Micrometer Accuracy?

[jabilli]

Hey guys :-)

I noticed just earlier today that my micrometer readings can vary greatly by how hard I squeeze with my calipers, and how I measure the boolit.

It's very elementary, and really I thought I had it down... But I guess one thing that brings an element of fun to this hobby is that you can always learn something new (I assume I'm doing something wrong).

If you'd please... A few pointers for proper and most accurate use of a micrometer?

61918

[wrench man]

Calipers and Micrometers are two different tools, Micrometers are far more accurate than Calipers.
To get consistent readings with your Calipers practice your thumb pressure by returning it to the zero, to light or two much and you can see the difference, soon you'll get a "feel" for it.

[.22-10-45]

Hello, jabilli...Don't intened to sound like a s.a...but first you need to HAVE a micrometer for accuracy...not a caliper!..you answered your own question..."readings can vary greatly by how hard I squeeze..." A caliper no matter the quality will never equal the accuracy of a quality pair of mics. You can introduce error the same way with micrometers also.if you don't have a light touch...best buy one with ratchet or slip thimble.

[trevj]

Well, first, you need to get a micrometer, and leave the accurate measuring for accurate tools.

The digital calipers you show in your pictures, are a dandy tool, but need to be checked against something of a known accurate size to be able to give you the best measurement that it will for you. You will need to get both the tool adjusted correctly, as well as adapting yourself to being able to apply a consistent 'feel' to the way you hold the measuring tool, so that you get repeatable, accurate results.
Micrometers, esp. the ones for larger diameters than an inch, usually come with a "Setting Standard", either in the form of a disc or a rod, that often has a plastic handle section in order to slow the effects of your fingers body heat affecting the length of the rod.

If you hope to repeatably measure to half a thou, you definitely need a micrometer. And some time with somebody to teach you how to read them.

Most Shop Class textbooks cover this stuff, too. Technology Of Machine Tools by Krar is a really common one. An older, used copy would be a really good buy.

To start with, clean the faces of the caliper in your picture, by closing on,and drawing a sheet of paper out from the jaws. When they are clean, then close the caliper and set to zero. Play with it, and you will see that when you push too hard, the reading changes too. That will give you a really good idea how hard to push against what you want to measure. You want it in contact, but not with much pressure that will flex the jaws, or give you a bad reading.

Have fun!

Cheers
Trev

[jabilli]

*Headbonk* I didn't know the difference between calipers and a micrometer. I thought the name was used interchangeably. Again, always learning stuff in this hobby. :-p Thanks guys!

Great cleaning tip with pinching a sheet a paper and pulling it through! Did it just now and it pretty good amount of gunk came off.

So to summarize your answers-

1. Calipers and micrometers are both measuring tools- Micrometers are more accurate. (I Googled it just now...A lot more expensive too.)
2. The pressure from your zeroing should be the same as the pressure applied when measuring.

Howsabout whether someone should measure their boolits long-ways or cross-ways? I'd imagine that longways could give you a figure that would represent the fattest part of the bullet that would interact with your bore...but I also find it a bit more difficult to measure from true center. Any tricks or suggestions?

Trev- I'm hoping to buy a drill press in the near future, I think that would be a good idea to snag a copy of that. Looks like I can snag a used hardback for 12 bucks using Amazon.

[P.K.]

NOT A HIJACK!

Jabilli, what is that Boolit?

[jabilli]

I don't understand the purpose of your question...? (Guessing you mean to use the Socratic Method.)

If you mean to point out that typically a boolits composition is primarily lead, to which it can tolerate being slightly over-sized as it is kinda "sized" through the bore, or, that is soft enough to obturate in a slightly larger bore, It certainly is a good point, and yes, I should not worry about the size so much about .0005". :-)

[texassako]

It was suggested recently on the forum that I get a micrometer instead of using calipers. Used ones actually are not that expensive. I was shopping fleabay for a decent one but picked a 0-1" Starrett at a local pawn store for $10, about what I found on fleabay minus shipping. I have noticed I can distort the readings with a caliper if I squeeze to hard.

[williamwaco]

"Depending on how hard I squeeze"

Every caliper I have ever owned had a ratchet to insure consistent pressure.
You do not squeeze, you roll the jaws closed with the ratchet until it slips.

Notice the little silver wheel ;



http://www.google.com/imgres?hl=en&biw=1467&bih=672&tbm=isch&tbnid=PJPu5yZQsJpFvM:&imgrefurl=http://www.northerntool.com/shop/tools/product_200343096_200343096&docid=oE1cVVfB2XVzrM&imgurl=http://www.northerntool.com/images/product/images/433301_lg.jpg&w=400&h=400&ei=tr8mUe3ZBsOs2QX0vIGgAg&zoom=1&ved=1t:3588,i:128&iact=rc&dur=1805&sig=107900492181417674669&page=1&tbnh=218&tbnw=218&start=0&ndsp=18&tx=89&ty=96

[P.K.]

I don't understand the purpose of your question...? (Guessing you mean to use the Socratic Method.)

If you mean to point out that typically a boolits composition is primarily lead, to which it can tolerate being slightly over-sized as it is kinda "sized" through the bore, or, that is soft enough to obturate in a slightly larger bore, It certainly is a good point, and yes, I should not worry about the size so much about .0005". :-)

No I actually mean what is it? Mould # maker etc.

[Bullwolf]

"Depending on how hard I squeeze"

Every caliper I have ever owned had a ratchet to insure consistent pressure.
You do not squeeze, you roll the jaws closed with the ratchet until it slips.

Notice the little silver wheel ;


Excellent advice!

Remember, a caliper is not a pair of pliers or vice grips. You are trying to get a consistent measurement using a consistent amount of pressure each time. Using excessive leverage and over applying clamping force with the calipers will give you erroneous readings.

Using an actual micrometer will allow you to take smaller precise measurements. You can also use the micrometer to educate yourself on how to take more accurate measurements using the calipers.

By checking and confirming your micrometer measurements with your calipers, you will likely get a better feel for how to use the calipers properly.

http://castboolits.gunloads.com/attachment.php?attachmentid=52388&d=1305432442

Think of the slipping of small silver wheel on your calipers, much like the clicks from a torque wrench. Use the micrometer much the same way, (by turning the small knob on the end) and stop applying pressure when it clicks. Even a Micrometer will give inaccurate readings if you manually try to crank it down as if you were tightening a wing nut on a C-clamp. Applying excessive force when using a precision measuring instrument can wreck your zero, and damage the calibration of your tool.

Just like reloading there is a learning curve involved when it comes to taking accurate measurements with micrometer, or a caliper.


- Bullwolf

[jabilli]

NOT A HIJACK!

Jabilli, what is that Boolit?

Oh. Haha! I read into your question way too far. It's the Lyman #225626 . I forgot that number about a half a dozen times until I noticed that 225 is the size that it casts. Sometimes people might refer to the mold as the 646...But, seeing that not a whole ton of folks cast in .223, I'd personally stick with the whole number when talking about it. :-P It's a steel 2 cavity, wheel weight alloy and a gas check boolits weigh in at about 62 grains. Linky here- http://www.midwayusa.com/product/790896/lyman-2-cavity-bullet-mold-225646-22-caliber-225-diameter-55-grain-semi-point-gas-check
Also, you might find the articles written about casting .223 here useful - Keep in mind while I find a lot of the info useful, remember to consider your source and think critically about what he says. http://www.castpics.net/subsite2/ByCaliber/default.html


"Depending on how hard I squeeze"

Every caliper I have ever owned had a ratchet to insure consistent pressure.
You do not squeeze, you roll the jaws closed with the ratchet until it slips.

Notice the little silver wheel ;



http://www.google.com/imgres?hl=en&biw=1467&bih=672&tbm=isch&tbnid=PJPu5yZQsJpFvM:&imgrefurl=http://www.northerntool.com/shop/tools/product_200343096_200343096&docid=oE1cVVfB2XVzrM&imgurl=http://www.northerntool.com/images/product/images/433301_lg.jpg&w=400&h=400&ei=tr8mUe3ZBsOs2QX0vIGgAg&zoom=1&ved=1t:3588,i:128&iact=rc&dur=1805&sig=107900492181417674669&page=1&tbnh=218&tbnw=218&start=0&ndsp=18&tx=89&ty=96

While I do use the wheel to operate the tool, I've never thought to use it kind of like a breaker bar. While squeezing the calipers harder for the photos I was pressing the little silver wheel harder against the rail. I'd be concerned that how one adjusts the knob on the top would affect the "breaking point", but on the other hand I'm reasonably certain it's not a precision function. Right? Good to know, thank you. :-)

[wrench man]

"Depending on how hard I squeeze"

Every caliper I have ever owned had a ratchet to insure consistent pressure.
You do not squeeze, you roll the jaws closed with the ratchet until it slips.

Notice the little silver wheel

Dial and good digital calipers usually have the wheel, neither pair of my vernier calipers have the wheel nor do the cheapo digitals the company supply's, but I've NEVER!?? noticed that the wheel "slips"? like the slips/ratchets on micrometers do?, the wheel on my MITUTOYO digitals don't slip on a bet!

[Flinchrock]

That's why machinists call them "very nears"...

[kysunfish]

My old lyman calipers will measure within .002 Use the wider surface when measuring outside instead of the knife edge

[W.R.Buchanan]

OK,,, there is a few things that were left out of the above discussion.

When measuring with calipers,,, First you need to zero them. This is especially true with digitals. Wipe the jaws with your clean finger before closing them as the slightest amout of dirt will cause problems.

Then when you measure the OD of a part you must ALWAYS take the smallest reading you get and you MUST get that reading several times. Just closing the caliper down on a part once and running with that, is a perfect way to get a bogus reading. You ALWAYS check by measuring several times.

It is easy to get bogus readings with dial calipers, and it is even easier to get them with digitals.

When measuring round parts rotating the part while holding pressure on the caliper jaw will help you to get good readings. Also you must insure that the caliper is SQUARE to the part. If the Caliper is cocked up or down you will get a reading that is larger than actual. Wiggling the caliper slightly to insure you are square is necessary and watching the dial for the smallest reading is how you tell if you are square. Harder to do with digitals but you'll have to learn how to cope with that.

When doing inside measurements all of what I have explained is amplified. The caliper must now be square to the part on two axises. You are now looking for the largest repeatable reading.

All of this takes practice and I get still bogus readings ocasionally after 35 years of doing this daily. This is why you must always CHECK!

Lastly; If the reading actually matters and needs to be really accurate then you need to use a micrometer. Most good micrometers have a slipping clutch thimble. This allows you to repeat the same amount of twist onto the thimble everytime. Then of course you must learn how to read it.

Randy

[johnp]

As a tool and die maker that has made my living with precision measuring tools, a pair of calipers is only good for a .005 tolerance. You can get use to the feel and be fairy accurate and repeatable with them but at the end of the day they are still a .005 tool. Micrometers are only good for a .001 tolerance regardless if they have the vernier scale on them or not. That is not to say that calipers are not useful on the reloading bench because they are, its just important to know the limitations of the tool and the user.

['74 sharps]

Practice measuring the shank of a drill bit.

[John Boy]

Practice measuring the shank of a drill bit. Better yet, test accuracy using ISO Certified Bore Plugs

[VladViscious]

If you truly need to get a good measurement on a round part particularly one with multiple groves and taper, and are looking to have just a Maximum dimension, I would suggest using a couple of gage blocks on either side of the part to be measured. Just ring both blocks together after cleaning them with alcohol, and zero the Micrometer, or if the accuracy requirement is met by the tolerance and resolution of the caliper, on the two gage blocks. The Block sizes are not relevant since it is a relative measurement based upon the zero. Position the part you want to measure with a block on either side and take several readings to get repeatability. This will give you a maximum outside measurement, and the blocks being what they are are flat to a degree that your caliper or Micrometer cannot match. also depending on how often you want to make different measurements you can look into removable anvil and spindle Micrometers. They can be had to make many measurements much quicker and with greater accuracy and precision that just using a flat spindle and anvil model. Also it never hurts to purchase a small set of gage blocks (http://www.ebay.com/itm/MITUTOYO-PRECISION-CALIBRATION-GAGE-BLOCK-SET-GRADE-3-/251231096753?pt=LH_DefaultDomain_0&hash=item3a7e8a4fb1) 36 dollars on EBay. These will be able to calibrate your tools, just remember they are set blocks not welding pieces. If you want even more accuracy or just want to make sure that they are good, you can have them calibrated by a lab, it is what I do, and it is not very expensive if you just get a basic calibration on a small set. This is a pretty good sight on how to use measuring tools. (http://www.anyimeasuring.com/guide/ ) The most important thing in using these tools is to practice, and this is where have a gage block is helpful since you know its exact value, and just work with it until you get a good rung reading and can repeat it and get YOUR touch down.


TANSTAAFL!

[Kent Fowler]

It was suggested recently on the forum that I get a micrometer instead of using calipers. Used ones actually are not that expensive. I was shopping fleabay for a decent one but picked a 0-1" Starrett at a local pawn store for $10, about what I found on fleabay minus shipping. I have noticed I can distort the readings with a caliper if I squeeze to hard.

Excellent choice and very good price.

[Case Stuffer]

Starret,Brown & Sharp and I would guess other companies make precession standards to use to calibrate micks and calipers. Checking at closed (zero) if fine but that does not mean that they are dead on at 1.000" ,2.000" etc.