Buying guide for best mechanical beam scales
Mechanical beam scales have been around for at least 4,000 years, and while digital scales are now more common, the simplicity and accuracy of beam scales means they still have an important role in science labs, medical practices, food production, jewelry making, and a whole host of other businesses. They’re even used by some people to weigh shot for loading their own ammunition!
While the basic principle is straightforward enough, there are hundreds of variations, as you’ll soon find out if you want to buy a mechanical beam scale, and those differences can make choosing the right model difficult.
BestReviews has been evaluating a wide range of models so we can help you pick the right one for your needs. Our recommendations cover a selection of great value medical versions, probably the area in which they’re most often used. For those who have other requirements or would like more detail about specific features, we’ve compiled the following buying guide.
Key considerations
How a mechanical beam scale works
Although the physical configuration of levers and sliding weights gives a visual difference between one type of mechanical beam scale and another, they all use the same basic principle: a combination of a beam and a fulcrum (balance point).
Put two different weights on either end of a beam, and you can make both ends balance by adjusting the position of the fulcrum along that beam. By using a number of known weights, you can mark divisions along the beam (in other words, calibrate it). Once the beam is calibrated, you only need to keep one known weight. Sliding the fulcrum to the balance point will then give you the unknown weight of whatever is on the other end.
Some models (generally those used for scientific use or weighing small amounts) still look much like this. Medical and industrial models are upright, with a plate at the bottom and a visual indicator at about chest height. Not only does this make it easier to accommodate people and large objects, it also means the operator doesn’t have to keep peering at the floor or bending over to take readings, as is often the case with digital scales.
Types
While there are variations, the three common forms of mechanical beam scale are triple beam balances, medical (or physician) scales, and platform scales.
Triple beam balances: These have three scales (horizontal beams), each with an increasing amount of precision. For example, the first beam weighs in ounces, the second in tenths of an ounce, and the third in hundredths of an ounce. As a result, these scales are capable of weighing very small amounts. They are usually used in laboratory environments or by jewelers and assayers.
Medical scales: These are the scales most people recognize. Indeed, many of us have been on them. They provide a convenient place to stand and are easy for the medical practitioner to work with. These scales generally have an upper limit of between 350 and 500 pounds.
Platform scales: These are the industrial version. They have a large platform for products, hence the name. They’re usually constructed of welded steel and are capable of handling as much as 1,000 pounds.
A mechanical beam scale doesn’t need a power source or batteries, so you can use one anywhere! However, if you’re using a sensitive model outdoors, you might need to shield it from the wind.
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Features
You probably have a good idea of the type of mechanical beam scale you want, but there are a few important details to think about.
Increments
We’ve already mentioned weight capacity, but you also want to know the increments — the smallest individual units — and thus the scale’s sensitivity. Sometimes a maximum is given, for example from 0 to 350 pounds, then there’s a counterweight that moves the maximum up, for example to 500 pounds. However, it moves the whole scale up, too, so it will no longer read to 0. Switching the counterweight in and out is relatively quick and easy, but it’s important to understand that this type is not the same as a scale that reads 0 to 500 pounds.
Platform
Scientific scales usually have a flat plate to hold whatever you’re weighing, but if you need to weigh powders or liquids, you need a tray or bowl. That either means choosing a different model or buying the required container. However, if the container isn’t part of the scale, the weight of the container must be subtracted each time, which you might find inconvenient.
Positioning
Some triple beam balances come with clamps, so you can fix them securely to the bench so they can’t slide around.
Some means of leveling is useful, too, particularly for benchtop models where small variations are critical. If a mechanical beam scale is not absolutely level, there can be errors in the results.
Finish
Whichever type you choose, you want to check the finish. Chrome is great for resisting corrosion, while some parts may be painted. On high-quality medical models, the finish is often enamel, which is more durable and easier to wipe clean. Heavy-duty platform scales sometimes have an electrostatic paint coating designed to survive the kind of bumps and knocks you might expect in busy industrial environments.
Maintenance
Maintenance is usually just a question of keeping your beam scales clean. A wipe with a damp cloth plus occasional light lubrication may be all that’s required. Nevertheless, you should check the owner’s manual carefully. Any advice it provides is designed to extend the life of your equipment and maintain its accuracy.
DID YOU KNOW?
The earth’s gravity is not constant. It can vary by up to 5% between different locations. If you weigh 250 pounds, that’s a difference of up to 12.5 pounds. If you move your scale, you should always recalibrate it.
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Other considerations
Rod
A number of medical models include an upright measuring rod so you can check the height of a patient at the same time as their weight. These are usually easy to detach when not required. Rod specifications are worth checking. They don’t usually start from 0 (30 inches is common), and they have a maximum of perhaps 78 inches. That’s sufficient for measuring the height of most people, but it probably won’t be enough if you’re measuring a basketball team!
Legibility
You also want the measurements to be easy to read. Some beams have painted numbers or a glued-on printed plastic strip. Other scales have numbers cast into the beam itself, so even if the beam experiences a lot of wear, the markings are still visible.
Casters
If you need to move the scale around frequently, weight is a consideration. Some scales have casters, which help. You also need some way of locking or removing the casters. The last thing you want is for your scale to move around when you’re using it.
Certification
If you’re selling something by weight, your mechanical beam scale must be certified as either “legal for trade” or “trade approved,” which guarantees it has been tested to a defined level of accuracy. The manufacturer should state this.
Warranty
The standard warranty is 12 months, but some are longer. We’ve seen up to 5 years, which gives you additional confidence in the build quality.
If you’re concerned about the accuracy of your mechanical beam scale, you can buy a set of calibration weights. These sets come in various ranges so you can choose the most appropriate one.
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Mechanical beam scale prices
Inexpensive: Given the range of potential uses and big differences in physical size, it’s not easy to give an all-encompassing guide to prices. The cheapest mechanical beam scales we’ve seen are those used for reloading ammunition or general laboratory use. These start at around $60. Medical models start at around $150.
Mid-range: The greatest choice in most types of mechanical beam scales is between $200 and $400. This covers the majority of high-quality scientific and medical devices.
Expensive: The most expensive are the platform scales used for industrial purposes. Heavy-duty models can run from $600 to well over $1,000.
FAQ
Q. Are mechanical beam scales accurate?
A. Yes, as long as they’re calibrated regularly. Those used for scientific purposes can measure thousandths of an ounce, and those for loading ammunition are also very precise. The medical type can register with great accuracy, though most don’t show very small increments on the measuring beam itself. Two ounces is frequently the minimum, so being any more precise than that is always an estimation on the part of the user.
Q. Is a mechanical beam scale difficult to calibrate?
A. No. Most are very straightforward. There’s a calibration screw that needs to be turned to position the balance indicator (pointer or arrow) in the center of what’s called the “trig loop” (basically the 0 point). It’s important that the scale has no weight on it and is level. Even a small slope can upset the reading.
Q. Is there any difference between a mechanical beam scale and a balance beam scale?
A. Not really. While there is some variety when it comes to mechanisms, they both use the same basic principle. You’ll also see them called balance scales and weight balances. All are different names for the same device.
