Need help understanding measurements on caliper

[tjndaltx]

I know this is a really ignorant question but I'm not very mechanical so need some help.

When reading a digital caliper......

If the maximum cartridge length is supposed to be 2.494 and you want to reduce the length by 20 thousandths would you reduce it to 2.474 or 2.294?

Please help. Thanks!!!!!

[JSnover]

2.474 would be 20 thousandths (.020) less.

[Edubya]

tjndaltx, if you're holding the calipers in your hand, move it between the 2.474 and 2.294 indicator. Which one is reducing the size?!
EW

[tjndaltx]

tjndaltx, if you're holding the calipers in your hand, move it between the 2.474 and 2.294 indicator. Which one is reducing the size?!
EW

Going towards the 2.294, I think.

[tjndaltx]

Thank you for your replies. Very much.

[Boondocker]

TJ when you figure a dial indicator the numbers to the right of the decimal go up to 999 then proceeds to 1.000. 1.000 is a thousand thousanths. so .040 would be .020 + .020 would be .040 thousanths. I hope this helps.

[machinisttx]

.000X" = tenth of a thousandth
.00X0" = thousandth
.0X00" = ten thousandths
.X000" = one hundred thousandths

2.494 - .020 = 2.474


Most digital calipers have both absolute and incremental measuring modes. You can use them as a calculator by switching back and forth between modes. In absolute mode, measure an object. Switch to incremental mode(without moving the slider) and move the slider in either direction(larger or smaller) whatever amount you want. Switch back to absolute mode and you'll have the original measurement, with the amount you moved the slider either added or subtracted to/from it, depending on which direction you moved.

[geargnasher]

I just went and studied my calipers after reading all this, and all mine has are a bunch of little marks that aren't spaced the same!:kidding:

Never had much use for those fandangled digital and dial contraptions [smilie=b:

Gear

[Gohon]

Folks he is using a digital caliper, not a dial caliper.


holding the calipers in your hand, move it between the 2.474 and 2.294 indicator. Which one is reducing the size?

That may be a little confusing to one. Remember he wants to reduce 2.494 by .020, not 2.474 by .020.

The 2.474 is what you were looking for. You'll get the hang of it real fast. Don't worry about ignorant questions. Everyone here was ignorant the first time they picked up a set of calipers until someone showed them how they worked.

[armyrat1970]

tjndaltx, if you're holding the calipers in your hand, move it between the 2.474 and 2.294 indicator. Which one is reducing the size?!
EW

Both will if he is reducing from 2.494.
I know what your saying but if he is reducing from 2.494 move it to 2.474 or 2.500
to see which one is reducing from where he's at.
Anyway dropping to 2.474 is what you're looking for.
I prefer dial calibers. I know each mark is equal to 1 thousandth when graduated over or under the previous mark.

[theperfessor]

Don't know if this will help but I put this together to provide a reference for my students when learning to read micrometers and verniers

(inch based micrometers)
http://www.usi.edu/science/engineering/machasst/meastool/readmic.htm

(inch based verniers)
http://www.usi.edu/science/engineering/machasst/meastool/readvern.htm

The main site has some other useful machining related information:
http://www.usi.edu/science/engineering/machasst/machasst.htm

Note that not all the sections are complete as it is an ongoing project.

[Cadillo]

:shock:Not trying to be mean, but I sure hope he can read his powder scale correctly. Potentially scary stuff!

[Blacksmith]

Perfessor
Thanks for the links I bookmarked the first two and will send them to some grandsons who need to learn how to use my old fashion tools.
The third link would not open.

Blacksmith

[theperfessor]

Blacksmith-

A big OOPS! :groner: on my part. I didn't check it after pasting it in and it got truncated somehow. Try this:

http://www.usi.edu/science/engineering/machasst/machasst.htm

[machinisttx]

I just went and studied my calipers after reading all this, and all mine has are a bunch of little marks that aren't spaced the same!:kidding:

Never had much use for those fandangled digital and dial contraptions [smilie=b:

Gear

Like these?

http://i16.photobucket.com/albums/b20/imakechips/100_0706.jpg

:grin:

[machinisttx]

Don't know if this will help but I put this together to provide a reference for my students when learning to read micrometers and verniers

(inch based micrometers)
http://www.usi.edu/science/engineering/machasst/meastool/readmic.htm

(inch based verniers)
http://www.usi.edu/science/engineering/machasst/meastool/readvern.htm

The main site has some other useful machining related information:
http://www.usi.edu/science/engineering/machasst/machasst.htm

Note that not all the sections are complete as it is an ongoing project.

The easiest way I know of to get a feedrate for a drill is to divide drill diameter by .0625 and divide again by 1000. Gets a ballpark number when you don't have a feed chart laying around.

[Blacksmith]

Perfessor
Thank you again. As a former Manufacturing Engineer and Tech Ed teacher I collect these things. Your links are well done and easy to use.
Blacksmith

[Blacksmith]

Machinisttx
You don't say if you are measuring inside or outside but I make the outside to be .045".
Blacksmith

[machinisttx]

Machinisttx
You don't say if you are measuring inside or outside but I make the outside to be .045".
Blacksmith

It's hard to tell since the camera isn't looking directly on at those lines. I'd put it at .045" or .046". They're just laying in the original wooden box though, not measuring anything. :-)

[Blacksmith]

Ok a challenge to the Electronic Caliper crowd. What is the Inside measurement shown in the picture above? You are allowed to visit the Perfessors link to help you figure it out. Old Machinists who have done this before let the new people give it a try.

Blacksmith

[nonferrous]

It would be, .044.

[theperfessor]

I've owned several electronic 6" calipers. No longer. Every time I needed one the battery was dead. And I think they give a false picture of the accuracy of a beam type caliper. Just because it reads to 0.0005" or 0.0001" doesn't mean you'll get the same measurement every time or that the measurement is actually the true size of the part. A beam caliper with a standard vernier scale gives a reading that is much closer to representing the accuracy of the instrument and the true size of the part. Same for a dial caliper - read it to the nearest 0.001" and you've done the best you can do.

A micrometer with a 0.0001" vernier scale is quite capable of yielding measurements that are representative of both the accuracy of the instrument and the true size of the part.

I am using a definition of instrument accuracy as how close a measurement of a certain value (say 1.0000") is to an established standard size of 1.0000". The closeness of the measurement to true size of the part is dependent on how the instrument is used and its mechanical configuration. A micrometer is easier to set to an accurate size and easier to use to properly measure a part.

Trust me, I love digital readouts and such, but my 30 year old vernier caliper is still just as accurate as the day I got it, and it doesn't have batteries to die or a gear track to get a chip caught in it. It works every time, and I can read it as fast as a dial. Same with my old fashioned analog micrometers with 0.0001" vernier scales.

Blacksmith - should one of us post a picture of a depth micrometer and the backwards reading scale on it?

P.S. It gets harder every year to teach students doing CNC programming the direction of clockwise and counter-clockwise rotation since a lot of them have never had an analog watch!

[theperfessor]

nonferrous - try again.

[joeb33050]

nonferrous - try again.
Technology is an applied science, i.e., it translates the discoveries of theoretical science into practical application to man’s life. As such, technology is not the first step in the development of a given body of knowledge, but the last; it is not the most difficult step, but it is the ultimate step, the implicit purpose, of man's quest for knowledge. [Ayn Rand, 1969]

Ayn is as wrong with this as she was when spelling her first name. Talk to the folk with the beaver rings. "Technology" is the study of techniques-generally techniques involved in some productive effort, such as sweeping a floor or making an integrated circuit. "Technology", like "Geology", is an ology, a science, in the "Tech" end, about techniques or methods.
"Engineering" is "an applied science, i.e., it translates the discoveries of theoretical science into practical application to man’s life."
Al Greenspan was a pal of Ayn's; she influenced his economic thought which brought us to where we are today.
Ayn was and is very good at selling books, check it out-zillions of dollars a year.
joe b.

[machinisttx]

Adding to the electronic caliper criticism---if you get a drop of sweat on the read surface, those calipers will go crazy if they aren't the "coolant proof" models.

Lots of folks seem to have a hard time understanding the difference between accuracy and resolution. Most digital calipers have resolution to .0005, but I have yet to see a caliper manufacturer(dial or digital) guarantee greater accuracy than +/- .001" in six inches...and some won't guarantee any better than +/- .005" in the same distance.

Always fun when someone forgets a negative sign, or puts one where it shouldn't be, when doing circular interpolation. LOL

[Blacksmith]

Perfessor
I don't have a depth mike to take a picture of, if you do go ahead. We could really drive them crazy with a patternmakers shrink factor ruler; I almost bought one once just to drive students wacko. Do you think we need a thread on measuring tools and math?

After the SHTF there are a lot of electronic and electric tools that won't be much good. Electric casting pots won't melt much without electrons to feed them.

Blacksmith

[theperfessor]

I've thought about updating/converting the Machinist's Assistant site to be more gun related and including sections on using a lot more measuring tools and small machine tools. Trouble is that (a) I don't have the time to do it all, (b) I'm a lousy web programmer and haven't kept up with coding conventions.

That being said, it would be a real hoot to have something like this for a ready reference, with different sections being contributions by various people. I'd like a better and more organized structure that would be easy to navigate directly to find certain information, for example lathe faceplate dimensions or a change gear threading calculator or how to square up a milling machine head or ... you get the idea.

Would anybody be interested in having something like this available online to use as reference? Would anybody be willing to contribute illustrated material ready for editing? Would the contributors and the mods here let us use some of the stuff in the classics and stickies?

Any thoughts/comments?

[machinisttx]

A change gear calculator should be pretty easy to set up in an excel spreadsheet.

One of the instructors I had in college had a really nice one set up to calculate thread depths and stuff. I had a copy of it on a 3.5" floppy at one time, but I don't have any idea where it is now.

[Blacksmith]

Perfessor
Perhaps the CastPics section would be a logical place as it seems to be set up for information formatted like you describe. Just a thought. I think I could provide some content.

Blacksmith

[nonferrous]

Ok, Ok, eees .343.

Eees no my fault eees in English Senor. You gringo's are no politically correct.

'Badges? We ain't got no badges. We don't need no badges! I don't have to show you any stinkin' badges!

[armyrat1970]

Ok, Ok, eees .343.

Eees no my fault eees in English Senor. You gringo's are no politically correct.

'Badges? We ain't got no badges. We don't need no badges! I don't have to show you any stinkin' badges!

Never used one but I was thinking something like .344

[theperfessor]

nonferrous, armyrat -

You're both right and it illustrates my point and machinisttx's point. A beam caliper of any type (vernier, dial, or electronic) is only accurate to the nearest +/- 0.001" at best, no matter what the reading says. You're both within that range and truth be told that's as close as you're going to get with a caliper.

By the way nonferrous, I wasn't trying to be a smart*** with my "try again" post, I hope you didn't take any offense. You got the hard part (0.001 scale) right but overlooked the reading on the beam (0.1 scale). The jaws on most larger (>6") calipers don't come to a point and read zero when they're closed, they butt together and have rounded outer surfaces to read inside measurements from bores. In this case those jaws are a total of 0.3" thick when caliper is closed, limiting them to measuring holes of this size or larger.

[nonferrous]

No offense taken here,
I was just trying to make light of the fact that in my haste to be first, (pick me, pick me), I didn't read what was written on the beam.
Also, not being able to see the points for inside kind of threw me off. Then the Dog got into my notebook and ate,,, no, forget that one.
Give me a little more time and I should be able to come up with a few more excuses other than the fact that they were labeled in English.

Thanks, Good Thread

[Jeffery8mm]

:shock:Not trying to be mean, but I sure hope he can read his powder scale correctly. Potentially scary stuff!

Dude, the OP never stated he was having trouble reading his powder scale, only his caliper.
Jeff

[theperfessor]

Not to hijack thread any further, but I found out that if you understand the process of reading a measuring tool, and pay attention to the scale markings, it is just as easy to read a metric mike or vernier as it is to read an inch-based one. Or a slide rule for that matter, but that's another thread completely (even though one of the first true sliderules was invented and used by Napolean's head artillery officer to compute elevation for cannons).

In one of the classes I took I developed an "easier reading" mike that used 50 threads per inch instead of a standard micrometers 40 TPI. Anybody want to guess what the advantages and disadvantages are for this arrangement?

nonferrous - It is a natural human tendency for careful people to focus on the most "difficult" part of a task and pay less attention to the "easy" part. When I do work where measurements fall into the ten thousandths range, I tend to make most of my measurement errors with the 0.025 scale markings. If I had a nickel for every time I've cut a part to within a few ten-thousandths tolerance, and still be exactly 0.025 off one way or the other - well, we could both go out and have a fine steak dinner! :D

[castalott]

As a humorous aside, I want to mention the "Navy" method....

1. Measure it with a micrometer.
2. Mark it with a piece of chalk
3. Hack it off with an axe.
4. Paint it the correct color...it will be ok....


Dale

[nonferrous]

I would imagine that 50 TPI would give the advantage of having a finer feel than 40 Tpi.
The trade off would be that it would be a little slower I would think.

[nonferrous]

As a humorous aside, I want to mention the "Navy" method....

1. Measure it with a micrometer.
2. Mark it with a piece of chalk
3. Hack it off with an axe.
4. Paint it the correct color...it will be ok....


Dale

Dale,
When I was a kid, I was in the Coast Guard. That's the system we used in the Deck division. However when I joined the Black Gang and became an Engineman, (do they even still have that rate?), that was no longer acceptable.

[lwknight]

It looks to me to be .046 to .047 but like machinisttx said. its hard to tell from the pic.
I have the dial mine and also use a regular micrometer on critical stuff.

[stephen perry]

You guys make my head spin and I think some of yours are spinning over this Thread.

Honestly all that is need for Cast and Reloading is a .001 caliper. The one RCBS sells will do the job. No one needs a .0001 caliper or mic for reloading. These are machinist quality instruments and need a set of gages to justify them I have many of both.

Instructions come with a RCBS unit and are worth reading. For many years I used a Craftsman caliper and mic both .001. Still have them in good shape. Reading verniers is something you learned in shop or science class.

Stephen Perry
Angeles BR :brokenima

[lwknight]

Stephen, there are still people in the world that cannot ead a regular tape measure.
If I were going to stereotype boolit casters, I say that we are mostly all the do-it-yourself types that learned about tools when we were young.

[lwknight]

And there are those like me who cannot type no matter how many times I re-read before hitting the post button

[theperfessor]

Stephen -

I wouldn't disagree with your assertion that most reloaders could do quite well with a 6" caliper as their only precision measurement tool, although I think an inexpensive 0-1" outside mike would be nice to have too. Until I started getting my shop together all I had was a Craftsman 6" vernier caliper and a Lufkin 0-1" mike w/no 0.0001 vernier scale. I keep them in my reloading area and still use them.

But it seems to me that most of the people that gravitate to this site are the ones that aren't average. They are the ones that buy pin gauges to measure revolver throats and micrometers to slug their bores. They come up with neat ideas, make neat things, and enjoy reading about neat ideas and things that other people come up with.

I think a lot of folks enjoy reading and learning about various measuring tools and how they're used to measure things, even if they never buy or use some of the tools a machinist might have.

If you want to find spin on this site, just start a thread on twist rates vs bullet velocity! :-D

[armyrat1970]

Just my .02 but I believe a TPI of 50 would give a much finer reading because of less slack in the threads. The advantage. The disadvantage would be that it would be a little harder to get that fine adjustment and measure because the tool is so much tighter.

[theperfessor]

Armyrat1970 -

One of the main reasons for a 50 tpi thread is that it would make the increments on the main scale be 0.020 apart, with five instead of four divisions. People are more "used" to counting in increments of 2, 4, 6, 8 etc. Its a lot easier to read as 0.020, 0.040, and so on before you add the 0 to 20 (thousandths) reading on the thimble. And when you read the thimble and get for example 18, then the final measurement will always end in 8 and not 8 OR 3, preventing 0.005 errors. I see this all the time when my students read mikes. Also, the second digit from the right will always be 0 if the thimble reading is less than 10, and an odd number if the thimble is 10 to 19.

Think about it a minute, then think how many measurement errors could be prevented.

Here is a picture of my Brown & Sharp depth micrometer. Anybody want to guess what the reading is?

[jhrosier]

.343

Jack

[theperfessor]

Right on, Jack!

[jhrosier]

I cheated.
I've worked in manufacturing for 40 some odd years and my job depends on being able to measure things accurately, with whatever ancient measuring device is provided.

I can even use a slide rule in a pinch, but prefer an Excel spreadsheet.;)

It does give me a good feeling to know that I can still function if the electricity goes out though.

Jack

[stephen perry]

I still feel for reloading purpose a caliper vernier or electronic reading in .001 will get the job done. A caliper will do most of what a micrometer will do. You can measure OAL and neck diameter just fine with a caliper. I did mention I have the same .001 Craftsman mic I started reloading with.

I now use a .0001 micrometer digital or electronic to measure swaged jacketed BR bullets I make but that is not in the realm of average reloading on this Thread. I also use pin gages, gage block standards, and depth gages but that is approaching machinist work. We are now way beyond the scope of the Cast bullet maker/shooter.

Stephen Perry
Angeles BR :brokenima

[jhrosier]

...
I now use a .0001 micrometer digital or electronic to measure swaged jacketed BR bullets I make but that is not in the realm of average reloading on this Thread. I also use pin gages, gage block standards, and depth gages but that is approaching machinist work. We are now way beyond the scope of the Cast bullet maker/shooter.

Stephen Perry
Angeles BR :brokenima

Stephen,

Come on down off your high horse and notice the number of craftsmen, machinists, gunsmiths, mould and die makers that hang out around here.

Many of us are more than familiar with tenths of thousandths of an inch and have the patience to help newcomers get the most from their equipment without talking down to them.

Jack

[JIMinPHX]

I would have called it .3431. Even when I don't have the vernier scale to help me, I still try to estimate 1 extra decimal place on a good quality mic like a B&S.

[John Guedry]

Perfessor many thanks for the links and your guidence. I learned alot of this info in my misspent youth, but 50 odd years later have trouble remembering a lot of it. I have bookmarked these pages to share with my grandson because you explain it a whole lot better than I can.

[Bill*]

I get .345?
OOOOPS......Pays to make sure your on the last page before posting. I think you'll find .345 is the inside measurement on the calipers shown on the first page:oops: post #15