May 2007
Another day in the life of a gunsmith
Spent part of last Tuesday at the
range, schmoozing with A Famous Gun Writer Who Wishes To Remain
Anonymous (hereafter referred to as "AFGWWWTRA".) We tested a few
guns, talked about revolvers - the kinds of things you'd expect a
gunsmith and a gun writer to do on a range.
AFGWWWTRA happened to have a Ruger Alaskan model in .454 Casull that was being evaluated. Since I hadn't yet gotten the chance to shoot one, I really wanted to see what it was like with full-house loads. I elected to shoot a couple of cylinders worth while AFGWWWTRA took pictures of the whole debacle. (AFGWWWTRA, it turns out, is easily amused by masochistic idiots. I'm sure it was meant as a compliment.)
The first cylinder was fired, sedately, in single action from the 25-yard bench. At that point I was thinking "heck, that wasn't bad. I wonder what it'd be like in rapid fire?" The second cylinder full, standing from about 7 yards, was fired as quickly as I could get the gun back on target between shots.
The second cylinder hurt more. A lot more. As in: my poor wrists may never be the same. What the hell was I thinking?
Just to retain my machismo cred, here I am in the midst of that sequence, the mighty .454 loads in full fireball-producing glory:
Courtesy of AFGWWWTRA
Note the flash from the round just fired, and yet the gun is back on target and the hammer is about to drop again. Yes, I am just that damn good! (I must be - I tell myself so all the time!)
-=[ Grant ]=-
AFGWWWTRA happened to have a Ruger Alaskan model in .454 Casull that was being evaluated. Since I hadn't yet gotten the chance to shoot one, I really wanted to see what it was like with full-house loads. I elected to shoot a couple of cylinders worth while AFGWWWTRA took pictures of the whole debacle. (AFGWWWTRA, it turns out, is easily amused by masochistic idiots. I'm sure it was meant as a compliment.)
The first cylinder was fired, sedately, in single action from the 25-yard bench. At that point I was thinking "heck, that wasn't bad. I wonder what it'd be like in rapid fire?" The second cylinder full, standing from about 7 yards, was fired as quickly as I could get the gun back on target between shots.
The second cylinder hurt more. A lot more. As in: my poor wrists may never be the same. What the hell was I thinking?
Just to retain my machismo cred, here I am in the midst of that sequence, the mighty .454 loads in full fireball-producing glory:
Courtesy of AFGWWWTRA
Note the flash from the round just fired, and yet the gun is back on target and the hammer is about to drop again. Yes, I am just that damn good! (I must be - I tell myself so all the time!)
-=[ Grant ]=-
FRIDAY SURPRISE: The rest of my plumbing story
Friday, May 25, 2007 Filed in:
Friday
Surprise!, Completely
irrelevant
Someone reminded me that I
promised to tell you the story of my little plumbing adventure.
Personally I don't think it's all that interesting, and there isn't
even a moral to the tale. It is, however, interesting in the same
way that highway accidents are!
It started, innocently enough, with a knock at the door. Standing on my porch was a nice gal from the city's Public Works department, who said something along the lines of "we think you have a problem!" The Finance Department had called them with the news that our water bill had jumped during the month from our normal $73 to a whopping $233, and that maybe they should come out and have a look.
She did, and didn't see anything. She did suggest that I call a leak detection company to locate the source, after which a call to a plumber might be "a good idea."
(It's worth noting that normally I take care of such matters myself, having grown up on a farm where we never hired such work out. However, I've got so many other things to do right now I just couldn't tackle the project. As you'll see, it was probably for the best.)
The leak guy came out and did his little magic (pumping the lines full of helium and listening for the popping sounds of the gas escaping from the leak site.) Nothing. He did the test again - same result. We were both standing in my side yard, wondering where this leak could be, when I heard a sound.
"Pop-snap-crackle" (trademark concerns, you understand.) We walked around in circles, trying to find the source. At one point I decided on a likely direction and followed the sound into....the middle of my neighbor's back yard, where a tiny geyser was erupting!
We theorized that at one point back in the 1940s both houses shared a common water service, but sometime later the neighbor got their own service. At that point they apparently cut the tie at their house and capped the now-unused stub, which finally rusted out and started leaking.
At least, that was the theory.
The leak guy traced what he thought was the offending pipe over to the leak site, marked everything, and left. That's when I started calling plumbers - and calling plumbers, and calling plumbers. An even dozen, in fact. I called half on Thursday and the other half on Friday, and none of them returned my calls. Finally, on Monday I found a plumber who actually answered his phone, and one of his crews came out to start digging.
The plan was to dig down 32 inches, where the line was, to the 't' fitting where the stub line originated, then cap the stub off at that point.
They got down to the point, and found only an elbow going into my house. They started digging a trench - 32 inches deep, by hand, mind you - in an effort to find the stub and it's fitting. The dug 8 feet of trench without finding that connection, and would have followed it clear to the water meter, were it not for one little problem: the garage was built on top of the water line, and the pipe went right under the cement floor!
At this point things got really expensive, as we elected to have them bring in a horizontal drilling rig and install a whole new service line. A couple grand later, and it was in - and the leak, naturally, ceased. I'm now glad I didn't try to tackle this myself.
On the plus side, those boring machines are pretty cool. They put a hole from the water meter, down under my garage, up the hill and into the end of the trench that had been dug - and got within a couple inches of center. The actual drilling probably took them 10 minutes, but the setup and takedown kept them here about an hour. Quick and easy, as long as one has a full checkbook!
There you have it. Hope it was as exciting as you were expecting!
-=[ Grant ]=-
It started, innocently enough, with a knock at the door. Standing on my porch was a nice gal from the city's Public Works department, who said something along the lines of "we think you have a problem!" The Finance Department had called them with the news that our water bill had jumped during the month from our normal $73 to a whopping $233, and that maybe they should come out and have a look.
She did, and didn't see anything. She did suggest that I call a leak detection company to locate the source, after which a call to a plumber might be "a good idea."
(It's worth noting that normally I take care of such matters myself, having grown up on a farm where we never hired such work out. However, I've got so many other things to do right now I just couldn't tackle the project. As you'll see, it was probably for the best.)
The leak guy came out and did his little magic (pumping the lines full of helium and listening for the popping sounds of the gas escaping from the leak site.) Nothing. He did the test again - same result. We were both standing in my side yard, wondering where this leak could be, when I heard a sound.
"Pop-snap-crackle" (trademark concerns, you understand.) We walked around in circles, trying to find the source. At one point I decided on a likely direction and followed the sound into....the middle of my neighbor's back yard, where a tiny geyser was erupting!
We theorized that at one point back in the 1940s both houses shared a common water service, but sometime later the neighbor got their own service. At that point they apparently cut the tie at their house and capped the now-unused stub, which finally rusted out and started leaking.
At least, that was the theory.
The leak guy traced what he thought was the offending pipe over to the leak site, marked everything, and left. That's when I started calling plumbers - and calling plumbers, and calling plumbers. An even dozen, in fact. I called half on Thursday and the other half on Friday, and none of them returned my calls. Finally, on Monday I found a plumber who actually answered his phone, and one of his crews came out to start digging.
The plan was to dig down 32 inches, where the line was, to the 't' fitting where the stub line originated, then cap the stub off at that point.
They got down to the point, and found only an elbow going into my house. They started digging a trench - 32 inches deep, by hand, mind you - in an effort to find the stub and it's fitting. The dug 8 feet of trench without finding that connection, and would have followed it clear to the water meter, were it not for one little problem: the garage was built on top of the water line, and the pipe went right under the cement floor!
At this point things got really expensive, as we elected to have them bring in a horizontal drilling rig and install a whole new service line. A couple grand later, and it was in - and the leak, naturally, ceased. I'm now glad I didn't try to tackle this myself.
On the plus side, those boring machines are pretty cool. They put a hole from the water meter, down under my garage, up the hill and into the end of the trench that had been dug - and got within a couple inches of center. The actual drilling probably took them 10 minutes, but the setup and takedown kept them here about an hour. Quick and easy, as long as one has a full checkbook!
There you have it. Hope it was as exciting as you were expecting!
-=[ Grant ]=-
Woo-hoo! I'm SOMEBODY!
Wednesday, May 23, 2007 Filed in:
Other
resources, Shooting
industry
Seems that Michael Bane, host of
the television shows
Shooting Gallery and
Cowboys (and general firearms
bon
vivant),
has seen fit to mention me in his
blog. Much
appreciated, and I am flattered by the attention, though being
named in the same column as radiation-squelching undies leaves open
questions of the sort I'd rather not contemplate.
As to this screed being ghostwritten, I'll only say "yestidday I couldn't spell intirdnet, today I is in it! Thank you, Al Gore!"
-=[ Grant ]=-
As to this screed being ghostwritten, I'll only say "yestidday I couldn't spell intirdnet, today I is in it! Thank you, Al Gore!"
-=[ Grant ]=-
The Second Amendment Carnival is back!
Some great stuff (like
always!)
The Second Amendment Carnival
(Hopefully my plumbing nightmare is over...full report later this week.)
-=[ Grant ]=-
The Second Amendment Carnival
(Hopefully my plumbing nightmare is over...full report later this week.)
-=[ Grant ]=-
FRIDAY SURPRISE: Glow in the dark
Back when I was a teenager, I
apprenticed to a master watch- and clock-maker. He was an older
fellow - in his early 70s - and had been in the business for a very
long time.
I enjoyed looking around his shop in spare moments, as he had many old and wonderful gadgets on his jam-packed shelves. One one high shelf, way in the back, was a little vial of off-white liquid. I asked him what it was, and he said "radium paint. We used to use it to make the numbers on dials visible in the dark. Don't touch it!"
He never did explain to me why I shouldn't touch it, but I obeyed his command and forgot all about it. That is, until I ran across this article on US Radium, the company that made the paint in that little bottle.
-=[ Grant ]=-
I enjoyed looking around his shop in spare moments, as he had many old and wonderful gadgets on his jam-packed shelves. One one high shelf, way in the back, was a little vial of off-white liquid. I asked him what it was, and he said "radium paint. We used to use it to make the numbers on dials visible in the dark. Don't touch it!"
He never did explain to me why I shouldn't touch it, but I obeyed his command and forgot all about it. That is, until I ran across this article on US Radium, the company that made the paint in that little bottle.
-=[ Grant ]=-
Another day of no blogging
Wednesday, May 16, 2007 Filed in:
Blog stuff
My favorite powders
Monday, May 14, 2007 Filed in:
Ammunition, Accessories
Every reloader has his or her
favorite powders. When I first started reloading handgun
cartridges, I used what everyone around me used - which I found
weren't always the best choices for my needs. After experimenting
with lots of powders, I settled on a few favorites.
As a general rule I prefer flaked powders over ball (spherical) powders. I've found that they meter more consistently in a wide variety of measures, and they seem to burn a bit cleaner than their ball equivalents - this may have something to do with the graphite coating all ball powders appear to use.
For all-around use in a wide variety of pistol cartridges I really like Hodgdon Universal Clays. It is extremely clean (the cleanest I've yet used) and is useful in a large number of calibers. My only complaint is that is isn't suitable for light loads in spacious cases, because it often fails to burn fully. This results in lots of unburned powder flakes that always seem to end up under the extractor. I'd like to find an equivalent powder that is more suitable for light loads, but haven't found it yet.
For magnum cartridges, I like Alliant Blue Dot. It is very consistent, burns cleanly, and gives superb velocities. I've used it in the .357 Magnum, the .44 Magnum, the fire-breathing .445 SuperMag, and the obscure .451 Detonics Magnum. In each case it performed superbly. So pleased am I with Blue Dot that one of these days I plan to try some of the other "Dot" powders.
Though I've tried lots of others, these are the ones I keep coming back to. There's nothing like "old friends" that you can count on!
-=[ Grant ]=-
As a general rule I prefer flaked powders over ball (spherical) powders. I've found that they meter more consistently in a wide variety of measures, and they seem to burn a bit cleaner than their ball equivalents - this may have something to do with the graphite coating all ball powders appear to use.
For all-around use in a wide variety of pistol cartridges I really like Hodgdon Universal Clays. It is extremely clean (the cleanest I've yet used) and is useful in a large number of calibers. My only complaint is that is isn't suitable for light loads in spacious cases, because it often fails to burn fully. This results in lots of unburned powder flakes that always seem to end up under the extractor. I'd like to find an equivalent powder that is more suitable for light loads, but haven't found it yet.
For magnum cartridges, I like Alliant Blue Dot. It is very consistent, burns cleanly, and gives superb velocities. I've used it in the .357 Magnum, the .44 Magnum, the fire-breathing .445 SuperMag, and the obscure .451 Detonics Magnum. In each case it performed superbly. So pleased am I with Blue Dot that one of these days I plan to try some of the other "Dot" powders.
Though I've tried lots of others, these are the ones I keep coming back to. There's nothing like "old friends" that you can count on!
-=[ Grant ]=-
FRIDAY SURPRISE: Folks, I don't make this stuff up...
The Friday Surprise articles
usually present themselves well in advance of the time I need them.
There's just so much interesting stuff going on in the world that I
usually have no problem finding a topic.
Not this week. It really shouldn't have surprised me, as this week has just been a disaster from the start, but it did annoy me. I just couldn't find anything interesting to write about.
Luckily my old nemesis, The Squirrel, went on another rampage.
-=[ Grant ]=-
Not this week. It really shouldn't have surprised me, as this week has just been a disaster from the start, but it did annoy me. I just couldn't find anything interesting to write about.
Luckily my old nemesis, The Squirrel, went on another rampage.
-=[ Grant ]=-
Allow me to elaborate...
In last Monday's post I mentioned
that the Ruger Mini-14 demands factory magazines to work reliably.
That statement may have given a bit of a wrong impression.
The point I was trying to make, and apparently didn't, is that the only reliable Minis I have seen were using factory magazines. I have actually encountered many examples that wouldn't run, and changing to factory mags made them work properly. All is not perfect in Ruger-land, though - in my experience, there is still a large percentage of Mini-14s that are not reliable, even with factory magazines.
The other side of the coin is that I have never seen a reliable Mini using aftermarket mags. Ever. Aftermarket Mini-14 magazines consistently cause Minis - every one I've ever seen - to choke.
Bottom line: factory mags alone will not ensure that any given Mini will run well. However, using non-Ruger magazines is a virtual guarantee that you will have trouble making the thing work properly. (I won't even get into their renowned lack of accuracy, but that isn't the fault of the magazines!)
I hope this clarifies things a bit.
(Oh, by the way - the cheapest I've been able to find Ruger factory 20-round mags is $55.00. That's three times the cost of good quality AR-15 mags. Wow!)
-=[ Grant ]=-
The point I was trying to make, and apparently didn't, is that the only reliable Minis I have seen were using factory magazines. I have actually encountered many examples that wouldn't run, and changing to factory mags made them work properly. All is not perfect in Ruger-land, though - in my experience, there is still a large percentage of Mini-14s that are not reliable, even with factory magazines.
The other side of the coin is that I have never seen a reliable Mini using aftermarket mags. Ever. Aftermarket Mini-14 magazines consistently cause Minis - every one I've ever seen - to choke.
Bottom line: factory mags alone will not ensure that any given Mini will run well. However, using non-Ruger magazines is a virtual guarantee that you will have trouble making the thing work properly. (I won't even get into their renowned lack of accuracy, but that isn't the fault of the magazines!)
I hope this clarifies things a bit.
(Oh, by the way - the cheapest I've been able to find Ruger factory 20-round mags is $55.00. That's three times the cost of good quality AR-15 mags. Wow!)
-=[ Grant ]=-
Have those primer tube blues?
Unless you're using a Lee
reloading press, one of the biggest bottlenecks in reloading is the
chore of filling primer tubes. It is definitely a time waster, and
anything that can speed up the process is welcome here!
Yes, I know all about the Dillon primer tube loader. It only works with Dillon tubes, isn't all that fast, and is really expensive. Luckily, the folks at Midway came up with a solution: the Frankford Arsenal Vibra-Prime!
This little doohickey takes a package of primers and, with the pull of the trigger, loads their own primer tubes - which, happily, easily interface with Hornady, RCBS, and even Dillon presses.
This thing is fast - easily 2 or 3 times as fast as it's Dillon competition. The great part? It's only $32.99! Check it out.
-=[ Grant ]=-
Yes, I know all about the Dillon primer tube loader. It only works with Dillon tubes, isn't all that fast, and is really expensive. Luckily, the folks at Midway came up with a solution: the Frankford Arsenal Vibra-Prime!
This little doohickey takes a package of primers and, with the pull of the trigger, loads their own primer tubes - which, happily, easily interface with Hornady, RCBS, and even Dillon presses.
This thing is fast - easily 2 or 3 times as fast as it's Dillon competition. The great part? It's only $32.99! Check it out.
-=[ Grant ]=-
I'm playing catch-up today
Back from serving as assistant
teacher in a rifle class this weekend, and am just beat. My back
hurts; my chiropractor has been making a mint off me for the last
few months, as I seem to injure myself with greater regularity as I
age!
Students reported that ammunition (this class required 700 rounds) was extremely difficult to find, particularly in .223 (5.56mm, if you prefer.) It wasn't so much the price - although ammo prices are high, and getting higher by the minute. No, the major stumbling block was availability; they almost couldn't find what they needed in sufficient quantity for the course.
As a result, we saw a lot of "second tier" ammunition in this class: Fiocchi, Sellier & Bellot, and Wolf.
Luckily, no major ammunition problems presented themselves. In the past, S&B .223 has shown a disturbing tendency to lose the primer cups during ejection. Invariably, those little things would work themselves into the trigger mechanism, and tie up the action. This time we saw none of that. Perhaps S&B has gotten their act together (again)?
Fiocchi seemed to work fine, and the Wolf steel cased is....well, Wolf. I'd personally restrict its use to those guns (Communist-bloc) designed for steel cased ammunition, as the steel is rough on extractors designed for a diet of brass cases. If you insist on using it I'd recommend you keep a spare extractor on hand.
After working these classes for the past several years, and seeing all kinds of autoloading rifles used to shoot large amounts of ammunition over a weekend, I've come to a conclusion guaranteed to raise hackles amongst rifle debaters: the AK-47 series of rifles have proved to me that they aren't as reliable as scuttlebutt makes them out to be, and the AR-15 series of rifles aren't as fragile as that same scuttlebutt says they are. This particular class proved that again: two AKs experienced problems while all of the ARs ran flawlessly.
Boy, am I gonna get hate mail for that one!
(Final thought: if you have a Ruger Mini-14, use only Ruger magazines. Period. Nothing else will be reliable in that model. This opinion is validated in nearly every class, as it was again this time. Yeah, I know Ruger only makes 20-rounders; if you want more, get a different rifle!)
-=[ Grant ]=-
Students reported that ammunition (this class required 700 rounds) was extremely difficult to find, particularly in .223 (5.56mm, if you prefer.) It wasn't so much the price - although ammo prices are high, and getting higher by the minute. No, the major stumbling block was availability; they almost couldn't find what they needed in sufficient quantity for the course.
As a result, we saw a lot of "second tier" ammunition in this class: Fiocchi, Sellier & Bellot, and Wolf.
Luckily, no major ammunition problems presented themselves. In the past, S&B .223 has shown a disturbing tendency to lose the primer cups during ejection. Invariably, those little things would work themselves into the trigger mechanism, and tie up the action. This time we saw none of that. Perhaps S&B has gotten their act together (again)?
Fiocchi seemed to work fine, and the Wolf steel cased is....well, Wolf. I'd personally restrict its use to those guns (Communist-bloc) designed for steel cased ammunition, as the steel is rough on extractors designed for a diet of brass cases. If you insist on using it I'd recommend you keep a spare extractor on hand.
After working these classes for the past several years, and seeing all kinds of autoloading rifles used to shoot large amounts of ammunition over a weekend, I've come to a conclusion guaranteed to raise hackles amongst rifle debaters: the AK-47 series of rifles have proved to me that they aren't as reliable as scuttlebutt makes them out to be, and the AR-15 series of rifles aren't as fragile as that same scuttlebutt says they are. This particular class proved that again: two AKs experienced problems while all of the ARs ran flawlessly.
Boy, am I gonna get hate mail for that one!
(Final thought: if you have a Ruger Mini-14, use only Ruger magazines. Period. Nothing else will be reliable in that model. This opinion is validated in nearly every class, as it was again this time. Yeah, I know Ruger only makes 20-rounders; if you want more, get a different rifle!)
-=[ Grant ]=-
FRIDAY SURPRISE: How do you fix an undersea cable?
That's right - an undersea cable.
I'll bet you thought that undersea cables were a thing of the past,
right? You probably had it in your mind that satellite technology
had rendered the undersea cable a relic of a bygone age, didn't
you? As Gomer would say, "surprise, surprise, surprise!"
The vast majority of telephone and internet traffic flows on undersea cables, to this day. Compared to satellites, cables are cheaper and have much greater bandwidth. As a result, there are hundreds of cables in use today, and well over 1,000 cable landing sites (where the cables come ashore) around the world. Here's a good graphic of the undersea cables - and their load - in use today. Wikipedia has a good article on cables, with lots of links to other sites that can tell you everything you ever wanted to know about the subject!
Of course, all those cables sitting on the ocean floor are subject to lots of forces, and sooner or later they break. So, how do you repair a cable that might be thousands of feet deep, well below the ability to use human divers?
Find out here.
-=[ Grant ]=-
The vast majority of telephone and internet traffic flows on undersea cables, to this day. Compared to satellites, cables are cheaper and have much greater bandwidth. As a result, there are hundreds of cables in use today, and well over 1,000 cable landing sites (where the cables come ashore) around the world. Here's a good graphic of the undersea cables - and their load - in use today. Wikipedia has a good article on cables, with lots of links to other sites that can tell you everything you ever wanted to know about the subject!
Of course, all those cables sitting on the ocean floor are subject to lots of forces, and sooner or later they break. So, how do you repair a cable that might be thousands of feet deep, well below the ability to use human divers?
Find out here.
-=[ Grant ]=-
"Bullshit Tenths"
Pardon my French!
This is a term used by tool & die makers to indicate unobtainable levels of (perceived) precision. Why do I bring this up?
Last week, I was advising a reader on selecting pin gages for use in measuring chamber throats. The discussion revolved around which gages to buy, and whether or not he needed both plus- and minus-tolerance gages (no, in case you're wondering.) He was concerned about their variance of .0002" (that's 2/10,000th of an inch, or 1/20th of the thickness of an average human hair. In machinist parlance, that would be "2 tenths.") As I explained to him, in practice it's not really possible to measure to that level.
As I thought about my answers to his questions, I flashed back to a conversation related to the posts I've made about measuring tools. A fellow who identified himself as a gunsmith contacted me to argue about my advocacy of quality measuring tools. "I don't need any of them overpriced tools - I use [insert name of well known retailer of low end Chinese tools here], and I can measure down to a ten-thousandth!" I asked him if what he was measuring was under the same environmental conditions as the calibration on his micrometer, and he replied "my mic reads to a tenth - it don't need to be calibrated!"
Sigh.
When a measuring instrument is calibrated - that is, checked against known standards and certified as to accuracy - the environmental conditions of that calibration are recorded. The calibration is really only valid for those same conditions; if the temperature goes up or down, that accuracy is not guaranteed.
How much different does a change in temperature make? I did a little experiment. I got out my Grade 2 Brown & Sharpe gage blocks, and picked out the .125" block. (The tolerance for Grade 2 blocks is +/- .000002", or two-milliionths of an inch.) On the calibration certificate, it gives you the deviation from the nominal dimension in millionths of an inch for each block. In the case of my .125" block, it has no variance - in other words, it is guaranteed to measure .125000" at 68 degrees F. Coincidentally, that is the temperature that my shop generally maintains outside of the coldest winter and warmest summer months.
After checking the temperature, I pulled out my best Etalon (Swiss) micrometer and the .125 block. I handled the mic with gloves while I secured it in its stand; the block was handled with insulated tweezers (yes, there are such things.) I measured the block under these conditions, and not surprisingly it measured .1250" on the nose.
I took the block out of the micrometer, and held the non-measuring surfaces between by thumb and forefinger for about a minute, then remeasured. Guess what? Just that small amount of heat had caused the gage to grow to a bit more than .1251" (a typical mic only measures to a ten-thousandth, and this fell just between the .1251" and .1252" marks.) Had I held on to it longer, it would have grown a bit more. Had I held the mic in my hand while measuring, it too would have been "off."
That's why they're called "bullshit tenths" - because, without knowing exactly the temperature of both the micrometer and work, and at what temperature the micrometer was last calibrated, you really don't know to the ten-thousandth of an inch how big that part really is. In other words, until you've met all of the above, you can't measure to a ten-thousandth of an inch, no matter how optimistic you are!
Since pin gages are usually held in the hand, as is the piece to be measured, it would not be possible to get closer than several ten-thousandths. Factor in the other environmental variables, it's clear that a) the gages are more accurate than they need to be for the job asked of them; b) you can't measure to the limit of the gages, so you don't need both the plus and minus coverage; and c) worrying about their allowed +/- .0002" isn't at all productive. Save your stomach lining for more important things.
Hope this all makes sense!
-=[ Grant ]=-
This is a term used by tool & die makers to indicate unobtainable levels of (perceived) precision. Why do I bring this up?
Last week, I was advising a reader on selecting pin gages for use in measuring chamber throats. The discussion revolved around which gages to buy, and whether or not he needed both plus- and minus-tolerance gages (no, in case you're wondering.) He was concerned about their variance of .0002" (that's 2/10,000th of an inch, or 1/20th of the thickness of an average human hair. In machinist parlance, that would be "2 tenths.") As I explained to him, in practice it's not really possible to measure to that level.
As I thought about my answers to his questions, I flashed back to a conversation related to the posts I've made about measuring tools. A fellow who identified himself as a gunsmith contacted me to argue about my advocacy of quality measuring tools. "I don't need any of them overpriced tools - I use [insert name of well known retailer of low end Chinese tools here], and I can measure down to a ten-thousandth!" I asked him if what he was measuring was under the same environmental conditions as the calibration on his micrometer, and he replied "my mic reads to a tenth - it don't need to be calibrated!"
Sigh.
When a measuring instrument is calibrated - that is, checked against known standards and certified as to accuracy - the environmental conditions of that calibration are recorded. The calibration is really only valid for those same conditions; if the temperature goes up or down, that accuracy is not guaranteed.
How much different does a change in temperature make? I did a little experiment. I got out my Grade 2 Brown & Sharpe gage blocks, and picked out the .125" block. (The tolerance for Grade 2 blocks is +/- .000002", or two-milliionths of an inch.) On the calibration certificate, it gives you the deviation from the nominal dimension in millionths of an inch for each block. In the case of my .125" block, it has no variance - in other words, it is guaranteed to measure .125000" at 68 degrees F. Coincidentally, that is the temperature that my shop generally maintains outside of the coldest winter and warmest summer months.
After checking the temperature, I pulled out my best Etalon (Swiss) micrometer and the .125 block. I handled the mic with gloves while I secured it in its stand; the block was handled with insulated tweezers (yes, there are such things.) I measured the block under these conditions, and not surprisingly it measured .1250" on the nose.
I took the block out of the micrometer, and held the non-measuring surfaces between by thumb and forefinger for about a minute, then remeasured. Guess what? Just that small amount of heat had caused the gage to grow to a bit more than .1251" (a typical mic only measures to a ten-thousandth, and this fell just between the .1251" and .1252" marks.) Had I held on to it longer, it would have grown a bit more. Had I held the mic in my hand while measuring, it too would have been "off."
That's why they're called "bullshit tenths" - because, without knowing exactly the temperature of both the micrometer and work, and at what temperature the micrometer was last calibrated, you really don't know to the ten-thousandth of an inch how big that part really is. In other words, until you've met all of the above, you can't measure to a ten-thousandth of an inch, no matter how optimistic you are!
Since pin gages are usually held in the hand, as is the piece to be measured, it would not be possible to get closer than several ten-thousandths. Factor in the other environmental variables, it's clear that a) the gages are more accurate than they need to be for the job asked of them; b) you can't measure to the limit of the gages, so you don't need both the plus and minus coverage; and c) worrying about their allowed +/- .0002" isn't at all productive. Save your stomach lining for more important things.
Hope this all makes sense!
-=[ Grant ]=-