Seams are one of the shortcomings of many 3D-printed objects—at least for objects printed using the FDM printers like those I use to make the Platypus pens. I have previously written about how I can often avoid them by printing pen parts that consist of a single helical extrusion, a process that is often called “vase mode” printing. Those parts look great but they are not very strong by themselves, and so my pen parts are made in multiple layers glued together with marine epoxy. That makes them ‘plenty strong’, but having to effectively laminate all of the parts is inconvenient and can sometimes limit the designs that I can work with. A better way would be better! At least sometimes…
Enter the scarf seam (not a neck-warmer)
I first devised a way to minimise the visibility of seams more than a year ago and have been using it in a limited way with good results. I called the results a ‘scarf seam’ because of its resemblance to a woodworking method for joining timber end to end, the scarf joint (or sometimes ‘scarph’ joint). Scarf joints can be a simple matched pair of tapers or can have complications that help to hold them together without glue, or while the glue sets.
The picture shows one of many scarf joints used in the reconstruction of a historic sailing ship by the Sampson Boat Co. The construction of the Tally Ho is nearly complete and a long series of YouTube videos document the process. I enjoyed watching them very much and look forward to watching it sail!
The scarf seam that I devised for hiding seams in 3D printed parts is an adaptation of the tapering layers that I use to start and end helical vase-mode extrusions. I realised that if I followed the upward taper with a downward taper then I would have the 3D printing equivalent of a scarf joint. I tried it out and found that it worked remarkably well.
If you have a recently made Platypus Model 10 pen then you will have scarf seams on the grip below the first bulge. You may not be able to see it as, after all, it is designed to be hard to see! There are also scarf seams on parts of the section liners of both models 1 and 10, but they are even less visible as they are glued inside the grip.
How it works
The magic of the scarf seam in the extrusion of the outermost perimeter is that it allows the printer nozzle to be moved away without any need to change the extrusion rate or the height of the nozzle. That results in almost no blob or gap at the seam. Internal perimeters and fill are printed before the nozzle moves back to the outer perimeter still without any vertical movement, and the next scarf seam begins. In that way the seams start and end with zero height and zero extrusion (or very close to it) and, ideally, it is all but invisible.
So you want to print a scarf seam…
It is worth noting that I was able to make scarf seams only because of the unusual way that I generate the g-code that drives my 3D printers. The custom programs that I write to generate the g-code algorithmically give me full control. Most people who print things with their 3D printers work differently.
Conventionally g-code is generated by first modelling a 3D shape using a CAD program or similar. That model does not have any seams or layers. That 3D model is then loaded into a program called a ‘slicer’ that divides the shape into 2D patterns that we call slices or layers, and then makes the g-code that tells the printer how to reproduce the slices. Seams are inevitable because each layer has a start and an end, and the nozzle has to be raised between one layer and the next (unless, of course, the slicer is set to ‘vase mode’). If your slicer program cannot make a scarf seam then you cannot get a scarf seam when you print your model. Until very recently no slicer was able to make scarf seams.
Enter open-source software
Last November I decided to share scarf seams with other 3D printing enthusiasts, with the intention that someone (not me!) would be able to incorporate them into a standard free slicer software package. I posted demonstrations and notes on it on Reddit and a couple of forums dealing with 3D printing and slicer software. Eventually the idea was taken up by a developer of the slicer OrcaSlicer and it is now part of the latest beta release of that software!
You can read about the scarf joint seam in the OrcaSlicer release notes here and see the first scarf seam YouTube video, by fellow Australian Michael Laws (not me, Michael Lew), by clicking the thumbnail image below.
I am grateful to the person known as @Noisyfox doing so much work to go from the basic idea to working slicer code.
