Spirit level question


I see two kinds of 4' spirit levels at the Borg: one kind with just one straight horizontal vial (like the FatMax), and others with two curved vials (both curve away from each other). I note that when I hold one edge of the dual vial against a level surface, the vial closest to that edge shows level, while the vial above it is not level. I assume the knowledgeable user knows which edge to associate with "level."
What is this kind of level used for, and what are the advantages of this dual vial?
TIA, Chuck
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Mr360 wrote:

In a spirit level all vials have a slight arc. If they didn't the bubble would just spread out across the entire length of the vial when level.
The dual vial level is (generally) more accurate when the level is used on either side.
--
Jack Novak
Buffalo, NY - USA
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no(SPAM)vasys wrote:

Some manufacturers (and generally more expensive) use "360-deg" vials which basically are a straight vial w/ the interior barrel shaped so the bubble can rise to the center regardless of the orientation of the level itself.
The prime advantage of a dual-vial level is that one doesn't have to pay attention to which side you pick up and place the level down with pointing up--the upper will be in the proper orientation either way. The advantage of a single vial is that if it is unidirectional, it's (nearly) equally easy to read from below as from above.
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If you see a level vial that appears strait, it is ground to a barrel shape on the inside. This was the original and best way to make them. Somebody then got the idea that it would be cheaper just to bend a strait tube dispensing with the relatively expensive grinding (the best are ground) or molding of the tube. On the finest levels made, the vials are ground. Look at a high end Starrett some time.

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CW wrote:

Not arguing, but curious about "original" way to make a level vial...is there any history available on the first vials? I would think the first might well have been curved owing to the difficulty in forming the barrel type but I don't have any sources (and a _very_ quick google didn't find much real historical info)...
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I'd surmise that for early glass technology, it would have been easier to grind the inside of a short tube to exacting standards than it would have been to curve hot glass to those same standards.
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Upscale wrote:

Possibly, I don't know. I was thinking of molding, but on reflection that probably wasn't the way any were ever done--or at least rarely, if ever.
Do you have even an idea when the _first_ glass vials were made for use a level? I realized I had no feel even for how long they've been around in a similar form but I'm thinking there must have been some early attempts "way back"--I'm curious what/when those were.
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"dpb" wrote...

Joseph Moxon in "Mechanick Exercises or the Doctrine of Handy-works" published in 1678 illustrates a level in Plate 8 being of the plumb-bob type. Imagine an equilateral triangle sitting with a point up. Cut a notch exactly in the center of the base. Hang a bob from the apex, and it will line up with the notch on the base when the base is sitting on a level surface. This is the type of level that's used as the Senior Warden's emblem in Freemasonry.
I've never seen a spirit level made before the nineteenth century. Hope someone here has info on when they first appeared.
-- Timothy Juvenal www.tjwoodworking.com
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Wikipedia thinks Thevenot invented them, in the mid-1600's.
I would not be surprised if the tubes in early levels weren't tapered by glass-blowers. Skilled glass-blowers can produce work to a remarkable degree of accuracy.
John
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John McCoy wrote:

That would be my guess as well. Date sounds plausible but the page doesn't mention anything at all about the "how" nor cite any useful references. Again a quick google didn't turn up anything more concrete.
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wrote in message

Yes, it was. I read something on it years ago (about 30 years ago) but I don't remember what the name of the book was.
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Upscale wrote:

I'd bet that they didn't have to worry about bending the glass to exacting standards. Here's what I'd do:
1. Bend glass to as close to the ideal shape as practical. 2. Fill, seal, and install the vial in the body of the level. 3. Place level on a reference (level) surface. 4. Mark the location of the outer edges of the bubble on the surface of the glass. 5. Done!
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