telescopic guages: measurement accuracy to 5 microns

Ive a fella at work who believes he could measure any given bore size with a telescopic gauge to within 5micron accuracy of the nominal size.... 5 mirons=5um=.00019inch (i think)

is this a valid statement, i would think not so I ask you all to please input if you view this.

Really ??? Be real now, what's he smoking ? Has he been to Kalliefornia recently?

He would be doing well to measure within 5 tenths (0.0005 inch).

Might hit it within 5um most of the time if his tecnique is good, bore size is in medium range and bore is very smooth.
I wouldn't base my production on that tho.

Very much operator dependent. Ask the person to make 100 measurements and see what the distribution is.

Tom

I'm inclined to believe that. There are factors that greatly influence the measurement. One of the biggest is surface finish. A rough surface is impossible to get a repeatable measurement on. It also matters the diameter and depth of the feature.

I think that for typical engine lathe work where you are going to be pushing it to hold +/-.0005, the telescoping gauge is a good tool. If you are running an ID grinder or a honing machine, maybe you need a dial bore gauge or air gauge or whatever the job calls for.

camscan said:

What we really need is for someone to point us in the direction of his video on YouTube. Until then I am going to say no chance of getting that close to size.

Click to expand...

My experience is is that my (crappy) telescope gauges show 10-30um oversize if you use them as supposed(single sweep trough hole.)
On a very smooth(and preferably hardened) hole like bearing race you can manipulate and wiggle the gauge sideways until you happen to get it to a size that juust barely passes the bore with absolutely minumum drag. Repetability is really good but it takes lots of time and some dexterity to jiggle and wiggle the telescope gauge so that it doesn't get stuck off-center in the hole.

I'm not sure I'd guarantee 5 microns, but with experience the size and repeatability can be pretty good. When I was the jig borer operator on my shift many years ago we used telescoping gauges. It's dependent on feel and experience.

The previous operator who taught me said the process was: Insert the gauge a little canted in the hole, snug up the lock but not too much, wiggle sideways to be sure you're across the largest section of the bore and then draw it through center by tilting JUST ONCE. Take it out and measure with the mic, again waving back and forth between the anvils to be sure you cross center while you slowly close the mic being sensitive to exactly the same resistance through the anvils that you felt in the bore.

One repeat job was grinding steel rings that would be shrunk fit onto carbide blanks. A little tolerance but not much between cracking the rings and having the blanks just fall out.

I expect the key to doing it well is to be able to spend some time practicing with a known workpiece so you get the feel and consistency. Even if you find your measured size is different from the gauge ring, if you can be consistent you know what to calculate for the actual size.

I was told that the guy who followed me on that machine when I moved got the shrink fit job and when everything cooled the carbide blanks just fell out the bottom. It's all in the "feel." Can you sell that to your foreman (or to the women)?