With our huge selection of high quality materials and a wide range of available thicknesses, it can be overwhelming to pick the right size for your project. Let’s go over the aspects of material thickness you will want to take into account when designing your projects, including:
- Stiffness
- Strength
- Weight
- Tapping
- Corrosion
- Fine details
- Overall Part Size
- Aesthetics
Stiffness
Stiffness is a measure of how much a part deflects or bends when a specific force is applied. Just about everything behaves like a spring. If you push or pull on it with some force, it moves some amount. Parts that have a high stiffness may not seem like they move, but they do. Even a solid block of steel compresses some small amount if you press against it. You can think of the stiffness of your parts as an effective spring rate: sometimes it’s desirable to have a part flex when force is applied and you want to control that rate, and other times you want your part to be as stiff as possible to minimize how much it deflects under load. Material thickness is one factor in controlling part stiffness.
Simple Beam Bending
It’s clear that a thicker part will be stiffer than an otherwise identical thinner part, but by how much? Is a part that’s twice as thick also twice as stiff? In most cases, no, it isn’t. There are simple formulas called beam equations that can be used to calculate the deflection of a material based on the way it’s constrained, its material properties, and how it’s shaped (including its thickness).
Simple beam formulas have been around for a long time so they’re easy to find in textbooks and on the internet. Without getting too technical, let’s take a look at an example.
Here we have a simple beam, its beam bending diagram, and the beam bending formula to go along with it. In this case, the beam, or your part, is constrained on one end and free on the other. A force (F) is applied a distance (L) from the fixed end and causes the part to bend. The distance the end of the part moves is d. E is the elastic modulus, a property of the material you can find on its corresponding page on our website. I is the moment of inertia, a property of the shape of the cross section. Moment of inertia is where material thickness comes in. Moment of inertia can be calculated or looked up for simple shapes. The formula for the moment of inertia of a rectangular (or square) cross section is shown below.
That’s enough letters, let’s put some real numbers to our example. Let’s start with a piece of .063” thick, 5052 aluminum, 5 inches long and 1.5 inches wide, fixed at one end, with a 8 lb force applied at the other. Using the formulas above, we can calculate the end of the part will have a deflection of approximately 1.1 inches.
We can check that math against a real part, and sure enough, we see the end of the part bent down a little over an inch.
So the formula works. It wouldn’t have been around so long if it didn’t. But how does that help us select the material thickness? Using that formula, we can calculate exactly how much stiffer (how much less deflection for the same 8 lb force) our part would be if we doubled the thickness. Spoiler: it’s much more than twice as stiff. If we double the thickness to from .063 to .125 inches, the deflection drops to .14 inches! That’s nearly 1/10th the deflection from doubling the thickness.
So increasing material thickness increases stiffness, but what if your design is limited in how much material thickness you can use, or what if the material you want to use just isn’t available in the thickness you need? Another option is to change the shape of your part.
If you take the .063 x 1.5 inch part and turn it on its side, the width effectively becomes .063, but the height (or effective thickness) becomes 1.5 inch. With an 8 lb force, you wouldn’t even see the deflection in the picture. That works great in one direction, but what if you want to keep your part stiff in both directions? Something as simple as a small bend along the long edge can dramatically increase the stiffness of your part.
Let’s compare another example to our .125 inch thick part by adding some short bends along the edges. How thick does our example part made of 5052 aluminum need to be in order to limit the deflection to the same .14 inches when we put a .30 inch tall bend along each of the long sides? Rather than .125 thick, it only needs to be .04 inches thick!
These two parts have similar stiffness with significantly different material thicknesses.
Changing part geometry to increase material depth will generally increase part stiffness. This can be done through material thickness, including bends, or other formed processes like dimple dies.
Beam formulas are great for calculating stiffness for constraints and loading conditions, and as long as you can calculate the moment of inertia of your shape, the possibilities are nearly endless. But it’s important to note that beam formulas will only be accurate up to the point the stresses in the part start to reach the strength of the material. Beyond that, the formulas aren’t going to be accurate.
Strength
Material thickness can be a very important factor when it comes to the strength of your part. Strength is a measure of how much stress a part can see before it is either permanently deformed (bent, dented, etc.) or broken (cracked, fractured, split, etc.). The units for strength (and stress) are force divided by area, commonly kilo-pounds per square-inch (ksi) or in metric, megapascals (MPa). A pascal is a Newton per square-meter. Strength is a property of the material, and can be different depending on how the part is stressed/loaded. When you look up the strength of the material, you’ll commonly find a few different strengths listed corresponding to the ways the part can be stressed.
Tensile Strength
Tensile strength is used when the part is stretched or compressed (some materials may have a different strength in tension versus compression). When you’re looking at permanent deformation, like bending but not breaking, that’s called Yield Strength. When you’re looking at going past bending all the way to breaking, that’s called Ultimate Strength.
Shear Strength
Shear strength is used when the part is being sheared. (Think of the two blades on a pair of scissors cutting paper. That’s shearing.) Shear can happen in any number planes at the same time. Generally the more shear planes you can spread the force across, the less stress each individual plane will see.
Ultimate, yield, and shear strength are all properties of the material and can be looked up. We provide this info on our material pages.
Fatigue Strength
The last type of strength we’ll discuss here is fatigue strength, also sometimes called endurance strength. Fatigue strength is generally less than the materials yield strength. It refers to the level of stress the material can safely see repeatedly without failure. Stresses above the fatigue strength but below the yield strength may be ok, but there are a limited number of times your parts can see that stress before they fail from fatigue. The further past the fatigue strength, the fewer the number of cycles before failure. If your parts never see stresses higher than the materials fatigue strength, it should be able to withstand an infinite number of cycles without fatiguing. As with the other strength properties, you can find fatigue strength listed on our material pages.
Effect of Material Thickness on Strength
Depending on how your part is stressed, increasing thickness can increase the cross sectional area. Since stress is force divided by area, more area means less stress.
Similar to stiffness, there are ways to improve strength without increasing material thickness. (Technically you’re reducing the amount of stress your part sees rather than increasing material strength, since strength is a property of the material.) The shape of your part and how it’s constrained versus how the forces are applied can make a big difference. The material you choose can also make a significant difference. If you need your aluminum part to be stronger, but can’t change the shape or thickness, look at using a stronger alloy like 6061 or even 7075 over 5052. For steels, 1095 High Carbon Steel and 4130 Chromoly will be much stronger than Mild Steel. If the strength of your part is a driving factor in your design, using a stronger material can allow you to reduce the material thickness.
Additional Notes on Strength
When it comes to strength, things can get much more complex than we’ll discuss here. Depending on how a part is used, there can be combinations of tensile and shear stress in the same areas at the same time. There are options to help determine those stress levels, both manually and using simulation software. If your design fits into one of the categories covered by the beam formulas, they can be used to compute beam stresses along with deflections.
Safety
It’s typically good practice to design your parts with some factor of safety, meaning your parts are designed to be able to carry loads higher than what they’ll actually see in use. A bracket strong enough to support a 500 lb weight that will only ever see a maximum of 250 lb has a safety factor of 2.
Orientation
Another point to note is that not all materials behave uniformly in all directions. Most metals like aluminum, steel, stainless, copper, brass, titanium, etc. will behave the same way no matter which way they are oriented. The same is not necessarily true for materials like plywood, certain plastics and carbon fiber. Those materials can have different properties in one direction versus another because of the way they are constructed.
Buckling
The last thing we want to mention regarding strength is buckling. Buckling is an issue with long, thin parts loaded in compression. The material may be plenty strong, but due to minor irregularities in physical parts, long thin parts will start to bend to one side and will no longer be able to support the load without collapsing. You can see this effect when you stand a flat metal ruler up on end and push down. It’ll buckle and start to bow out to one side. Similar to beam formulas, there are simple column buckling formulas you can look up and use to be sure your part won’t have buckling issues. Some of the methods we discussed to increase stiffness can also be applied to improving buckling. Increasing thickness, reducing length, and adding bends or other shapes like dimpled holes can all reduce the point at which your part buckles.
Weight
Aircraft parts, race car parts, drone parts, and even parts meant to be carried like camping gear are all likely to be designed to minimize weight. It should be obvious that reducing the thickness of your part will also reduce its weight and vice versa. When weight reduction is a primary driver for your design, you’ll typically reduce weight until strength or stiffness become limiting factors, and we’ve already covered some different ways to increase those without having to increase material thickness. For some designs, you’ll want to control how weight is distributed over your part. Maybe your design needs to be balanced or you want additional weight at the bottom for stability. By selecting thicker and thinner materials strategically, you can fine tune those aspects of your design.
Tapping
We included tapping here because it can often be overlooked when choosing a material thickness. Whether you’re tapping your own holes or having us do it for you, you’ll want to pay attention to material thickness. The materials page for each of the materials we offer shows both whether or not the material is suitable for tapping, as well as the maximum and minimum recommended tap size. This differs by material thickness, so if the thread size you need doesn’t fall within the recommended range, try moving up in thickness. If you know your threads will see higher forces, you may want to aim higher than the minimum thickness to ensure you have enough threads to carry the load.
Corrosion
Corrosion tends to be an afterthought for a lot of parts. Selecting the right material for the environment can often be enough to eliminate corrosion problems. Stainless steel and aluminum withstand exterior weather well on their own, but typical steels need to be coated. A protective finish, like paint or powder coating, can also extend the life of your parts. Sometimes, however, corrosion can’t be prevented. When it’s inevitable, selecting a thicker material can buy your parts more time in service before they’re corroded enough to need replacing.
Fine Details
Laser cutting is a great way to get fine detail cut into your parts much easier and cleaner than would be practical by hand. But even with laser cutting, there are limits to the details that can be cut cleanly. In general, the thinner the material, the easier it is to cut small details without issues. As material thickness goes up, so should the size of the cutouts in your parts. We use the general rule that interior cuts shouldn’t be smaller than about 50% of the material thickness. You can read more about this in our laser cutting guidelines.
Similarly, if you’re having your parts bent, material thickness will be a factor in the bend radius. Typically thicker materials have larger bend radii. If you need to put a hole close to a bend, you may want to consider the size of the bend radius.
Overall Part Size
Some material thicknesses are not available in all sizes. Generally, thicker material isn’t as easy to make small parts from due to removing it from the surrounding material. Maximum part size is not usually limited by material thickness but is more a limitation of handling and shipping. Keep in mind that oversized parts made of thin material will be more flexible and prone to deformation.
Welding
With the right equipment and skills, any thickness of metal can be welded. If you’re a beginner welder, you’ll probably find it easier to weld thicker materials as thinner materials are easier to burn through. Welding different thicknesses together can also be a little more challenging for new welders. Thicker materials require extra heat while thinner materials may melt through. On the other hand, welding thicker materials ¼ inch and up might require a machine with some more power. If you’re just starting out welding or you’re limited to a smaller machine, material thickness might be something you’ll want to consider for your design.
Aesthetics
The last topic we want to discuss here is arguably subjective, but choosing the right material thickness for your parts can play a huge role in getting the right look. For purely functional parts, like brackets and braces, they’re mostly driven by factors like strength, stiffness, weight, etc., with appearance further down on the priority list. But some parts are driven almost entirely by aesthetics. If you’re designing signs or decorative parts, you will want to pick your material thickness to get the look you need.
Choosing the Right Material for Your Project
When choosing the right thickness for your parts, there are all sorts of factors to consider. What you’ll use your part for can help you determine which of those factors are most important. Structural parts like brackets and braces may be driven by strength and stiffness. Sometimes minimizing weight while maintaining strength and stiffness is important. When you need to have tapped holes in your part, thread size may push you to a minimum material thickness. Similarly, when your design requires finer details or small holes, you may need to decrease the material thickness to achieve your desired results. Parts that will be welded could influence your decision on which thicknesses to choose depending on your skill level or equipment.
Some materials are available in a wider variety of thicknesses than others with a few materials only available in a single thickness. When selecting your material, a specific thickness availability may drive you to use one material over another.
In the end, there are a lot of factors to consider when selecting the thickness of your materials. Sometimes a single factor drives the decision, sometimes it’s a combination of many factors, and the final choice is a compromise between performance, ease of use, and looks.
Visit our materials page to get more details on each of the materials we offer to help you with your next project. Once you’ve selected your material and thickness, upload your design for instant quoting!
