doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Measuring

A friend recently found a Starrett vernier caliper, 5 in., which is marked in thousands on one side and the back side is in 64ths. The 1934 Starrett catalog shows a 5 inch vernier caliper but does not list it as available. They start with 6 inch and go up to 48 inch with longer sizes available on special order. When did machinists start using thousandths and leave fractions of an inch.

I remember in the 1960s hearing a Boeing machinist complaining that Boeing was requiring them to work with ten thousandths with lathes made in the early 40s calibrated in thousandths.

Can anyone help?

I spent many years as a machinist and to hold a tolerance of .0001 is very, very hard and when using hand measuring tools everyone's feel is different and must be done with an optical comparator.
For a lathe to follow that tolerance the compound cross slide dial would have to be one to one which means moving the dial 1 turn removes .001 from the diameter and I have not seen one that reads .0001.
Lathes made in the 40's to get that close, I believe it would have to be hand finished.

paul buchanan,
Machinists have worked in thousanths of an inch( or tenth of mm)ever since " before the Corps of Engineers issued the permit to dig the Chatahooche river".I understand John M Browning, himself, did his design work and thinking in fractions of inch, but he was not trained as a machinist( he made prototypes and someone else drew the patent drawings).BTY your friend's caliper is collectable itself,they are fine tools.To work consistently to a ten thousanth would almost require a precision grinder(we were talking old tools, not CDC).
Mike

Surprisingly long ago.Henry Maudslay 1771-1831 Invented a bench micrometer capable of measuring 1/1000th of an Inch.He nicknamed it the Lord Chancellor (Arbiter of all disputes)Also worked on numerous machine tools. The family were in business for years. I started my apprenticeship with the Maudslay Motor Company in 1970.See Wikpedia for more details ( Maudslay, not my apprenticeship!!!)

When I read threads here and measurements come up, I often see what I'd call inaccurate application and understanding.

An example might be, "Off Face". That is a yes or no question and answer, but is applied in an improper way far too often.

I just wanted to add, that "tolerance", + or- the desired measurement as acceptable, rarely is discussed in these threads. Nor is "stack" or cumulative error.

When these questions are posed, it seems as if the poster might be better served with measures of acceptable tolerance, rather than go/no go suggestions.

I am pretty confident that many doubles left the factory in conditions that many would condemn as off face. True in the yes or no sense, but well within tolerance for sale.


It seems to be a bludgeon inappropriately applied quite often to old doubles.

"When did machinists start using thousandths and leave fractions of an inch."

I believe that this started with the making of interference fits where a simple fraction was nowhere close enough to work with.

I have seen some 6" scales with 100ths on them, meaning 100 lines to the inch. Every line would be .010, try looking at that for some time, 1/64th is hard enough. And the scale better have a satin finish.

I have seen Vernier Calipers which were graduated to both .001" & 1/128" (.0078"). I much prefer my set graduated to 3.001" & .02mm (.00079"). If its closer than that I want something besides a caliper to measure it, matters not if its vernier, dial or digital.
In one shop I worked in we had a large bench micrometer we called a Super mic in inspection. It was set to the desired measurement or very close to it with gauge blocks while looking into a window. As you put pressure on the anvil by turning the thimble there were light beams visible in the window you watched to see bend so constant pressure was always maintained taking "Feel" out of the equation. I ground some small pins once which were checked on this machine, after being brought to a stable temp, which had a tolerance of +.0002", -.0000".
I had a much older machinist once tell me that while working in a railroad shop he once had the turn some parts for a interference fit with some pre,bored mating parts. All the measuring tools they had to do this with were large inside & outside spring joint calipers. He set the inside calipers to the hole then the outside ones to them. To get the fit he held one leg of the outside calipers against the bottom of the part & measured how far across the top the upper leg "drug" as it was pulled over center. As best as I recall the part was some 12"-14" in diameter & he had to get a �" "Drag". Some of the oldtimers dis amazing work with limited tooling, but they didn't Spit it Out at the speeds expected today.

Miller that brings back memories, our inspection department was in a climate controlled room, the inspectors wore cotton gloves (for those not familiar with this it was so that their bare hands did not raise the temperature of the piece and increase the size). We called the gages Jo blocks and when handling them they also wore cotton gloves. It was amazing how precise they were ground, by rubbing them together they would stick as there was no gap between the two for air.
We also had a retired WW II gentleman that was in charge of our heat treating department. He used a file and could get within 1 degree Rockwell of hardness when later put on the diamond tester.

Hugh,
If I remember correctly,Maudslay was the one that invented the first screw cutting lathe also.
Mike

I studied Mechanical Engineering some 50 years ago and fractional dimensions never came up - - - I believe that is the dimensioning civil engineers worked with ;-). We had some old machine tools that may well have come off the ark; one male and one female and both calibrated in thousandths. Hence the source of all aged machine tools.

DDA