usaret
having dreams about rocks
Member since October 2012
Posts: 52
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Spheres
Nov 2, 2012 23:18:02 GMT -5
Post by usaret on Nov 2, 2012 23:18:02 GMT -5
What are some ways to create sphere forms ? Thanks
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Steve
has rocks in the head
Member since June 2005
Posts: 506
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Spheres
Nov 3, 2012 23:13:06 GMT -5
Post by Steve on Nov 3, 2012 23:13:06 GMT -5
I'll try to answer this. There are many methods - here's mine. First you cut a cube. The more accurate the cube the better the preform you will get. For the next step you will need an angle. You can make one from a piece of wood a 2 by 4 works. I have some steel welded angles that work great. _______ | | | /\ | | / \ | |/ \ |
where the inside angle is exactly 90 degrees --
Use a sharpie to draw a circle on the top of your cube. Place the angle in the saw and put the cube in the angle. Be sure to clamp your angle down securely - you do not want it to move when you rotate your preform. Set the saw so that the cut will just hit the outside edge of your circle. (Note: Actually I measure for this cut rather than drawing the circle. The cut starts at 0.2929 times the length of the cube and ends at the same length on the next side.) After the saw is properly set you should not adjust the saw again. I always make sure that when my saw is set that my adjustment crank has the handle down, so that the vibration will not cause any carriage movement.
Cut off the corner, turn cut off the corner, repeat, repeat. Now you have an octagon. Lay this on it's side in the angle. I prefer to align it so that the top - the side away from the angle is the side to be cut. If you want you can angle it the other way and cut the bottom - either way works. Cut, turn cut, repeat, repeat, repeat, repeat, repeat, repeat.
Turn your preform over and repeat the process on the other side.
You now have a sphere preform. This method takes a min of 6+4+8+8= 26 cuts
I usually slab down to the cube so I actually do many more cuts than this.
This process makes a whole lot more sense once you do it.
Also you need to be aware that making sphere preforms is really hard on your blade. You are always cutting into the rock at an angle so you're aways pushing the blade out, which tends to dish it. If your saw can adjust the feed speed, use the slowest possible. Also turn your blade over after making a few preforms.
Steve
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Post by jakesrocks on Nov 4, 2012 0:17:22 GMT -5
You can also buy a set of 3 special angle blocks from Covington Eng. Part # SAC001 for $29.00. They fit right into the jaws of your slab saw vise, and let you cut the proper angles. Again, as Steve said, it's very important that the cross feed of your vise doesn't move. To prevent blade dishing, feed the rock to the blade very slowly by hand until you've started a small groove for each cut. Then you can engage the power feed. Also a much more expensive sphere indexing tool can be surchased from Sphere Products, at over $200.00 www.sphereproducts.com/slabgrabber-sphereindexing.htm
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Deleted
Deleted Member
Member since January 1970
Posts: 0
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Spheres
Nov 4, 2012 13:17:30 GMT -5
Post by Deleted on Nov 4, 2012 13:17:30 GMT -5
Then as Steve describes we move to hand grinding. Using a stacked set of 6" diamond saw blades mounted onto a grinder motor we hand grind the stone to be as close to spherical as possible.
From there we go to the sphere machine. Usually 2 or 3 heads each with circular cups grinding on the surface of the stone. It's hard to describe but the surface of the sphere is defined by these cups.
In class we use grit just like tumblers for cutting the stone. I am switching to braised diamond cups as soon as practical. They last longer, are cheaper to use and do the job faster.
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usaret
having dreams about rocks
Member since October 2012
Posts: 52
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Spheres
Nov 7, 2012 22:51:38 GMT -5
Post by usaret on Nov 7, 2012 22:51:38 GMT -5
Thanks for the tips.
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