Explanation of the concept of "infinity"

Unfortunately, the print head (extruder) when printing concrete cannot yet stop the flow of material and move to another place and resume it there and continue printing again. Unlike printing with molten plastic (FDM), where this is possible. The concrete could harden in the head during the flow stop during the crossing. Especially if we print with a combination of a 2-component head + printing material. (For more information, see the article Printing materials and Printing head). In such a case, the mixture begins to solidify a few seconds after it leaves the printing nozzle. Therefore, when designing an object, we must take into account that the head will have to "draw" one of its layers in one stroke, that is, without interrupting the flow of concrete. Below are some techniques for achieving this.

Start and end of printing

The start of printing means that after the flow of material out of the head has stabilized, the robot operator manually diverts it, for example with a trowel, when the head passes the starting point of printing on the print bed (bed). Similarly, when the head passes the end point of the entire printing trajectory and moves to the parking position above the waste container, the flow of material is also manually diverted to prevent the surface of the printed object from being contaminated with concrete flowing out during this crossing.

One-stroke trace

Ideally, the print trace starts and ends at the same point, after going around the entire perimeter of your object. It then moves to the next layer (see the Layer Transition article for more details). Typical candidates for this are vases and generally circular and rectangular closed objects.

The footprints touch somewhere

Sometimes, for reasons of increased strength or design, it is necessary for the print tracks to touch in some places. In such cases, we must ensure that both tracks are slightly interlocked, the materials go a little "over each other" (approx. 3 - 4 mm). This is because 3D concrete has approx. 1-2% dimensional shrinkage and there should not be a gap at the point of expected contact.

Double print footprint

If it is an open (unclosed) object and at its open end it is necessary to return to the beginning of the print with a similar (parallel) trajectory, we will have a double print track. We will also use it if it is necessary to reach a thicker wall of the object than the max. diameter of the print nozzle allows for in one pass. In this case too, it is necessary to ensure that this second track goes a little over the first one (approx. 3 - 4 mm). So that it does not form between the tracks during hardening and shrinkage. Typical objects with a double print track are those with a U or V shape.

Crossing the track

Typically, we use it when it comes to a combination of the above-described double print track and a closed circular object. For printing in one stroke, it is necessary to ensure that the outer track is "exchanged" with the inner one in one place. This crossing also occurs in "figure eight" type objects, when the tracks must cross in one place. If this crossing occurred in the same layer (and therefore also in height), we would apply the printing material to the crossing point twice and it would not look good. Therefore, it is desirable to place either a jump to a new layer (seam) in this or directly use a transition between layers in a spiral (vase mode) for the entire print. For more information, see the article Transition between layers.