A maker going by the handle I Changed a thing has tackled one of the most persistent headaches in laser layer adhesion 3D printing by strapping a pair of lasers directly to the print head, producing results that push ABS parts close to isotropic strength and substantially improve PLA performance too.
Why Layer Adhesion Has Always Been the Weak Link
Anyone who has snapped a 3D-printed part along its layer lines knows the problem intimately. In a standard fused-deposition machine, each new layer of plastic is extruded onto a surface that has already cooled. The bond you get is a fraction of what the material itself can deliver, and the z-axis of a finished part is almost always the one that lets you down first. For functional prototypes, brackets, enclosures or anything that will see real mechanical stress, that anisotropy is not a minor inconvenience, it is a genuine design constraint that forces over-engineering or awkward reorientation of parts on the build plate.
The numbers bear this out. Without laser assistance, ABS samples in I Changed a thing’s tests broke along the z-axis at 60% of the strength measured in the x-direction. PLA fared even worse, coming in at just 41%. Those figures will be recognisable to anyone who has put printed parts through any sort of tensile testing.
Laser Layer Adhesion in 3D Printing: How the Fix Works
The approach I Changed a thing has taken is elegantly straightforward. Two lasers are mounted close to the nozzle, positioned to pre-heat the top surface of the previously deposited layer a moment before fresh molten plastic arrives. The idea is simple enough to state in a sentence: molten plastic bonding to molten plastic makes a far stronger joint than molten plastic landing on something that has already gone cold and rigid.
There is a secondary benefit as well. The laser-warmed zone stays at elevated temperature a little longer once the new extrusion lands, giving the two layers more time to intermingle at a molecular level before the whole thing solidifies. Both effects compound, and the results are a considerable step forward.
With the lasers running, ABS z-axis breaking strain reached 94% of the x-direction figure. That is not purely isotropic, but it is close enough to change what you can reasonably ask a printed ABS part to do. PLA improved from 41% to 77.9%, which is again not perfect parity but is a very different proposition for functional use. Full details of the printing process and additional test data are in the video I Changed a thing published alongside the project.
The Trade-Off: Mass on a Fast Printer
The laser hardware does not come free, and the principal cost is physical rather than financial. Mounting two lasers on the toolhead adds mass, and on the fast coreXY motion systems that have become the dominant architecture in enthusiast printing over the past few years, that extra weight matters. CoreXY machines achieve their speed partly by keeping the moving mass of the print head as low as possible; adding even a modest amount of hardware to that assembly affects acceleration limits and, in turn, print speed. For a bedslinger or a slower Cartesian machine the penalty would be less painful, but a high-speed Hackaday-featured coreXY build would feel the difference.
If adding hardware is not an option, I Changed a thing notes an alternative that costs nothing: varying the layer pattern itself can improve a print’s z-strength without any modification to the machine. It is a smaller gain, but worth knowing about.
The tip for this project came from Josh Pensel. For anyone interested in the broader community work on improving laser layer adhesion in 3D printing and fused-deposition strength generally, RepRap remains a long-running open-source reference for material testing methodology and printer modification projects of exactly this kind.
