I have been using pieces of granite countertops for things like marking and testing with vee blocks. There is a lot of commenting on the web about how unsuitable these things are and how the beginner should just get a cheap granite surface plate at Enco when they have their free shipping days. Recently, there was an estate sale in my neighborhood and someone bought a beat up old table saw and left the table. The seller convinced me to pay $5 and besides, I was curious about how flat it was. It looked flat. I held up a straightedge to it at the sale and did not see any light, so I bought it.
After I got it home, I ran a dial test indicator mounted on a stand over it. This cast iron table was way worse than a granite sink cutout!!! There was about a 0.010" variation over a 3" arc. Even worse, the indicator base did not lay flat. On close examination, there was light under a straightedge and there was a visible gap under one corner of the dial indicator stand. This thing is not flat! I took a junk wood chisel and carefully scraped it over the surface. A fine layer of brown rust got scraped off. It took a lot of care removing the rust, since the rust was not really loose. When a few square inches of rust was removed, the indicator showed less than 0.001" over the same 3" arc. In contrast, the sink cutout had no indicator motion for the same measurement.
There were two lessons learned from this experience. The cast iron table saw top is not always better than the free granite remodeling remnant. Not even close, this time! And second, even a tiny bit of apparently tight rust can really ruin a machine's precision. This gives me a new view of Craiglist ads which show mills with really rusty tables stored outside for sale for well over $1000. If the ways are severely rusted, the whole operation will be severely compromised.
After I got it home, I ran a dial test indicator mounted on a stand over it. This cast iron table was way worse than a granite sink cutout!!! There was about a 0.010" variation over a 3" arc. Even worse, the indicator base did not lay flat. On close examination, there was light under a straightedge and there was a visible gap under one corner of the dial indicator stand. This thing is not flat! I took a junk wood chisel and carefully scraped it over the surface. A fine layer of brown rust got scraped off. It took a lot of care removing the rust, since the rust was not really loose. When a few square inches of rust was removed, the indicator showed less than 0.001" over the same 3" arc. In contrast, the sink cutout had no indicator motion for the same measurement.
There were two lessons learned from this experience. The cast iron table saw top is not always better than the free granite remodeling remnant. Not even close, this time! And second, even a tiny bit of apparently tight rust can really ruin a machine's precision. This gives me a new view of Craiglist ads which show mills with really rusty tables stored outside for sale for well over $1000. If the ways are severely rusted, the whole operation will be severely compromised.
