Gallery, Projects and General > How do I??
Quartz Surface Plate?
krv3000:
well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat
sparky961:
--- Quote from: krv3000 on September 13, 2015, 05:25:58 PM ---well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat
--- End quote ---
Hmm... indeed, but a bit of a paradox, isn't it? If I had a piece of glass I knew to be flatter than the plate I'd just use the piece of glass. :)
That said, are you talking about regular thin "window" glass, or thicker "plate" glass? If window glass is flat enough I'm sure I could rustle up some of that. The thicker stuff could be an issue.
sparky961:
So, I had a chance to take a closer look at my haul tonight. Spoiler alert: Don't get too excited.
Good news is that I was able to measure flatness deviation. Bad news is that it wasn't difficult to measure.
To start off, my setup is far from ideal so take everything here with that in mind. I have a shiny rock (could be granite, but how would I know?) about 26 x 26 x 1-1/4 sitting on a relatively rigid small table made of MDF. Between the rock (we'll call it "granite") and the hard place (the table), there are three strips of minicell foam about 1" thick and maybe 12" long, placed somewhat evenly to support the plate. Why? I had some left over and it seemed this would allow the plate to "float" the best way possible with available materials. With the indicator set up I pushed in various places and with a lot of pressure could move the indicator by about 2 tenths. As you'll see in the next paragraph, proper support is the least of my concerns at this point.
After cleaning the slab, I proceeded to jury-rig my DTI to my height gauge. Yet another tool/adapter thing to make.... The gauge base is about 5" long and my first setup put the indicator point about 6" from the end of the base. Moving this around the plate in no particular pattern yielded a rough average of +/-0.005" deviation over 6", with a maximum of about 0.008". The gauge base didn't slide nicely in many spots like you'd expect on a surface plate. This probably explains the "grabbing" I noted earlier while doing my lapping trial.
One of the pictures below shows the granite floor tile I picked up at Home Depot. It was more difficult to measure because there isn't a lot of room to move the gauge around. I shortened the reach to about 4" and deviation seemed a bit better, maybe +/-0.003". Given the smaller distance, this may or may not actually be any better.
So, in summary I don't think granite countertops are a useful surface plate as supplied. If you're ok with +/- 0.010 or so then go for it, but I'm looking for better than that.
I'm going to continue working with some of the pieces I have to see if I can't find an effective way to improve the flatness.
sparky961:
Man, I really should have gone to bed after that last post but I had an idea as I was writing it that I had to try. Yes, I'm sure lots of you here know the feeling.
So it turns out it was a great idea! Don't give up on granite.... more to follow.
Pete.:
--- Quote from: krv3000 on September 13, 2015, 05:25:58 PM ---well a piece off glass will let you no watts hi and watt is not put engineers blue on the table then place the glass on top remove the glass the glass that has blue on is hi and the glass that has no blue on is lo if the blue is all over the glass then the top is flat
--- End quote ---
The only problem with that is if you put a piece of glass on a surface plate it might well be flat but if you put it on anything else - especially with a chunk of iron on it - it will bend and not be as flat as it was when you checked it.
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