Rocking Chair Design

[Jeff]

This is a spinoff of a related thread titled "Porch Rocker" in this forum. Rocking chair design has been bugging me for a few days and I'm not gonna pay $1000 for a teaching class for a one-off rocker or two.

So I began with the rocker runner as the foundation for "what makes it rock" and what are the key dimensions? For this exercise I chose a 38" radius of curvature for the initial rocker runner.

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Shortened the runner by 2" at each end. The vertical rocking rise is 4" at each end so it may teeter-totter ok without falling off or tipping over backwards.

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Maybe it's a start for planning a rocker. The left runner has a 4" rise while the other one has a 3" rise for a slightly different roll. They're both 34" l.

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I can download the Sketch Up files if you all want to play with them.

 

[KenOfCary]

Still studying this and can't quite get my head around it. What I intend to do next is go measure one of the two teak rockers that are on the front porch. I'm not sure that the legs are of different lengths - I don't think that they are.

But I will know more soon. So keep the cards and letters coming and I'll get back to you. I think a lot of us are interested in this and don't want to pay $1K + $1K travel/board to learn. In person one-on-one might be the best way to learn but there should be better ways to get a leg up on this.

 

[thrt15nc]

Here's the article I was thinking about when I posted in the other thread.

http://www.rockingchairuniversity.com/rocker-radius.html


Tom Swortzel

 

[Jeff]

In person one-on-one might be the best way to learn but there should be better ways to get a leg up on this.

I agree entirely. That's about where I started from scratch too.

 

[smallboat]

I've had the opportunity to look at a bunch of rockers this weekend and two observations
first, to my eye and without any measurements, the rockers appear to have a changing radius.
They aren't a consistent arc of a circle, so one end will be "faster" than the other.

The other observation is they don't act as a teeter totter pivoting on a fixed point as much as they act like a wheel rolling back and forth.
The point of contact changes as the chair rocks.

The chair will try to settle on a place where the cg of the sitter(s) is over the point of contact with the floor.
weight back- chair rocks back, weight forward - chair forward.

Maybe its just me but it helps me to think in terms of shifting your weight side to side in a canoe.
The boat rolls to find a new equilibrium

my $.02 worth

 

[Jeff]

Sorry, I hit the send key accidentally.

My only rocker was a seat-of-the-pants journey from a picture and a few dimensions like this. The quoted rocker length is 32", but I naively made mine 38" without understanding the dynamics of the arc curvature and the vertical height of the rocker ends from the floor. As a result it's kind of a flat "rock" and needed more rise to it-I've only got about a 2-2.5" rise.

http://www.globalindustrial.com/pro...gclid=CIrNj4a89L8CFc1_MgodVSoA6w&gclsrc=aw.ds

Take a closer look at pics 2 & 3 above and compare those with the length and rise of your teak rockers. The Cracker Barrel rockers are made by the Hinkle Chair company; their Bradley and Plantation models have 34" long rockers but they don't specify the vertical rise. Maybe stop by Cracker Barrel with your tape measure. ???

http://www.hinklechaircompany.com/index.php/rocking-chairs/adult-rockers.html

BTW, Tom's post is a good read for some fundamental understanding and I'm still digesting that.

 

[Jeff]

Maybe its just me but it helps me to think in terms of shifting your weight side to side in a canoe.
The boat rolls to find a new equilibrium

That's a good analogy and thank you. The radius of curvature doesn't change, but the point of contact in that radius does. So we rock back and forth from the vertical center point of 17".

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[CrealBilly]

Jeff when i built this little walnut rocking chair for my grandson several years ago - i built the chair and the rockers then placed the chair onto the rockers marked where the chair looked to be fairly straight on the rocked then mortised it in. You have been warned every cut and joint is a angle don't say i didn't warn you

http://www.ncwoodworker.net/forums/showthread.php?t=35703

 

[Jim Wallace]

Jeff is correct in my opinion. The way I have always designed rockers is by trial and error. You build the chair then cut two rockers out of scrap (plywood is good for this) and clamp them to the chair and test the look and the rock. Make changes as necessary to get it all right.

If you are copying a chair be sure to check the leg lengths. Some rockers are built with the rear legs shorter than the front when measured down from the seat.

The first consideration when designing your rocker is that the chair must sit correctly when at rest. It can't sit too vertically or it won't look inviting or seem comfortable when sitting. It can't sit back too far or not only will it not look right, but it won't be comfortable when at rest and it may be hard to get out of. If you've clamped your test rocker tightly enough you need to sit in the chair. Before you rock just sit in the chair's resting position. This may or may not be the same as the position it rests in without an occupant. It will probably be close. but may not be the same. Are you comfortable? Adjust for comfort. If you've adjusted it, examine the empty resting position again.

Now consider the rock. It should be smooth and effortless. Especially rocking backwards: you should not feel that you'll rock right over. The rockers need to be long enough to prevent this and should not curve so much that they throw your weight back too far as you rock. The chair should rock back slowly without too much acceleration. If your core muscles tighten naturally as you rock back, you'll probably never really relax in the chair. The chair should gently return you to the resting position. Making the rockers in the shape of an arc may be a good place to start, but the final curve may not be a true segment of a circle. Adjust as needed. If you've adjusted it, examine the empty resting position again.

Once you are sure that you are satisfied, you have a template from which you can make your rockers with confidence.

 

[KenOfCary]

Well I measured the teak rocker on the front porch. I should mention that these are fairly large rockers with a very comfortable feel. The runners are 31" long. The front of the runner is 4" off the deck when at rest and the back is a little over 2" off the deck. Both legs are the same length 14-1/2" from top of the runner to the top of the chair seat. The 31 inches is divided into 2" in front of the front leg 18-1/2" to the back of the back leg and 9-1/2" to the back of the runner. (doesn't quite add up but there is some inaccuracy in the measurements due to the curvature.) The seat is 21-1/2" wide between the arms and the back is 31" tall from the top of the seat. When I look at it sideways the top of the chair is behind the end of the runner slightly when at rest.

Not sure what all that means yet except it's a start for a sketchup diagram. All the members are about 6/4 I think - didn't really measure that. The runners close to 2" tall and 1-1/2" wide.

Still digesting all of this also.

 

[KenOfCary]

None of the pictures in that link to the other post are showing up for me. Too bad - would have liked to see it Jeff.

 

[Roy G]

John Shea in his book American Shakers and their furniture has a measured drawing of one of the Shakers rocking chairs. He has the rockers at 30 1/2" long.

Roy G

 

[Jeff]

Ken,

Maybe we're getting closer to collectively understanding this design stuff.

I think that this is a close depiction of your porch rocker in its resting position. A 2" rise at the back and 4" at the front. The leg spacing is 18.5" per your measurements.

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If the chair is sitting nearly vertical then the rise of the runner should be about 3" at each end. Check it to see if we're right.

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[smallboat]

just got back in town and realized I have a cracker barrel rocker on my front porch- it was a gift.
If there is interest I can take fairly extensive measurements and make some drawings.
Let me know if that is helpful.

 

[Jeff]

just got back in town and realized I have a cracker barrel rocker on my front porch- it was a gift.
If there is interest I can take fairly extensive measurements and make some drawings.
Let me know if that is helpful.

That's an excellent idea with some pics too! How does your chair feel and rock?

The Cracker Barrel rockers are a production design that probably lack a custom fit like a Maloof rocker but that's okay for this discussion and a clearer understanding of the chair dynamics.

Jim Wallace offered some good advice on the fine tuning of a chair earlier in this thread.

Now I'm playing with the idea of how to mortise the rockers and then cut angled tenons on the leg components. Or should it be a straight tenon and an angled mortise? ???

 

[Jim Wallace]

You mentioned a shaker rocker. This brings up another design aspect to consider. The shakers were very industrious. They hung their chairs on the wall after meals so no one would be tempted to sit down even while working. A shaker rocker with no arms was influenced by this work ethic. The chair sat up pretty straight and was comfortable for knitting or shelling peas. On the other hand a big porch rocker with arms, like the Cracker Barrel rocker, sits much further back: perfect for napping while rocking, or napping without rocking. It's not like there is one perfect design.

As for joining the rocker to the chair, some of the shaker rockers had narrow rockers that ran through the bottom of the chair legs and were pinned. The big porch rockers that I've repaired for people generally have a round tenon turned on the end of a turned leg post. This is mortised into a wider rocker and it too should be pinned although I've seen them that were not. I will say that it's easier to replace the rocker if it hasn't been pinned, and you might be surprised to see how fast they can wear.

You know the old blues song --

Trouble in mind I'm blue
But I won't be blue always
I'm gonna sit right down
And rock on away from here.

 

[CrealBilly]

just got back in town and realized I have a cracker barrel rocker on my front porch- it was a gift.
If there is interest I can take fairly extensive measurements and make some drawings.
Let me know if that is helpful.

Cracker barrel rockers are mainly turned members and are much easier to assemble with all the angles than square members are... All those angles are what gave me fits and turned me right off to pursuing any further rocker building. We have six rockers on our porch 5 are made with mainly round members the one I built for the my grandson is all square members and what a pain it was figuring out all those angles.

Every piece is a angle don't say I didn't warn you a second time. And yes even your rockers will require some angle on the bottom of the arch which is not shown in the sketchup drawings.

Adding some more... one thing I did learn on my own which really helped... was to cut the angles as close as I could and get creative with thick rubber bands and lengths of innertube to keep members in place while a ran stips of sand paper through the joint to make it fit perfectly as a butt joint first. Then add a loose tendon and epoxy in place.

There are several members here who build rockers my suggestion is to go hang with them and maybe even help build one with them to learn the tips and tricks before venturing out on your own like I did.

 

[CrealBilly]

None of the pictures in that link to the other post are showing up for me. Too bad - would have liked to see it Jeff.

Yeah... broken links there is nothing special about the rocker. My grandson now 5 has not out grown it yet his butt still fits in it and still rocks in it everytime he is over. He's a big boy and you know how rough boys can be... the rocker has held up with no issues so far.

Pics just taken a few mins ago...






I hope you can see all the angles needed. This is your third warning :lol