Post by sparkles on Mar 1, 2009 11:16:49 GMT -5
Hi Folks,
Well you asked for it so here it is... How to cut rounds and circular groove cabs. Please bear in mind that this is how I do it, and may not necessarily be the right way to do it! It’s just the way that works for me. Nevertheless, I hope you find of interest.
I start with a selection of chips and off cuts, you could use thick slabs or other appropriately flat chunks. If necessary, take them to the tile saw and cut them in to more appropriate shape and sized pieces.
After choosing your rocks, put them across a coarse lap to smooth the tops and bottoms and ensure that they are level and “true”, then you can mark out the circles. I like to use an aluminium scribe, and a standard cabochon template. The edges are then “nibbled” with the tile saw to roughly trim the blanks to shape.
Using the grinding machine, the blanks can now be shaped in to pre-forms (ground to the marked line). The process is quite a slow one, but by constantly rotating the piece against the cutting head running on a moderate speed, the stone will slowly begin to shape up. By using deeper slabs, the process slows even more, but the increased depth in the dome is well worth the extra effort!
With the circles shaped and ready for lapping, the final stage is to add a groove if required. The process is very similar to grinding, except the narrow thin blade can be run much more slowly. The stone is rotated against the blade and the groove will quickly form, I tend to rotate the stone right around several times, cutting the groove more gently to avoid over-cutting the depth.
OK, so you’ve got a preform, but to really do the job properly, I’d suggest dopping it to an appropriate stick. This is a bit of a fiddle, but when it works you have a trick that can be used to cut stones of all sizes and it gives the all important control that’s needed to cut sweet high domes. Here’s my dopping kit.
As you can see I use a simple candle powered “incense” burner, which makes a fabulous wax pot, and a small tin to place the stones in a warm place, I like to use the grill above the oven as it gets quite warm when the oven’s on, but not too hot to damage the stones. Dop sticks are just wooden dowels dunked in the wax.
The technique is to warm the stone and the wax, then “dunk” the stick in the wax and quickly place the blob on the back of the stone. Gentle pressure is applied and the wax is shaped using a wet finger to provide a support behind the stone. After the stone and wax have cooled, give it a wrench, if it comes apart, re-dop the stone, but it normally grips quite tightly, this is far better than loosing a stone later when you start to lap the dome!
So the time has come to cut those domes, for me, this is the fun bit! ;D Start by running a bevel around the preform, working slowly on a coarse lap (depending on material about 170-325 grit), Rotating the dop stick while holding the stone at a steady angle takes a little practice, but by working slowly and checking the cutting action regularly, you should be able to cut an even bevel all around the stone.
The next step is to change the angle and cut another bevel to establish the height and shape of the dome. Using the same cutting technique but changing the angle at which the stone contacts the lap, proceed to cut the top bevel, this should leave an even border around the stone and a small circular flat on the upper surface. This is a useful check to maintain the evenness of the shape.
With the bevels cut, the next step is to smooth and shape the dome, this requires a new stroke technique. Starting with the stone at a shallow angle (to cut the edges), rotate the dop stick and slowly raise the angle to cut up the edge of the stone and on to the upper surface. By swinging the stick between the vertical and horizontal, the rough shape can be gently smoothed and evened out.
The final stroke involves holding the top of the stone against the lap and rotating and swinging the dop stick in small circles, this cuts the top of the stone in to a smooth even dome and will prevent any flat spots from affecting the final shape.
Using these two strokes, the shape of the stone can be refined, before moving to a finer grade lap (600 grit) to prepare the stone for sanding and polishing.
With the shape established, all that remains is to smooth out and polish the stone using “soft” diamond lap pads. You can find my tutorial for making these here...
forum.rocktumblinghobby.com/index.cgi?board=hmequip&action=display&thread=26785
Work through the pads in sequence using the strokes as before, and the stones should take a keen shine. The process described can be used to cut stones of all sizes, and after a few attempts, the technique of rotating the stick, and changing it’s angle to the lap will become much easier.
Grooved cabs obviously need to be polished on both sides, so the stones must be reversed after cutting the initial dome. By placing the stick and stone in the freezer, the wax shrinks and the stone usually drops off the stick. It can then be re-dopped on the polished side so that the back can be cut and polished. I am always surprised at how well the dopping wax grips the polished dome of the stone.
So that’s it! Circles and grooved cabs - Sparkles Style. Hope you found this interesting and if you have any questions - just ask!
Cheers
Sparkles.
Well you asked for it so here it is... How to cut rounds and circular groove cabs. Please bear in mind that this is how I do it, and may not necessarily be the right way to do it! It’s just the way that works for me. Nevertheless, I hope you find of interest.
I start with a selection of chips and off cuts, you could use thick slabs or other appropriately flat chunks. If necessary, take them to the tile saw and cut them in to more appropriate shape and sized pieces.
After choosing your rocks, put them across a coarse lap to smooth the tops and bottoms and ensure that they are level and “true”, then you can mark out the circles. I like to use an aluminium scribe, and a standard cabochon template. The edges are then “nibbled” with the tile saw to roughly trim the blanks to shape.
Using the grinding machine, the blanks can now be shaped in to pre-forms (ground to the marked line). The process is quite a slow one, but by constantly rotating the piece against the cutting head running on a moderate speed, the stone will slowly begin to shape up. By using deeper slabs, the process slows even more, but the increased depth in the dome is well worth the extra effort!
With the circles shaped and ready for lapping, the final stage is to add a groove if required. The process is very similar to grinding, except the narrow thin blade can be run much more slowly. The stone is rotated against the blade and the groove will quickly form, I tend to rotate the stone right around several times, cutting the groove more gently to avoid over-cutting the depth.
OK, so you’ve got a preform, but to really do the job properly, I’d suggest dopping it to an appropriate stick. This is a bit of a fiddle, but when it works you have a trick that can be used to cut stones of all sizes and it gives the all important control that’s needed to cut sweet high domes. Here’s my dopping kit.
As you can see I use a simple candle powered “incense” burner, which makes a fabulous wax pot, and a small tin to place the stones in a warm place, I like to use the grill above the oven as it gets quite warm when the oven’s on, but not too hot to damage the stones. Dop sticks are just wooden dowels dunked in the wax.
The technique is to warm the stone and the wax, then “dunk” the stick in the wax and quickly place the blob on the back of the stone. Gentle pressure is applied and the wax is shaped using a wet finger to provide a support behind the stone. After the stone and wax have cooled, give it a wrench, if it comes apart, re-dop the stone, but it normally grips quite tightly, this is far better than loosing a stone later when you start to lap the dome!
So the time has come to cut those domes, for me, this is the fun bit! ;D Start by running a bevel around the preform, working slowly on a coarse lap (depending on material about 170-325 grit), Rotating the dop stick while holding the stone at a steady angle takes a little practice, but by working slowly and checking the cutting action regularly, you should be able to cut an even bevel all around the stone.
The next step is to change the angle and cut another bevel to establish the height and shape of the dome. Using the same cutting technique but changing the angle at which the stone contacts the lap, proceed to cut the top bevel, this should leave an even border around the stone and a small circular flat on the upper surface. This is a useful check to maintain the evenness of the shape.
With the bevels cut, the next step is to smooth and shape the dome, this requires a new stroke technique. Starting with the stone at a shallow angle (to cut the edges), rotate the dop stick and slowly raise the angle to cut up the edge of the stone and on to the upper surface. By swinging the stick between the vertical and horizontal, the rough shape can be gently smoothed and evened out.
The final stroke involves holding the top of the stone against the lap and rotating and swinging the dop stick in small circles, this cuts the top of the stone in to a smooth even dome and will prevent any flat spots from affecting the final shape.
Using these two strokes, the shape of the stone can be refined, before moving to a finer grade lap (600 grit) to prepare the stone for sanding and polishing.
With the shape established, all that remains is to smooth out and polish the stone using “soft” diamond lap pads. You can find my tutorial for making these here...
forum.rocktumblinghobby.com/index.cgi?board=hmequip&action=display&thread=26785
Work through the pads in sequence using the strokes as before, and the stones should take a keen shine. The process described can be used to cut stones of all sizes, and after a few attempts, the technique of rotating the stick, and changing it’s angle to the lap will become much easier.
Grooved cabs obviously need to be polished on both sides, so the stones must be reversed after cutting the initial dome. By placing the stick and stone in the freezer, the wax shrinks and the stone usually drops off the stick. It can then be re-dopped on the polished side so that the back can be cut and polished. I am always surprised at how well the dopping wax grips the polished dome of the stone.
So that’s it! Circles and grooved cabs - Sparkles Style. Hope you found this interesting and if you have any questions - just ask!
Cheers
Sparkles.