Inside caliper vs telescoping gauges

[pugglewuggle]

Inside spring caliper vs telescoping gauges

Hi,



It seems that a good quality inside spring caliper should be capable of making the same measurements to the same type of accuracy as a set of good telescoping gauges. So - why would I buy a set of telescoping gauges instead of a good inside caliper that can handle all of the hole sizes the set would?



Thanks!

 

[rusty65]

Just different eras of tools. You are correct a pair of inside spring calipers are just as accurate or perhaps more accurate according to some people. I’ve read posts on practical machinist saying he knows people who can hold .0005 or better with inside spring calipers. With two point inside measuring tools it mainly comes down to getting the correct feel on the tool.


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[pstemari]

Calipers are not particularly accurate, and can easily score the inside of a bore.

Inside micrometers are much better, but still not as accurate as telescoping gages and an outside mic in the ranges they cover.

I would trust typical calipers to 0.003”–0.004" when measuring the inside of a bore, inside mics in the 1"–2" range to 0.001", and telescoping gages to 0.0002". Old style calipers with the rounded ends are better, probably good to 0.001”–0.002",

The other big difference is reach. Micrometers and calipers can only measure at the mouth. Telescoping gages can measure deep inside a bore.

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[pstemari]

Oh, spring inside calipers are a different animal. I was talking about slide calipers, in particular the ones with the sharp inside jaws on the back. The spring ones require very good technique to get accurate readings with a mic or slide calipers.

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[noid]

Its a lot easier to manufacture a telescope gauge to a tighter tolerance than a spring joint caliper.

Because of that a telescope gauge is more accurate.

 

[pstemari]

Re: Inside spring caliper vs telescoping gauges

I don't know about that. The biggest problem with spring joint inside calipers is the spring. The legs will flex in as you try to mic them. The same can happen with a telescoping gage, but they are generally much stiffer when locked.

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[rusty65]

Re: Inside spring caliper vs telescoping gauges

I don't know about that. The biggest problem with spring joint inside calipers is the spring. The legs will flex in as you try to mic them. The same can happen with a telescoping gage, but they are generally much stiffer when locked.

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Also the biggest thing with the spring calipers is that since your applying the pressure or feel to the tool with adjusting nut is that you can use a very similar feel then with the od micrometer. I could be mistaken but that’s just my feeling on that.


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[Air21]

What are you measuring? I never touch my telescopes since I've got bore gages, they're faster and more accurate. Changing the indicator gives me any resolution I need and extensions let me measure anywhere I like in a Boeing 777 landing gear cylinder which is plenty big for anybody!

 

[M6erfan]

Calipers are not particularly accurate, and can easily score the inside of a bore.

Inside micrometers are much better, but still not as accurate as telescoping gages and an outside mic in the ranges they cover.

I would trust typical calipers to 0.003”–0.004" when measuring the inside of a bore, inside mics in the 1"–2" range to 0.001", and telescoping gages to 0.0002". Old style calipers with the rounded ends are better, probably good to 0.001”–0.002",

The other big difference is reach. Micrometers and calipers can only measure at the mouth. Telescoping gages can measure deep inside a bore.

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^^^Yup

 

[bugnut]

Answer depends on what accuracy level you want. If you're measuring bolt hole diameter that are loose fits >.003 than either will work. If you're measuring for press fit bearing races or similar <.002 than you need better tools. Whole studies in industries on methodology and tools to use.

http://leansixsigmadefinition.com/glossary/gage-rr/

 

[OccupantRJ]

On a dial type or digital caliper, you are only measuring at the mouth of the opening, no measuring of bore taper. If the tool is set at zero with the OD jaws and then used, it does not mean the ID jaws are zeroed, due to manufacturing tolerances. This is aimed at anyone considering using this type for bore measurements.

 

[pugglewuggle]

What are you measuring? I never touch my telescopes since I've got bore gages, they're faster and more accurate. Changing the indicator gives me any resolution I need and extensions let me measure anywhere I like in a Boeing 777 landing gear cylinder which is plenty big for anybody!

You want to tell me what you’re using and how you’re doing it? I’m getting started off as an A&P and want to buy good stuff from the get go instead of messing around with 3 iterations of cheap stuff. Thanks!


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[matt_i]

All the calipers I got from my grandfather and great-grandfather were inside spring calipers. I keep them for sentimental reasons but I use telescoping gages for inside measurements.

I haven't messed with the spring calipers much but I regard them as older technology; at the time it was the best they had. Holding one in alignment with a micrometer doesn't seem very ergonomic.

3 point bore gages are best but also cost the most $$$$.

 

[speed bump]

I use spring calipers for speed and typically only measure to a 1/16". I get out the inside mics or a similar tool when I need high accuracy.

One other application for spring calipers is the ability to transfer dimensions. This is somewhat underappreciated in my experience but very handy.

A lot of machinists probably owned spring calipers over the years because acceptable measuring tools used to be stupid expensive. Not too long ago the decision was: do I spend $250 on inside measuring tools or $40 on calipers when I make $400 a week.

 

[Packard V8]

The best, most repeatable bore measuring tools are, in order of accuracy and also expense:
1. Spring calipers read with an outside micrometer
2. Dial/digital caliper
3. Snap gauges read with an outside micrometer
4. Inside micrometer
5. Dial bore gauge with setting fixture.

FWIW, as mentioned, spring and firm joint calipers are an acceptable means of transferring dimensions and were most often used by millwrights. Their job was to install and maintain machinery in plants. Make this bearing fit that shaft. Make that shaft fit this bearing.

jack vines

 

[Provincial]

The reason the dial bore gauge is the most accurate is that it is the only one that does not require the operator to "feel" the pressure of contact.

If the operator is consistent with the "feel" he can make very accurate comparison readings with a telescoping gauge or inside micrometer. If comparing to a standard (precision ground piece of known accurate dimension), he can match a dimension call-out. If measuring to match a "master" part, he can make it match almost precisely. But it is all about skill/experience overcoming variation in the "feel."

 

[Packard V8]

The reason the dial bore gauge is the most accurate is that it is the only one that does not require the operator to "feel" the pressure of contact.

If the operator is consistent with the "feel" he can make very accurate comparison readings with a telescoping gauge or inside micrometer. If comparing to a standard (precision ground piece of known accurate dimension), he can match a dimension call-out. If measuring to match a "master" part, he can make it match almost precisely. But it is all about skill/experience overcoming variation in the "feel."

For true; I've been using all the above for fifty years and even though I've got the feel part of using telescoping and inside, the dial bore gauge is so much quicker and it repeats. Even the most experienced user will have difficulty getting manual gauges to repeat to the level of accuracy a dial bore gauge provides every time.

Then, there's reading the result. Get the feel with a telescoping gauge and then repeat the feel when measuring and reading it on an outside micrometer. Two chances to lose the tenths.

When I look in my machinist's chest, the red leatherette case for the Starrett inside micrometer, which I bought thirty years ago, still looks like new. It's the most challenging to repeat accurately and thus is seldom used. The Sunnen and Mitutoyo dial bore gauges get used every day.

jack vines

 

[GrayFlattop]

The best, most repeatable bore measuring tools are, in order of accuracy and also expense:
1. Spring calipers read with an outside micrometer
2. Dial/digital caliper
3. Snap gauges read with an outside micrometer
4. Inside micrometer
5. Dial bore gauge with setting fixture.

FWIW, as mentioned, spring and firm joint calipers are an acceptable means of transferring dimensions and were most often used by millwrights. Their job was to install and maintain machinery in plants. Make this bearing fit that shaft. Make that shaft fit this bearing.

jack vines

6. C.M.M. (but also the largest and least portable and CNC CMM is more accurate than a manual CMM).

But back in the world of somethng portable and accurate, Dial bore gages are the tops.

 

[Air21]

I work at a Part 145 repair station overhauling components. As an A&P I'd think you would rarely need to precisely measure any kind of bore, it should hit a time or cycle limit, or demonstrate wear or corrosion or I guess fail in service for you to pull it and send it somewhere to get fixed. I'd be afraid if you are working at any kind of air carrier and they want you to do that they'd be setting you up for an eventual run-in with the FAA, leave this stuff to the professionals who will send you a bill and a fresh 8130.

Anyplace that needs this sort of measurement done already owns the right tools. I do know a popular General Aviation engine overhaul shop uses telescopes to measure bores but I'd bet there's a few thousandths tolerance there, Lycomings aren't the tightest engines on the planet.

But if you think you need precision measuring tools you will never regret buying Mitutoyo. If it's digital then buy it new because they upgrade the internal parts pretty regularly and you don't want to be stuck with something so old they won't fix it. Buy good micrometers first because you will use them more and if you really need a bore gage you can buy a ****** Peacock or SPI one if you need to save money because they are only measuring relative to the standard you use.

If you use them a lot keep an eye on the contact points, both the button and the extensions because they can wear out and develop flat spots which will gradually throw off your measurements. And if you're just being gung-ho I'd make sure whoever follows your work, either another mechanic or a QC guy isn't going to flip **** if the contact points on the bore gage leave lines on the surface, it happens especially in anodized aluminum cylinders (low pressure ones like they use to open CFM56 cowlings) since the gage tips are chromed balls or tungsten carbide, and even in hard chrome bores. You won't be able to measure the marks from the gage but you'll see them and they can be a PITA to polish out.

Also, don't buy Sunnen gages, the dials are rebranded Mitutoyo but the funky screw adjust tips on the end are frustrating to use.