Levels of Precision

[Roderick JenkinsParticipant @roderickjenkins93242]

I thought this photo might be mildly interesting:

All 4 levels sitting on my surface plate. On the top "precision" level the bubble is hard against its stop. (They all show the same deviation when rotated through 180 degrees)

Rod

[Roderick JenkinsParticipant @roderickjenkins93242]

Comparison of spirit levels

[DC31kParticipant @dc31k]

Do they exhibit differing levels of precision or does each one have a different resolution?

About half of the concept of 'precision' is repeatability (reproducibility being the other partner) and from your closing sentence, they all repeat very well. Perhaps enlist Mrs Jenkins to test reproducibility.

[Pete RimmerParticipant @peterimmer30576]

Here's a vid I made of a builder's level, a 10 second level and a 5 second level.

https://www.dropbox.com/s/nzcfyqn9quz1lvx/levels.mp4?dl=0

[old martParticipant @oldmart]

Every one shows the tilt of the table, with varying degrees of sensitivity. I have a Moore and Wright 6" level with adjustability and a secondary bubble at rightangles, and have never known what its sensivity is. I should check it with slips and a sine bar one day.

[Mark RandParticipant @markrand96270]

 

 

Edited By Mark Rand on 04/09/2022 19:37:44

[Clive HartlandParticipant @clivehartland94829]

I seem to remember from my Instrument training that a 20sec,. bubble, the internal shape has an arc of 50meters?

In the old days they were ground internally by hand but now by machine.

The collimators i used to use were exceedingly sensitive, levelled end for end at 0900hrs, but by mid afternnon had shifted. This was caused by the South side of the building being heated by the Sun.

[not done it yetParticipant @notdoneityet]

Posted by Clive Hartland on 04/09/2022 22:29:38:

I seem to remember from my Instrument training that a 20sec,. bubble, the internal shape has an arc of 50meters?

In the old days they were ground internally by hand but now by machine.

The collimators i used to use were exceedingly sensitive, levelled end for end at 0900hrs, but by mid afternnon had shifted. This was caused by the South side of the building being heated by the Sun.

I understand that some large, high-precision construction machines used to be operated only between certain times – in order to retain accuracy – because the tides affected the machine levels.

[Clive HartlandParticipant @clivehartland94829]

Not done it yet, one case we handled was a jig for the manufacture of Helicopters, Lots of trouble with the frames. A visit and all levelled with a precision level (N3) and off to lunch on the company, back at 1400hrs and the jig was all over the place. The tide had come in since lunch, shifting the concrete foundation of the building.

Conclusion, move to a building further away from the tidal riverbank.

[John PurdyParticipant @johnpurdy78347]

Old Mart
If your level is a M&W #305/6 (the same as mine ) according to my old James Neill (M&W) catalogue the sensitivity is quoted as "2 minutes – Bubble movement of one division (2.5mm/ 1/10 in. )indicates an off level of 0.18mm per 300mm or .007in. per foot". The sensitivity of the 8,12 and 18in. versions is listed as 1/2 of the above.
John

[Mick B1Participant @mickb1]

Thank you for this, I'd known there were very precise levels used in metrology departments, but the illustration of the differences is graphic. This forum is great for glimpses into fields we've never explored.

From what I can see of the markings on the top glass I'd guess its nominal resolution is 15 seconds per division. If the bubble is supposed to fit closely between the solid lines, then I'd guess it's reading the plate as about 2 1/2 minutes out of level.

Considering how hard it is to read a 5 minute discrepancy on a M&W vernier protractor, I have to think this isn't much for most practical purposes.

Me, I've been using a grubby and scratchy (but pretty robust)  Stanley 43-220 for a lot more years than I can remember, and the books and even the titchy toy cars I've made haven't slid off the shelf…

Edited By Mick B1 on 07/09/2022 12:13:39

[Howard LewisParticipant @howardlewis46836]

Rod,

You now have to decide which one to believe.

Since they all show the same whichever way round, based on the lower ones, your surface plate is fairly level.

I would feel inclined to adjust the upper one,since it is supposed to be the most precise (finest resolution ) until it shows level, in both directions and then adjust any of the others to match.

Howard

[Mick B1Participant @mickb1]

Posted by Howard Lewis on 07/09/2022 12:35:51:

Rod,

You now have to decide which one to believe.

Since they all show the same whichever way round, based on the lower ones, your surface plate is fairly level.

I would feel inclined to adjust the upper one,since it is supposed to be the most precise (finest resolution ) until it shows level, in both directions and then adjust any of the others to match.

Howard

I might stand corrected, but I'd *think* that since it shows similar deviation at 180 °, it's likely the plate that'll have to be adjusted.

The lowest level just doesn't have the resolution to show a 2 1/2 minute discrepancy, and the next one up can only just give an indication etc.

But then, what'll happen when the sun comes out, or a butterfly flaps in Kamchatka?

Edited By Mick B1 on 07/09/2022 12:54:55

[Michael GilliganParticipant @michaelgilligan61133]

Probably the most important ‘take-away’ from Rod’s excellent demonstration is that it illustrates why it is futile to try ‘levelling’ a lathe with anything but a sensitive level.

MichaelG.

[Clive HartlandParticipant @clivehartland94829]

One rule when using a level, 'Never touch the Bubble'. I had to drum this into the heads of the gunners when setting up the guns.

Finger/body heat will send the bubble flying from the central position.

Direct sunlight has the same effect.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Clive Hartland on 07/09/2022 15:26:03:

One rule when using a level, 'Never touch the Bubble'. I had to drum this into the heads of the gunners when setting up the guns.

…

Can you explain how guns are set up Clive, I've always wondered?

I've got a couple of books that explain Naval Gunnery in a lot of detail, and very complicated it is too! On land, a 15" Naval Gun could land shells inside a tennis court 18 miles away, the shell taking over 70 seconds to travel that far. In addition to accurately knowing both positions and the range, this level of accuracy required corrections for Coriolis effect, humidity, wind speed, air temperature, state of the rifling, temperature of the barrel, and temperature of the propellant. Extra difficult at sea, because the gun platform is manoeuvring in a sea-way and shooting at a distant target that is also manoeuvring. Thus the firing solution has to predict where a target that might be when the shell lands up to a minute or so after being fired, and has to take account of the ship's roll, pitch and yaw. But unlike on land, ships don't need an accurate map because they can see each other. Artillery on land has a different problem – the shooter and target can't see each other, so some other method must be used to find range and direction.

Say a unit turns up in a field with a battery of guns and has to fire over a range of hills at invisible targets beyond. How are the guns oriented accurately before the shoot so that the range and angle to the target can be calculated accurately? And how is the position of the target described to the battery – map references?

I suppose today that GPS simplifies the 'where are the guns relative to the target' problem considerably, but how was it done in places like WW2 Burma that weren't accurately mapped? It implies to me that Artillery units must be supported by a substantial mapping/survey effort.

I guess it's a bad idea in the field to group the guns and their ammunition too close together but that means the range and angle from each gun to the target must be slightly different. How are the corrections managed?

Seems to me the technical characteristics of an individual gun might not be as important as the organisation behind it! Is aiming and firing guns in the Army just part of a rather sophisticated system designed to hit targets quickly and efficiently?

Sudden thought, perhaps exactly how Artillery works isn't described on the web because it's a secret…

Dave

[Author]

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