Digital calipers

[Bill Shields]

An inch is an inch..

[earlgo]

Bill: Almost anything will work, drill blanks, dowel pins, tap shanks, or gage blocks as long as you know what the measurement is by checking with a precision 10ths micrometer first. As I understand it, the whole point of this conversation was how does one know if the calipers are accurate. The answer is to verify with a known standard, whether traceable to the NBS or to a micrometer measured item.
--earlgo

[Greg_Lewis]

A little late to this conversation, but I often think of something someone once said to me. I was just a teenager with no machining experience and I asked a friend with a small mill and lathe to machine something for me. The first thing he said was, "How accurate does it have to be?" And I also remember the legendary Gene Allen of live steam fame, saying that you make the part to the accuracy required by the print, and anything more is a waste of time. So I'd suggest that digital calipers are OK if the accuracy required is within said caliper's margin of error. If not, use more accurate methods.

[Bill Shields]

Which is why a lot of my steam loco parts are profiled with a belt sander.

Most of the brake rigging (for example) never sees the light of day and always designed to be laid out with a ruler and scribe, hand punched and drilled on a drill press and finished with a file.

Digital calipers did not exist. I still have many sets of verniers.

[Greg_Lewis]

Which is why a lot of my steam loco parts are profiled with a belt sander.

Ditto. I sometimes wonder about a few folks on the live steam section here who over-think and over-build. That's not to accept sloppy, but to recognize what needs to be done in each case. My avitar is just for laughs but there is some truth in the quote.

[liveaboard]

I often think of your pal Mediocrates when my work is less than perfect, but close enough for the job.

Another is a quote my brother picked up from a defense contractor employee; "Close enough for government work."

[rmac]

I sometimes wonder about a few folks on the live steam section here who over-think and over-build.

To each his own. Sometimes overthinking and overbuilding can be the main point of a project.

-- Russell Mac

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[Harold_V]

In support of the "over thinking, over building" notion, one thing to keep in mind is that one gains skills by doing. That's one of the reasons a journeyman can usually outproduce the layman, in both quality and quantity. A good comparison is to think of the endless practice one must apply to master playing a musical instrument.

If one always works to the lowest possible level, achieving greater quality when required happens by chance, not design.

There is no right or wrong in this topic. Some folks are perfectly happy to have a shorn or torch cut edge on a plate, while others prefer it be machined to a high degree of precision. So long as the end result brings happiness to the individual, it's all well and good.

H

[Greg_Lewis]

I take your points. I admit that sometimes I work to .001 when .010 will do, just for the fun of it. But I don't let it get oppressive. If I miss the mark, I just keep going. I also think there is a difference between always working to the lowest possible level and working to the level required for the part. Another comment I got from the legendary Gene Allen: when he said he made parts to the print, he also said he also made sure they were safe and they met the customer's expectations for looks.

A thread I've at times thought about starting here would be titled, "A Sense of Rightness," the notion being that many of us with mechanical aptitudes have an innate sense of when something is right. My goofy sig line includes, "That Looks About Right," and I think there is some validity there. I don't really know how to explain it. We often can tell just by looking that something just doesn't seem right. Of course, this does not substitute for measurement and testing, but I think you know what I mean. When the Greeks built the Parthenon, they didn't have the means we have today to test the strength of materials, but the proportions look right. What's left of my memory recalls an article I read many decades ago that someone tested the proportions and dimensions they used with modern techniques and found they passed, which is obvious today.

[mklotz]

...
When the Greeks built the Parthenon, they didn't have the means we have today to test the strength of materials, but the proportions look right. What's left of my memory recalls an article I read many decades ago that someone tested the proportions and dimensions they used with modern techniques and found they passed, which is obvious today.

In order to get things to "look about right" the Greeks had to do some real precision work. The stone columns are 6 feet in diameter and 34 feet high. In order to get them to look straight from a distance, they had to introduce a swelling in the middle of the column of 1.6 inches.

The columns consist of many individual 'barrels', which were carved at ground level before being assembled into a finished column. So, this swell had to be distributed over several barrels. Certainly, barrel-to-barrel fitting at ground level, if it was done at all, would have been supremely difficult.

There are other subtle geometric curves built into the building to create the visual impression the builders desired.

[Mr Ron]

I work my projects using thous of an inch. That is because my calipers and mics read in thous. I try to work to a thous, but if I miss it, I just keep going. To me it's a hobby. I don't have to make a living at it. I doubt that I could even make something to a tenth. At 88, it's too late for me to start thinking in tenth's.

[Mr Ron]

While we are on the subject of calipers, I have a 6" dial caliper made by Helios that I bought new over 65 years ago. I wonder if anyone has an idea as to how much it's worth.