Mechanical Foamcore Models

I’ve been asked a lot about how to get started building mechanical contraptions and I always mention Keisuke Saka’s excellent book Karakuri, how to make mechanical paper models that move. The book has actual printed template pages that are meant to be torn out and used as building materials. The first time I encountered this book it was on loan from a friend that had built most of the models already, so I set out to replicate the basic mechanisms using materials that I was comfortable with, and that were quick and easy. Foam core, paper clips, skewers, paper, and plastic bits from yogurt containers.

I like this approach because paper craft can be intimidating for new makers as it requires patience an precision, and when it comes to working mechanical models it is sometimes easier to take a more forgiving approach.

These pieces are not new work. They were the precursors to the one month of small machines project so I wanted to document them even though they aren’t pretty. Page 6 of the books offers a summary of the basic mechanisms:

Most of the models are built on a foam core base that is roughly 2.75″ x 2.75″ by 2″. And for the completists out there, I didn’t build a Crank B.

Cam A – The rod makes a repetitious vertical motion
Cam B – Two rods make a vertical movement alternately.
Cam C – The rod makes a repetitious horizontal movement.
Cam D – The rod slides repeatedly in a linear motion.
Crank A – The rod sways repeatedly in a circular motion.
Crank C – The turning of the crank is converted into vertical motion.
Gear A – The gear turns horizontally to the handle.
Gear B – the gear turns perpendicularly to the handle.
Geneva Stop – A wheel makes turns in a discontinuous rhythm.

For making the gears I used I printed them on paper, glued on the foam core and then cut by hand. The Gear B needs some beveling to make it work.

This is a really good set of mechanisms to get started. Each mechanism will have a set of problems to solve, and solving these problems in whatever material you choose will translate to other materials. I like foam core and hot glue, but you might choose cardboard or wood. Good luck with your builds!

Also if you want an easy way to share these, grab them from my giphy channel here: Cam A, Cam B, Cam C, Cam D, Crank A, Crank C, Gear A, Gear B, Geneva Stop.

walking man automata


One of the most popular pieces from the small machines series was the walking man from November 6. I received videos and pictures of other people making their own versions and recently a school in Barcelona used the idea for their classes, this really made me happy because it’s really rewarding to inspire others to make something. My intention with first designs was to use common materials and methods to keep them accessible, but I can’t deny my love and appreciation for digital fabrication so I decided to design a version for the laser cutter.

I’m still using wood and paper but decided to skip the use of wire. In this case the simple crank works well made out of wood. I’m using 3 mm birch plywood and some 90 lb paper but the paper thickness doesn’t affect the design very much so use whatever you have at hand. The paper is glued with regular white glue and you might have to glue the wood depending on the kerf of your laser cutter. Download the files from this github repository.

And check out this embedded video for the assembly. I would love to see your builds so please tag me on social media or send me an email.

A new high contrast baby mobile

A previous post described my process for making a plywood mobile. I’ve since added a new tool and some materials to my process so I thought it would be relevant to document this latest build.

This mobile was commissioned by a close friend (disclaimer, I struggle a lot with commissions so I don’t take them easily). I started by drawing several sketches by hand and then putting them into a digital document as a mockup. I made several but I’ll show you only the one my friend chose:

mobile mockup

The fish are a salmon and a flounder since I wanted to have some species from California. I’m particularly proud of the salmon drawing. At this point I converted the images to vector drawings and started cutting them on the laser cutter. I used 1/8″ birch plywood. Every piece was cut in two parts that were mirror opposites. The plywood had masking tape which allowed me to precisely cut the mask for the shapes I had drawn.

In order to glue the pieces, I made registration holes that fit a paper clip. Conveniently I could later use the registration holes for hanging the pieces. The holes were 0.03″ in diameter and 0.03″ apart.

I pre-treated one side of the plywood with spray-on shellac and a light sanding before applying the masking tape. I found that a light coat of shellac allows me to remove the masking tape without raising the grain and it’s a good surface for painting.

two salmon pieces coming out of the laser cutter

Flounder ready to be glued with the paper clips aligning the two pieces.

Never too many clamps when gluing. I used plain wood glue for this part.

The fun thing about scoring the masking tape is that I don’t have to re-trace the drawings and I get to paint one of the colors with a blunt tool. For the black, I did two coats of Montana water-based acrylic paint, and for white two or three coats of Golden high flow acrylic. I like high flow acrylic because it can be applied with a brush or a quill for finer detail.

acrylic paint
acrylic paint

Weeding out the mask to uncover the black sections.

Ready to paint

It’s nice to wear gloves for this step.

Peeling the mask for the white sections.

There was a little bit of bleed.

The bleed wasn’t too much of a problem on this project because I had a two-color palette but, incidentally I just saw this video where they suggest applying a clear coat before painting to clog the edges of the mask. I have to try that next time. On the last picture, I’m applying paint with a small brush and a quill for small areas.

Ready to hang!

I didn’t do all the pieces at once because I wasn’t sure the proportions were right on the mockup. I worked from the bottom up and at some point, I even re-cut the pieces that go on the flounder. The process could be more efficient but at the end, I was happy with the results.

For the lines, I like using bead stringing wire. It’s flexible, strong, and it looks really clean. The one downside is that you need to purchase crimp tubes and a crimping tool. I think you could skip the crimping tool and use regular pliers if you are in a pinch. The crimping tool just gives you a slightly cleaner and more consistent look.

In order to make the pieces face down for the baby to see, I used this triangular arrangement:

Perhaps the most challenging part of this project was taking pictures of the finished product. It’s really hard to convey the experience in still images. Here are my attempts, thanks for reading!



Laser cut posable arm lamp

I started using an inexpensive video LED light for taking pictures and then I realized it doubled quite nicely as a desktop lamp. Adam Savage suggested something similar as a custom workbench lamp.

My first attempt to make some arms was too simple and flimsy so I decided to replicate the classic design of the posable lamp base with materials I had at hand. I got some inspiration from a design by Matthew Phillips I found on Instructables (he also provides cut files if you wanna go that way). He used rubber bands instead of springs which I thought was pretty clever.

I drew mine from scratch because I wanted a specific size and I had a bunch of #8-32 screws to assemble it. I also made a base that fit the needs of my current desk but I can see how this can be improved with some sort of clamp system.

The base is made out of 3/4″ plywood and its wedged in between the wall and the desk.

Accidental Pixar

Rubber band for tension and wing-nuts to secure it when needed.

Feel free to use this SVG file for your own needs and inspiration with some notes and disclaimers:

  • I used¬†#8-32¬†machine screws but I made the holes with a really tight fit to provide some extra friction.
  • Where there are slots they were sized to the plywood I used and the kerf of my machine, so you might want to adjust that to your needs. My plywood was 0.125″ thick.
  • The holes for the rubber bands are sized to the bamboo skewers I had at hand, so as with everything else your mileage may vary.

It’s a simple design so I’m sure you can adapt it to your needs quite easily.

There is a very similar version of this post on the glowforge forums in case you want to glean some extra wisdom from the community.

on the Root Simple podcast

Kelly and Erik have been a source of inspiration to me for years. Their blog,, and their books¬†have enriched my life and given me ideas for lots of experimentation. Beekeeping, fermentation, baking, gardening, organizing, and even cleaning. At some point, they’ve helped me directly or I’ve reached for their solutions (we use their “almost universal cleaning spray” daily around the household, a blend of 50/50 vinegar and water). That’s why I was so excited to be on their podcast.

We had a wonderful conversation that spanned many topics. Erik was very encouraging and he almost made me forget there was a microphone in front of me. You should head over to their website to listen and check out the show notes. Although if you are in a hurry you can just hit play right here:

Listen to “108 Artist/Maker Federico Tobon” on Spreaker.

Here are some bonus pictures and notes:

I found the actual comment about the Michel Pollan inspired rules for social media. I wrote: “Post positive things. Mostly yours. Not too much.” It’s not a very strict rule, and I would probably reevaluate it if I had different goals for my social media presence, but I mostly abide by it.

My CNC router is specifically a ShapeOko 2 with a few modifications. It lives in the utility room of my apartment it perhaps it occupies more space than it deserves.

Here is some information for the CNC aficionados: That red box houses the electronics (power supply, Arduino, GRBL shield and motor controller) and I¬†added some buttons and switches to the top for easy access. Other mods are the LED strip on the Y rails and the HDPE waste board. It’s humble by today’s standards but I do enjoy the little beast. Behind the red box, there is a raspberry pi that helps me control it via WIFI using the wonderful chilipeppr¬†grbl workspace.

My ShapeOko 2

This video shows the ShapeOko 2 in action making some pockets for the color pencil inlays:

The 3D printer turned laser engraver we mentioned is a circa 2012 Solidoodle 2. The company has gone extinct but some things stay alive beyond their creator’s intentions. I followed the directions on this instructable almost to the letter to turn it into a laser engraver. It’s not pretty but it does some jobs.

My Solidoodle 2 3D printer with a laser head

In action while working on the Opposable Thumbs Challenge:

We were talking about cat training on the podcast so here is a video of our cat Kuro jumping between two tables and doing a high five:

Erik mentioned some of my sewing projects. Some time ago I designed and made a lot of messenger bags. My messenger bag pattern was based on the golden ratio, more of an intellectual exercise than an actual belief in its powers to make things better, but it was fun:

golden ratio messenger bag

messenger bag pattern
The messenger bag pattern


And finally, this is a picture of the beehive we moved to the roof with Erik’s help, I wrote a short blog post when we did it with some more details and a couple of videos.

Our beehive back in 2010

Head over to Root Simple for the rest of the show notes.

a podcast on crafting security

This month I was a guest on episode #8 of the opposable thumbs podcast. The podcast is hosted by Rob Ray and Taylor Hokanson and on each episode, the hosts and a guest tackle a creative challenge and then discuss the results, discoveries, problems, and solutions. I was very excited about it when I listened to the first episode so a made a gift and sent it their way last April.

This was my first podcast and it was a really nice experience. Rob and Taylor were super welcoming and very organized. They had an agenda and documents about what to expect as a guest, which was very helpful. And while recording the podcast we were able to exchange notes and pictures using slack.

I wanted to post a couple of pictures of the thing I made here but you should go listen to the episode and look at the other projects on the opposable thumbs website.

Part of my inspiration was XKCD comic number 936 on Password Security. My intention was to make a sort of analog password generator that looked good and was nice to handle. So I made a “flexi-cube” (I’m not sure if this is the technical name). This video tutorial by pocket83 was very helpful, I mostly used it for inspiration but it really covers the basics if you want to make your own.

Part of the fun was making a jig for cutting the poplar squares using the table saw sled:

cutting the grooves

This is a closeup of the Jig, I had to add a thumb-rest after cutting a few cubes because my thumb was getting sore:

After cutting the cubes I engraved the words using the laser on my converted 3D printer (an old solidoodle-2 with a 30 dollar 1/2 a watt purple laser that I modified following this instructable).

engraving with a laser

After engraving the cubes I assembled them using elastic hair bands. I made 3 different versions: the first one has only English words, the second one is bilingual (English and Spanish) and the third one has Japanese words written in Hiragana with their corresponding translation. I finished the poplar with olive oil to bring out the color.

English Version is shown flat

English and Spanish version is shown as a cube

This is, of course, a proof of concept, but the basic idea is that you would be able to generate simple 3 or 4-word memorable passwords by playing with it. There are a lot of possible combinations. Each version has 27 cubes with 2 words per face. That is a total of 324 words in the English language one and 162 words on the bilingual ones. It’s also just a fun toy. On the subject of passwords, don’t take my word for it, there is more to it and there are more sophisticated ways to generate them, do you research.



diy belt sander

In my last post I documented my budget bandsaw repair. This one is about documenting a little belt sander I built with mostly found parts. There are tons of home made belt sander builds on the internet and I don’t feel like I’m adding anything new, but I still wanted to put it out there, maybe I will inspire your own build.

I tried to keep it as simple as possible and the most obvious consequence of doing that is that it’s not particularly pretty. But it works and I made it with minimal parts and expense.

This sander uses a 1″ by 30″ belt. That means the belt is 1″ (inch) wide and has a 30″ circumference. It’s useful for sanding small parts and inside corners. It’s also very easy to change the belts in case you want to use different grits. It’s also particularly nice for sharpening knives and other tools.

The starting point was this 1/2 hp motor from a pump that a friend was getting rid of:

My first step was to drill and tap the axle:

Here I’m starting the tap with the drill press to keep it straight:

And then finish it with the hand holder:

I used a 1/4″ – 20 bolt but in retrospective I think something thicker would be better.

The next step was to cut and glue a couple of plywood circles:

And mount them to the motor:

This is after some turning and sanding. I secured the motor to the table and used a chisel against the 2×4 improvised tool rest to turn the piece and give it a crown:

Not bad:

After that I started working on the idler pulley. I had a skateboard wheel, I secured it with a bolt and some washers:

And mounted it on the drill press:

I did the rough shaping with this rasp:

Finished it and crowned it with this set up. The Blade is secured to the 2×4 with a screw. The 2×4 is clamped to the drill press table. This allows for fine control of the turning.

Detail. This blade is really thin but it did the job. I think if i were to do it again I would use a thicker utility blade.

The next step was the structure. I started by making a sleeve for the metal post:

Then I positioned this door hinge on top of the sleeve

And trimmed the excess metal:

After that I added the tension adjustment bolt. In this picture I’m setting it up to weld the nut in place:

The tension adjustment bolt needs to rest on a flat surface so I added this piece to the main post:

This is the main post after welding the base:

And it comes together when bolted the the plywood base:

After I made sure everything was working I took it apart and painted the metal parts and made some wood knobs. The top knob adjusts the tension and the side knob tilts the wheel to adjust the tracking.

Added some 3/4″ plywood for the front and the table:

In order to mount the switch I hogged out a pocket with a router bit mounted on the the drill press. Not super clean but it does the job:

The switch. Wired and protected with shrink-wrap tubing:

Here you can see the switch from the front and other final details. That knob in the front threads onto the table to secure it in place. I wanted to be able to remove it easily for changing the belt and cleaning.

And here is a closeup of the backing plate. I found an aluminum l-bracket and cut it to size:

And it’s done. I finished it with shellac. I love the feeling of making your own tools (almost) from scratch. I mean, if I were to buy a $70 belt sander I wouldn’t put it on my resume.

Budget bandsaw repair

The “workshop” part of the wolfCat workshop name means a few things to me. One, it is a hope: I aspire to build that ideal workshop, my ideal workshop. For years I’ve made do with whatever is at hand: empty balconies, borrowed kitchen tables, benches in forgotten places, corners in someone else’s garage. I’ve also worked in very nice workshops with really clever people. I love workshops and I love making. My current situation is not that bad. I share a one car garage with a group of folks. We have a few nice tools and as shared spaces go this one is pretty organized.

For a while now I wanted a bigger bandsaw and had been looking online for used deals. I had also been considering building one following Matthias Wandel’s plans. As it happened this ended up being something in between. A little disclaimer: I posted a short version of this build on imgur.
I happened to find this bandsaw listed for $70 USD with some crappy pictures. I texted the seller to ask if it was still available and he told me someone had stolen the table and I could have it for $30. I figured I could make a table and said I’d pick it up. When I got there the top wheel and the tension mechanism where missing too. I took it for $25 since I was there already. Worst case scenario, I thought, ¬†I could use the motor for another project.

The finished project

I didn’t document the building of the tension mechanism but this is what I came up with. A 1/4″ plate with some 1/2″ – 13 bolts and nuts. The tilt adjustment is a solid rod I tapped with a 1/4″ – 20 screw.

Then I added the clamp for adjusting the tension. Here it is seen from both sides:

Attentive bandsaw users might notice I’m not using a spring. I just didn’t have one strong enough and I wasn’t about to go buy one. I decided to just try it and add one later if necessary.

Next I started building the wheel. I took a lot from watching Matthias Wandel’s bandsaw builds on youtube so if you are looking to do something similar I can’t recommend him enough. Check out his build at

I started by cutting two 14.25″circles (the final wheel needed to be 14″) with this simple circle cutting jig out of some 3/4″ birch plywood:

Then some holes. Mostly convenient for clamping (next step) and for rotating the wheel with your hand when adjusting the blade:

Gluing the two circles. Is it possible to ever have too many clamps?:

The next step was to make some bearing holders. That sketchy looking circle cutting tool is very convenient if you want to cut really precise circles. I took about 4 attempts until I found the right size. The bearings are press fit on the wood so a very tight fit is important.

Mounting the bearing by pressing it with the vise:

And this is how I made the axle. I call it the poor man’s lathe. 1/2″ bolt mounted on the drill press and the angle grinder with a flap disk to shape the nuts.

Making sparks:

Halfway there:

Checking the fit:

The final result. I think I had to shape the outside nut a bit more later on but you get the idea. I’m not so sure that this 1/2″ bolt is going to last though. I’m expecting it to bend a little. Perhaps I’m going to have to get a real solid axle a few months from now.

Once I had the axle I was able to mount the wheel to the table. The screw mounted to the wood block is for truing the wheel. There are two bearings. One of either side of the wheel. You glue one first, then you assemble the whole thing and position the second one making sure the wheel doesn’t wobble. If you want a better explanation see how Matthias does it in this video

And this is how I turned the wheel. Another sort of poor man’s lathe. I made a “tire” with inner tubes around the drill chuck. A spring holds it tight against the wheel. The 2×4 on the opposite side is screwed on the table and that is the tool rest. I rounded and crowned the wheel using a couple of woodworking chisels. Side note: in the gif it looks like the wheel is spinning counter-clockwise. But it was actually spinning clockwise:

Once the wheel was rounded and crowned (incidentally this video on how crowned pulleys work is pretty good) I balanced it by drilling holes where it was heavier.

And a final coat of shellac to make it last:

A 10″ bicycle wheel inner tube is the tire. Another one of Matthias’ brilliant ideas:

The top blade guides were missing too so I made a new set with some plywood and walnut. This was the hardest wood I had lying around, we’ll see how long it lasts. Someone on reddit suggested dipping the guides in hot wax for lubrication. I’ll be trying that soon.

Top blade guide installed on the saw:

The table trunnions are based on a circle with 2″ radius:

This started as a quick prototype out of plywood scrap and ended up being the final one. You know how it goes:

The trunnion assembly:

I shaped the washer so it would rest flush on the round trunnion:

Filed a square hole for the carriage bolt:

And this is how they look on a temporary table I made out of crappy pallet plywood:

I made the final table out of 3/4″ birch plywood. Here it is with the jig I made to cut the insert pocket with the router:

The pocket is 1/4″ deep for using 1/4″ plywood inserts. I had to make the¬†round corners into square corners with a chisel:

Then I made the miter slot using the table router:

Mounted after a few coats of shellack.:

After cutting the slit that allows you to replace the blade I added this extra piece of wood that keeps the table flat. It swivels out:

And it’s held underneath by this knob. You can make some neat knobs once you have a semi functional bandsaw:

I thought the switch was in a very awkward place so I decided to rewire it:

After a trip to the Home Despot. That part to the left is a strut clamp, you can find them in the electrical section:

Very convenient that strut clamp:

New switch position:

I felt I needed a switch fence to avoid starting the bandsaw unintentionally:

More shellack:

You know. Going for that metal + wood look:

The last touch was adding a light:

I had one of these IKEA JANSJ√Ė LED work lamps and after taking off the base I mounted it to a piece of plywood and clamped it to the bandsaw arm. I might make something nicer in the future but this works ok for now:

After using the light for a bit I got tired of switching it on and off so I added this outlet under the base. Now the main switch turns the motor on AND also the left side of the outlet where I plugged in the IKEA light. I figured the outlet would be convenient if I wanted to add dust extraction in the future:

Cat Tax:

I hope my budget bandsaw build was interesting to you. I just love bandsaws and this one has become one of the most used tools in our garage.