# Design considerations for LSAM, part 2

> In this article we continue discussing the world of LSAM (Large Scale Additive Manufacturing) and its design principles.

## Understanding Angled Printing
Angled printing is a strategy similar to vertical plane printing but utilizes a unique slicing angle. This approach is highly valuable in LSAM for reducing or eliminating the need for support structures in geometries like molds or roofs. By changing the slicing angle, designers can often avoid segmenting prints or constructing complex bridges.

In vertical printing, gravity and adhesion forces act in the same direction (parallel to the Z-axis). In angled printing, gravity remains constant, but adhesion forces align with the printing direction, perpendicular to the slicing angle.

## Managing Material Deposition and Wall Thickness
Experiments have shown that wall thickness can vary due to how layers align, which impacts both design and machining. Gravity can influence material flow in overhangs or roof regions, leading to deviations from intended tolerances.

To mitigate these issues:
*   **Dimensional Compensation:** Identify areas prone to uneven flow and slightly increase dimensions during the design phase. Some slicing software allows for "offsets" to automate this.
*   **Layer Height Adjustment:** Reducing layer height helps minimize asymmetric extrusion effects by spreading path offsets across more layers, though this increases total printing time.
*   **Algorithmic Tweaks:** Future research may focus on adjusting material flow specifically for roof printing through advanced slicing algorithms.

## Balancing Gravity and Adhesion
A critical aspect of angled printing is ensuring that the force of adhesion to the previous layer remains stronger than the pull of gravity. If gravity dominates, layers may collapse. 

*   **Slicing Orientation:** For rectangular shapes, slicing along the shorter edge helps maximize layer adhesion and minimizes the area susceptible to overhang collapse.
*   **Multi-Axis Slicing:** Adjusting the slicing orientation along two axes can improve edge printing, though it results in varied cross-sectional tool paths.

## Addressing Start and End Point Challenges
When slicing along two axes, the distance between the start and end of a tool path can be very short, leading to insufficient solidification and potential deformation or adhesion failure at the print bed.

*   **Integrated Ramps:** Designers can use Boolean operations in CAD to add extra ramps at the start and end of the print. These ramps provide a gradual transition and can be removed via machining or sawing after the print is complete.

## Bed Adhesion and Stability
Proper adhesion is fundamental to LSAM success. 
*   **Bed Materials:** Testing various surfaces revealed that uncoated medium-density fiberboard (MDF) or "hard board" provides excellent adhesion for materials like UPM Formi without requiring glue or a heated bed.
*   **The "Raiser" Technique:** For parts prone to thermal deformation or those requiring heavy machining, a "Raiser" can be printed beneath the part. This structure mirrors the bottom profile of the part and includes a "Lips" feature that can be clamped to the print bed for added stability.

## Custom Support Structures
For large, flat surface areas, standard angled printing may result in weak or flexible structures. To maintain a continuous printing path without extrusion stops, custom support structures can be integrated:
*   **Groove Integration:** By adding grooves to the bottom of the part during the design phase, the slicer creates internal support walls for roofs. This method is currently performed manually, though algorithmic automation is being explored.

## Layer Height and Cooling
While vertical printing typically uses a 2–4 mm layer height, angled slicing often performs better with a 1–3 mm range. 
*   **Gravity vs. Adhesion:** Smaller layer heights reduce the amount of material per layer, weakening the pull of gravity relative to the constant adhesion force.
*   **Cooling:** To maintain shape during cooling, printing speed is often reduced and cooling is increased. Note that this may result in a slight decrease in the mechanical strength of the final part.