Post by callmerob on Apr 20, 2021 23:29:49 GMT -5
This is my biggest roughing saw - a Milwaukee 14” abrasive cutoff saw, on sale at Home Depot for $160. Removed the vitrified rubber abrasive blade (for steel) and substituted a cheap 14” diamond blade. Water flood in the cut from a fountain pump in a 5-gal bucket. Both plugged into a ground-fault-circuit-interupter (GFCI) outlet which trips in milliseconds - better than a common household circuit breaker.
We call the saw “The Beast” because it howls and draws 15 amps on start. It also spins too fast - 3900 rpm, which I’m just now learning is over 14,000 sfm on a 14” blade. No wonder I smoked the blade on a chunk of jasper (which apparently likes about 2000 - 3000 sfm). More on that later maybe. Still working on squaring the blade to the back fence, and repeatably holding the part square in fixtures. The saw doesn’t much care at all when cutting the softer serpentine, though.
My sculptor friend had several serpentine rocks which just did not “speak” to him - no interesting shape or false-jade veins, just blobs, and a little small. I got one from him and my wife noticed dirty white crystal stuff on the surface. Did we get lucky? It’s full of calcite/quartz(?)! This piece of serpentine is a little lighter green color than the first one. Pre-treated the rough rock with water-thin super glue to strengthen any cracks. Six cuts get a not-quite-a-cube about 3.6”
Trying not to subject my neighbors to any more howling of The Beast, so I built a slow-speed drop saw for the smaller cuts - 120-rpm 12-volt DC toy motors, water drip, gravity feed, counterweighted, cheap industrial 10” diamond blade. 10” blade @ 120 rpm = 314 sfm.
Sawing the not-quite-an-octagon…
It is still too loud and annoying for a condo patio with neighbors very nearby, so I put it in a sound-deadening cabinet. Sound insulated with 5/8” drywall, spray painted. It’s not sound-proof, but it’s much better - can barely hear the blade noise. Slow saw rpm means it doesn’t throw water all over the inside of the cabinet and drywall, but every cut takes more time. The saw sits in a mortar mixing tray from Home Depot, cut down to fit in the cabinet.
Sawing the not-quite-an-octahedron…
Treated all the sawn surfaces with water-thin super glue to strengthen and seal any cracks.
Nail polish on the flats to visualize the surface of the sphere. When all the nail polish is gone, it’s round. Wet grinding by hand on a Lortone 6” combo machine to round the sharp edges and points with a cheap silicon carbide wheel. Grinding takes 1 hour, and I didn’t like this SiC grinding wheel, so I didn’t grind very much off the corners and edges, which will add to the sphere-grinding time. Treated all the ground surfaces with water-thin super glue as cheap insurance against fractures or chunks falling out of the sphere. I really don’t like chunks falling out.
The toy sphere machine is quiet enough for condo living. It’s quieter than a sewing machine or a conversation. Upgraded the motors to 120 rpm. The rock beat on the machine a lot and kept kicking the grinding pads way up, then falling into the mud, until I put some wing nut pressure down on the outboard spring to resist kicking up. Also temporarily clamped angle brackets to be a hard stop for the pivot arms kicking back. After a few hours in the grinder I relaxed the springs a little to let the rock dance more freely. Note the comparison between the new / old motors. I like ‘em.
In the sphere machine...
After 8 ? hours...
I lost track of the exact time from here because this rock is turning into a fire drill. Can’t get anything to work well. I wish all this white stuff was calcite (similar Mohs to serpentine), but this rock is fully 2/3 quartz, so the sphere machine plastic diamond pads struggle to grind it. Got 3 steel diamond 2” flat grinding discs to try to rip off more of the quartz, but there is still preferential grinding of the softer serpentine, so the rock is not rounding, has lumps of quartz and low flat spots in the serpentine. I’m learning a lesson on grinding mixed hard/soft rocks, so this sphere is going to be a loser. Wife still likes “her rock”, so gonna still try to finish it - lumpy, but shiny.
I learned this lesson before with hard/soft rocks… Here’s a fragment of the Granite Planet that was too small, so I epoxied white marble polar ice caps on it. Also a fragment of a 1” thick granite countertop with marble glued to it. Those two have a symmetrical distribution of hard/soft and are oblates, but the serpentine/quartz is uneven, 2/3 quartz, and preferentially grinding the serpentine. Forgot that I already learned that lesson. Duh, Robbie.
This sphere is now a not-quite-a-round rough - 30 grit. Roughing in the 120 rpm sphere machine takes about 16 hours and some swear words. It’s important to note the random motion of the sphere. It should not be merely spinning or rolling around uniformly, but moving randomly. It’s a dance.
Finishing with 50, 100, 200, 300, 400, 500, 600. 800, 1000, 1500, 2000, 3000 grits. Finishing grits are only removing the scratches from the previous coarser grit, and I can’t really see the scratches, so I just pick some arbitrary time like 1 hour or more, and call it good enough. If the rock is very hard or large (much greater surface area), add more time. I make slight adjustments to the outboard spring wing nut to increase compression on the spring, decrease the lay-back pad angle and, slightly increase the grinding pressure/area (about 1/2 turn on all 3 wing nuts equally). Back off the wing nut if the rock starts just rolling or spinning uniformly. It should move randomly. It’s always a dance. Finishing this rock with 12 successive grits takes about 12 hours.
Polishing with 1-micron cerium oxide powder, wet into a paste, on plain rayon buffing pads. I wet the pads with a little water to begin with, but no drip after that. Polishing takes 2 hours.
All done, about the size of a squished softball. Total time was most of a week of sawing, grinding, swearing.
North pole
South pole
East
West
I’m not too thrilled with the not-quite-a-sphere, but my wife likes “her rock”. Hope you like it, too.
We call the saw “The Beast” because it howls and draws 15 amps on start. It also spins too fast - 3900 rpm, which I’m just now learning is over 14,000 sfm on a 14” blade. No wonder I smoked the blade on a chunk of jasper (which apparently likes about 2000 - 3000 sfm). More on that later maybe. Still working on squaring the blade to the back fence, and repeatably holding the part square in fixtures. The saw doesn’t much care at all when cutting the softer serpentine, though.
My sculptor friend had several serpentine rocks which just did not “speak” to him - no interesting shape or false-jade veins, just blobs, and a little small. I got one from him and my wife noticed dirty white crystal stuff on the surface. Did we get lucky? It’s full of calcite/quartz(?)! This piece of serpentine is a little lighter green color than the first one. Pre-treated the rough rock with water-thin super glue to strengthen any cracks. Six cuts get a not-quite-a-cube about 3.6”
Trying not to subject my neighbors to any more howling of The Beast, so I built a slow-speed drop saw for the smaller cuts - 120-rpm 12-volt DC toy motors, water drip, gravity feed, counterweighted, cheap industrial 10” diamond blade. 10” blade @ 120 rpm = 314 sfm.
Sawing the not-quite-an-octagon…
It is still too loud and annoying for a condo patio with neighbors very nearby, so I put it in a sound-deadening cabinet. Sound insulated with 5/8” drywall, spray painted. It’s not sound-proof, but it’s much better - can barely hear the blade noise. Slow saw rpm means it doesn’t throw water all over the inside of the cabinet and drywall, but every cut takes more time. The saw sits in a mortar mixing tray from Home Depot, cut down to fit in the cabinet.
Sawing the not-quite-an-octahedron…
Treated all the sawn surfaces with water-thin super glue to strengthen and seal any cracks.
Nail polish on the flats to visualize the surface of the sphere. When all the nail polish is gone, it’s round. Wet grinding by hand on a Lortone 6” combo machine to round the sharp edges and points with a cheap silicon carbide wheel. Grinding takes 1 hour, and I didn’t like this SiC grinding wheel, so I didn’t grind very much off the corners and edges, which will add to the sphere-grinding time. Treated all the ground surfaces with water-thin super glue as cheap insurance against fractures or chunks falling out of the sphere. I really don’t like chunks falling out.
The toy sphere machine is quiet enough for condo living. It’s quieter than a sewing machine or a conversation. Upgraded the motors to 120 rpm. The rock beat on the machine a lot and kept kicking the grinding pads way up, then falling into the mud, until I put some wing nut pressure down on the outboard spring to resist kicking up. Also temporarily clamped angle brackets to be a hard stop for the pivot arms kicking back. After a few hours in the grinder I relaxed the springs a little to let the rock dance more freely. Note the comparison between the new / old motors. I like ‘em.
In the sphere machine...
After 8 ? hours...
I lost track of the exact time from here because this rock is turning into a fire drill. Can’t get anything to work well. I wish all this white stuff was calcite (similar Mohs to serpentine), but this rock is fully 2/3 quartz, so the sphere machine plastic diamond pads struggle to grind it. Got 3 steel diamond 2” flat grinding discs to try to rip off more of the quartz, but there is still preferential grinding of the softer serpentine, so the rock is not rounding, has lumps of quartz and low flat spots in the serpentine. I’m learning a lesson on grinding mixed hard/soft rocks, so this sphere is going to be a loser. Wife still likes “her rock”, so gonna still try to finish it - lumpy, but shiny.
I learned this lesson before with hard/soft rocks… Here’s a fragment of the Granite Planet that was too small, so I epoxied white marble polar ice caps on it. Also a fragment of a 1” thick granite countertop with marble glued to it. Those two have a symmetrical distribution of hard/soft and are oblates, but the serpentine/quartz is uneven, 2/3 quartz, and preferentially grinding the serpentine. Forgot that I already learned that lesson. Duh, Robbie.
This sphere is now a not-quite-a-round rough - 30 grit. Roughing in the 120 rpm sphere machine takes about 16 hours and some swear words. It’s important to note the random motion of the sphere. It should not be merely spinning or rolling around uniformly, but moving randomly. It’s a dance.
Finishing with 50, 100, 200, 300, 400, 500, 600. 800, 1000, 1500, 2000, 3000 grits. Finishing grits are only removing the scratches from the previous coarser grit, and I can’t really see the scratches, so I just pick some arbitrary time like 1 hour or more, and call it good enough. If the rock is very hard or large (much greater surface area), add more time. I make slight adjustments to the outboard spring wing nut to increase compression on the spring, decrease the lay-back pad angle and, slightly increase the grinding pressure/area (about 1/2 turn on all 3 wing nuts equally). Back off the wing nut if the rock starts just rolling or spinning uniformly. It should move randomly. It’s always a dance. Finishing this rock with 12 successive grits takes about 12 hours.
Polishing with 1-micron cerium oxide powder, wet into a paste, on plain rayon buffing pads. I wet the pads with a little water to begin with, but no drip after that. Polishing takes 2 hours.
All done, about the size of a squished softball. Total time was most of a week of sawing, grinding, swearing.
North pole
South pole
East
West
I’m not too thrilled with the not-quite-a-sphere, but my wife likes “her rock”. Hope you like it, too.
. You appear to be crazy handy with the machinery and I've never tackled (and probably never will) sphere-making ... I'm super-impressed! If you want some rough to play with (keep some, send me back some), let me know. I'll gladly ship up some material's for you to play with in exchange for a sphere!
... to the New Guys from The ChatBox V.2 Crew