A level is a simple tool only slightly more complex than a trowel. The spirit level, much as we know it today, was invented by M. Thevenot in 1661. Many believe bubble levels did not come into widespread use until the beginning of the 18th century because the earliest surviving examples come from that time. However records show "levels of the Thevenot type" were used on a French expedition to Madagascar in 1666.
Since they've been around for hundreds of years and haven't changed much in principle over that time, comparing today's level with one from the 1700s wouldn't point up the real difference: the accuracy built in from quality manufacturing. Al Karraker, Director of Marketing for Empire Level Manufacturing in the Wisconsin town of Mukwonago, puts it this way: "Accuracy is our most important goal in making a level. To do this, we consider three components: frame, machining and the vial. Every step of the way, we make sure these are of the highest quality and made with the best equipment and materials."
"To begin," Karraker says, "the durability of components is a major part of making the manufacturing of a product successful. The frame itself must be made to very exacting tolerances not only to work with our equipment, but for the final accuracy of the product. Then machining is done using high-quality tooling and equipment. These machines certainly cost more, but are well worth it in the quality they provide to the end product."
At Empire, the frame can be aluminum, wood or composite (PolyCast®). Many companies focus on making only wood or metal levels. One of the latter is Master Level of Barrie, Ontario. Don Reid says about their levels, "We make box beam levels using an aluminum alloy heat treated to a hardness equal to T6. That means it's fairly stiff but it's also like a spring if you bend it, it will flex back. Sure, if you bend it beyond its yield point, it can stay bent a little bit but it can be straightened back. If you bend it too far, it's hard enough that it will break. So if somebody drives over it with a truck it can break. That's beyond its normal use."
To Machine or Not?
Karraker mentions machining the level. Reid disagrees: "I don't mill the surface of the top or bottom, although some companies do. What happens when you mill is you're adding work hardening stress to that surface. Unless you clamp the level and stress-relieve it by bringing it up to 300-plus degrees, it can pull and warp. For years people said aluminum levels warp in the sun, but that's not true if they're done right. Another reason I don't machine the surface is because when you're taking a level and putting the level against a block wall or a piece of masonry, it's not a machined, flat surface. We can maintain our straightness within 1/64 of an inch over 36 inches just by using care with the extrusion. All our levels, when they're cut, punched, coded, heat treated or stressed, we go back over them with a dial indicator to check it for straightness within the accuracy we guarantee."
Stabila is a German company with more than 110 years in business. Mike Fraser, President of Stabila's North American operations, with headquarters in South Elgin, Ill., says, "We machine the reading surfaces of our levels up to 48 inches long. The measuring surfaces of all Stabila levels are very flat and smooth, which is a must if accurate readings are required. The reading surface must be flat and smooth so that it is easily wiped clean and will not hold dirt. We do not mill the surface of levels six feet long and longer because this operation has no value whatsoever and is a cost adder."
The vial is the heart of any level. Spirit levels feature a slightly curved glass tube that is partially filled with a liquid, usually a colored ethanol hence the term "spirit" leaving a bubble in the tube. Ethanol is often used because of its low freezing point, which prevents it from freezing in cold weather. Two notches or marks indicate where the bubble should be centered if the surface is level.
Karraker explains, "The main area of change over the last few years has been in molding. We were able to move from bent glass vials to our new 'Advanced Concentric Molding' technique. We are now able to make vials more accurately and with more durability than ever before possible. This technique results in accuracy of 0.0005 inches per linear inch in all 10 working positions." Empire also introduced its True BlueTM vials featuring dark bands on both ends. This banding strongly enhances bubble visibility.
While Empire molds its vials, other companies do things differently. Fraser of Stabila says: "We form an acrylic compound, an extremely durable material, into solid blocks that are then cut, machined and polished. In this process, the surfaces of the vials are not distorted so they provide uniform light refraction and minimum reflections."
Stabila makes its hairline indicators out of spring steel, placed into precisely positioned, machined grooves. The vial fluid is a family-owned formula that maximizes bubble versus line contrast, stands up to destructive temperature swings as much as -5ºF to 165ºF and eliminates the "bad read" problems associated with static charge.
Mechanical or Epoxy?
Master Level also uses an acrylic material but has a different way of mounting the vial in the beam. Reid explains, "It's all held in place mechanically, there's no epoxy used at all. Take the vertical vial look at the level and you'll see a little round hole above the vial. The vial hangs on that and has a spring tension screw so that it's like being on a pendulum. It's held in place with a spring with sufficient tension that it won't move. You hammer it, bang on it, do whatever you want, it won't vibrate out. But you have the ability to adjust it if you want to set a grade or if it does get knocked out of accuracy for whatever reason."
Continuing, he says, "The horizontal vial doesn't touch the top or bottom of the level; it uses the same principle. My vial holders rest on a lip in the side wall of the aluminum, held in place with a couple of springs. It basically floats. Because aluminum expands a bit more than plastic, if you laid our level out in the sun, the heat is not going to affect the accuracy because the vial is not touching the top or bottom. It's also not affected when a mason hammers the top of the level!"
Contrasting that approach, Fraser points to Stabila's level and says, "Stabila vials are definitely fixed, and definitely not adjustable. We permanently epoxy and weld them in place. We do not use any springs, screws, rivets, nuts, bolts, etc. The vial is assembled into a plastic housing. The housing is epoxied and welded in place. The accuracy of the level is set. Then it is checked about halfway through the curing cycle. Then, after it is cured, the accuracy is certified. Then the level is packaged and sold. There is no need for a prospective buyer to sort through the stack of levels, looking for the most accurate. They are as accurate as the label states."
Sighting the Bubble
Accuracy is affected by several factors, not the least being readability of the bubble in the vial. Empire makes its bubble easier to read with its blue end caps; Stabila uses a special fluid formula and precise hairline spring indicators. Reid notes that Master Level "has a little strip underneath the vial that's fluorescent so it picks up light you can always get some light, even in a dim area and it glows so you can read it almost in the dark."
Reid is also proud of the craftsmanship that goes into his company's levels. "We hand-set every vial, in every level. We don't rely on machinery. True, a person can mess up, but if he does and something happens, we can correct it right in the field. You never have to send a Master Level back for repair. Any of the stores that sell our levels, they've all been given training on how to check a level for accuracy."
It may seem strange to be talking about engineering, design and manufacturing tolerances with something that gets tossed around and hit with a hammer on the job. But, as they say, the devil is in the details, and all the level companies make certain they track each and every factor that can make the level accurate or inaccurate in service.
For example, Reid points to the size of the bubble in his vial. "Remember, the bubble is an air pocket. The day it's manufactured, that air pocket can vary slightly in size. You'll notice in our levels, the bubbles are fairly large, very close to the lines about as close as we can possibly make it without having that bubble go outside the lines when it gets below zero. You see, air pockets expand as it gets cold. If you took our level and you set it on a surface that was off just a little, and you took someone else's level with a smaller bubble and it was off the same amount, their small bubble wouldn't show off nearly as much as our larger bubble would. The closer the bubble is to the lines, the easier it is to judge when you're accurate."
Fraser concludes, "If you take a look at levels, you'll find that there has been very little refinement and evolution, even within the concept of level, plumb and straight. I admit it: it's hard to get a guy who uses a wood level to switch to an aluminum level. But once they do, they never go back. It changes the way they work, and it usually takes only a week."
Return to Table of Contents