Ebay bargain -gage blocks.
There is a 84pc set-81 pc. set plus the 25, 50 and 75 millionths blocks. They are Do-All A+ grade. +1/-2 tolerance. All the blocks are there. Some of them may not be original or perhaps it's just the way they were put in the box. I would have bought them myself but I had just closed on another set on Ebay. Search Do-all precision gages to find the listing. All the usual disclaimers,etc etc. The buy it now price is $99.05!
Used gage blocks are a crap shoot 100% of the time ... each wringing wears the gage block a measurable amount, even though it is less than a millionth. When bought used, godonlyknows what size each block is, and the cost to send a set to a cal lab is high.
The best bargain on a shop grade (B) set is the Starrett 81 piece set, about $350 retail at MSC and 1/4 less when they have a sale. You can bet money that they are dead on.
IF any set does not come with a NIST traceable cert, they are somewhat less than useless Most eBay sets come with a cert from FooManChu cal lab, located in WhangDang Province.
Used gauge blocks may be "useless", but they are amazingly handy to have in a shop.
I still have ALL the ones I bought over 40 years ago from the then P&WA surplus store (numerous solid carbide examples), and I have three sets of P&W HOKE blocks. These of course do not have to "wring" since you can bolt them together in stacks with the attachments provided.
They are all still way better than something that would have to be made to do the same job.
I only own one non HOKE block - a .400", the odd ball in that drawer.
If you Mean quantifiable I am with you. If you can't do it where your at, it aint measurable. Hell I bet only a few places in the world could quantify the wear caused by a single wringing....
Clifford Kennedy, who wrote the best book I've ever read on this subject (Inspection and Gaging, ISBN-13: 978-0831111496, http://www.amazon.com/Inspection-Gag.../dp/0831111496) when blocks are wrung together, any corrosion on the surface is scraped off. "Add to this the natural burnishing and shaving action, the mechanical wear from wringing, and the blocks may lose an unnoticed millionth of an inch at a time." That's a direct quote from Kennedy.
A millionth doesn't sound like much, and it isn't, but a set used every day in a factory may get wrung dozens of times during one shift. Senator Everett Dirksen is credited with the saying "“A billion here and a billion there, and pretty soon you're talking real money." With gage blocks, pretty soon you're talking about real wear ... figure 50 wringings may take off 50 milliionths, a number that any one of us can read on a $200 digital micrometer.
OK, who is going to get out their two least used blocks, wring them 50 times and report back?
smt, with P & W Electro-limit on standby....
one millionth is a lot of iron atoms to shave off each time. I did not go back and do the math as it gets complicated by the material structure and lots of assumptions. I'm sure Kennedy is a good source but it sounds more like a comment in his writing that indicates they can wear - like errors of a millionth can creep in unnoticed, not necessarily on each wringing.
I don't have any spare gage blocks - if someone wants to send me a pair, I'll volunteer to wring them 50 times and measure before and after with a tesa 50millionths gauge.
What on earth is "wringing"?
Can someone explain it to a mere hobby machinist - who always thought gauge blocks are just very precise parallels and feeler gauges...
Rubbing (squeezing and rotating) blocks together to make them stick to each other due to the molecular attraction. This eliminates any space between the blocks making sizing more precise. That's what you're supposed to do when you're stacking blocks.
Originally Posted by jhovel
The gage blocks surfaces are flat and smooth to the point that they will stick together with some force required to get them apart. Wringing them, is the way that they are slid together to minimize the gap between the two blocks. You slide the two faces together. Done correctly, the guy on the shop floor will not be able to measure the difference between a built up stack to a nominal sum equal to the same amount made up from a single gage block. (I think I phrased that reasonably well.)
You should be able to stack up 2 inches of blocks, and have them measure the same, for all intents and purposes, as the 2 inch gage block.
See Starrett's page on "Wringability". Good explanation and sketches.
Wringability - The L.S. Starrett Company
I knew of the concept ever since college, however never got to see it (or try it) till I bought a set recently - I think its amazing. If you are checking out used gage blocks and they will not wring then I would definitely think of them as spacers.
I really hope this done. It would be extremely interesting. If noone near you can just hand a couple of blocks, i would send you a couple. There is nothing like a real hands on test of an assertion ( that seems dubious).
Originally Posted by PaulM
I have a NIST manual on gage blocks ("The Gauge Block Handbook") and there's very little discussion on wear, change in length seems to be more a function of age and heat treatment of the block in production than anything else. From what I can read the wear is more scratching than anything, and that leads to an inability to wring the blocks.
You wouldn't think that piston rings, sliding inside a smoothly honed cylinder, would wear ... but they do.
There is nothing like a real hands on test of an assertion ( that seems dubious).
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.
Originally Posted by*precisionworks*
You wouldn't think that piston rings, sliding inside a smoothly honed cylinder, would wear ... but they do.
Really? Why shouldn't one expect them to wear given the fact that they are operating at high speed in a high pressure, high temperature, and relatively caustic environment? On the other hand I think itis truly amazing that they don't wear more. After all, an average passenger vehicle engine would go through about*900 MILLION*cycles to travel 180,000 miles in its lifetime. And that ignores idling time. If they wore a millionth per cycle there wouldn't be much engine in short order.
So, once again, I really hope there is someone out there with the capability of actually doing the experiment who can provide some real facts in this matter. Quotes from speculating experts are sort of interesting. But real measurements carefully done actually mean something. *Speculation is just what its name implies.
Kennedy's book (now published in the sixth edition) is excellent reading, and is a great companion to Machinery's Handbook. First published (IIRC) right around WWII, still the best practical metrology book available. Well worth the small price & often available used at Half.com, eBay, Alibris, AbeBooks, etc.
Quotes from speculating experts are sort of interesting.
Then again, he probably just made everything up, being nothing more than a "speculating expert"
Kennedy done it, huh Barry?
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.
Originally Posted by precisionworks
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.....
As a home shop guy, I have a set of cheap gauge blocks all of which are accurate to within .00005 according to the FooManChu calibration sheet. I tested the 1" and 2" blocks against mic standards and get the same readings on the micrometers to within .0001. So for me that's more than good enough.
So far I have used mine for setting a sine block and for checking mics where I don't have a standard.
While super accuracy is both beyond me and not needed, I would like to know how much is removed by wringing two blocks together. Curious minds want to know.
If my calculations are correct, for a 5" sine bar at 30 degrees, one second of angle corresponds to a 21 millionths difference in the height of the gauge block stack.
Certainly that 21 millionths will make a difference for critical aerospace components and anything else needing that kind of precision, but nothing I'm working on will require that kind of precision.
A minute of angle change requires 13 tenths and a degree, 7.5 thou. That's a lot of wear on a gauge block before I'll notice any difference.
That's why us hobby guys are willing to take those used gauge blocks off your hands for cheap :-)