Metrology 101

Re: Total Indicated Runout.

Since I am generally a lazy man, it would probably be easiest just to read:

https://en.wikipedia.org/wiki/Total_indicator_reading

The highlight of the article would be:
The purpose of emphasizing the "total" in TIR was to duly maintain the distinction between per-side differences and both-sides-considered differences, which requires perennial conscious attention in lathe work.

Jim
 
nobog said:
..........snip...........

What’s a Silver and Deming Drill?

Again, I have no idea how that name came about but the long and short of it is that they are drill bit sizes from .5” dia to 1.5” dia. Most have ½” shanks. They are not made of silver. Large bits can take huge bites of materials and may not be suitable for a hand drill. A drill press or mill is recommended for these larger sizes.

......snip......

Jim
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I may not have the history totally correct, but "Silver & Deming" was a brand name of a Blacksmith Drill Press, that was hand operated back in its day, before the 1900's. They were generally post mounted and had a spindle that had a 1/2" hole in the spindle with a square head set screw that held drill bits in place. And of course, the drill bits always had a 1/2" shank on them!

Ken
 
Tony Wells said:
Surface roughness, in its various forms of specification is measure with a profilometer. I have one. There are several ways to evaluate surface finish, and these instruments can give various readouts according to what parameters you wish to see.

Most machinists however, use a fingernail comparator to make a physical comparison to a sample, usually machined in small sections on a plate. Each method, such as turning, milling, grinding, etc, have their own characteristics, and these sample plates have several of each, typically what is seen on engineering drawings. 500µ, 250µ, 125µ, 63µ, 32µ, 16µ etc.
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I haven't seen roughness scale in years. I usually did my best to have a fine surface finish on my final cuts. If it didn't look good to me and had stock I might pull out some fine grade sandpaper to cleanup scratches. That depended on the amount of time allow on the job. I was referring to non-grinding operations.
 
chips&more said:
Excellent reading for the home shop machinist…good job. But, if you think you have finally stopped the world from misusing/transposing the words “precision” and “accuracy”, think again. I tried for 40 years with no luck!
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A very good point about transposing the words. Expectation and reality are two more words that can get misused. What the customer whether it is yourself, family or stranger expects to see or pay for and what what they get can be two totally different realities. Just in the mind's eye I guess.
 
Tony Wells said:
Surface roughness, in its various forms of specification is measure with a profilometer. I have one. There are several ways to evaluate surface finish, and these instruments can give various readouts according to what parameters you wish to see.

Most machinists however, use a fingernail comparator to make a physical comparison to a sample, usually machined in small sections on a plate. Each method, such as turning, milling, grinding, etc, have their own characteristics, and these sample plates have several of each, typically what is seen on engineering drawings. 500µ, 250µ, 125µ, 63µ, 32µ, 16µ etc.
Click to expand...

I've always told inspectors that my calibrated fingernail was better than their profilometer could check to any day! They didn't like that. I was the engineer and pretty much could over ride what their findings were!
 
I think most people overlook what the main purposes of providing a finish specification are. It's one thing to say, "Everything I make, I like to put a mirror finish on." vs I just make it as fast as I can. Really, it's not much different in a non-hobby shop to size tolerance. To minimize the time (=maximize the $$), there is no point at all in taking additional cuts to bring a feature closer to nominal size if it is within allowed limits. I'll admit being guilty at one time of being the machinist on the floor who would do exactly that, until it was drummed into my head that you can make more money using the tolerances given. It can really have a large bearing on time invested if the parts are large simply to make another (unnecessary) pass to bring a part closer to nominal.

It's the same with finishes with an additional aspect. I have seen instances where the surface can literally be toosmooth. I have pushed on a few cases to have drawing changes to make the point officially stated rather than have a part rejected by a receiving inspector based on his internal knowledge of part requirements.
 
Two notes: stub/screw machine drills are shorter to gain clearance in multi- tool
holders ; also good to gain working height in small mills/ drills.BLJHB. Also,
In serious work, check each drill across the lips to check for diametric wear.
 
Although I knew, or at least have known most of this stuff, it's always helpful to see it altogether in one place, and sometimes just to hear, or read it, in somebody else's words, helps clear things up. Don't know why, it just is. And, I have always wondered why "Silver & Deming". I own a complete set, so it's nice to clarify that, for the most part, it doesn't really mean anything. Thanks for taking the time to bring this information to us.
 
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