Kennedy done it, huh Barry?
piston rings, sliding inside a smoothly honed cylinder, would wear ... but they do.
The most popular blocks are hardened tool steel, ground, polished, and lapped to dimension. Since they are relatively soft, wringing them together causes wear.
Premium blocks are available that wear much more slowly, and maintain their accuracy for a longer time. Chromium carbide (CroBlox) is what Starrett-Webber offers in a premium block. Mitu, Starrett-Webber and others also offer zirconia ceramic blocks, usually less expensive that chromium carbide but higher priced than tool steel.
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Barry Milton
With appologies before hand Barry, 'cause I'm a
big fan but you lost some of us way back at
"IF any set does not come with a NIST traceable cert, they are somewhat less than useless", makes me wonder if you are aware of any use for gage blocks other than for high cert metrology, a surprisingly narrow view.
When I am building a prototype and need to machine paired parts to a "specific" (
I do the specifyin') angle, I've never even considered whether a millionth here or there could have any effect whatsoever on the stack under the sine bar, because for
many op's, there is
NO detriment. That alone sorta' takes it out of the "
less than useless" category and by the way, how is "useless"
usefully modified by "less than"? but I was willing to let that pass....
..but then you went on with,
"hardened tool steel and relatively soft" oddly being combined together and then adding,
"You wouldn't think that piston rings (which are regularly end-gap fitted with a file made of tool steel),
sliding inside a smoothly honed cylinder, would wear ... but they do..." kinda' sealed the deal on this one. Terrible analogy.
...your piston ring thing, starting with
"you wouldn't think..." leaves you wide open to "you talkin' to me?"
In the case of engine cylinders, you make the mistake of substituting "smoothly honed" (never) where the actual case is roughly "cross-hatched honed", to provide tooth for oil retention and self abrasion-fitting of rings to cylinder, though they do eventually smooth themselves but certainly nothing approaching
"lapped gage blocks with less than a millionth deviation" kind of smooth.
I won't even address the advisability of comparing carefully wringing gage blocks together - to several piston rings edge-scraping their cylinders for several inches, 5,000 times every
minute @ a moderate 2,500RPM for say 200,000 miles, under
less than "climate-controlled clean-room metrology lab" conditions.
Again, sorry Barry, just struck me as a little presumptive and misdirected.
All - the premise, application, analogy
and blaming Kennedy, because "worn" (by your standards) gage blocks are most
certainly very useful in most machine shops and less than a hundred bucks for a complete set?.... shh...
I sometimes even use a 6" Starrett rule to
measure with
.....
well..when no one is looking.....
Bob