Here at Motion Ai’s Industrial Framing Center, we almost always recommend using internal fasteners when building industrial aluminum t-slot framing because they are super strong and look better as they are virtually hidden. But internal fasteners do require some machining of the bars – basically large or small holes where the fasteners fit into or access holes to reach and tighten the fastener. Overall, internal fasteners are the strongest way to go, but they are not the only way to build.
We often meet people who want to build without machining the bars. Some are looking to keep their bars in pristine shape as they plan to repurpose them in the future and don’t want to be limited by prior configurations of the internal fasteners. Prototyping is a common reason to use external fasteners. Others just like the look of external fasteners and the idea that they don’t need to have the bars pre-machined. Whatever the reason, building aluminum t-slot framing using only external fastening methods is common.
To help illustrate this type of building, here is an overview of the external fasteners used for 90-degree connections. The two basic types are fasteners that go into the internal corner and plate fasteners that go on the side.
These are seven common types of external corner fasteners that go on the inside of the corner:
Hidden Corner Connector – These are cute zinc-only fasteners that rely on two small threaded 3 mm hex screws to tighten to the bar once they are in the right place. They come in two varieties: inside-inside and inside-outside. Inside or outside refer to where the wrench will tighten the set screw. These are one of the least strong fasteners and also one of the most expensive, so they are not used that often. But if you don’t need a lot of strength in your frame, you may want to look at using these.
90-Degree Inside Corner Connector– Like the hidden corner connector, these fasteners use threaded set screws to fasten themselves to the bar. But unlike the hidden corner connector, it uses four screws instead of two, so it’s a little stronger. The set screws are limited to inside-inside access, and please note that they do extend into the inner frame space, so they are pretty noticeable. They come in both aluminum and zinc and are slightly stronger than the hidden corner connector, but they are still pretty expensive.
Two-Hole Inside Corner Connector – This is the most common and economical external fastener, and it only requires two screws and two t-nuts to connect two bars together. There are lite and standard versions. Because it uses standard t-nuts and screws, it is substantially stronger than the hidden corner connector or the 90-degree inside corner connector. A version of the two-hole inside corner connector with a slotted hole is available when you need some flexibility in where the connector will go. It is perfect for mounting bars to other objects. For even more strength, look at the remaining fasteners.
Four-Hole Inside Corner Connector – This is almost identical to the two-hole inside corner connector, but as its name implies, it uses four holes and four t-nut/screw combinations to grip the t-slot of the bar even stronger. Four-hole inside corner connectors come in tall and tall lite versions.
Inside Corner Connector with Support – These are the least expensive connectors and are made of steel with a zinc finish. They are the least attractive fasteners, but they get the job done. Inside corner connectors with support come in single-sided support or heavier-duty dual-sided support. They are only compatible with a few bar types, so they may not be available for the extrusion you want to use. The dual support versions have optional cover caps available.
Two-Hole Gusseted Corner Bracket – These are one of the strongest corner fasteners, utilizing two screw/t-nut combinations with thick, strong supports. They are a very popular external fastener.
Four-Hole Gusseted Corner Bracket – These are the crème de la crème of external corner fasteners. They are strong because they use four big screws and four t-nuts to grasp the bars (two each), and they look good as they are clear anodized aluminum, just like the bars.
These are six common types of external corner fasteners that go on the side of the two bars:
Two-Hole Straight Plates – These weak fasteners are fine for prototyping, but you probably want more strength if you use your frame for anything heavy. Sometimes, they are added to strengthen corner fasteners.
Three-Hole Straight Plates – Like two-hole straight plates, you will have at least one bar with only one connection point if you use this fastener. So, it is mostly for prototyping and slightly stronger than a two-hole straight plate.
Four-Hole Straight Plates – These are good for connecting a single-slot bar to a double-slot bar – but that situation is uncommon. It’s better to look farther down this list if you need stronger side fasteners.
Five-Hole L-Flat Plate – This is one of the best and strongest side fasteners, as you will have two screws attached to one bar and three to the other. It also covers the bar union, so it looks pretty good and adds a traditional beefy look to your frame. It is the most popular side fastener.
Five-Hole T-Flat Plate – This is a strong side fastener for mid-bar connections. Mid-bar connections are common on larger framing projects and offer the same strength as the five-hole l-flat plate. In theory, it can be used to join three bars, but that is far less common and offers a weaker connection.
Five-Hole 90-Degree Angled Flat Plate – This is another popular plate for attaching single-slot bars together. Although slightly stronger than an l-plate, it does cover part of the frame opening.
Many other types of brackets and flat plates can connect aluminum t-slot extrusions to create an infinite variety of framing solutions. We offer free CAD drawings for commercial industrial framing projects and sell high-quality t-slot extrusions. Contact us at [email protected] or visit ai.motion.com to learn more.