i kind of get it. The “cool kids” are using aluminum extrusion and getting fantastic results with it, but take a step back and think of what the extrusion is for.
In a nutshell, it’s for precision placement of the fittings in it, and for getting nice square corners, for when you don’t have say, a CNC machine to get that precision.
The aluminum extrusion is not and was never intended to be an inexpensive solution. It was meant to be a solution for those who want a platform which can be used as a basis for precision fittings with relatively low weight and good rigidity.
With a CNC router, we really don’t need it. There is no reason whatsoever that we can’t get as good or better precision, nice square corners and excellent rigidity with lower cost materials, once there is a CNC router in play, assuming that the CNC router is properly squared up.
If you want the aluminum structure, we should be able to use 3/4" square tubing, which is readily available, and much less expensive than 2020 extrusion. More importantly, it doesn’t depend on the T nuts and fittings that get stupid expensive really fast. For less money you can buy thread taps for common bolt sizes and use those to fasten everything together. Or instead of tube, use angle. This can be thicker, and you can have easy access to the other side for nuts or other fasteners. With a CNC machine the options are much greater
So in terms of a CoreXY mechanism, which is really cool, and keeps the moving mass to a minimum, resulting in better possible speed and precision with less ringing and other artefacts, we have some nice lightweight options that are superior to extrusion available to us simply because we have some tools available to us that most printer builders do not.
Being able to (for example) put holes in a piece of 3/4" aluminum square tube every 25mm to bolt a piece of MGN12 linear rail to will give very similar options to a piece of 2020 extrusion, but at about a third the cost, before even getting to the specialty fasteners. Or put those holes in a piece of 1/2" MDF for the stationary rails.
I don’t mind the bed moving in the Z axis, but for sure, my next printer design isn’t going to be a bed flinger.
I’m going to go for something that can compete with the guys who are putting out 4 digit price tags for print quality, but stay as far as I can away from things that are needlessly expensive.
I see extrusion profile as something that is a substitute for better tools, except I think that the Primo/LR2 are the better tools.