!
|
|
thankyou
off to a rocking start
Member since January 2020
Posts: 12
|
Post by thankyou on Jun 16, 2020 18:05:03 GMT -5
There is also a jig for a faceting machine for shapes .. if you just need one or two .
|
|
|
|
Post by stardiamond on Jun 16, 2020 18:20:13 GMT -5
1. Mark the circle so that the line remains. Be sure to stay out side the line until the dome is complete and then grind the girdle very close to the line. You can always subtract material. Unless they need to be calibrated a larger circle parallel to the line is still round. Leave room for the finer sanding and pre-polishing wheels.
2. Start with a thicker slab so that adjustments to the dome can be made and still have some height. Grind in a circle and stay above the girdle line. Unless a person has become very proficient with cutting circles adjustments will need to be made.
3. With softer material, use a higher grit wheel and be patient.
|
|
gemfeller
Cave Dweller
Member since June 2011
Posts: 4,063
|
Post by gemfeller on Jun 16, 2020 19:06:13 GMT -5
There is also a jig for a faceting machine for shapes .. if you just need one or two . You don't really need a jig on a faceting machine to cut a round. Just free-wheel the quill by hand until the blank is ground down to a near-perfect circle. More work, yes, but it avoids buying a jig/preformer. You can even set your girdle angle at the same time. |
|
