Tuesday, April 10, 2018

Patterned, Extruded Ceramic Vases

This post documents some new methods I've been experimenting with in making vases made by extruding clay. This work is built on previous projects documented here and here. I've been using a new algorithms to generate the forms and applying decorative patterns to the surfaces.

New Form Generator

Some of the new forms are generated using a simple but interesting algorithm. The basic idea is to have a polygon sided cylinder, make a circular array of these such that they overlap a bit, union them together, then twist and taper the final form.


The parameters are listed below:

Here are some computer renderings of type types of form you can generate:


Here's a sample prior to bisque firing:


Here are a few after firing with a clear glaze.

With the view from above you can see the base polygon and the polygon that was arrayed:

Pattern Methods

There are several pattern methods used:
  • Generating random, but repeating perturbations to the surface
  • Bumping out the surface at repeating intervals
  • Bumping out the surface using an image
  • Sculpting a high resolution mesh and using that as the form to extrude

Random, Repeating Patterns

Another technique involves using "noise" to randomly bump out the points, but then repeat those bumps so they produce a noticeable pattern. If you look carefully you can see the pattern swirling around this form:

Bumping Out the Surface

This technique involves bumping out points on the surface at controlled intervals. You can bump out every N points on every N levels. The vase below has every 4th point bumped out on every 2nd level.

There is also a "basket weave" effect. This one uses a sine wave to push the points out and pull them in. You can control how many repetitions of the wave occur in each level, and how many levels to skip between pushing points out. And you can control how far they push out. In the example below it is every other level. Note how the algorithm shifts the pattern alternately between levels. That's what gives it the basket weave effect.



Image Based Alterations to the Surface

You can use an image to map onto the surface. The lighter the pixels the more the surface is pushed out. This one was made by Taubman College student Julia Hunt using an image of a leaf.

The image map can be combined with the bumping. So areas which are white are bumped a lot and area which are black are not bumped at all. The following vases were created by Taubman College students Jasmine Almomar, Teruaki Hara, Jad Ismail, Akshay Srivastava:


By slowing the robot motion as the bumps are pushed out loops of clay can be generated:

Time-Lapse Video

Here's a time-lapse video of the process. The people in the video created it. They are some of my graduate students in Arch509 Robotics at Taubman College. This is the work of students Jasmine Almomar, Teruaki Hara, Jad Ismail, and Akshay Srivastav:



More Updates

I frequently post new work on Instagram. Here's a link.

Other Work

I came across a presentation by Tom Lauerman and Jonathan Keep titled Clay, Computation, & Culture. It was presented at the National Council on Education for the Ceramic Arts conference. The video is well worth watching.




Sunday, March 25, 2018

5-Axis Router Toolpath Setup

This post documents getting 3D geometry ready to cut on a 5-axis router. The two methods covered are 3+2 Milling and Swarf Milling. The software discussed is Rhino for modeling and Mastercam for toolpath programming. The issue of holding the work during cutting is also addressed.

Definitions

First, a few terms are defined:

3+2 Milling

In this form of programming the 5-axis router is treated like a 3-axis router which is operated on an arbitrarily rotated plane. That's where the name 3+2 comes from, functioning like a 3-axis with 2 additional degrees of freedom for orientation of the cutting plane. In the images below the end of the work piece is 3+2 milled. It's consists of a pocket and a contour but at an odd angle.
  

Swarf Milling

In this form of milling the 5-axis router is cutting with the edge of a tool, following a surface. That surface needs to be a ruled surface. Simply put that's a surface defined by sweeping a line through space. If you visualize the edge of the tool doing the cutting as the line, and the motion of the router as the sweep, you can picture why that geometry is what we are dealing with.

Fixturing

A key element of using the 5-axis router is how you hold the work for the milling to take place. The work piece must be held securely but must also allow freedom for the router to move around the part to mill it. The process of holding the work is called fixturing.

There's another term which is sometimes (mis)used: Jig. However, a jig implies that the work is held and the tool is guided by the jig. In the case of a CNC router the tool is guided by G-Code. So the term fixture is the more correct one.

Example 5-Axis Projects

This section provides links to a few furniture design and small object scale projects cut on the 5-axis router at Taubman College. 

Rhombic Triacontahedron Fabrication - This simple project uses swarf milling to cut the parts. The fixturing of the work piece is done using vacuum pressure.
  

Origami Side Table - The joinery for this table was cut with swarf milling. Some material clearing was done with 3+2. The fixturing was done with double-sided carpet tape to hold the part to an MDF panel which was held by vacuum pressure.
  

Torus Knot Table - This project uses both swarf and 3+2 milling. Several fixtures were needed to cut the parts for this table.
  

Hexagon Table - This project used both swarf and 3+2 milling. The fixturing was all done with vacuum pressure. Simple MDF fixtures were made to allow the vacuum pressure from the table to be transmitted to the surface of the part to hold it.
  

3+2 Milling Geometry

To program a toolpath using 3+2 milling you first need to define a plane that the cut will take place on. You can use the tools in the Planes tab of Mastercam to create and manage your planes.

Use the + icon at the top left to create a new plane.

It's easy in Mastercam to use the normal of a surface to define the plane. Or use the From line normal... menu item to do so from a line drawn perpendicular to the plane. In Rhino use can use the Normal option of the Line command to easily create such a line.

After you define the plane you can set it as active in the toolpath setup dialogs. Here's a Contour toolpath example. Select the Planes branch in the tree view on the left. The Tool plane name is shown in the middle column. Click the circled icon to change it to one of your defined planes.

Once the planes are set you can program just like 3-axis routing. For details on those toolpaths see Mastercam Toolpath Setup.

Swarf Milling Geometry

To set up a toolpath in Mastercam for swarf milling you need either two rail curves or a surface and a lower rail curve. The bottom edge of the tool will follow the lower rail. The edge of the tool will ride along the surface or the other curve.

In Rhino you can use the ExtractSrf command to extract or copy a single surface from a solid (polysurface). You can use the DupEdge command to create a new curve from the edge of one of your surfaces.

From the Torus Knot Table example the geometry was generated with a Python script. It output each part and the surfaces used for milling:

Each part was put in its own file and moved to the origin for cutting. Here is all the geometry for a part including the bounding box of the wood. Note that the front face of the wood is the 0,0,0 point:

What's required is just a subset of that. Minimally you need edge curves to swarf mill. For example, the three side surfaces which don't have dovetail components are swarf milled. The required lower rail is the lower curve and the corresponding upper edge is upper rail.

Inside Mastercam you can create Swarf Milling toolpath using the toolbar in the Toolpaths panel:

Inside the dialog presented you can choose the geometry to follow:

As you would expect controls are available to manage the lead-in/out, direction of cut, step-down and step-over, etc. These are set up in a similar way to the three axis milling.

Fixturing Parts

Holding the work piece steady during milling is critical. Here are some work holding examples from the projects above.

The Origami Table uses MDF spoilboards and heavy duty carpet tape to hold the parts. The tape can be cut through and doesn't affect the wood or the finish.


In the Rhombic Triacontahedron Fabrication project the parts are very small - about 2" x 4". They are held by vacuum pressure and two tiny pins. Without the extra friction from the pins the parts wouldn't hold. With them, they usually hold. Every 10th one would still fly across the room while cutting! The pins could have been pushed further into the wood to completely eliminate that but it would involve more work to remove them (deeper sanding or planing). I chose to leave them.

The Hexagon Table uses milled MDF fixtures with rubber gaskets to hold the work pieces:

Here you can see the MDF held to the pods. Some suction comes through the MDF onto the work piece to hold it to the MDF.

The Torus Knot Table also uses MDF held on pods. In this case the stock block is glued to the MDF.

Once 5 sides have been cut the 6th is cut holding the part in another fixture - in this case by the previously milled dovetail:

In the Wolff Sleigh Bed large MDF fixtures were used to hold curved parts:

Here the faceted part was smoothed on the other side:

You can also simply screw larger boards to the spoilboard. Note that you don't have an automatic tab generator as part of the swarf milling toolpath programming. So you'd have to create those with your own modeled geometry.

Part Origin / Router Alignment

Another key to successful setup is having a consistent and measurable origin point. That is, you tell the router using a work offset where the 0,0,0 point is located in space. That's the point that matches the 0,0,0 point in your Rhino and Mastercam files.

When the part is cut from a large block, as long as you are fully within the block, the accuracy is not super critical. Just make sure you are within the block!

When the parts are already milled and you need to match up to them then more accurate measurement is required. In this case a dial gauge is used to measure the exact position of the fixture to 4 decimal places.

The coordinates can be read off the router screen:

These are then entered as a work offset and the router position and the Mastercam positions are perfectly coordinated.

Reference

Here are some links to other related blog posts:

Taubman College 5-Axis Router Operating Procedure

Mastercam Toolpath Setup


Tuesday, January 30, 2018

Plywood and Fiberboard Sheet Goods

This post discusses many different types of plywood and fiberboard sheet goods.  These are engineered wood products made out of wood plies or wood fibers. Types of fiberboard include particle board, medium-density fiberboard (MDF), and hardboard.

The great majority of the material featured on this page are available from Fingerle Lumber in Ann Arbor, Michigan. Others can be purchased from All American Plywood in Detroit, Michigan.

Note: For information on hardwoods and veneer please see Wood Basics.

Plywood

Plywood is a composite material made up of thin layers or "plies" of wood veneer. The plies are glued together with the wood grain of adjacent layers rotated relative to one another. There are several important benefits to the cross-grain orientation of the layers:
  • It reduces expansion and contraction of the panels due to moisture changes in the atmosphere. This provides much improved dimensional stability over hardwood.
  • The strength of the panel is consistent across all directions. 
  • The wood is less likely to split when nailed or screwed near the edges of the parts. 
Below are some videos describing the process of making plywood:

Plywood Grading

Plywood grades are established by the APA – The Engineered Wood Association (the initials APA come from the associations previous name of the American Plywood Association). In the United States, there are four basic plywood veneer grades: A, B, C and D.

Each plywood sheet will have two grades, for example AC. The first letter is the grade of the face veneer, and the second is for the back veneer grade. Some plywood sheets have a third letter, X, that designates them for exterior use.

A Grade: This material is the highest quality. It is sanded smooth, and is paintable. Some neatly made manufacturer repairs are acceptable, however you can generally expect the material to be free of repairs and knots.

B Grade: This material is a solid surface with some repairs, usually football-shaped patches and/or wood filler. It may contain tight knots up to 1 inch in diameter, however no chunks of wood are missing. There may be some minor splits.

C Grade: Contains tight knots to 1-1/2 inches in diameter with knotholes to 1 inches in diameter. There may be some splits and discoloration.

D Grade: This is the lowest grade and the material may contains knots and knotholes up to 2-1/2 inches in diameter. Some splits are likely present. Generally no repairs have been made to the material.

Baltic Birch Plywood

This material is commonly used in CNC routed projects. The wood species is Birch and it is sourced from the regions surrounding the Baltic Sea. In the case of the material we get in the Taubman Fab Lab it comes from Russia.

It's a veneer core material meaning all the plies in the sheet are free of voids. Well in theory... as you can see in the examples below there are sometimes small defects which you can see in the cut edges. In general however you won't find any large voids as you would in lesser grade stock.

There is often a superior face side and a lesser side. The non-face side may contain what are known as footballs. You can see one in the lower right of the piece below. It is a patch placed into a defect area of the veneer. It looks better than seeing a knot, but it does break the flow of the grain across the sheet. Keep this in mind as you are designing - if both faces are visible in your final product you may want to position your parts on the sheet for cutting as to avoid the area with footballs.

Paint Grade Birch Plywood

This is a low-cost product which accepts paint well. Generally the face veneers are not as clean in terms of the grain but they are free of defects so the paint application will be smooth.

CDX Plywood

CDX refers to "C-D Exposure 1". The faces are graded C and D and the glue used in the plywood is exterior glue. While the material is moisture resistant it cannot be exposed to outdoor conditions for an extended period of time. This is a low-cost material commonly used in construction. 

Radiata AC Plywood

This is a 7 ply material with thick exterior plies. The A grade side is high quality and has a marked grain pattern to it, similar in appearance to Pine.

Face Veneer Plywood

Below are a few examples of plywood with pre-finished veneers or lower quality material in the internal plies with high quality hardwood face veneers.

Pre-Finished Baltic Birch Plywood

This is a very high quality material composed of 13 thin plies. Both faces are pre-finished so it is ready for use immediately after cutting. The edges are free of any significant defects (voids).

Red Oak Veneer Plywood

This material has 5 plies and a Red Oak veneer on both sides.

Birch Veneer Particle Board

This material has 5 plies and a Birch veneer on both sides.

MDO (Medium Density Overlay) Fir Plywood

MDO is an exterior grade plywood with smooth, brown medium-density plasticized overlay. It's good for accepting paint and resisting exposure to moisture. The painted surface won't show any grain.
This material is available with the overlay on one side or two. 

Other Sheet Materials


Below are some videos describing the process of making Medium Density Fiberboard (MDF) and Oriented Strand Board (OSB):

Medium Density Fiberboard (MDF)

MDF is an engineered wood product made by breaking down hardwood or softwood into wood fibres, combining it with resin binder and a small amount of wax, and forming panels by applying high temperature and pressure. MDF is generally denser than other sheet goods such as plywood and particle board. This material is heavily used in the furniture industry.

Ultralight Medium Density Fiberboard (UDF)

This material is a light-weight version of MDF. It is much more porous than MDF and so is often used as spoilboard material in CNC routing applications. UDF allows the vacuum pressure from the CNC machine's vacuum table to be transferred right through itself to hold down the material resting on it. It can be planed flat over and over to restore a smooth surface. 

Melamine

Melamine has a compressed wood core, similar to particle board, which is covered with a resin and paper finish. Melamine is often used for cabinetry when a durable, smooth, wear resistant finish is needed.  The top coat is smooth and resists moisture. It's not as durable as a layer of plastic laminate (the melamine surface is much thinner) but is often used as a low-cost substitute. Sharp cutters are needed as edge chipping is sometimes an issue.

Particle Board

This is an engineered wood product manufactured from sawdust, small shavings or wood chips combined with a binder, which is then pressed and extruded. Particle board is cheaper, denser and more uniform than plywood and is used when cost is more important than strength and appearance. Particleboard can be painting or covered with wood veneers to improve the appearance. Though it is denser than conventional wood, it is the lightest and weakest type of fiberboard.

Birch Veneer Particle Board

A singly layer of Birch veneer is applied to a particle board core.

Maple Veneer Particle Board

This material has 5 plies and a Maple veneer on both sides. 

Oriented Strand Board (OSB)

Oriented strand board (OSB) is an engineered lumber formed by compressing layers of wood strands in combination with an adhesive (usually a resin that has been coated onto the flakes). OSB has desirable mechanical properties that make it suitable for load-bearing applications in construction. It is also sometimes used in furniture construction where a strong, low cost material is needed.

Cedar Flake Board

Flake board is another name for oriented strand board. This material is composed of strands from Cedar trees. It's strong and has the pleasant smell of cedar. It is used in closet lining or chest lining applications.

Sound Deadening Board

This fiberboard product is lightweight and porous. It is used as wall and ceiling material in noisy environments to absorb reflected sound waves to decrease the overall volume level in a space. 

PVC Azek

This material is different from all the other materials in this post because it does not contain wood fibers which can promote mold growth. It is strong and lightweight. It can be cleaned with soap and water. The material is color-fast and stain resistant and is extremely scratch resistant.

Bending Material 

Some types of plywood or fiberboard are designed to be used in applications where the material needs to follow curves or be bent into shapes. The material is classified into barrel type (4' edges bend) or column type (8' edges bend).

Bending Plywood

1/4'' Neatform Bendy MDF