Introduction: Ratchet Strap Chair

This chair is made from a 1/2 sheet of plywood, uses no glue or fasteners, and is held together by a single ratchet strap. I made this chair because I was interested in the forces at play to make a chair stand up: the different parts in tension and compression that make up the structure. It's also part of a broader study I'm up to experimenting with ergonomics- trying variations on the dimensions and posture of Mies van der Rohe's Barcelona Pavillion Chair (1929).

Step 1: 3D Model

I designed this chair in Fusion 360 (it's recently become my go-to modeling program). The file is attached here, please download it and tweak it yourself! Fusion 360 is free for students and hobbyists, and there's a ton of educational support on it. If you want to learn to 3D model the kind of work I do, I think this is the best choice on the market. Click the links below to sign up:

Student/Educator

Hobbyist/Startup

Step 2: Tools and Materials

Tools

  • I used a Metabeam Laser Cutter to cut out the pieces, because it's fast and we have one. A Shopbot would make short work of this, and you wouldn't have any burn marks to manage later.
    • IF YOU DON'T HAVE A CNC MACHINE: Before I had access to CNC machines, I did lots of projects that were just as complex using full-scale prints from Kinko's, spray-gluing them to plywood, and cutting them out with a jigsaw. Check out my Lace-Up Chair instructable for more details on doing it that way.
  • An orbital sander, finishing at 180 grit.
  • OPTIONAL: I also used a table router with a 1/4" fillet bit for some nice rounded edges.

Materials

  • 1/2 sheet (4' X 4') of 3/4" plywood.
  • One ratchet strap (1" strap).

Step 3: Cut Out the Pieces

My Metabeam settings are as follows:

Material: "Hardwood .25"

Power: 100

Speed: 40

Step 4: Finish the Pieces

I started at 100 grit to get the burn marks and smoke residue off the wood, then stepped down to 180 grit for a smooth finish.

I used the fillet router bit on all of the edges of each piece.

Step 5: Assemble the Chair

  1. Slot the truss into the back legs
  2. Add the front legs
  3. Add the seat
  4. Slot in the seat back

Step 6: Strap It Together

Each piece has a notch to keep the ratchet strap in place. The ratchet strap is looped around the seat, the front leg piece, the truss, and the seat back. When the ratchet is tightened, the chair becomes rigid.

Step 7: Sit in the Chair

It's pretty comfortable, and super-rigid! I think if I go for another iteration, i'll make the back legs less pointy and try to use even fewer pieces.

Comments

author
Shawn Stanford made it! (author)2014-09-08

So, here's the thing: I'm a Soldier and I deployed to both Iraq (in '04) and Afghanistan (in '08). Among the egregious incidents of poor planning and spending is the fact that the military will actually haul huge, heavy, expensive pieces of civilian-style office and barracks furniture into war zones. But, we also take enormous amounts of plywood for construction of shelters (barracks, offices, etc.). A suite of simple furniture designs (bunks, desks, shelves, etc.) cut from 3/4" plywood, slot-and-tab assembled, and held together with ratchet straps would be invaluable!

author
JON-A-TRON made it! (author)JON-A-TRON2014-09-08

That's a great idea. People have been making flatpack furniture for long-term camping trips (burning man, etc.) for a while- it's a great way to make sturdy, comfortable furniture without having to ship all that volume. I think the dead-simple design of this project is probably even better for this kind of use: http://www.treehugger.com/sustainable-product-desi...

All the zoomy lines and fussy details of mine require more time to cut out by hand, not so efficient.

This is another awesome flat-pack project, housing for disaster areas: http://www.wired.com/2013/11/a-disaster-relief-she...

The idea is that you show up with a CNC machine and a ton of 3/4" plywood, and you've got all the buildings you need.

author
jmwells made it! (author)2014-08-07

Update on my comment. Did the cardboard thing. Worked after a fashion. Until a 350lb friend decided to plop down in it. Legs folded.

author
JON-A-TRON made it! (author)JON-A-TRON2014-08-07

Pictures please!

author
jmwells made it! (author)jmwells2014-08-07

I was preparing to shoot some when Carl crushed it. The legs were still too pointy and thin. I'm going to put on another layer, or two at the bottom of the legs. Perhaps feet too. I used contact cement between layers, the bond didn't break. The paper did. I went five layers of cardboard, for a thickness of about 3/4". The seat and back held up fairly well. We used it for a bonfire starter. Next time I'm thinking seven layers, 1"+,-. If the prototype holds up I'll spray the pieces with an epoxy paint for durability and water resistance. Got other projects right now, will update in a few months.

author
PetersPJones made it! (author)2014-08-04

do you have pdfs of the pieces rather than fusion 360 format?

author
JON-A-TRON made it! (author)JON-A-TRON2014-08-05

Just uploaded a full size PDF to Step 2. If you ever need to convert a DWG file to PDF, just do it on this site for free: http://www.zamzar.com/convert/dwg-to-pdf/

author
lensman888 made it! (author)2014-08-03

Great for moving day and you already have the strap to tie up the pieces!

author
JON-A-TRON made it! (author)JON-A-TRON2014-08-05

Hadn't thought of that! I cut the strap so that I wouldn't have to figure out what to do with the excess, but it makes sense to come up with some kind of attractive clip solution so you can still use the strap for other purposes.

author
fred3655 made it! (author)2014-08-01

Now for the ratchet strap table and foot rest! This awesome, can't wait to make one.

author
JON-A-TRON made it! (author)JON-A-TRON2014-08-05

That's the plan! Can't wait to see what you come up with.

author
andrea biffi made it! (author)2014-08-03

great project!

author
Todd Gehris made it! (author)2014-08-02

That thing is freaking cool!

author
travderose made it! (author)2014-08-01

This is rad! Great job

author
JON-A-TRON made it! (author)JON-A-TRON2014-08-01

Thank you!

author
CobyUnger made it! (author)2014-08-01

Cool dood!

author
JON-A-TRON made it! (author)JON-A-TRON2014-08-01

Thanks Man!

author
rimar2000 made it! (author)2014-07-31

Interesting design.

author
JON-A-TRON made it! (author)JON-A-TRON2014-08-01

Thanks! I'm hoping it's the first of many ratchet strap furniture pieces. I got the idea from this project: http://dornob.com/no-nails-sans-screws-ratchet-strap-wood-furniture-series/#axzz39A6fNK66

author
howtobasic made it! (author)2014-08-01

So ratchet ?

author
jmwells made it! (author)2014-07-31

Think I'm gonna try cardboard, laminate it with alternating internal fibers, and make the legs less pointy. Looks great for a picnic chair. Easy to pack and move.

author
JON-A-TRON made it! (author)JON-A-TRON2014-07-31

Cardboard's a great idea. I would recommend laminating so that they're at least 1" thick when you're done.

You're so right about the pointy back legs! They're on a 1/2" radius, they should be more like a 2" radius like the front legs are.

I agree, this is best suited for outdoor use. But that means I'll need to finish it (everyone's least favorite part).

author
mcep5f2009 made it! (author)2014-07-31

Pretty cool!

author
crank_girl made it! (author)2014-07-31

Rather neat! B)

author
JON-A-TRON made it! (author)JON-A-TRON2014-07-31

Thanks!

author
amandaghassaei made it! (author)2014-07-31

pretty pics!

author
lebowski made it! (author)2014-07-31

Nicely done!

author
audreyobscura made it! (author)2014-07-31

AWESOME!

About This Instructable

21,106views

333favorites

License:

Bio: I'm a full-time Designer at the Instructables Design Studio (best job ever). My background is in residential architecture, film set design, film animatronics, media ... More »
More by JON-A-TRON:Retro Bluetooth BoomboxZoetrope Fidget SpinnerLearn to Draw
Add instructable to: