I assume that you're referring to the mounting brackets?
All of our mounting brackets are made from steel and a certain type of stainless steel. Those are hard materials compared to aluminium. The latter lends itself well for CNC machining because it's soft, so it doens't require a lot of time to make a nicely shaped pad from a solid block of material, though you'll have a lot of useless waste for a reasonably small bracket... But we don't use aluminium brackets for a good reason. Our steel and stainless steel brackets are a hard type of material that would require a huge amount of machining hours to make those brackets from a solid block to the actual bracket. Machining hours are
verrrryyy expensive.
And aluminium is not an option because it's a bad kind of material to use for this purpose. When the frame slider takes a hit, aluminium brackets will hardly bend; they will break right off... Our materials will
absorb the impact (meaning the might bend a bit in strategic places, a bit like crush/crumple zones in cars).
What we do in stead, is take large steel or stainless steel bars, laser cut them while they're flat and then robots precision bend them in the programmed angles. This has proven to be the most secure solution. People like T-Rex cut every piece apart and then weld it all together, but compromises the strength and fit because hot material tends to bend in directions you don't want it to. Robot bent parts like our brackets are very strong (waaaayyyy stronger then welded parts) and the material is hardly subjet to metal fatigue (unlike aluminium!!!). Bending is only possible when 2 bends aren't too close to eachother, so we also have to weld sometimes...
Our sliders themselves and the auminium parts are CNC machined though...