Whats up with my calipers?

[fatelvis]

The other day I noticed that my cheapo digital calipers that I've used successfully for years, measured two different 6mm bullets, (Hornady 108 ELDs and Berger 105 Hybrids) at .2425" diameter. I checked them with my Lyman micrometer, and they both read .243". I figured the calipers gave up the ghost after about 7yrs service, so I bought a good pair of digital calipers (Mahr 16 EWR) and low and behold it also measured both bullets at .2425" also! Whaaaat?
Please help me figure this out.....

 

[retired]

put new batteries in.
if the mic is only .001 do not worry until
a .0001 mic disagrees.
the calipers at .0005 and the mic at .001 are essentially the same.

 

[fatelvis]

I just put a brand new battery in it.

 

[suasponte]

do you have automotive shims. check them with a known thickness, or get a 1 2 3 block. Basically a block machined to .0001 tolerance that is 1" x 2" x 3".
Terry

 

[suasponte]

 

[suasponte]

This is why I really like a 1 2 3 block. It lets you know that you calipers are accurate out to the 3" range.
I always check my equipment at least once a month for accuracy. Digital calipers are nice for readout without having to squint at the dial. This is peace of mind that you are getting what you expect to be getting.

 

[hogpatrol]

Digital calipers are NOT precision measuring instruments, especially the cheapos. They're ballpark, plus or minus .001. Stick with high quality micrometers if you want to accurately measure something. Aside from that, if the Lyman mic is made in Guangdong province I would not bet my life on it being correct.

 

[Dusty Stevens]

calipers are not micrometers and shouldnt be used past .001 no matter what the display says. in addition to that micrometers shouldnt be trusted without a standard since an unskilled hand can make them read anything they want. a $35 digital caliper cannot read half thousandths. buy good tools and theyll last several lifetimes. mitutoyo or starrett at a minimum if the measurement actually matters. if you have to buy shars buy it with a plan of replacing it as money allows and make that a priority. measuring case bump cheap calipers are fine and you dont need a federal indicator to check case runout so you just have to decide what its worth to you to be repeatable. getting a certified standard is cheap enough if you dont get the higher grade stuff. use a basic standard to get the feel of how to operate your mic or calipers. you dont need to measure case bump to the half thousandth so just get a regular set of calipers and be done with it.

 

[Dusty Stevens]

https://www.amazon.com/dp/B0006J4DOO/?tag=accuratescom-20

here you go- even comes with an insulator since heat from your fingers will change the length

 

[dmoran]

^^^^ that is what I use also (1" calibration rod), and calibrate all my micrometers and calipers to it.
Mine is a Fowler (that came with a Fowler micrometer).
Donovan

 

[hogpatrol]

https://www.amazon.com/dp/B0006J4DOO/?tag=accuratescom-20

here you go- even comes with an insulator since heat from your fingers will change the length

When you start talking ten thousandths of an inch or smaller, Jo blocks and other checking standards change with temperature changes and are only calibrated and certified at a specific temperature, IIRC it's 68 degrees.
Back in the day in one of my first shops, all measuring instruments were company owned and provided and calibrated in a temperature controlled environment. When you got a job ticket, you went to the tool crib and checked out whatever size OD/ID mikes, calipers or Pi tapes needed. You didn't take a steel gage block out in the shop where it was 95 degrees to check your mikes, etc.

 

[Dusty Stevens]

When you start talking ten thousandths of an inch or smaller, Jo blocks and other checking standards change with temperature changes and are only calibrated and certified at a specific temperature, IIRC it's 68 degrees.
Back in the day in one of my first shops, all measuring instruments were company owned and provided and calibrated in a temperature controlled environment. When you got a job ticket, you went to the tool crib and checked out whatever size OD/ID mikes, calipers or Pi tapes needed. You didn't take a steel gage block out in the shop where it was 95 degrees to check your mikes, etc.

luckily we dont need that type of precision in our reloading process.

 

[JohnKielly]

Mt old metal shop had a motto:

Measure with a micrometer
Mark with chalk
Cut with an axe.

Seemed OK to me.

 

[akajun]

Remember to clean between the faces of your mics with a piece of clean notebook paper pinched between the faces every now and then. An almost invisible crust of dirt and dry oil will build up on the faces you can’t see but is good for .0005-.001 extra length.
Clean, insure return to zero, the measure.
That said if your worried about a half tenth measured with suspect import measuring tools on a bullet your going to shoot , you are concentrating on the wrong things to improve your accuracy

 

[ranger3]

I have 5 harbor Freight calipers, 3 are accurate the other two are in my welding shop. Those three measure like my I gaging calipers. I check them regularly with a couple of known items for accuracy and consistency. There is nothing like a high quality tool.

 

[carlsbad]

If you are looking below .001", leave the calipers in he drawer.

 

[Stan Taylor]

Here is what I measure .with.PS after a couple cold ones I take better pictures.lo l

 

[dmoran]

My favorite "less expensive" calipers are the "iGAGING Absolute Origin IP54".
The 6" are around $40, a 2-year warranty, and data output.
Have 2 of them, and also the USB Data Cable, which works with there micrometers as well.
Donovan

 

[McFred]

Like what was said above, Calipers are usually held to a relatively low tolerance compared to any micrometer. About any fresh set of calibrated mics should be able to measure to .0001". Gauge blocks are handy to verify your calipers as well.

With any calipers you need to verify that the moving parts aren't loose on the rail after any reasonable period of use. There are usually a couple small grub screws to adjust the sliders for wear/tension (opposite the OD jaws). Sloppy fit can mess with your numbers.

If you're using cheap calipers the jaws themselves might not be ground parallel either. Measuring on the tips of the jaws vs at the root of the jaws might yield different numbers if not parallel (with the caliper jaws fully closed you can often see light through the gap). Also depending on the force applied by your thumb you can make some numbers read differently if you measure with inconsistent force. Cleaning the jaws with paper, as mentioned, is good on both caliper jaws and mic anvils.