dfitch
off to a rocking start
Member since June 2008
Posts: 10
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Post by dfitch on Jul 20, 2008 21:15:32 GMT -5
Hi! I rebuilding a Star Diamond grinder. It has a combination pulley on the main shaft - it appears to be maybe 3",4 ",and 5". I am wondering what the optimal grinding speed might be for agate / chalcedony materials. I suspect the situation may be similar to saw blades in that it is measured by SFPM (surface feet per minute) - Sinkankis has a chart for saw blades. My Gem Cutting Manual is packed away so I don't know if he listed something similar for grinders. Any suggestions for a grinding wheel with a grit of a range of 80 to 600? The faster the speed, the more it will heat up the stone (with or without a water bath). You figure SFPM as a multiple of the rotation speed and the diameter of the wheel or blade. So a 6" wheel is going to have a different value than an 8" for a motor with same RPM and will consequently remove material at a different rate.
In the absence of anything better, I am planning on using a 2" pulley on the motor. And will run the belt between that and the 3" pulley on the shaft. That will give me a shaft rotation of about 1170rpm. Then I can move the belt to the larger pulleys on the shaft if I want it to run slower for a softer or more heat sensitive main material.
Any suggestions? All are welcome. Thanks. Dave
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Post by bobby1 on Jul 21, 2008 8:34:26 GMT -5
I have an 1 1/2" pulley on the motor and a 4" pulley on the main shaft. Because I run an 8" expandable drum I want it to run slower so it will be softer and will get the flat spots out easier. Years ago when I built my machine I had step pulleys on it but I never changed the speed. When I rebuilt the unit I took them off. For softer stones I just use a lighter touch on the wheels. Bob
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