rxscram
spending too much on rocks
Member since August 2011
Posts: 484
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Post by rxscram on Nov 8, 2013 0:37:29 GMT -5
Hi All,
I have read that firebricks are one of the preferred methods for dressing a slab saw blade.
I purchased some online but when I got them they were very low density and soft, not at all what I was expecting. Is this the right stuff, or is there another kind of fire brick I should be looking for?
Thanks! Jeff
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QuailRiver
fully equipped rock polisher
Member since May 2008
Posts: 1,635
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Post by QuailRiver on Nov 8, 2013 0:46:47 GMT -5
I haven't used fire bricks but have used old low temperature fired 19th century bricks from old building demolition. These bricks are soft and a little crumbly. But I still prefer to use pieces of old 100-220 grit lapidary Silicon Carbide grinding wheels to dress my blades.
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Post by catmandewe on Nov 8, 2013 0:58:12 GMT -5
Fire bricks are rated for heat resistance, (used in chimneys and fire walls) what causes them to be heat resistant is that they are made up of approx 90% Silicon Carbide. Regular bricks have a low Silicon Carbide content (0 to 20%) and thus do not help sharpen your blades, so you need to make sure you have a fire brick and not a regular building brick.
You can usually get one at a building supply store for a couple of bucks. If you still can't find one I can send you one or two that I have pulled out of old abandoned chimneys, but the shipping will be more than a couple of bucks.
Tony
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LarryS
freely admits to licking rocks
SoCal desert rats
Member since August 2010
Posts: 781
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Post by LarryS on Nov 8, 2013 8:46:11 GMT -5
I use these 6" bench grinder wheels from Lowes, medium grit. Think they're made by Porter Cable in the tool department for $7. Our Home Depot only had course. They work great. They gently remove the metal, unlike some lapidary blade stones which work very aggressively.
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Post by rockpickerforever on Nov 8, 2013 9:59:32 GMT -5
Before I got a slab saw a few years back, I had a whole locker of used/worn down/worn out silicon carbide grinding wheels. Kicking myself for getting rid of them...
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Post by johnjsgems on Nov 8, 2013 11:45:07 GMT -5
I would try the fire bricks you have and see if they work. The commercially available 60 grit aluminum oxide dressing sticks and blocks are also very soft. I've cut the sticks with a hack saw.
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Post by 1dave on Nov 8, 2013 11:55:20 GMT -5
Fire bricks are rated for heat resistance, (used in chimneys and fire walls) what causes them to be heat resistant is that they are made up of approx 90% Silicon Carbide. Regular bricks have a low Silicon Carbide content (0 to 20%) and thus do not help sharpen your blades, so you need to make sure you have a fire brick and not a regular building brick. You can usually get one at a building supply store for a couple of bucks. If you still can't find one I can send you one or two that I have pulled out of old abandoned chimneys, but the shipping will be more than a couple of bucks. Tony I thought what made them heat resistant was they were 90% cristobalite - high temperature SiO 2. What made them handy for sharpening saws is that they are abrasive on the metal that has pulled over the diamonds. I think old silicon carbide grinding wheels work better. A source for the old rock they made grind stones out of would be outstanding!
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Post by johnjsgems on Nov 8, 2013 12:51:38 GMT -5
The "old rock" is a man made pile that is covered with a foil like cover and hit with high voltage. The center of the pile becomes green silicon carbide, the outer material black. I don't know how they compress it and bind it to make wheels. I see grinding wheels at garage sales and flea markets for very low prices. Pretty much anything abrasive will work. I tried the red bricks the old books said to dress new saw blades when I first started. Talk about bright red oil. Worse than red jasper.
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juzwuz
has rocks in the head
Member since April 2010
Posts: 526
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Post by juzwuz on Nov 8, 2013 14:56:03 GMT -5
A while ago I got a fire brick from Home Depot for about $1.50. It wasn't on their website but I just asked one of the workers and they located a pallet of them in the store. I think it was called a medium duty fire brick. It was light yellowish in color and around 10 pounds.
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usaret
having dreams about rocks
Member since October 2012
Posts: 52
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Post by usaret on Nov 10, 2013 19:16:42 GMT -5
I've used the old grinding wheels also. How often should I dress my blade ?
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Post by johnjsgems on Nov 11, 2013 11:05:21 GMT -5
No more than needed. If you listen to your saw you can tell. Or if hand feeding it is readily apparent. Sometimes you start to see saw marks where the cut was smooth. Every time you dress open a blade you expose new diamond but you also remove a little blade.
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