distantmermaid
off to a rocking start
Member since August 2017
Posts: 3
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Post by distantmermaid on Sept 12, 2017 22:22:29 GMT -5
I'm very new to making cabs, I've made 2 actually. I don't have a machine yet so I'm using my dremel with diamond burs and sand paper after to smooth and polish. I have this cool stone that I want to make a cab out of, it has different hardnesses throughout. I keep ending up with bumps and waves when I'm trying to shape it, where the softer parts are grinding away faster. Is there any way to prevent this from happening, if so any help would be awesome. Or does it just come with practice? I'm having a he'll of a time with it and the stone isn't very big so if i keep messing up there won't be anything left lol Thanks 😊
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Roger
fully equipped rock polisher
Member since January 2013
Posts: 1,487
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Post by Roger on Sept 12, 2017 22:35:08 GMT -5
The dremel is probably the problem. Unless you can slow it wayyyyyyyy down, it is going to cut very aggressively. The diamond burrs have no real surface area and if they are spinning at 5000 rpm, they will chew through the softer portions of your stone much faster than the harder areas.
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Post by gmitch067 on Sept 13, 2017 1:29:31 GMT -5
The dremel is probably the problem. Unless you can slow it wayyyyyyyy down, it is going to cut very aggressively. The diamond burrs have no real surface area and if they are spinning at 5000 rpm, they will chew through the softer portions of your stone much faster than the harder areas. I cab by hand, and have noticed the same problem Krissi... and have ruined a few stones in the process. As Roger stated, the dremel grinding is very aggressive and is at the root of your problem. If you use a large dremel diamond grinding wheel it will contact the stone over a larger area than a small wheel will - distributing the grind more evenly... BUT you must combine that with a light touch to realize your goal. A smaller grinding wheel will dig in when it hits the softer stone. I have varied the speed of the large wheel and seen big differences in the grind - both in smoothness and in cutting. I have settled on a rather fast speed. Not only does it NOT rattle the stone to pieces, it does a better job of cutting. There is a catch however... Whether the speed is slow or fast, the large wheel tends to be the wrong choice when working with brittle stones - like Obsidian or Malachite... Too harsh of a grind... Causes large flakes and chips to go flying (especially with a stone of mixed hardness). For those, it is usually best to make the saw cuts further away from the template line, and use a small wheel at high speed... still... use a light touch. Try to keep the stone cool and wet. Note in the photo the different sizes of the grinding wheels... The wheel in the dremel bit is the small one. I think the large wheels (both fat and skinny one) are equivalent to 80 grit, while the small one is equivalent to 220 grit (I am not 100% sure of that... I am going on feel there)
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Post by coloradocliff on Sept 13, 2017 2:04:57 GMT -5
I'm very new to making cabs, I've made 2 actually. I don't have a machine yet so I'm using my dremel with diamond burs and sand paper after to smooth and polish. I have this cool stone that I want to make a cab out of, it has different hardnesses throughout. I keep ending up with bumps and waves when I'm trying to shape it, where the softer parts are grinding away faster. Is there any way to prevent this from happening, if so any help would be awesome. Or does it just come with practice? I'm having a he'll of a time with it and the stone isn't very big so if i keep messing up there won't be anything left lol Thanks 😊 Is there a local rock club around where you live ? Maybe use some of their equipment and hands on help.. Wouldn't be the first rock that just kind of disappeared on most all of the members. Either dropped, ripped out of your hand by a wheel, broken in the saw, dropped on the floor or tumbled to mud trying to get it perfect. Yep some rocks just have to die in the process. Just practice on the ugly ones. Hehehehe
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Post by gmitch067 on Sept 13, 2017 2:46:49 GMT -5
When you do your sanding Krissi, do you hold the stone in one hand while applying the sandpaper with your other hand...Or do you place the sandpaper on a table top (or other flat surface) and rub the stone around? When working with stones that have hard and soft areas, using the table method produces less "wavy" texture. The flat surface helps distribute your hand pressure over a larger surface area producing a more even sanding - keeping the softer stone from wearing faster than the hard. Keep the stone turning on the sandpaper as pressure is applied across the sheet. As the first, middle, and maybe the ring-finger applies pressure to the grind, the thumb is used to rotate the stone. The constant rotation prevents focusing the pressure on just the soft areas. You will quickly see where those soft areas are and learn to vary the pressure and amount of time spent there. In the picture, I am wearing rubber finger-tip protectors. This keeps my finger nails from contacting the sandpaper. The rubber also helps control the rotating pressure of my thumb on the stone without slipping. (Keep the sandpaper wet)
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Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,456
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Post by Sabre52 on Sept 13, 2017 6:20:24 GMT -5
I find that mixed hardness stone undercut less when I use very worn diamond wheels and a very light touch with lots of movement so the diamond does not cut in one spot to long. New wheel or pad surfaces have lots of fresh sharp diamond that really gouge the softer areas in a mixed hardness stone even when your touch is very light....Mel
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Post by coloradocliff on Sept 13, 2017 8:46:09 GMT -5
Mel, Thanks for this important tip. I just avoid stones that undercut and play with other material but this makes total sense. distantmermaidIf you don't have equipment yet the shaping and polishing with the sandpaper and finger protectors makes sense. You can buy preformed cabs and finish them yourself. Also after you have preformed cabs shaped like you want them you can polish them to perfection in a vibe tumbler. Christmas is coming and it might be a good thing to put on the Hubble's radar screen for a nice gift..
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minerken
Cave Dweller
Member since August 2013
Posts: 466
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Post by minerken on Sept 13, 2017 13:35:15 GMT -5
the table method as mentioned should work well but taking a page from expando and soft wheels add a sponge under your sandpaper like a thick Scotchbright pad this will produce what they call drape and conform to the convex surface, you can use plain old wet silicon carbide sand paper. I have never done this myself so take it FWIW
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Post by rockjunquie on Sept 13, 2017 18:20:11 GMT -5
You can also put mouse pads under your sanding paper. I do that when hand sanding metal. It has juuust enough give. I bought a gamer's mouse pad. It's bigger than a normal one.
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Post by rockjunquie on Sept 13, 2017 20:36:04 GMT -5
I should have mentioned that the mouse pad grips the paper if you flip it over to the back side.
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Post by gmitch067 on Sept 14, 2017 17:35:35 GMT -5
the table method as mentioned should work well but taking a page from expando and soft wheels add a sponge under your sandpaper like a thick Scotchbright pad this will produce what they call drape and conform to the convex surface, you can use plain old wet silicon carbide sand paper. I have never done this myself so take it FWIW I just tried using a 1/4 inch 8"x10" sheet of foam rubber gasket material under the sand paper like both you and Tela (Rockjunquie) suggested and LIKE IT a lot! I will add this mod to my hand sanding repertoire. It works especially well when sanding small cabs and rounded free-form stones. The stone I was sanding was a piece of Amber found in amongst a load of Desert Jasper (sneeky little devil... but beautiful! I'll cover this in another thread). Silicon Carbide wet/dry sandpapers from 1000 grit to 5000 grit conformed nicely to the curves of the stone due to the foam backing. Larger grit sandpapers (400, 600, and 800) bent a bit into the Amber's contours, but I noticed more grind on the peaks than the troughs. 80 grit and 220 grit sandpapers showed little bend as I tried them out on an 18mmX25mm agate cab (I was not even going to consider either of those coarse grits on Amber! ... no, no NO!)
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minerken
Cave Dweller
Member since August 2013
Posts: 466
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Post by minerken on Sept 14, 2017 19:42:36 GMT -5
Glen glad it works for you
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Post by stardiamond on Sept 15, 2017 11:27:46 GMT -5
My first cabbing set up was worn 80 280 diamond wheels, 400 grit belt sander and tin oxide on a leather pad. Undercutting was one of the reasons I got a Genie. All diamond makes things easier.
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