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Let's Talk Precision Measuring Tools

Glacier991

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It has occurred to me there has not been a thread here about precision
measuring tools. Back in the 70's I worked for the Astrogeophysics Instrument Shop at the University of Colorado. I got introduced to all kinds of precision stuff, including measuring tools. Back then even the cheapest stuff cost more in actual dollars (not adjusted for inflation) by FAR than it does today.

I hope this thread might serve as a place we can show the various precision measuring tools around, and maybe give newbies some idea of the cost and utility of each.

PLASTIGAGE

I will try and find some pix of this.... but believe it or not a thin string of plastic is a measuring tool. In the case of a bearing (like a rod bearing or main bearing) you put the string across the bearing surface at right angles and torque the bearing down... then you open it up and measure the squish - eg. how WIDE is the little string of plastic once it has been squashed? The gauge is the paper the string comes in!

DSCN7125.JPG


This one measures from .001 to .003 by gauging the width of the "squash". Perfect cap main bearings and rod bearings in an engine.

It is incredibly precise and has been used for over 50 years, unchanged. So the first tool isn't a tool per se... But is a tool. A precision one.

"REAL" TOOLS

let's start by looking at the nuts and bolts of measuring tools... here are a few...

15286DSCN5263.JPG


What you are seeing is a dial caliper (digital version) on top...two micrometers, old style, on right...expanding bore gauges at bottom, and on the left is a depth micrometer. Let's start with the most versatile of all precision tools in my mind... the caliper...


DIAL/DIGITAL CALIPERS

15286DSCN5265.JPG


In the old days they were like a slide rule... stamped steel

DSCN6975.JPG


they had what was called vernier markings, and you could "guess" at the accurate measurement by what line was the one aligned

DSCN6974.JPG


cost back then in 70's dollars ? About $15-20.

Then we had dial indicator types.... here is a 70's model made of composite material. Cost in the 70's ? $20-40... a bargain. My first and I was excited...

DSCN6976.JPG


In order of magnitude is was ok within plus or minus a thou or two....(a pretty rough measurement)

Then there was the stainless dial model...

DSCN6978.JPG

DSCN6977.JPG


Cost in the 70's nearly $75.

To read it, you had to see the tenths bar on the slide and then add the gauge... here we know we are between .400 and .500..

DSCN6981.JPG


this reading? Can you guess?

DSCN6979.JPG


did you guess 0.574 inches?

The caliper measures not only internal thicknesses (like diameters) but can measure bore sizes (assuming they might be uniform - unlike a cylinder in an engine) and also measure depth too! (Not crazy about this depth part of this one though, too big !)

DSCN6980.JPG


* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Enter Asia into the market in a big way... In the 1990's cost of a Digital model of a caliper fell from hundreds into way under a hundred. Today they can be had for less than the cheap vernier models in the 70's - UNADJUSTED for inflation.

Here is a $20 current model

DSCN6982.JPG


Whereas back then there was no reason to spend the $$ for an expensive tool you might not use, today there is no reason NOT to have one. They can measure outside diameters, inside diamters and depth, all in one tool. (pics coming of each function)

MICROMETERS

Long thought of as THE precision tool. They measure by rotation of a thread. In fact here is a little quiz. If each revolution is .025 inch.... what is the thread pitch? Think....







(A. 40 TPI)

Micrometers only measure outside measurements and are not as versatile as a caliper. A SET of 3 can be had for under $30 these days on sale.... and they have carbide tips (no wear point) and are accurate to under a thousandth, closer to a ten thousandth. BUT, you will need to learn to read them. (If there is interest I can do a thread on how to read an old fashioned micrometer gauge).

Digital models exist for about twice the price of the old style. Much easier to read. Here is the set I own. Notice my name on them? This set has been stolen, recovered and returned to me!

DSCN6984.JPG


Individually?

15286DSCN5269.JPG




DEPTH MICROMETER
More or less a micrometer without the anvil.... you use it to measure the depth of things. Usually sold as a set with replacement rods that allow meaurement to a depth of 4 or 6 inches.

15286DSCN5267.JPG


My set, can you guess what lengths predominate my usage ?

DSCN6989.JPG


The digital caliper does this just as well. Still, of my precision tools I love my old depth micrometer. It is just a pretty tool. Oh and while we are here, let's look at the markings on the shaft, all about how you read one...

DSCN6990.JPG



PRECISION TOOLS THAT MOVE AS THEY MEASURE
The DIAL INDICATOR


The dial indicator is a tool that displays on a dial face the extension of a rod. As such it can be used in dynamic environments to display changes in measurement, as in runout on a rotor for example. Inexpensive 0.0 to 1.0 inch indicators can be had for under $15 today. The base to hold them costs as much. Here is one such import:

15286DSCN5270.JPG


Recently I picked up a digital version of this dial indicator - for $22!

DSCN6909.JPG


A dial indicator and a magnetic base are valuable tools, next right after the dial/digital caliper in my book.

15286Dscn5271.jpg


INDIRECT MEASURING TOOLS

There are tools that do not measure per se, but all you to gauge something and then measure the gauging tool for a final number.... for bores, you can use expaning collets for small ones (no pics as I do not own a set) and for larger bores, expanding gauges

DSCN6987.JPG


These are spring loaded gauges you compress (arrows show in and out movement of the business end), and then lock in place by tightening the nut at the end of the shaft (single arrow). You unlock and move around to gauge the bore, and then tighten the securing nut and remove and measure THIS tool with another precision measuring tool. I paid under $20 for the set.

DSCN6988.JPG


Also plain calipers, inside and outside will do the same thing..

(pic forthcoming)

THICKNESS GAUGES

These are the plain Jane of precision measuring tools.... next to plastigage. They consist of flat steel (or stainless or brass) feels of measured thickness. They act in most cases as "go" or "no go" tools. The last one that fits is the measurement, more or less. In the days of points in distributors they were in every tool box. I see them less frequently today. Wire versions are used to measure spark plug gaps.

(pics coming)
 


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vrytired

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any suggestions on what brands have the most bang for the buck? i'm nor sure i trust the cheap harbor freight stuff but the stuff in the MSC direct catalog is crazy expensive.
 




Glacier991

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Well let us remember that the Asians were one of the best makers of precision tools way back in the beginning... Mitutoyo was and is a highly respected brand. So when Asia ventured into tools for the West big time starting in the late 80's and 90's, it is no surprise that the precision tools were a place they excelled. They continue to do so. MOST of my precision tools are Harbor Freight precision tools. THAT is the most bang for your buck. PERIOD.
 




ExplorerDMB

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I have a MATCO digital caliper (since it was discounted via school). It really is a great tool - especially for differential bearing shims :thumbsup:

-Drew
 




section525

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Digital calipers is definitely on my list. I've needed that tool more than once for my latest project. Good post Glacier.
 




spindlecone

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Great post
as a home shop machinist, precision measuring tools are dear to my heart, mitutoyo indeed makes some great tools.
Don't know about harbor frieght tools, I got all my tools from my dad who was a long time gunsmith, all are american made by starrett, great tools will last many lifetimes if taken care of
 




rookieshooter

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Love these kinda of tools. That depth mic is so nice. Used to use them alot when measuring piston at TDC to deck of block.

PICT6201.jpg


Here's one I used a great deal on my project. It's made by Frankford Arsenal. It's part of my reloading equipment also. Yes it's made in China, but it has worked flawlessly for me. I like the way it toggles from mm to inches. And it also has a depth gauge at back of handle.
 




BrooklynBay

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Glacier991

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Yes.

There is no question that Starret tools are beautiful things, and, as you say, will last a lifetime. ( I have a couple too) Same for Mitutoyo and others... but the $20 Harbor Freight caliper serves my everyday knockabout needs perfectly and every time I check it against the standards in my micrometer set, it is dead bang on....

DSCN6986.JPG


and I've been using it for about 5 years now. Maybe the best $20 I ever spent.

For the home shop folks.. if you shop "On Sale" you can buy a Digital 6 inch caliper for under $20, a magnetic base for a dial indicator for around $10 and a 0 - 1 inch dial indicator (non digital) for about $8. (Digital is about $22) For under $40 (less tax) you will have a lot of capability in your toolbox. (Prices at Harbor Freight).
 




Brian1

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I am not a huge fan of the digital readouts on hand measurement tools, just personal prefrence. I prefer to read the dial. I am always using the calipers to measure something from un-marked drill bits to depth readings and steel sizes including wall thickness. I would recommend it as your first precision measurement tool. I have all of the others listed as well and I have found the Harbor Freight items to be just fine if cared for properly. I have used mine for machine work on mills, lathes and for setting up a few diffs. I also have Starret measurement tools but usually just pull out the HF stuff. The only problem I have had is the HF indicator base cracks its plastic knobs easily.
 




Glacier991

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Brian I understand. It is like reading a book versus reading the same thing online. I am very comfortable with using/reading a micrometer-depth gauge, just as easily as reading a digital readout. But...On balance though, the digital is nice. For newbies... nice to start out digital.
 




rookieshooter

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You can have 10 people use the best measuring devices out there that has been checked against NIST standards and still come up with different numbers. You still have to know how to properly measure something. You can turn this thing too much or not enough. You may not have the telescoping gauge in the bore just right. It's just like 10 nurses can use the same blood press. tool and damn if some of them come up with different numbers. Just because you may have the best dose'nt mean you will get the right numbers. It does take some practice.
 




Glacier991

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Excellent point Rookieshooter. When I started I was sent home with several standards and tools to measure them with... told to measure and remeasure until I got the feel. Even now I can come up with different measurements on successive tries, whhich is why critical measurements get done multiple times. Now bores? Expansion gauges? I have so much trouble with those....ALL over the map. A friend who builds engines says to get a bore gauge... you save time (he says) by having instantaneous readout as you move it about. Fortunately, or unfortunately, my engine building days seem to be behind me.

Anyway.... Thank you for making this point Rookieshooter! So ...you guys buying tools... play with them ... learn their idiosyncracies... learn the touch, and always measure multiple times on a critical measurement.
 




Glacier991

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The one tool in this category I want and still think is overpriced? The "vice-grip" holder for a dial indicator... a flexible mount from the vice grip to the indicator.... still too pricey for me. I WANT ONE though! Perfect for brake rotor runout measurements!
 








spindlecone

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i think one thing that needs to be defined in this thread, is precision, it will never be exact with a $15.00 caliper, long term.
You want precision, you need to spend some bux.
for example, some of my mics are 40 yrs old (all starretts)The measuring rods are carbide tipped, they will never wear out, they are dead nuts accurate (checked against gage blocks)
If being within say a few thou, than the cheap stuff may suffice for the DIY types.
If you use precision tools to make a living, use them every day, than you need to buy the best, they will last a lifetime.
ebay abounds with very highend starrett, Brown and sharp, mitutoyo measuring devices, if you need and want the best of the best.
 




Glacier991

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While I normally agree with everything my friend Spindlecone says, I may have to mildly disagree with him on this one. The mic's I showed are carbide tipped and accurate to 5 tenths easily. The dial caliper I will admit is not the robust quality of say a Stainless steel Mitutoyo or Brown and Sharp, but accurate to only a couple thou? No way. It is dead bang on after 5 years... well within a thousandth, and i will bet a few tens maybe. I posted a pic of gauging my 2 inch standard. See for yourself.

So... I think my friend you underestimate the accuracy of this stuff. It's GOOD. Better than you might expect unless you used it often.
 




spindlecone

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agree glacier, but making a living machining precision medical componants, calls for the best of the best.
15 buck harbor stuff, just will not cut it
 




Glacier991

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Ok, on that point I agree you need the best available - I guess what I took issue with was the notion that this stuff was accurate to a couple thous at best. It will not I am sure last like the high end stuff, and whereas you may have repeatability of a few tens this may only be twice that. But honest to gosh, it's pretty damned amazing, esp for the price - but for serious DIY'ers.

Hmmm... I have some transmission aluminum pistons I need turned.... suppose if i sent ya a HF caliper .... ;)
 


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spindlecone

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Glacier991 said:
Ok, on that point I agree you need the best available - I guess what I took issue with was the notion that this stuff was accurate to a couple thous at best. It will not I am sure last like the high end stuff, and whereas you may have repeatability of a few tens this may only be twice that. But honest to gosh, it's pretty damned amazing, esp for the price - but for serious DIY'ers.

Hmmm... I have some transmission aluminum pistons I need turned.... suppose if i sent ya a HF caliper .... ;)
glacier
with alum pistons, you would be better off buying new pistons,IMO
 




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