Kerf Bending

In our studio, we take an active interest in digital fabrication techniques which produce minimal material waste. It’s a good challenge to create efficient templates for subtractive manufacturing, and successful results allow us to create more prototypes with limited stock material. This post focuses on creating digital models for kerf bending, a traditional method for creating efficient and flexible forms out of rigid materials.

Kerf bending is implemented in a variety of ways, but in short, it’s a way of strategically removing material to allow for flexibility while maintaining a continuous surface. One kerfing technique uses a laser cutter to create a 2-dimensional kerf by patterning the cuts (Ex.1, Ex.2). This geometric application is applied for a lot of uses, ranging from fruit sleeves to coronary stents. Similar structures are implemented (although not as a single form) on large scale building components.

A more common method for kerf bending involves a series of cuts on a table saw. This generates a thin layer where the material is to be bent, allowing for the sculpting of a once rigid object into a curvilinear form:

The technique for flexibility here is simple and geometric. As long as the material can maintain its internal structure, it can become increasingly malleable as selective portions are removed. And although the overall strength of the member is reduced by the cuts, notice how the exterior surface is preserved, allowing for the form to read as one piece while maintaining its cladding.┬áIt’s a simple approach, but it has fascinating implications for architecture. I’d like to see this applied to the scale of a building, maybe in a giant kerfed mass all bent into place by an array of post-tensioned cables.

But back to the matter at hand, the table saw kerf brings a large margin of error when compared to the intended form. Upon bending, the gaps created by the kerf reduce the precision of the construction and compromise its stability. Instead of creating basic cuts with a table saw, we’re looking at creating more precise cuts related to the curvature of a form. We’re considering a technique somewhere in between a kerf bend and a series of miter joints, which we’ll call a mitered kerf. With this technique, a triangle is cut (on a laser cutter or a router) out of the material. The triangle’s shape is determined by the curvature of the generating form so that the faces within each kerf cut become flush when the object is bent into place.

By using a kerf pattern to create the circle, we’re saving about 33% of our material vs. laser cutting the circle directly. The material savings increase significantly when the tool is used for more complex and volumetric forms.


We’re using Grasshopper and Hoopsnake to generate the cutting templates for these forms, and the digital process works like the fabrication process in reverse. The definition starts with a complete digital model from which contoured polylines are created for the cut.

The video above shows the tool being tested on some digital test models. The model could be bent in place permanently (by gluing together at each cut) or remain as flexible objects. Our intention is to develop a method for fabricating complex forms without steam-bending or molds, which use a lot of energy and generate waste. The next step is to test out some physical prototypes.

6 Comments

  1. jon bailey says:

    Could the strips shown in the video be combined with memory shape alloy metal fibers to control shape, allowing it to change based on certain external conditions/temperatures? Or perhaps like Omar Khans installations that use more of a polymer based product rather than wood, a surface such as the one shown is more like a rubber, molded around memory flex wires to allow it to move in response to [movement, co2 levels, temperature, etc.].

    Great work.

  2. ekatzenstein says:

    Thanks Jon. Muscle wire is the leading contender for applying a kinetic feature. We’re hoping to play around with this stuff after doing a round of physical prototypes to figure out the right thicknesses. But it’d be interesting to have a member woven through the cuts which tenses and relaxes…and maybe even adds torsion to the material.

    Erick

  3. ekatzenstein says:

    We just got word of a similar process by SchindlerSalmeron. Really interesting work: http://www.schindlersalmeron.com/index.php?option=com_content&task=view&id=27&Itemid=29

  4. clevie says:

    Very cool. Beautiful visualizations.

    This approach seems like it would pose some fun/thorny problems with regard to structural integrity in certain design cases.

    Looking forward to seeing what happens with the physical prototypes.

  5. Clayton Binkley says:

    Nice stuff. You’ll want to check out the design to production zip shape chair – a great example of this process.

    http://www.designtoproduction.ch/content/view/14/44/

  6. Emma Chris says:

    I would like to know what is the logic in grasshopper. How do you design and control the digital “kerfed panel” in order to make it reflect the behavior of real wooden panel (bending the panel so that the kerfs have the same size when they get closer to each other and then controlling the degree of bending). Are there any tutorials or indications for the use of grasshopper to make this kerfed panel?

Leave a Comment