Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.
pete wrote: ↑Sat Dec 29, 2018 4:39 pmIn my opinion hard to 100% verify accuracy items like this or something like a granite surface plates sort of invites a bit of less than truthful or even bogus numbers on the certifications if the manufacturer is less than honorable.
My first surface plate, a 9x12 chicom black granite, came with a certificate of accuracy for "0001".
It didn't say "0.001" nor ".0001", just "0001".
Remember, bad punctuation kills:
"Let's eat Grandma"
"Let's eat, Grandma"
JackF wrote: ↑Mon Dec 31, 2018 7:45 pm
Unless I missed it, a 5C spin indexer is handy. I got mine used for $30 and you can buy import collet sets or buy quality collets as you need them.
I was looking at some used gage block sets on Ebay, but can't tell from the pictures what the condition is. How wrong can I go buying a used set? Would they be off enough to make a big difference? Remember, I work only to thousands. Would a used set, say 70 years old from Dearborn for $100 be good enough for me? https://www.ebay.com/itm/Ellstrom-Dearb ... SwUulbv8LA
They would probably be ok, but like you I can only judge them by what's shown. Highly used blocks may or may not wring together as well as they should. Without physically testing that yourself there's no real way to know for sure. That would have been a high cost set when new. It would take a lot of noticeable wear to the surface of any block to make a 10ths difference in accuracy. I count 11 blocks missing in that set. A couple of the slots might have been for what are known as wear blocks though. Those missing one's are the smaller sizes and picking up those missing ones with individual replacements from Starrett or Mitutoyo wouldn't be all that much money. If that were a complete set then likely the asking price would be much higher. I think I'd counter offer with maybe $60-$80 and see if they bite? Even in a commercial shop there's likely many of those blocks that rarely or never got used. Any rust at all on any of the wringing surfaces would be a deal breaker for me though. There doesn't seem to be any on the block areas that can be seen in the pictures. I'd ask about that to be sure.
For multiple reasons it's a normal and accepted industry practice that to be somewhat sure of your measurements then they use what's called the 10 X rule. The metrology equipment should be reliable and accurate to ten times the tolerance your measuring to. For repeatable .001" measurements then 10ths capable equipment is used. However with commercial parts that rule is important, not nearly as much in a home shop for what we'd normally be making. Absolute accuracy to very close limits isn't really necessary for most of us. It still depends on what actual use you plan for those blocks though. One use is double checking almost anything you have for measuring equipment. Having every tool agree with each other or at least know there might be a bit of wear and inaccuracy is more important than absolute accuracy for most of us. I'm not 100% sure of what the empty space at the top right side of the box would have been for.
That space is for"special stone for gage blocks" readable in last pic. I'm suffering some optical illusion looking at the pics. Some blocks appear not to be there and another view seems to show they haven't even been removed. That stuff which was used to protect precision tools, is obvious in its absence of the blocks used.
Altogether a very interesting set.
Spro's correct about the stone ( a rectangular hard Arkansas). My Webber set came with one.
I'm not going to suggest that that set isn't worthy of being owned, but I don't like those rectangular blocks. No particular reason, I just don't like 'em, although one thing than helps make that decision is that, unlike the square blocks, you can't add a mechanical device that doesn't get in the way---the one that prevents the blocks from separating if the "wring" fails. Not using one offers the potential to drop blocks, something one should avoid. With the square ones, it' goes inside and doesn't get in the way.
H
Wise people talk because they have something to say. Fools talk because they have to say something.
John Hasler wrote: ↑Wed Jan 02, 2019 8:38 am
What is the stone for?
To remove any dings on the wringing surface of the blocks.
Yeah, I have a problem with that idea, too.
Blocks are exceedingly hard, no less than 62 Rc, and likely harder. They don't ding easily, but they can be damaged. However, seems to me that an item that is calibrated to millionths shouldn't have an abrasive applied. A stone is NOT selective. It will remove material (albeit very little) anywhere it makes contact. The degree of precision in gauge blocks demand that they not be altered in any way.
That said, I strongly suspect that the stone is to be used when a block fails to wring, yet displays no obvious issues. The slightest irregularity, which would manifest itself as a raised portion, would be much quicker to be removed and offers the opportunity for the block to wring once again. The question would now be, is it still parallel, and has the length been altered? Critical considerations when working to millionths.
H
Wise people talk because they have something to say. Fools talk because they have to say something.