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Designing Suspended Chair With Plywood

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Forum topic by jmeter posted 06-10-2015 04:19 AM 1196 views 0 times favorited 15 replies Add to Favorites Watch
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jmeter

11 posts in 548 days


06-10-2015 04:19 AM

Hello!

I am designing a chair that will be suspended from an I-beam in my apartment. I’ve created a design using 3/4” plywood and 1 1/4” wooden dowels. I currently have the wooden dowels passing through the seat back; they would be glued. I am wondering if this would be strong enough? If not, do you have any suggestions on strengthening this? I plan on screwing the dowels to the seat of the chair. The chair would be tied through 2 holes in the seat and 2 holes in the dowels at the back.



Any help would be appreciated!!

Thanks,

Josh


15 replies so far

View altendky's profile

altendky

169 posts in 1674 days


#1 posted 06-10-2015 11:17 AM

First, I would suggest hanging from the dowel at the front as well. Your present design causes the seat to be loaded so as to peel it off the dowels. Hanging from the dowels both front and rear would eliminate this and let the seat just sit on the dowel sub-structure (well, with screws, but only to keep things in place). It would also seem like having a flat on the dowel against the seat would be good and would allow for a bit of glue in addition to (instead of?) the screws.

I don’t really know but my gut says that the dowel will wallow out the hole in the seat back over time. A gradual recliner of sorts. Also, since you say this will be mounted from an I-beam this means that the rope/cable/chain will have to be angled forward/backward. It appears that the rear will end up running through the seat back.

With a little nuance and addressing the issues above I feel like you could turn this into a slick looking minimal design. Perhaps someone with some more experience here will provide some more concrete advice. Good luck!

View SirIrb's profile

SirIrb

1239 posts in 695 days


#2 posted 06-10-2015 11:21 AM

you need to triangulate the seat to the back and then find the center of gravity to hang it from. As it is now it will not hold the load.

-- Don't blame me, I voted for no one.

View pjones46's profile

pjones46

986 posts in 2107 days


#3 posted 06-10-2015 02:21 PM

This is an out of the box idea but how about trying to usie glued laminated layers bending plywood over a form to create the chair, and +1 SirIrb where the center of gravity must be considered.

-- Respectfully, Paul

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SirIrb

1239 posts in 695 days


#4 posted 06-10-2015 02:38 PM

I like the lam idea. It would take some time to create the form but if it is a winner the product can be sold and at least pay for the form.

The form will basically have to be the inside of the seat made by cutting gluing 3/4 ply. Then 1/4 ply may be able to bend around the form. I dont know if it is true but I was told that when lam ply to acct for 30% deflection from the mold. Basically make the back, bottom angle tighter by 30%.


This is an out of the box idea but how about trying to usie glued laminated layers bending plywood over a form to create the chair, and +1 SirIrb where the center of gravity must be considered.

- pjones46


-- Don't blame me, I voted for no one.

View hotbyte's profile

hotbyte

842 posts in 2439 days


#5 posted 06-10-2015 03:12 PM

If you’re open to deviating from the plywood, Tommy Mac did an episode on a bent form lounge chair using strips of wood with spacers between the strips. He used a form and steam bending technique. You could adapt his project to a swing chair.

Rough Cut Episode - Steam Bent Lounge

View jmeter's profile

jmeter

11 posts in 548 days


#6 posted 06-10-2015 04:31 PM

Very interesting, thanks for the input. I will look into the laminations.

I’m a little confused about the center of gravity part. I plan on joining the front and back ropes on each side and then connecting them to a dowel which will then be hung. So it would look like a triangle on either side and at the top, both triangles are attached to a dowel that spans the chair. The triangle certainly wouldn’t be symmetric, but couldn’t I just adjust the lengths of those ropes to make it level? Maybe I’m missing something major here haha. Is it just that it would tip easily since its a little off balance?

Also, altendky mentioned adding a flat on the dowels. I like that alot. What would be the best way to do that?

View jmeter's profile

jmeter

11 posts in 548 days


#7 posted 06-11-2015 05:01 PM

Hey altendky,

Do you know of any good ways of getting a flat on the dowels?


First, I would suggest hanging from the dowel at the front as well. Your present design causes the seat to be loaded so as to peel it off the dowels. Hanging from the dowels both front and rear would eliminate this and let the seat just sit on the dowel sub-structure (well, with screws, but only to keep things in place). It would also seem like having a flat on the dowel against the seat would be good and would allow for a bit of glue in addition to (instead of?) the screws.

I don t really know but my gut says that the dowel will wallow out the hole in the seat back over time. A gradual recliner of sorts. Also, since you say this will be mounted from an I-beam this means that the rope/cable/chain will have to be angled forward/backward. It appears that the rear will end up running through the seat back.

With a little nuance and addressing the issues above I feel like you could turn this into a slick looking minimal design. Perhaps someone with some more experience here will provide some more concrete advice. Good luck!

- altendky


View jerryminer's profile

jerryminer

528 posts in 905 days


#8 posted 06-11-2015 07:57 PM

Do you know of any good ways of getting a flat on the dowels?
- jmeter

Lots of ways to skin that cat. Jointer, planer, tablesaw, hand plane, bandsaw

Might help to jig-up with a V-block or something to keep the dowel stable while running through a machine:

View altendky's profile

altendky

169 posts in 1674 days


#9 posted 06-11-2015 10:05 PM

I wash imagining something along the lines of Jerry’s pics but I would strongly emphasize the ‘temporary fastening’ or clamping of some form The small piece (the dowel) should be quite well attached to the jig. I’ll let you know if I think of something particularly nifty.

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jerryminer

528 posts in 905 days


#10 posted 06-11-2015 11:17 PM

Or …

View Daruc's profile

Daruc

459 posts in 597 days


#11 posted 06-11-2015 11:32 PM

Edit

-- -

View jerryminer's profile

jerryminer

528 posts in 905 days


#12 posted 06-12-2015 12:41 AM

Or ….

View jmeter's profile

jmeter

11 posts in 548 days


#13 posted 06-12-2015 05:52 PM

Awesome, thanks Jerry. I will try that out this weekend.


Or ….

- jerryminer


View BinghamtonEd's profile

BinghamtonEd

2281 posts in 1834 days


#14 posted 06-12-2015 07:12 PM

If you have hand planes, I’d just chuck it in a vise and go at it with a #5. It’d probably be done in less time than it would take to set up the jig and table saw for the cut.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View CaptainSkully's profile

CaptainSkully

1437 posts in 3022 days


#15 posted 06-18-2015 04:19 AM

The problem isn’t dowel flats or laminations, the seat is too long for sitting and too short for reclining. The size dowels you’re talking about are plenty strong to support a cantilevered load for a normal chair and a solid piece of wood 3/4” thick or more will be plenty.

I’m a sailboat rigger and I make dinghy lifting bridles every day, which is exactly what you’re doing here. There isn’t a very easy way of adjusting the rope. It looks great when it’s hanging there, then you sit on it and BAM. If you use 3 strand, you can do a splice, then if it’s not quite right, you could undo the slice and redo it higher or lower, but that stresses out the 3 strands. If you are willing to take an iterative approach, do the 3 strand splice, adjust it as necessary, even if it trashes the rope, then once you’re happy with the dimensions, rebuild it right the first time.

If you need help with a 3 strand splice, check out my post on www.boatpartsinfo.com

The load on the seat will be closer to the back than the front. You will have to take that into consideration. Have you ever seen a kid on a playground swing sit too far forward?

Another option would be to use a single braid like AmSteel, which is very easily spliced, undone, then respliced. Once again, those splices are covered on my blog posts.

Disclosure, the website is from a former employer, so no benefits my way, just sharing info with a fellow LJ. Good luck and let me know if you need any help.

-- You can't control the wind, but you can trim your sails

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