Where to measure from on Calipers??

[FamilyMan]

I know this is a noob question but I have had it for sometime now and when searching I can't find any info on it so here it goes and forgive me if it is basic.
When measuring the neck using calipers to determine bushing size or for just measuring in general for that matter is it better to use the sharp point of the blades out near the end or measure closer in to the base? I ask because ingest a difference of about .001 between the 2 spots I was told it has to do with flex in the tool when measuring out toward the ends by the redding guy but was wondering how y'all do it? I am just trying to improve my technique and get more accurate measurements
Like this?

Or like this?

 

[Andy Warhog]

Re: Where to measure from on Calipers??

I measure like in your 2nd picture

 

[FLIGHT762]

Re: Where to measure from on Calipers??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SlowNoisyDeadly</div><div class="ubbcode-body">I measure like in your 2nd picture </div></div>

Same here.

 

[Fuzzball]

Re: Where to measure from on Calipers??

If I see a difference between measurements in photo #1 vs. #2 I adjust the sliding jaw until the difference is corrected.

 

[Mike McBride]

Re: Where to measure from on Calipers??

On a good set of calipers there should be no difference so long as one uses a light touch when closing the jaws on the work being measured. If there is any slop in the instrument it will be most evident when measuring at the tips because there is a longer lever arm between the work being measured and the measuring beam itself. This is the "tool flex" you mention.

Even though there should be no difference, as a general rule one should position the piece being measured close to the beam for the reason above as well as the fact that the thicker crosssection of the measuring jaws helps to ensure the instument is normal to the work.

The tips of the jaws are beveled to get into tighter places where the thicker base will not fit, or when checking for a taper or other crossection that the thicker section may mask.

Even the best of instruments will yield inconsistent results if the measuremnts are not taken with a firm but light touch and at a perfect right angle. Even the best of machinist will occasionally mess up in the measuring process. If a measurement is critical a good machinist always makes multiple measurements before being satisfied.

The variation of 0.001" you mention really isn't too bad for electronic slide calipers. If you really want accuracy to the nearest thousandth of an inch or finer, you need a micrometer.

You can get a micrometer at harbor freight for 10 or 15 bucks. Use it to learn how, then after you figure out how to fuck up the lead screw, you can spend some bucks on a real micrometer and hopefully not damage it.

 

[Clark]

Re: Where to measure from on Calipers??

Buy a pin gauge and practice getting accurate with your calipers.

http://www.amazon.com/Vermont-Gage-Steel...2543&sr=1-8

 

[DocB]

Re: Where to measure from on Calipers??

FM,

Measure at the same spot the bottom of the wide part of the jaws hit with the thin jaws. Most case necks have some taper, so if you don't use the same spot to measure, you can get different results.

HTH,
DocB

 

[FamilyMan]

Re: Where to measure from on Calipers??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: OlTexasBoy</div><div class="ubbcode-body">You can get a micrometer at harbor freight for 10 or 15 bucks. Use it to learn how, then after you figure out how to fuck up the lead screw, you can spend some bucks on a real micrometer and hopefully not damage it. </div></div> So after i am done f****ng up the Harbor Freight ones, which brand do recommend I should spend the real bucks on?
(Caliper and Micrometer)

 

[pcschwenke]

Re: Where to measure from on Calipers??

Browne & Sharp, Mitutoyo, and Starret make the best calipers. The others are OK but, not in the same league. Either method you show above should give the same reading.

 

[Mike McBride]

Re: Where to measure from on Calipers??

Pcschwenke knows his tools. He lists the best. Even they are easily damaged if over-tightened just once, and they are very expensive. They are for professional machinists and inspectors.

There are other types around that are more affordable, yet high enough quality for intermittent use around the home. I cannot think of any brand names off-hand. All we use are the above mentioned for the real work, and the Harbor Freight in training classes. I was joking about buying Harbor Freight just to break one, but that is what we actually do where I work. Always make sure to only use the ratchet and never the thimble to close the spindle and you can skip that step.

If it is a manual read (not digital), the spindle and thimble have no play, and the lead screw and ratchet operate smoothly, it is probably okay. Brand new, the ones from Harbor Freight feel rough and wobble. Take it to a machinist and ask him to make sure it is in calibration. They have precision ground chunks of steel for that. It doesn’t take a second and I couldn’t see a guy charging for it. If it does not read within 0.0002, return it. Any decent micrometer has a vernier scale on the barrel that reads to the nearest 0.0001.

I use micrometers but do not buy them. A wild guess would be a Starrett will go for $300, but you can find one suitable for maybe $50, perhaps even less. Hell, maybe Harbor Freight has a batch of $15 ones that might actually work. Their quality has improved on a lot of things.

Do beware of inexpensive electronic instruments for PRECISION measuring. LCD readouts and computers are the best devices for arriving at the wrong answer with absolute confidence. If you stick with purely mechanical and treat it nicely, you do not need to worry too much about calibration for a long time. Even the best electronics drift with time.

Of course some people have trouble reading a mechanical micrometer, but once figured out, it is not difficult. It does require more attentive inspection that a digital though, hence more time. It is not like you are going to use it on every round.

 

[FamilyMan]

Re: Where to measure from on Calipers??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: OlTexasBoy</div><div class="ubbcode-body">Do beware of inexpensive electronic instruments for PRECISION measuring. LCD readouts and computers are the best devices for arriving at the wrong answer with absolute confidence.
</div></div> Those words sound like they came straight out of my grandfathers mouth! He is a retired firefighter that moonlighted as a machinist for 20+ yrs and to this day the only man I know that does his woodworking with machinist measurements he would even plane his boards and then mic them to the thousandths. I own a set of mid to low level digitals and and am doing just as you said learning to use them properly and accurately before I go buy better ones and for all intents and purposes I have yet to need anything different they seem to be more accurate then i am for now. But knowing me i will find a reason to need better ones sooner or later I always do

 

[pmclaine]

Re: Where to measure from on Calipers??

I work near Starrett (Athol MA). If you are thinking of buying a set of calipers please strongly consider Starrett. It will cost you more but I think you will get your moneys worth as well you would support an American company that has been providing jobs for a small town for a very long time.

I hate to say it but in our disposable culture I think the writing is on the wall for Starrett but when it goes I will have a tool box full of great tools and I will know I tried to help. I may not be out their donating to charities so I can get a tax write off but I consider the extra money spent on the American product as my charity, this as long as the product is quality and Starrett is a good product.

 

[Mike McBride]

Re: Where to measure from on Calipers??

Haha Familyman'

So I remind you of your gramps do I? I guess my age shows through. Actually, I thought everyone measured boards with micrometers!

Back in my college days I studied vacuum tubes along with other relics of Neanderthal technology, and have worked in electronic instumentation ever since. Hard experience has taught me that even the most modern electronics are subject to error. In precision measurment tools, that adds to the mechanical error. There is error in everything.

On the other hand, electronic is what I use because of speed of reading with these ancient eyes of mine. My micrometers at home are manual, but only becuase I found good deals at pawn shops and am too cheap to spring for good electronic ones. Only an idiot would prefer looking at those little bitty lines and adding all the numbers together.

Here is the rub. If precision is required I check calibration against a known standard first. It doesn't have to be tracable, just known, unless you are at work and subject to ISO standards.

My point was that a good set of mechanical micrometers are far less expensive than a good set of electronics and the mechanical set will reliably retain accuracy basically forever if never abused. One may never be certain of the electronics without standards to check. The standards must be cared for and used at the temperture they were defined.

 

[FamilyMan]

Re: Where to measure from on Calipers??

This thread has really opened my eyes to some things In regards to presicion measurement tools and I think I am gonna go order me a couple of those pins that were linked to. That way I have a standard to check against as mentioned so i can see how far off or close I am with things.
Thanks again for all the advise.
Brett

 

[Deadshot2]

Re: Where to measure from on Calipers??

Another key to uniform readings is to use the knob to close the jaws on your item. Don't press with your thumb against the sliding jaw. It's easier to judge pressure and on some calipers the knob limits the amount of pressure you can apply, just like micrometers with torque limiting clutches on the thimble.

Measuring in the most rigid portion is good but as it's wider it also measures to the highest part, not the lowest which the thin nose portion of the jaws will reach into.

 

[oldfatguy]

Re: Where to measure from on Calipers??

Another factor is the variation in the wall thickness of the case necks. Recently processed some new Lapua 260 brass. The neck wall thickness ran from 0.015" up to 0.017" (tube mics) on the same case. Biggest factor in getting good results in your measurements is consistancy.

OFG

 

[Clark]

Re: Where to measure from on Calipers??

When this one is on sale for half price, it is good enough to measure case neck thickness run out

http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=5260089&PMAKA=990-1889