What T-Slot Aluminum Extrusion Do I Use?

This document covers a simple method to decide what size and shape of t-slot bar is required for a particular project – based on the weight the structure must support. There are infinite ways of engineering a t-slot aluminum structure, but the method outlined below is simple, straightforward and easy to understand by non-engineers. Although we reference 80/20 brand t-slot extrusion data for reference in this article, you could draw usable conclusions for other t-slot aluminum profiles if their size, weight and shapes were similar to 80/20 Inc. t-slot products.

The basic principle of choosing the right bar is understanding when a bar starts bending (commonly referred to as deflection) under a specific weight load.

Nine common methods for calculating deflection for t-slot aluminum bars are outlined below:

Today, we look at the two-end supported method using load-centered weight. While the two-end fixed test method is closest to the common vertical corner post method of design, it assumes an unbreakable connection with the vertical post. As fastener strength will play a role in any fixed design strength, we will use the two-end supported method to better illustrate independent bar strength. In general, bars will bend easier when supported on each end versus being actually fastened between two vertical posts. Consequently, the data and conclusions provided here will have a magnitude of safety if used in a two-end fixed configuration.

How strong is each extrusion type or bar? We get that question all the time. As outlined above, it all depends on what you do to the bar. But in our opinion, the cleanest, simplest way to judge bar strength and deflection is to measure how far a bar bends if we put all the weight in the middle while supporting both ends.

At Motion Automation Intelligence, we usually use a target deflection of 1/10″ or under for bars and structures. If a bar has a chance of bending more than 1/10″, then we typically redesign with a stronger bar. So it is important to remember that target – a tenth of one inch or under.

Look at the chart below.

As you can see, the 80/20 t-slot called 1010 (which is a 1″ x 1″) bar will bend 1/10″ when 46 lbs. is applied to the center of a 36″ long bar while both ends are supported. If we were building a simple table, we might say that it could hold a maximum of 184 lbs. (four horizontal bars forming the tabletop) on the edges of the table. (How much the center of a tabletop could hold would depend on the tabletop material and thickness – a good subject for another day.) That same table designed with the 2020 series (2″ x 2″) could hold up to 2,304 lbs. on the edges.

Note: It is important to realize that some of the weaker fastening methods can only hold 200–400 lbs., so using a heavy-duty fastener is imperative to achieve the same strength as the bar. For example, there would be no reason to spend money on strong 2020 bars and match them with inexpensive and fairly weak corner brackets as the fasteners would break before the bar bent 1/10″. By using stronger connectors (like end fasteners and anchor fasteners) and external gussets, one can easily create connections that are at least as strong as the bar.

The graph above is a good starting point, but it is only one data point – for 36″ long bars. A longer bar would bend at a much lower weight, and a shorter bar would bend at a higher weight. Usually, when designing a t-slot aluminum structure, we will add supports so there are rarely long unsupported bars. For example, if a tabletop were 8′ long, we would normally put two additional cross braces under the tabletop, and at least six vertical legs – eliminating any long bar from carrying too much of the load.

Maximum load is one last thing to consider when designing t-slot aluminum structures or frames with 80/20 or any other brand of aluminum extrusions. While the cart, table or frame you are designing may only be used for holding a 50 lb. piece of equipment, what would happen if a large person stands on it to change a high light bulb? You should design for the worst-case scenario that you want your frame to survive.

In summary, here are the four simple steps to determining the t-slot aluminum bar needed for your frame:

1. What is the maximum load or weight that the structure will be exposed to?
2. What is the longest bar length that will be used in your design?
3. What deflection calculator works for the t-slot aluminum bars you are using? Here is an 80/20 online deflection calculator.
4. Using 1/10″ or under as a target, what is the proper bar type to use at the length identified in Step 2?

Motion Automation Intelligence offers free designs and quotations of high-quality t-slot aluminum framing projects for commercial applications – so please contact us, and we’ll be glad to help.