The Nerdy Derby Flat Track

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Cutting a Nerdy Derby Flat Track

Design Decisions:

The Nerdy Derby Flat Track project was created with three criteria:

  • It had to be shape-compatible with the original Nerdy Derby track, so that the same cars would fit on each track
  • All the parts had to be cut-able with a Handibot, so no part could be larger than 6” x 8”
  • It needed to be material agnostic, so that a set of parts could be cut out of whatever material was available. This allows them to be fabricated from waste material as described in Distributed Manufacturing as Waste Management

This Flat Track design has evolved through many versions, but two have bubbled to the top.  My favorite one I just call “Flat Track” and uses rubber bands, ORings, or hair ties to make a flexible, “fluid” connection.

blog elastic connection


The other version uses bowtie-shaped connectors that fit into cutouts in the tracks. It works just fine but has lots of little fiddly bits to keep track of.

blog bowtie connector


Files for both versions are included in the Project Download so that you can make up your own mind which one to make.

Materials and Bits:

Downloading the Project Files (link) will get you several folders and files. If you just want to cut track parts without fiddling with design files, the ShopBot Part Files have already been created for both nominal 1/2″ material that’s really 0.47″ thick, and nominal 3/4″ thick material that’s actually 0.73″ thick. They have been toolpathed for a 1/4″ bit that’s zeroed to the top of the material, and have speed settings for cutting with a Handibot. The files cut through the material an extra 0.015″ deep, with two tabs holding each part (More about this later)

The Project Files also include the tool database setting for the bit I used to toolpath those ShopBot files. It’s named “Bits for Flat Track files.tool”, is in the Shared VCarve Files folder, and if you use the IMPORT function in the VCarvePro tool database,a new tool group with this new bit will be created.

import bit

There’s a great video about working with the Tool Database on the Vectric website

Cutting Files:

If your material thickness is different than those two sizes, or you’re just feeling adventuresome, the VCarvePro files for each part are included in the project files.

The VCarvePro files uses an interesting feature called “Document Variables” that make it easier to modify the toolpaths. In our case, they are used instead of inputting a number in the Cutting Depth field when setting up toolpaths, but can be used just about anywhere in the toolpath. You can find the list of Document Variables at the bottom of the EDIT menu in VCarvePro, and opening it will show the three variables that I use.

Document variables form


The “groove_depth” variable is the depth that the groove is cut that holds the elastic connectors in the “Flat Track” files. It’s not used in the bow-tie versions. “pocket_depth” is the depth of the pockets that are machined to make the lower sections in the track that the car wheels ride on. The default value of 0.25″ matches the regular Nerdy Derby track, but since you’re creating your own set you can do what you want!

If you open the Groove or Pocket toolpaths and look in the Cut Depth field, you’ll see text where you usually see numbers. If you hover your mouse cursor over that textbox you can see its value.

hover value


Calculating with Variables:

The third Document Variable is “thrucut”, and is used a little differently. The Document Variables are defined by the creator of the file, but there are several  Special Calculation Characters that VCarvePro also understands.

special calculation characters

The one we use is “T” which represents the thickness of the material as defined in the Job Setup form. Adding the value of our “thrucut” variable to the thickness value lets us cut a little bit deeper than the thickness of our material to make sure that the parts are cut all the way out.

We define that total cutting depth in the “cutout” toolpath cutting depth field by typing “T”, then “+”, and then hovering with our mouse until a list of all of our Document variables appears. Select “thrucut” from the list and your new formula appears in the box. Hovering your cursor over it shows its current value based on our default material thickness of 0.73”.

old thickness calc

This may seem like an overly complicated way to set cut depths, and for simple parts like these it may be. It is a BIT more complicated than just typing in a number, but what happens if your material thickness changes? You need to find all the places that cut all the way through and change the cutting depth in each toolpath. Or if you want to it cut a little deeper (or not as deep) you’ll need to modify each toolpath!

Let’s say the material we have is really .55” thick. All we have to do is to open the Job Setup in the EDIT menu and change the current value of 0.73” to your new value: 0.55”

new thickness


To see this change you just need to recalculate the toolpaths, and anywhere you use the “T” value will be recalculated and will have the new cutting depth.

new calculated thickness

The Document Variables file that I used, “Nerdy Derby Flat Track.DocVars”, is include in the Shared VCarve Files folder. Don’t be afraid to play with these settings … you can always import this file from the Document Variables form to reset them if you get them messed up.

Using Merged Toolpaths:

create merged toolpath

The last fancy feature is only used in the files for the straight sections, because they have multiple toolpaths—grooves, pockets, and cutout—in multiple parts. If we had just selected the three toolpaths and generated a part file from them, it would have cut them in their order in the list. It would have worked fine, but wouldn’t have been particularly efficient. It would have cut the groove in both parts, then cut the pockets in both, and then cutout both. Lots of moving back and forth.

What we actually want to happen is to have the file finish cutting ALL the features in the first part before moving to the second. That’s what a merged toolpath does—combine the features in each part to make the cutting more efficient.

merged tooolpath form


One thing to be aware of is that merged toolpaths are NOT re-calculated when the toolpaths that they were built from have been modified. Don’t worry that you’ll forget though, because you’ll get lots of warnings after you’ve recalculated a toolpath that was used in a merged toolpath. You just need to delete the merged toolpath and generate a new one, that’s all there is to it!

Also remember that since the new merged toolpath was built from the other toolpaths, when you save your part file you ONLY use the merged file. I’ve renamed the merged toolpaths in the VCarvePro file to hopefully help you remember!

only merged


Want to learn more about using Merged Toolpaths? Watch this Vectric Video


blog track2

The project files can be downloaded from Handibot Projects in a zip file.  To help with prototyping and figuring out how many pieces of each you need, Sketchup files are available in the 3DWarehouse to build your own virtual track layout.

Enjoy your Flat Track and feel free to modify the files to fit your needs,


NOTE: These files are licensed under the Creative Commons Attribution 4.0 International License.

You are free to:

Share — copy and redistribute the material in any medium or format

Adapt — remix, transform, and build upon the material

for any purpose, even commercially.

To view a copy of this license, visit or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

ShopBot Helps UNC Students See the Stars


“Making” as distinct from “Building” is as much about knowing how each part is made as it is about arriving at a finished product. Through the exercise of planning and designing, we learn skills that apply to more than just the project at hand and we become more capable of creating new and better things.

Teaching a set of these skills is the goal of University of North Carolina’s BeAM Maker in Residence program; a project based class where students are guided through the creation of a complicated device by an experienced maker. BeAM facilitates this by identifying a project that will have a significant impact on campus and finding a local maker who can provide the know-how to pull it off. This year, their project was to design and build a large telescope that could be used in cooperation with the Morehead Planetarium and Science Center to teach students about astronomy at a series of free events on campus.

Raleigh Astronomy Club member Jim Presley, who has built a number of custom telescopes and helped with the observatory at North Carolina State University (NCSU) won the residency. I met Jim at a free sky-watching event where we both volunteer regularly with the planetarium. The kind of telescope that Jim creates is called a Newtonian Reflector. It consists of a large primary mirror that sits at the base of a long tube, the primary mirror gathers and reflects light towards a secondary angled mirror at the top of the tube and this, in turn, reflects the light through an eyepiece which magnifies and focuses the image for the viewer. The tube and mirror assembly is usually attached to a simple stand referred to as a Dobsonian Mount which allows the astronomer to pitch the scope up and down and swivel around to find his target.


Jim was operating one of his beautiful hand-made telescopes that night and we spoke about his process for creating them. Most of the components for the mount are typically designed with simple, straight lines so that they can be hand cut. I asked if he’d thought of using CNC to cut the parts for the project scope and Jim replied that he knew BeAM had a ShopBot but wasn’t sure if they were going to use it. I replied that I just so happened to work for ShopBot and would be happy to come to the class and help out if they wanted a little introduction to the tool.


A few weeks later Andy Martin, Anthony Wong, and I (employees of ShopBot) visited BeAM to provide a brief training session for anyone who was interested in learning more about the ShopBot. We brought along a Handibot that could be set in the center of a large table where everyone was seated while I projected my laptop screen onto a large monitor to give a demo of CAD/CAM and using the ShopBot control software. After a few test cuts with the Handibot, we moved over to the large 5×8 ShopBot to cut out parts for the telescope mount that had been designed for the student scope.


The project telescope turned out beautifully with a hand painted version of Van Gogh’s Starry Night around the body (with the UNC bell tower standing in for the big cypress tree in the original). The signatures of all of the participants were also laser engraved on the side of the mount.

On November 19, the class brought their new scope out to greet students after a planetarium show where the clouds cleared just in time to provide gorgeous views of the moon and stars.


Contributed by Brian Owen

A New Design Resource for ShopBotters Doing Collaborative Work: Fusion 360


I’m always on the lookout for resources for small shops doing digital fabrication – resources that will help these shops operate profitably by improving communications with customers and improving collaborations with partners working on the same project. For small shops doing CNC, 3d-printing, laser cutting, and applying other digital fab technologies, I think of these as essential platform tools for leveraging our digital production technologies. Such tools exist for those working within a corporate environment, but there are fewer resources available for small shops to use when working with individual customers or for interacting with others such as designers and collaborative partners.

Fusion 360 is a new cloud-oriented design resource from Autodesk. It is well-suited to the small shop and could become a supportive platform tool. I’ve been following it for a while and have recently described how it works on the 100kGarages blog. If you are new to the idea of cloud-based resources for design project work, you may want to check out the blog or go have a look on the Fusion 360 website. Fusion 360 is free for a trial month and for students and hobbyists remains free.


Distributed manufacturing as waste management?


Whether you’re a production manufacturer using CNC machines, a cabinet shop cutting panels with a table saw, or a garage hobbyist working on weekends, even the most efficient cutting tools and powerful design sofware don’t let us utilize every square inch of every sheet of material we cut. This often makes us feel wasteful and not only causes bad “environmental karma,” but also has economic repercussions. We’re throwing away useable material, which equals throwing away $$$$.

We all have techniques to minimize how much material ends up in the trash. We try to design for material efficiency, which is wonderful most of the time. But sometimes, those design decisions can have a couple of undesirable side effects. We make things larger or smaller than we really think they should be, just because we have material on the sheet available. This might not always hurt the overall design, but sometimes it does. Or we fill the rest of the sheet with parts we MIGHT need someday, and end up with buckets of spare parts to store. We might end up using them, but we might also make a change to that design, rendering them obsolete. Cutting lots of small pieces on a sheet also uses up valuable machine time on a large machine, time that could be used more efficiently.

12 gallons of wedges

In most cases we cut our parts and then trim our waste material into regularly-shaped blanks and store them for future use. Most of the time that means we spend time cutting off odd corners and lumpy sections with a saw and then stack them in the corner of the shop with the dozens (maybe hundreds???) of other oddly proportioned and oddly sized pieces. If we’re lucky, we eventually find something to do with those blanks, create a custom toolpath, and cut parts out of it.

telephones in scrap

Maybe there’s another option: Distributed manufacturing as waste management!

There are businesses that need large quantities of small parts that can be cut from sheet goods: wheels or gears for toys, spacers for packaging, acrylic covers for inspection electronics projects, etc. What if we could connect those businesses with fabrication shops that could cut those parts from their waste? Material would be used that would normally end up in the landfill so the per-part price could be cheaper… and the material cost is essentially zero!

The “consumer” business could post their product needs with details like the size and description of the parts, the materials they can use, the quantity they need, and any time constraints. They would be connected to “supplier” businesses that could cut those parts from the waste materials left over from their primary cutting jobs.

The suppliers could cut these parts on their production tools, maybe out of material that they’ve saved using the “trim and store” method, but that ties up time on their larger production machine and requires thought and skilled labor to figure out how to hold and toolpath irregular sized blanks.

A Handibot® Smart Power Tool can solve a lot of these problems. Since it can be placed anywhere on the material, no trimming is necessary – just find a large enough spot on the waste material. Place the Handibot in this free space and start cutting. Files could be supplied that were optimized for the Handibot’s 6”x8” cutting area, so that all the operator would have to do is to run the selected file. Processing can be done immediately after primary cutting is finished by semi-skilled labor, creating entry level jobs that give an easy introduction to CNC technology.

Manufacturers needing parts for existing products is certainly one market, but environmentally conscious designers could create projects with parts in the Handibot 6”x8” format. These may be one-piece projects or multi-part projects that are assembled in interesting ways. And a Handibot in a recycling center could be used for contract cutting of wood, plastics, cardboard, etc. from waste materials that have been collected. The skills are easily taught so that these cutting jobs could be done by unskilled labor.


My Latest Adventures in the World of Education

In my role doing community outreach for ShopBot Tools, I have participated in the installation of several new digital Fab Labs/makerspaces in public and private schools around the US. While each of the installations has been different, there are lessons to be learned from each one. Here are a few recent case studies:


IU1, Coal Center, PA (about an hour outside of Pittsburgh)

The Intermediate Unit 1 Educational Campus at Colonial School serves 25 schools in the counties south of Pittsburgh. Funded by Chevron at both the corporate and local level by a grant to the Fab Foundation and implemented by TIES, the stationary Fab Lab at the Colonial School includes a suite of digital fabrication equipment and an electronics lab.

One of the important parts of the installation effort of a Fab Lab is training and education. So before the installation team left, teachers and administrators were trained on the basics of each machine, and created a project to show how the various design software can be used cross-platform. For example, parts created in VCarve Pro CAD (computer aided design) software for full-size production in wood on the ShopBot were scaled smaller and cut out of cardboard on the laser cutter to test the concept and design. Likewise, files originally designed for printing on a 3D printer (additive technology, building up layers of material to create something from nothing) can be reformatted to machine out of a block of material with a ShopBot CNC (subtractive technology). After the educators have had a chance to experiment with the digital technology and electronics lab, TIES will return for additional professional development on how the Fab Lab can be used to augment the educational goals of the school system and engage the students and teachers.



Hathaway Brown, Cleveland, OH

Hathaway Brown is Ohio’s oldest continuously operating college preparatory school for girls. Walking the halls, one can see certificates of patents held by some of its students, art projects, and theatre or music production posters. Their former woodworking shop has been reformatted as a Fab Lab for the middle school age girls.

Who will use the lab? A faculty member from the theatre department participated in the trainings and brought files for a set for the spring production of… I was sworn to secrecy, sorry! The robotics program for the upper school girls will share the space and they are mentored by volunteers from think[box] at Case School of Engineering. Fab Lab Manager, Leah Jackson, is a graduate of Hathaway Brown, and is thrilled to be back at the school.


Hawken School, Cleveland, OH

Hawken School is creating new specialty spaces to expand programs in entrepreneurship and media studies: The Miller Fabrication Lab, Media Lab, Media Production Studio, and Screening Room. Nick DiGiorgio, formerly with the Cleveland School District in STEM education, is now the Digital Lab Manager at Hawken. Until the new spaces are complete, Nick is fitting the digital fabrication equipment into the space available – Hawken’s ShopBot is housed in the set production room of the theatre department, and the laser and 3D printers line the hall.

Nick’s long time collaboration with the Fab Lab/makerspace community can be seen in examples of the carts that he designed for three of the mobile Fab Labs associated with the Chevron Labs. While the mobile Fab Labs are a topic for another blog, this is a good point to talk about the community that arises around the Fab Lab/makerspace movement. Administrations and teachers and parents are talking to each other – the movie mentioned at the end of this post (“Most Likely to Succeed”) was screened at Hawken, and there was a panel of public and private school administrators to discuss the issues raised in the film after the screening. And Fab Labs/makerspaces are collaborating to exchange programming, design, and production services as needed.


Lorain County Community College, Elyria, OH

One of the longest running FabLabs can be found at Lorain County Community College in Elyria, Ohio. As a community college, LCCC is charged with a number of tasks, from GED prep to early college; from job (re)training to entrepreneurship; from continuing education and community outreach to 2 year degrees; and partnerships with 4 year institutions. Its Fab Lab does offer production services, as long as the services do not complete with a local business. The cabinetry for the three existing Chevron mobile Fab Labs was machined at LCCC, and here is a photo of the ShopBot table to prove it! As part of the US Fab Lab Network, Lorain’s David Richardson worked with the National Association of Community College Entrepreneurs meeting (NACCE) to educate and communicate to the attendees about adding makerspaces to encourage entrepreneurship.


To gain more of an understanding of why many schools in the US are interested in putting in makerspaces, digital FabLabs or the like, take a look at the film “Most Likely to Succeed.” It contrasts how students become (dis)engaged with math and problem solving skills when they are taught in a traditional lecture format, compared to a hands-on approach that includes project-based learning, making, and community engagement.

Digital Fabrication and your Museum

digifab image

As the affordability of CNC, and Digital Printing gets better, and using it becomes more intuitive, these technologies find their way into adjacent fields, like museums. This affects your institution in two very important ways.

dfab2  dfab3


  1. Cost Savings.

My work while at Field Museum, taught me much about how to build cost effective, conservation minded display cases.  The reality of the cost savings of building in house  is understood by all. The shift in technology from industry to small business, schools, and artists, makes what was once highly specialized knowledge, widespread. Now embraced by the underground, outsider culture, CNC and digital printing are changing the way we build. Even the most modest of museums typically have space set aside for either staging or repairs. Now that CNC systems are less expensive, we are seeing CNC as an integral part of these spaces.

While used for repair and signage at first, it is a simple transition to making furniture, and eventually cases. Furthermore CNC lends itself to improving the way things are made. stronger, simpler, less waste.  If your Museum has not transitioned into digital fabrication, it is no longer a question of “if,” but “when.” What was, at one time, a $100K investment, can now be realized for less than $30K, and at Field, we estimated our machine paid for itself in a little over a year.


dfab6a    dfab7a


  1. Attracting Patrons.

Museums experience periodic shifts in their visitor’s points of view. These paradigm shifts happen around major societal change. These shifts represent  shifts in public awareness. In the twentieth century, things like, “The New Deal” “WWII” or the first tour of “King Tut,” changed how viewers see the museum experience. These shifts, if taken advantage of,  are opportunities for our institutions to change.

Our current paradigm shift is centered around Maker Culture, created in 2006, and proliferating in the digital metamorphosis of our society. The Maker Culture is an immersed generation. Social Media, “Do It Yourself” trends, and prolific volumes of information at their fingertips, has produced a culture that has been brought up researching, sharing information and ideas, and solving problems for themselves.  This has produced an altogether different museum audience, one informed, instantly connected, and concerned.

Shifting Museum Culture, however, is not just the phenomenon of digital saturation, but also of the coming of age of what I refer to as, “Second Generation Greenies.” The average visitor now, knows that museums should protect and preserve heritage for future generations as well as showing cool stuff. Empowered through social media, and brought up on the idea that it is important to actively take part in helping preserve the environment, their sensibilities are different. They understand taking a socially responsible approach to museum operations. This translates into an opportunity to focus on collection preservation.


dfab1a   dfab11a

More patient, more informed, this generation is willing to wait, if it means exhibitions are built eco-friendly, and artifacts are preserved, much the same as they are willing to pay more for fair trade coffee. From a marketing point of view, they are just as comfortable seeing work in progress, as finished shows. This means no lost opportunities when slowing down our process to do things carefully. Furthermore, this generation understands the importance of a museum’s infrastructure. Many are just as happy to raise money to preserve a collection, as they are to mount an exhibition. They are excited by seeing behind the scenes content, like prep labs, collection visits, and are into events like the member’s nights. This generation is comfortable with simpler more humble looks and materials, such as plywood, or even cardboard, “It is what it is!” They revel in the materials, especially recycled materials, appreciate local sourcing, and are willing to accept extra cost if it means doing the right thing. That means for many institutions the time has come when it is possible to put artifacts above all else.

dafb12a  dfab13a

An Institution is benefited by generating a sense of ownership and empowerment, among its public. Digital fabrication makes this not only possible, but easy. Most important of all, while the “Second Generation Greenies,” are our Museum visitors, the first generation greenies, or “The Earth Day Culture,” has now become our donors and benefactors.  Institutions on board with digital fabrication, and its benefits, will have the tools to connect as never before.

For those interested, I will be speaking at Smithsonian American Art next month with colleague Shelley Paine, and I have an abstract on this subject submitted to AAM for the upcoming Washington event next year. With a little luck, I will see everyone there, where we can discuss this extensively. Cheers!


ShopBot participates in conference on Cultivating an Entrepreneural Culture


What happens when the NACCE (National Association for Community College Entrepreneurship) has their annual conference? Inspired conversation.


Sallye Coyle, Educational Outreach Coordinator for ShopBot Tools, and I held a round table at the NACCE event. Attendees learned about the 100kGarages online network for bringing makers, designers, and fabbers together. We shared a presentation highlighting the continuum of ideation through manufacturing to delivery of a product, offered up alternatives to sending manufacturing oversees, and discussed the power of networked communities to get things designed and made locally. The whole group joined in to share experiences at their colleges that have sparked regional efforts to encourage more small businesses, incubators, and co-working spaces for various disciplines.


The NACCE organization is focused on “cultivating an entrepreneurial culture.” Many of the speakers, including EJ Carrion, Co-Founder and Chief Evangelist Officer at Student Success Agency and Johnny Earle of Johnny Cupcakes, shared their experiences of success through community college and the efforts of being a motivated entrepreneurs with supportive networks.

We were also able to talk with attendees about the benefits of digital files and digital fabrication techniques and how cross-platform training in the design software (CAM) can offer people greater flexibility in creating rapid prototypes and manufacturing techniques on a suite of tools from ShopBot CNC tools to laser cutters to wire benders and 3D printers.

Across the country there is an exciting movement to “create economic vitality through entrepreneurship” that community colleges are helping to make happen. They are not only teaching people about starting a business, but helping them succeed by providing ongoing support and resources. 100kGarages may become one of those resources to network and map local hubs of entrepreneurs or “garages” around these community college initiatives. We’re definitely excited about the collaboration opportunities that ShopBot and 100kGarages can bring to the table.

Photos courtesy of NACCE

Learn more about NACCE at

Contact us if you’d like to continue or contribute to this conversation.

2nd Annual Seasonal Décor Challenge


How does this season inspire your creativity? We invite you to “CNC it” and share it in our 2nd Annual Seasonal Decor Challenge! Whatever holiday you may celebrate, share your CNC project with ShopBotters and Handibotters everywhere by helping us decorate our tree at ShopBot World Headquarters in Durham, NC.

Last year we received a lot of creative and fun entries so we look forward to seeing yours now!

We’ll be awarding some cool prizes to our favorite entries: one-year subscriptions to MAKE: magazine and fun ShopBot t-shirts!

Be creative and have fun! We ask that you make your item using a ShopBot or Handibot as the primary tool – feel free to use other techniques and tools as well.

We’re building a CNC’d tree at ShopBot that we’ll use to display all submissions. With this in mind, your creation should be similar in size to a tree ornament (no larger than 3”–8” on any axis) and weigh less than 1 pound. It must fit in a flat-rate box or envelope for shipping. Your final design can be 2D or 3D, as long as it fits within the rest of the parameters.

Submissions must be received by December 18th, 2015.
The tree will be fully decorated by December 24th, 2015 and a photo of the completed tree and the design submissions will be posted to the ShopBot blog and Facebook page. The tree will remain up through New Years 2015.

Please send your item (packed carefully) to:
ShopBot Tools, Inc.
Attn: Holiday Decor Challenge
3333 Industrial Drive
Durham, NC 27704

Please include your name, email, and any information you’d like to share on how you made your piece and any references to resources and materials you used to design and create the submission. Tell us your story, about your inspiration for the project. You and your design could wind up being featured on the ShopBot blog some time in the near future!

THE FINE PRINT (Please Read!)

We encourage you to upload a photo of your submission on the ShopBot Tools Facebook page, but this is not required to take part in the challenge.

By submitting your CNC holiday decor challenge entry, you are authorizing ShopBot to publish your project in upcoming publications and promotional materials, on our websites and in our other e-media, as well as to possibly display it at shows.

We welcome the use of open source or licensed projects, as long as your submission does not include any elements that are protected by copyright without the expressed written permission from the person or institution that holds the copyright.

ShopBot will not be held responsible for loss or damage due to circumstances beyond our control.

Contact Jeanne Taylor at with any questions.

My love/hate relationship with plywood

plywood pile


What an incredible time to be a fabricator! We have digital tools with incredible accuracy and precision and can make just about anything we can imagine. In reality though, we rarely need that much precision… we’re not making artificial heart valves! But if we had a need to fabricate something with ultra precision out of plywood, could we?

Let me start by saying I’m one of plywood’s biggest fans and have done some projects that used 600+ sheets. It’s easy to find, and relatively inexpensive compared to other materials. It is strong for its weight and is available in a multitude of styles and species. It’s available in big sheets and can span large distances, but can be flexible if needed. It can be easily glued, and when fastened face-to-face it holds fasteners well. It can be left plain or covered with paint, clear coatings, veneers, Formica, solid wood, and lots of other finish options.

So what’s the problem?

In many ways plywood is perfect for CNC fabrication, but unfortunately it also can be an incredibly frustrating material to work with. Plywood is almost never as thick as it claims to be and like 2×4’s that are never really 2″ x 4″,  1/2″ plywood is rarely actually a 1/2″ thick. It’s almost always thinner than it’s supposed to be, but not consistently thinner.  A sheet of 1/2″ Pine plywood is almost never the same thickness as a sheet of 1/2″ Baltic Birch. And a sheet of 1/2″ Baltic Birch from one mill may not be the same thickness as a sheet from a different mill.

So how can you deal with this issue? You might think all that’s needed is an accurate measuring tool… you just measure a sample sheet of plywood, and design your chair or slot-together doghouse so that it fits perfectly for that thickness of plywood. And maybe you’ll cut one and it fits together perfectly. You’re a genius!

However, you might not be as much of a genius as you thought! Maybe you made your project during the cold winter and now it’s summer—and now the parts have swollen and are too tight to go together. Or you made a second one on the same day and that one is too loose? What gives?

Wood in general is a “living” material and can change dimensions based on temperature, humidity, and manufacturing techniques. Plywood from a particular mill may vary between batches, and even the sheets within a bundle of plywood can vary from the top to the bottom and from day-to-day because of environmental changes. It can even vary within an individual sheet, a sheet in the middle of a stack will generally gain and lose moisture in the edges but not on the faces. For projects where pieces need to fit together accurately for aesthetics and/or strength this can be a problem.

Should we give up on plywood? Not at all… we just need to learn some techniques for working with it:

What can a Fabber do?

1) Redraw the parts

We’re using tools that can accurately cut what the drawing says to cut, so the first instinct is to just keep redrawing the files and resizing the features to accurately reflect the material you’re cutting. This might be the best method in a lot of ways because you have an accurate drawing that really reflects the material you’re cutting, but it’s a ton of work and has to be done multiple times to hit the sweet spot for material with a wide variation in thicknesses. It also requires saving lots of versions of your files and keeping track of which one is which—not easy to do. If you’re not the designer the changes you’ve made can have unintended consequences, so be careful before making too many changes

2) Modify the existing drawings without redrawing the parts

You can also apply an offset to the drawing without redrawing the parts, essentially moving the edges in or out a fixed amount based on the fit you’re looking for. You can also sometimes scale the design to make everything fit. Remember that scaling is proportional, and if you were to scale things by 3% to make a slot fit just right it might be the perfect change for the slot, but features that were twice the size would show twice the change. Parts that were 24″ would grow by almost 3/4″ which might not matter in some designs, but in others, like chairs, it’s a big deal. Scaling certainly has its place and can work well in lots of cases, but it does require a lot of thought to be sure that you’re only scaling the things that help and not the things that hurt.

3) Make changes during toolpathing



We were asked to fabricate some very cool  Antler Chairs for  SketchChair’s Kickstarter campaign, that were cut from nominally 1/2″ Baltic Birch plywood. Since they slotted together without any fasteners and would be shipped un-assembled and flat-packed, the fit had to be just right or they would either be wobbly when assembled or too tight to put together. We took delivery of the plywood (25 sheets) and started measuring the thickness of the sheets with a set of calipers. And guess what? They varied form .458″ to .487″ within this one batch! If we created the files for the average thickness then only a couple of sheets would fit right, the rest would be too loose or too tight.

Instead of modifying the original drawing by applying offsets, we used a technique called toolpath allowances, a version of temporary offsetting that doesn’t change the drawing, it just affects the toolpath instructions. It works well for slotted designs, quickly making slots tighter or looser with small adjustments because all the changes are small. We got the chairs cut and they turned out great, but it required accurately measuring every sheet and then using that thickness measurement to pick the right file from 5 toolpath files that we had created. That’s a lot of trouble to go to just to make 25+ chairs.

Be aware that when using toolpath allowances there are some weird geometry changes that happen. The dimensions of some features like slots and mortises are changed by twice the allowance value, and others (like tenon lengths) not at all. But when thought through and applied selectively, it can work quite well and leave your original drawing unmodified.

4) Cut and sand to size

You can also cut all your files based on the thinnest sheet and then sand the thicker ones. In many cases the variation between sheets will be more than the thickness of the outside veneer layers, so you will sand through the face before you get the fit right which will look pretty bad! In some situations it works great though, especially if the variation is small, the outside veneers in the plywood are thick, and you are careful with a sander. It works especially well for times that you want a feature like a tenon to be flush with a surface—a little careful sanding can give a really nice finish. In more cases than not you can’t count on sanding for fit, and the chance of disaster with this method is pretty big.

5) Cut for a fit tight and pound it together

One great feature of wood is that up to a point it compresses if you apply enough force. This means you can cut things to fit the thinnest sheets and then when you cut it out of a thicker sheet just pound it together with a blunt instrument! It’s not a particularly elegant solution, but will work more times than you would expect, makes good tight fits, and give you a great workout!

6) Machine the mating surfaces

Instead of modifying the size of entities in the design or toolpath to get a good fit, you can add features to the drawing that let you use the tool to machine just the faces of any sections that fit together so that they are a consistent and predictable thickness. This works best when you zero the bit to the table surface rather than the material top, then the cut depth is based on a known point and not the top face of an inconsistent material. It can give really consistent and accurate fits, but can take a lot of time to cut.

What can Designers do?

1) Design for modification from the start

All of the above mentioned techniques work in the right situations, but the best way to deal with the problem is to use software that lets you modify the design on the fly based on the material you’ll actually be using. This requires a marriage of design thinking and programming skills, and a pretty good knowledge of toolpathing and how changes in one part will affect others. If done right, it can go a long way toward making designs easily modifiable.


parametric table

There are web-based apps that enable this kind of customization like the one shown above from our friends at AtFAB. Affordable parametric design software like Autodesk’s Fusion 360 allows you to define features with variables, instead of a measurement, so that a change to one instance changes every instance. Sketchup’s  Dynamic Components allows you to add customizable features to your models. All these techniques require more work upfront to create the drawing and a strong understanding of the sometimes complicated relationship between features, but in the long run it makes it much easier to make changes based on accurate material measurements.

2) Explore different joinery techniques

cnc joint

There are lots of connection techniques that are strong because of their design. Traditional Japanese joinery immediately comes to mind, along with joints modified specifically for CNC cutting like the fascinating 50 Digital Wood Joints. Other techniques include dovetails, mechanically fastening with wedges, 3d-printed connectors,  zipties, or good old glue.

The opposite of “make the fit tight and pound it together” is to make the fit loose on purpose and then use hardware to tighten it all up and make everything sturdy. There are all kinds of specialty fittings and knock-down hardware systems, but the simplest are screws and bolts. Screws can work fine, but have limited holding power in the edge of plywood, tending to split the layers instead of digging into them. They also require pilot holes to pull the pieces together. If not, they can leave a dimple that holds the parts slightly apart. They also get looser and looser as they are removed and replaced, which makes them problematic for pieces that have to be disassembled and re-assembled periodically.


bolted chair parts

Bolts are my preference. If two pieces are connected face-to-face so that you can get to both sides, traditional bolts and nuts can be used to make strong connections. Sometimes you can’t easily access the other side of a connection or you are connecting the face of one part to the edge of another. In those cases, you can use one of many kinds of threaded inserts to replace a nut. Some are meant to be screwed in, some driven in with a hammer, and some are inserted into a machined slot. Philosophically some of these techniques are a little worrisome when we’re using an incredibly accurate tool, but anything that solves the problem is okay in my book!

3) Design to minimize flush fits and joints

There’s an old woodworker’s trick that’s called a “reveal” that can be both visually interesting and helpful. It involves purposely avoiding flush fits and making parts longer or shorter than they normally would be to create a shadow. When it’s part of the design, it can be both interesting and helpful.

If a reveal doesn’t work for you, go the opposite way and add an overhang. Make the seat of a chair overhang the sides, or a table top overhang the legs, or the tenons extend all the way through the mortice, maybe with a decorative edge

4) Build strength into the design

When getting ready for MakeLocal in New York I learned a trick from the designer of the Valovi stool. It looked like it used regular slotted construction, but when I examined the parts a little better I discovered that the crosspiece that connected the bottom had its slots a little bit further apart than the ones at the top. That way, when it was assembled, the bottom slat built a little tension into the piece and helped stiffen it up quite a bit.

My intention is not to discourage you from using plywood. Even with its shortcomings it’s an amazing material and my material of choice for most projects. Just be aware that your CNC tool is just one part of the digital fabrication equation and that sometimes problems arise that require creative solutions.

Homebuilt Kits enable anyone to easily build a code-compliant home.

Habitat for Humanity home with Homebuilt framing

The housing market crash and economy-wide downturn of 2008 shook the lives of millions of Americans to the core. People lost jobs and started losing their homes. People stopped qualifying for mortgages to buy a home. One person’s response was this: Dennis Michaud, a successful architect and designer of high-end pre-fabricated homes, began to shift his focus to enabling people of lesser means to have their own home — without needing to qualify for or take on a burdensome mortgage.

Dennis’ company, Homebuilt, represents a whole new approach to affordable homebuilding. The company’s products are kits for code-compliant structures that you can build all by yourself (or with a friend, to make it more fun). Anyone can put together these buildings with no previous experience needed, and no tools required beyond a mallet and a hand-held power screwdriver (the kits can, of course, also be assembled by local pros). The structural pieces of a HomeBuilt Kit are precision cut, including the obvious numbering of each part, using a full size ShopBot Tool.

Lumber and Plywood Kit fresh off a Shopbot

Lumber and Plywood Kit fresh off a Shopbot

Check out this quick video of the Shopbot cutting the lumber….

I first spoke with Dennis over a year ago, and wrote about his vision for Homebuilt on the blog. Fifteen months later I thought it would be interesting to check in with Dennis on the status of his venture.

“Things are going really well, and I’ve learned a lot,” said Dennis. “We’ve sold about 15 kits over the past year, which could be viewed as not that many; but at this point I am most interested in learning about what customers like about the kits and what they want from a kit, so this level of activity is just fine.”

Dennis told me that he’s found that most buyers are interested in having their kits customized a bit to meet their own vision. Following their interest, Dennis has focused efforts on being able to fulfill on these custom requests.

Here a sample of the kit designs that Homebuilt offers:

"The Escape" Kit prices: $6,500 for full structure, up to $36,000 for everything (see below) beyond the foundation Exterior Dimensions:  27' x 20' x 15' (height) Conditioned Square Footage:  450 square feet Full Kitchen, Full Bath (shower), 3 Closets, Exterior Storage Nook Energy-efficient Heating, AC, and Hot Water Energy-efficient Windows and Doors Easily connect to power grid, existing house power, or solar panels No sewage needs - includes Swedish-made Seperett composting toilet

“The Escape” Kit prices: $6,500 for full structure, up to $36,000 for everything (see below) beyond the foundation
Exterior Dimensions: 27′ x 20′ x 15′ (height); Conditioned Square Footage: 450 square feet; Full Kitchen, Full Bath (shower), 3 Closets, Exterior Storage Nook
Energy-efficient Heating, AC, and Hot Water; Energy-efficient Windows and Doors; Easily connect to power grid, existing house power, or solar panels
No sewage needs – includes Swedish-made Seperett composting toilet


"Cabana"  From the site: This kit is ideal for anyone needing some extra space for something special.  Whether it's for a backyard office, an art studio, or just a place of your own to relax: pick a size, some options for finishes, and call a friend over to help you put it together.  Typical assembly time between 2-3 weekends, depending on the finish selections. See the Homebuilt site for size options and pricing.

“Cabana” From the site: This kit is ideal for anyone needing some extra space for something special. Whether it’s for a backyard office, an art studio, or just a place of your own to relax: pick a size, some options for finishes, and call a friend over to help you put it together. Typical assembly time between 2-3 weekends, depending on the finish selections.
See the Homebuilt site for size options and pricing.

“An important part of my development curve has been working with the production support team at ShopBot Tools to configure the ShopBot to handle non-standard materials. You generally think of a ShopBot as a tool for handling sheet goods such as 4 x 8 plywood. We’ve figured out how to use the tool to handle 2×4, 2×6, and 2×8 lumber. The challenges presented by this lumber is that pieces can be warpy and arrive with non-standard thicknesses. On the machining side, we’ve figured out hold-down issues by creating robotic ‘grippers,’ and on the software side, we’ve built in the intelligence that indicates where a piece of material needs to be held down appropriately so we can achieve the cut.”

Dennis says that he now has a process in place that makes it easy for the tool operator to work with lumber efficiently and easily.

Amateurs frame up a home with a Homebuilt Kit.

In the very early phases of the company, Dennis prototyped and built small structures such as backyard storage sheds. Over the past year or so, Dennis has wanted to be able to learn how his vision — for amateurs to build a livable home — would work in practice. The opportunity has come in his relationships with Habitat for Humanity.

Habitat for Humanity home with Homebuilt framing

Habitat for Humanity home with Homebuilt framing

The images you see below illustrate the use of a Homebuilt kit by the Springfield, MA chapter of Habitat for Humanity.  “In this case, the project had an extremely tight deadline – with funding contingent upon the deadline being met,” explained Dennis.  “Construction had already begun, and Habitat made a last-minute request for Homebuilt to provide the interior framing for both of two stories.”

“The Homebuilt kit fit perfectly into what was already started – adapting even to a later, major design change – and turned what could have been weeks of work into an easy weekend completion. All twenty-three (23) walls were assembled by a crew of 3-5 volunteers (including the future homeowners), without building experience, in about 8 hours… using only small, cordless screwguns and plastic mallets (not even tape measures!). The Homebuilt kit also removed the need to use saws on the site, making the build safer, faster, and more inclusive for volunteers without experience or comfort with using dangerous tools.”

Looking ahead, Dennis notes that the financial hurdle — a need for about $50K to fully build one of his kit homes with all of the amenities — is one that needs to be addressed if people of modest means will be enabled to participate in this DIY movement. A note of hope: He foresees that the growing micro-lending, or peer-to-peer lending, trend can enable a lot of people to be able to build for themselves. An example Dennis gave, “If a micro-lender can see that a $50k investment will allow someone to put up a quality, code-compliant 1,200 sq ft home in a neighborhood of homes that are valued around $200K, then that’s a great investment to make.”