FOG BANK: Sculpting Felt With an OMAX Waterjet




Introduction: FOG BANK: Sculpting Felt With an OMAX Waterjet

Artist: Kristina Larsen and Sebastian Martin

Title: “Fog Bank“

Instructables Link:

Description: Precisely cut layers of undulating wool felt combine to form a gently sloping hillside enshrouded in fog. With the unconventional use of a 5-axis CNC tool, fluid yet clean-edged shapes are machined from tangled organic matter, forming sinuous curves reminiscent of the laminar flow of water and clouds.

Medium: Industrial felt, hot glue, MDF, acrylic

Machines: waterjet, laser cutter, CNC router

Software: Autodesk Inventor, 123D Catch, Meshmixer

My collaborator Sebastian and I are passionate observers of nature and have grown to love the San Francisco fog, so we conceived of a piece representing waves of fog flowing down over a hidden hilly landscape. It made sense to us to represent something made of a combination of laminar and turbulent flow patterns with an aggregation of longitudinal slices, and we hoped that we might also capture the sense of dynamic movement inherent in the phenomenon.

We first prototyped the process of laminating industrial felt slices to build a 3-dimensional form in our Industrial Felt Vase project and detailed the process of using the Omax Waterjet machine to get precision cuts with this material in this Instructable: How to Cut Industrial Felt with a Waterjet

We wanted to push the limits of the process and the material so came up with a larger-scale project which would take advantage of an underused feature of the Pier 9 Waterjet machine -- 5-axis cutting.

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Step 1: Materials

F3 white industrial felt in 1”, .75”, .5” and .25” thicknesses, purchased from Sutherland Felt

3 24x36 sheets clear 3/8" thick acrylic

2 4x8 sheets 3/4" thick MDF

Mini hot glue gun and glue sticks

Roll of 48” wide pre-spacing tape

Spoil board: ¼” or ⅜” plywood (avoid plywood with masonite core and coated cardboard)


Sheetrock knife/razor blades

Snap-off blades

Cutting Mat

Shop towels

Folex Instant Carpet Spot Remover

Jacquard Silk Colors Liquid Dye

Eye droppers

Spray bottle (2)

Nickel-plated T-Pins

Step 2: Developing a Form Through Iteration

My collaborator and I used a combination of traditional and digital modeling techniques to arrive at our desired form.

We began by gathering photos of fog for inspiration and sketching chair-like forms of rolling fog cascading to the ground. To establish the overall lines of the form, I made a series of small plasticine clay models based on our concept drawing, and selected one we liked best.

We stuck the model onto a stand borrowed from a mini artist's mannequin to hold it off the ground plane and used the 123D Catch app on an iPhone to capture a 3D model.

From 123D Catch we brought the file into Meshmixer and cleaned up the mesh, repairing holes, deleting extraneous bits, simplifying the mesh, and refining the surface.

As we studied the simplified shape we realized there were a lot of things we wanted to change. We went back to the clay model and sculpted and refined its shape based on what we’d liked about the digital model, and repeated the process.

We added a couple of legs so it would be able to stand on its own, and then, to check our work, we exported an .stl file and 3D printed a small model of the finished design.

Step 3: Slicing the Mesh and Creating Parts

The bulk of the design work was done with Autodesk Inventor. We imported the .stl file and turned it into an Inventor base feature (solid model) using an Inventor extension app called Mesh Enabler. Great directions on how to perform this step can be found in Xander's Instructable: Make a 123D Capture into an Inventor Solid Model

Industrial felt is a sheet material, so in order to make a 3-dimensional form with it we needed to slice the digital model into pieces the width of the thicknesses of our felt.

We sliced our original solid model using the Split function and created sketch planes on each slice. Using a stylus for better accuracy, we re-drew the slices as spline objects. We could have used the polygon shapes that resulted from the slicing but it was important to us to have curving shapes instead of faceted ones.

We ended up with 36 spline cross-sections through our shape. In the next step, the creative sculpting happens. Each 2D spline shape was turned into a 3D part using Inventor's Loft feature to connect to its neighbor.

The OMAX Waterjet's 5-axis functionality is limited to angles of 59° or less, meaning that the change in slope between each slice is limited to 59° or less. This constraint presents a challenge but also serves as a rule for the construction of a 3D surface. Guided by this, we developed a construction technique which represented two conditions of fog, laminar flow and turbidity, with a series of smooth transitions interspersed with intentional disconnects or gaps.

Step 4: ​Creating a Naming Convention

Help your future self stay organized and come up with a part- and file-naming convention. Below you'll see what we did. You can emulate this or come up with your own, but be sure to use some kind of system.

Our sculpture is comprised of sections, which are groups of related slices. Many of the slices are divided into segments. Four of the sections are lofted and the rest are not.

Loft or not:

The first letter refers to whether the slice was part of a loft or not. (l = loft)

Material thickness:

It's important to indicate the thickness in the filename for sorting parts into layouts, and it helps you visually identify the right pieces during assembly. In our code, the second letter refers to the thickness of the slice. A = 1", B=.75", C=.5", and D=.25"

Slice number:

The first number in each part name refers to the slice number. Slices are numbered 1-30 from left to right as you face the piece.

Segment number:

The long slices were split into three segments so that they would nest more economically on the material. The segment closest to the top or head was always 1, the middle was 2, and the bottom or foot was three.


The first slice of the first lofted section is comprised of three segments: lA1-1-1, lA1-1-2, and lA1-1-3, and should be cut out of 1" thick felt.

Step 5: Transition From Inventor to IntelliCAM and OMAX Make

We used four thicknesses of felt, so created four corresponding Inventor assemblies, laying out all parts of the same thickness in each one. We exported each assembly to an .sat file.

Next we imported the .sat file into IntelliCAM and used the 3D-Pather function to automatically generate a 3D 5-axis toolpath. The user interface in IntelliCAM doesn't allow for making many changes. The only parameter to set is for Cut Quality to Water Only.


If the 3D Pather can't process a part it will return an error describing the problem (for example, an angle is larger than 59°). The only thing to do is go back to Inventor and change the part file.

Click on "Send to OMAX Make" to export the toolpath and open OMAX Make automatically.

OMAX Make settings should be accurate as imported from IntelliCAM, but it's good to double check. Cut quality should be Water Only, cutting speed 100-140, and the "Enable A-Jet" box should be checked.

Step 6: ​Prepping the Material

Cut felt down to size with a sheetrock knife. For thick felt you will have to make several passes along the cut line to gradually cut through the material.

Make a substrate to hold the felt in place while cutting. The board should be at least 2" wider than the felt on all sides (add 4" to your felt dimensions). Cut plywood down to size with a table or band saw.

About spoil board: We tried a few different substrates as spoil board, and found we got the best results when using 1/4 - 3/8" dense plywood. Softer substrates like coated construction cardboard and masonite get pulped by the jet and that pulp gets embedded in the felt. With thin felt it is particularly important to use a thick spoil board because the material itself absorbs less of the force of the jet, so the dirty water in the reservoir gets churned up and can splash up on the underside of the felt.

To further protect the felt from splashing, and to hold it in place on the board, cover it entirely with wide pre-spacing tape. First lay the felt out on the plywood and center it roughly. Unroll pre-spacing material and lay it lightly onto the surface of the felt. Working from the center, smooth the tape out over the felt, down the sides, and out along the plywood. Wrap any excess over the edge of the ply and stick it flat onto the bottom of the spoil board.

Step 7: Setting Up the Machine and Making Cuts

The first thing to do with the machine is flush out any garnet remaining in the system from previous jobs. Garnet is unnecessary when cutting felt and will only make your material dirty.

To flush garnet out of the system:

Position the nozzle over the bed in a place where there are no support ribs below. Stay within the left half of the tank, closest to the operator’s station, since this is the part of the bed with a reinforced bottom. Lower the nozzle until it’s about an inch above the water. In OMAX Make, select Test from the panel in the upper right hand corner. Select Water-only test, and set the duration for 20 seconds. Run the test.

You also don't need or want to flood the material with water. Lower the water level in the reservoir as low as possible with the joystick on the main control unit.

Put your material onto the bed of the waterjet and clamp it in place.

Follow the usual recommended procedures for zeroing the X,Y, and Z axes, and do a dry run of the path.

Run the job!


5-axis cutting of continuously changing angles is something experimental even for the people at OMAX. Sometimes it will work just as expected and other times the machine will seem to be controlled by gremlins, will freeze unexpectedly, and may even make you think you have broken a very expensive piece of equipment. We are working on an Instructable specifically about making these kinds of cuts and troubleshooting some of the errors that we encountered, and will link to it from here when it's done.

Step 8: ​Keeping Parts Organized

We used a 6-shelf rolling wire rack to keep the pieces organized as they came off the waterjet machine. It was an ideal drying rack, since we could roll the cart in front of the wall heater overnight, and it also made it so that our materials could easily be moved out of the way when we weren’t working in Studio 9.

We wrote the names of all of the parts from each assembly on notebook paper, cut them out, and as we removed the pieces from the waterjet machine, labeled them with their respective part names. We knew from previous experience that other types of pins or needles could leave little rusty spots, so we attached the labels with stainless steel non-corroding T-Pins.

Despite our best efforts, some of the parts got mislabeled. It's really easy to mix things up, so work carefully!

Step 9: ​Cleaning and Touching Up Parts

Some of the pieces inevitably got dirty in the waterjet machine. If they were really dirty we washed them immediately in the shop sink with very diluted dish soap. For the rest, we let the pieces dry, and then used a pet grooming brush to brush away the loose dirt. We then used Folex Carpet cleaner to work on the remaining spots. Following the package instructions, we sprayed it on the soiled area, lightly massaged it in to the surface, and blotted the moisture away with an absorbent cloth.

A few of the parts came out with little nicks, dents, cuts, and other irregularities. We touched up the edges of the parts by sculpting with a 9mm snap-off blade, shaving small amounts of material off at a time until the area matched the machined edge.

Step 10: ​Preparing for Assembly

Once all of the parts were cut we brought everything to our studio. We laid the parts out on a big work table. By using our numbering system we were able to group all of the 1, 2, and 3 segments into complete slices, and then set the slices out in the correct order.

The piece is made up of several sections that are lofted and therefore very smooth, with transitional sections between comprised of slices with a lot of variation in shape which help bring a sense of movement to the piece. We grouped the slices into these lofted and variegated sections.

For reference, we printed a set of drawings, where each page shows one complete slice with the next slice showing behind it.

We did include reference holes in the Inventor drawing but several of them ended up in the wrong places, for reasons which are mysterious and related to the performance of the waterjet machine, not the original drawings. We forged on ahead by eyeballing the placement and using the print-outs for reference.

Step 11: ​Gluing

Combining segments into slices:

We began by assembling each slice, gluing together the ends of the 1, 2, and 3 segments. We ran a thin bead of glue around the perimeter of a face, about a ¼” in from the edge, and carefully pressed the two faces together. We applied firm pressure to get the tightest bond possible, waiting 10-20 seconds for the glue to begin to set. Hot glue sets very quickly, which is one of the reasons we chose it, but you should nonetheless be careful with your bonds for the first 5 minutes or so.

As we assembled each slice we removed the pins and labels from the 2 & 3 segments, leaving only the label for the first piece of the slice.

Combining slices into sections:

Once the slices were together, we began assembling the sections. The lofted sections were easiest to align, so we started there. We stacked two pieces, moving them into the right position. Next we tacked down the ends. We lifted up the end of the top slice and, holding the rest of it in place, ran a short bead of glue around the very tip. We carefully dropped the tip back into place and applied firm perpendicular pressure to the stack. We repeated this with the other end of the slice.

After the ends were secured, we glued the middle section. We glued down 6”-10” lengths at a time, and alternated from one end to the other until we reached the middle. If we found that a piece had become stretched we would gently pull it and press it into place.

After the lofted sections, we worked through the variegated sections. Here we referred closely to the printouts to achieve the correct alignment. These sections were challenging to line up but we knew it wouldn’t look wrong if they were slightly out of shape. Once we had it aligned according to the drawings, we made slight changes based on what we thought looked best in real life.

Combining sections to build the form:

Once all of the sections were assembled, we glued them to one another. We made a temporary base out of cardboard and dowels to hold the overall shape. We started with the sections in the middle and worked our way out, alternating from side to side to keep things balanced.

Step 12: Dying

Before dying the piece we did a number of tests of different color combinations and dilutions to see what would work best with the form. Since the different thicknesses of felt are also slightly different densities, and wool is a natural material, there will be some variation in the way the dye is taken up from slice to slice. Rather than accentuate that additionally by varying the color, we used a single color across the whole piece and let light, shadow, and the felt itself produce a range of shades. We picked a light neutral grey made from a highly diluted black liquid dye.

We used a disposable graduated syringe to achieve the right ratio of dye to water and applied the dye with a spray bottle, mixing new batches as needed.

We sprayed the entire piece with plain water to dampen it completely. We then sprayed the dye on, working on sections at a time, thoroughly saturating each area with the diluted dye before moving to the next.

The sides of the slices -- the original pressed surface of the sheet -- are more resistant to the dye than the freshly cut surfaces, so we massaged the dye into the felt and went back over those areas a few times, all while the piece was still wet.

The underside is visible when it's installed on the base, so it was important that we cover both sides. After we had dyed the entire exterior surface of the piece, we removed it from the base, flipped it over onto a dropcloth, and did the underside.

Before the dye dries it can look very blotchy and uneven! Luckily our tests had proven that by the time it dries it becomes more uniform, gets much lighter in color, and has a nice watercolor-like appearance.

Step 13: Making the Base

Acrylic Uprights:

The felt form is suspended in air with the help of a series of five acrylic uprights representing profiles of the landscape that the fog has enveloped. We drew the profiles in at 10" intervals, and matched the top edge of the upright with the underside of the felt form.

We made a 2D sketch of the profiles in Inventor and saved it as a DWG file. In Adobe Illustrator we opened the DWG, saved a copy as an AI file, then dropped the five different shapes into three 24" x 36" layouts for the laser cutter. We used 3/8" clear acrylic, and used the recommended settings on the laser cutter for that material.

Pedestal Base:

The acrylic uprights are inserted into slots cut into a base plate made of three pieces of 3/4" MDF. These pieces were cut on a CNC machine. Using the slots as guides, we aligned the three sheets of MDF and glued them up into a solid block.

We sanded the cut edges and used wood filler to smooth over the seams. We rolled the block with two coats of white paint, sanding the first layer with fine sandpaper once it had dried and before applying the next coat.

Four 2"x8" pieces of .5" plywood serve as feet, both to create a subtle shadow line below the pedestal and to make it easier to pick up.

Step 14: Putting It All Together and Making Final Adjustments

We assembled the base by inserting the acrylic uprights into the appropriate slots in the MDF stack, and draped the felt over the uprights. We had to make some adjustments, pulling and pushing and compressing the form, to get the felt to sit in the right places on the uprights, and discovered that the glued-together felt was actually a bit wider than the uprights. We identified a couple of places where we wanted to change the curvature of the surface a bit by adding shims to the tops of the uprights. We lasercut pieces of acrylic to size and used acrylic glue to bond the shims to the tops of the uprights.

We finished up by brushing the surface and checking for bits of exposed glue and cleaning the acrylic. Then we rolled it outside and admired it in the sunlight with the beautiful San Francisco Bay in the background. There was not a cloud in the sky.

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    2 Discussions


    5 years ago on Introduction

    Wouldn't it be so nice if those were made by concrete and installed on public places like beaches. They look flowing,continuous like natural elements water/air, very artistic guys, well done !

    Really Beautiful! Love how you showed process with the sketches and models. Reminds me of work by Tara Donovan.