Folding Chair for Hand Tools or CNC Router

Intro: Folding Chair for Hand Tools or CNC Router

This folding chair was designed with the intention of laying it completely flat for storage (based on a Youtube video by "Mr. NK," which you can access at https://www.youtube.com/watch?v=yyEmcc5JLaY). We modified the video's design so that it has a higher seat, which is better for accessibility and comfort. It requires a roughly flat surface, so it can be used outside on even-surfaced lawns, in parking lots, or indoors. We made multiple prototypes of the chair before finalizing the design. At first, we used hand tools, which was effective, but not as clean as when we used a CNC router with a 1/4 inch bit. Either works well, but the attached drawings' dimensions in these instructions were made specifically for hand tools.

STEP 1: Dimension Drawings

a. If using the CNC router, either download the CAD file below, or draw your own with desired dimensions.

b. If using a jigsaw, make your own drawing of the chair, using the pdf. attached below.

STEP 2: Cut Out the Chair

a. Cut out the chair using the CNC router, using a 1/4 inch bit.

b. Cut out the chair using the jigsaw. Try to get as close to 1/4 inch margins as possible. It helps to trace an outline of the chair on the plywood first, using the drawing's dimensions above.

STEP 3: Sand the Curve at the Top of the Chair

3. Use a belt sander to trim down the back of the chair, so that the piece of wood is slightly curved. This makes it a more supportive and comfortable back-rest.

STEP 4: Use a Wood Router

4. Use a wood router to smooth out the sides. Use sandpaper to smooth out the sides, if desired/necessary. Then, use an orbit sander to smooth the surface of the entire chair. 

STEP 5: Sand the Chair

Use sandpaper to smooth out the sides, if desired/necessary. Then, use an orbit sander to smooth the surface of the entire chair. 

STEP 6: Make the Hinge Holes

Use a drill press to create holes for the hinges.

STEP 7: Screw on the Hinges

Using a drill, screw on the hinges. We used an internal hinge method for the upper legs of the chair at first, but the plywood actually broke due to its lack of thickness. We recommend using three hinges in total: one for the seat as shown above, and two for the chair legs.

STEP 8: Stain the Chair

Stain/finish the wood. Make sure to do this carefully to avoid drips.We used a blue and medium colored stain for our chairs, then coated them in a polyurethane sealant.

STEP 9: Optional: Attach Locking Mechanism

Attach some sort of locking mechanism to keep the chair from unfolding during transport. This is not completely necessary if the chairs are made for the same location and don't require frequent movement.

STEP 10: Done!

The chair is complete! We hope these instructions were helpful!

Comments

[HeinrichS]

Really nice design, and it seems easy to build. But how strong is this - any idea what the maximum weight limit would be? The hinges and seat locking pin seems to be the weak spot, and 3/4 plywood might not be strong enough to support 350-400lbs like other heavy duty folding chairs... Comments are welcome :-)

[ParKit]

We tested our chair to 350lbs but did not go to the point of failure. The plywood substantial, and the quality of the hinges can certainly play a role.

[ParKit]

Ours held someone in the ~350lb neighborhood, but you are right to see the hinges and seat locking as potential week points. We pull all of our stuff with an electric bike, so we make some compromises based on limiting the weight we are pulling. I think 1" birch (Baltic) ply would work well.

[infradata]

Mine is 3/4" OSB, not plywood, It holds a 350lbs man (my father in law) and a small dog at same time with no issues, Press Rivets can be used over screws

[charlessenf-gm]

At first I thought to add another section of plywood to the seat bottom - as wide as the hinged area and the depth of the seat (less the size of one side of its hinge) to add strength. capacity. That should help.
They I recalled that 'they' make thicker plywood - one inch for sure and quite possibly thicker. Then, as I typed this I thought about laminated lumber - so why not simply glue two sheets together and make a thicker chair?
Or use two sheets of thinner ply and a torsion box approach - after all, if you've got a CNC what's stopping you?

[ParKit]

Our limitations are that we carry these on a bike trailer as part of a larger kit of parts to create a small parklet. Thicker plywood will certainly provide strength/capacity, but it will be significantly heavier. Our chair has supported approximately 350 lbs. We have not tested it to the point of failure.

[ParKit]

All great thoughts! Let us know if you make one.

[cburg]

This looks to be a great project, one that I could do with my grandson and granddaughters. I would like to know what the seat height is when open. What are your thoughts on scaling this up and down for different seat heights. with bad knees I need a chair that is higher then most others.
Thanks for your time investment for both the project and sharing...

Cburg

[ParKit]

The seat height as designed is approx. 18". It is moderately adjustable within the current design and dimensions in that you can unfold the legs to a greater or lesser degree and adjust the placement of the mortise in the seat. The limits in going higher will be in the sacrifice of stability. I see no reason that you could not make changes to all of the length/height dimensions to make the seat height lower or higher as desired.

[ParKit]

There is a bit of flexibility with the seat height. Ours is approximately 18." If you spread the legs a bit wider, the seat gets a bit lower (and vice versa). The trick is finding that magic place that works well for you without making it too tippy (if the legs are really close together). You could also play around with the seat size and how far up it attaches.