The issue I saw with the large concrete extruders was the same problem with the MK7 extruder, Layers. However, one concrete company created side wedges that smoothed the layers creating a flat surface.
I like to invent stuff and at least figure out solutions to problems. This is one of those. Pellets drop down into the heater tube. PLA or whatever drains into the extruder, down into the nozzle in a liquid state. The PLA passes through the nozzle onto the surface while moving. As the whole system moves on the X/Y axis, a smoother plate smooths the sides.
The only problem then is changing the direction of the smooth to follow the direction of travel of the nozzle and layer. I was thinking of an RC system with two servos. that activates as the machine changes direction. I don’t have an engineering degree so this is beyond my purview.
A simpler way may be a couple of spring-connected rudders that pivot 360 degrees, smoothing as they follow the nozzle layer. When a direction change occurs, the change directions as they drag in the new direction.
I don’t think all this is so complicated as to warrant $4995 for a pellet melter. Anyone with some engineering background is free to PM me and see if we can make this happen. Check out the first 30 seconds of this video.