Never hurts to ask!

Turns out my dad has a set a feeler gauges down to 2 thousandths. Nowhere on the plate did it slip under the straight edge.
 
I just ordered the granite plate from Woodcraft, the "comeback" code work nicely for free shipping making the total $29.99 (call it $30). Thank ya'll for link and promo code.
 
I use broken marble counter top that I found in a container. I cut it roughly the size of a sheath of sandpaper.
 
The sink cutouts from stone countertop places are free and they tend to have lots of them.
 
Mr.Wizard said:
How can quarter inch thick glass act as a surface plate? It flexes with little provocation.
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Use 5 x quarter inch and they will not flex ;)
TwPuTZ8.jpg

Seriously guys , glass is more then enough flat for what are we doing............
 
Natlek said:
Seriously guys , glass is more then enough flat for what are we doing............
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I have to agree, especially because when I set the straight edge on top of the .002 feeler, it made a noticable and uniform gap across the straight edge. I can't say it's within .001, but it's gotta be pretty darn close.
 
I like glass because I can spray glue a piece of sandpaper on it, then razor blade it off and spray acetone and wipe down. With a 1/2 mfd wood backing it’s not flexing.
 
Mr.Wizard said:
I doubt they are very flat however. Great for flattening stones, not so great as a reference surface.
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Hmmmm....At first I thought I was missing something and maybe making a mistake using the sink cutout I have..."if granite/quartz/marble countertops are dead flat, why wouldn't the sink countertop be flat?" Then I noticed that I used the words "stone countertop." Granite, marble and quartz are "stone" countertop materials. We meant the same things....just didn't have the same meanings for words.
 
I'm probably wrong, but I was under the impression that granite surface plates were specially machined to be flat and counter tops aren't?
 
N.W. Gean said:
I'm probably wrong, but I was under the impression that granite surface plates were specially machined to be flat and counter tops aren't?
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Exactly. A countertop will be fairly flat, but there's no guarantee (or even expectation) that they're extremely flat. Even a cheap surface plate should be flat to within a couple tenths over the entire surface. I've seen granite countertop scraps out by fifty thou over a foot before. Good enough for some things, but not a precision surface.
 
R Randydb Actually polished granite tile and countertop can be substantially out-of-flat as CallumRD1 relates above; at the very least you need to check it with a trustworthy straightedge in several directions. Float glass should always be quite flat; my concern there was flex in thin pieces. Of course there's no point in chasing a tighter tolerance than we can actually use or we will end up using fused quartz optical flats.
 
Only 12k? I'll take 2 :D

In all seriousness, I'm glad we brought in some good resources for making things flat without spending a lot of cash in this thread.
 
N.W. Gean said:
Only 12k? I'll take 2 :D

In all seriousness, I'm glad we brought in some good resources for making things flat without spending a lot of cash in this thread.
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Make them three , i will pay you in one of my next life :D
So if you want .000001"...........12.000 $$$$ :eek:
 
Mr.Wizard said:
To whom it may concern: this plate is made in China.
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You can get surface plates all American from quarry to lapping Standridge Granite, or others.

Starrett sells that pretty pink granite.

But I'd be damned if I'd be sanding blades on an American surface plate.

This is an absolutely perfect instance of where cheap chinese stuff is perfect for our purpose.
 
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Unless you are just boycotting Chinese goods in general. Which I understand. And wish I could afford to do the same.

Just sayin'.
 
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