Rocking chair runners

[Darren Wright]

Before our Grandson was born, about 4 years ago, we bought this red chair. It used to have a mechanical rocker/swivel base under it. The base turned out to be very cheap and with all the rocking we did it eventually wore out. I removed it this past summer and kept the chair part thinking I'd just buy another mechanical base for it. My wife has asked me to make a wood rocking base instead.


I've been looking for either a calculator or a formula for calculating the size/shape of the rocker runners.

The following page states "π = 3.14159265358979323846264338327950288419716939937510…. multiplied by the finished height of your rocking chairs’ seat. That is all there is to it."
http://logfurniturehowto.com/radius-matters-how-to-make-a-rocking-chair-rock/

Are runners really round? I've always thought of them being more oval, but guess it may just be that they are offset to the rear more. Anyone made rockers from scratch? How did you come up with the size/shape?

 

[Ryan Mooney]

Huh, I never really thought about that.. they always looked like something not quite like a circle segment to me as well. I think the offset is definitely making it confusing but I'm not sure if that's all or not.

Perhaps a couple of scale mock ups from the laser cutter are in order?

Interesting thread here:
http://www.woodweb.com/knowledge_base/Rocking_Chair_Design_and_Construction.html

Seemingly knowledgeable anonymous contributor:

I use a 42" radius for my rockers. Only about 8" of the rocker is actually used for rocking. Once you go beyond that, it becomes more style than function. One fellow did say he used a catenary curve, but when I looked at where the rocker contacted the floor, it was really close to a 42" radius. A shorter radius is found to rock too fast and a flatter curve (longer radius) too slow. With a shorter radius the individual's head moves through a greater distance and longer radius gives a sense of less motion.

I use about 5 degrees as the front to back angle on each side. However, the most critical thing is to make all of the dimensions exact side to side. An error of 1/16th inch can cause the chair to "walk" sideways.

As for making the seat lower in the back, I have seen everything from flat to 1+ inches. I use a flat chair (front and back legs the same length) but the center of gravity of the chair tilts it back about 10 degrees and a person sitting in it rocks it back another 10 degrees. This is with a 5 degree back angle relative to the seat. The customer can change the back angle to 10 degrees if they wish, by a simple adjustment.

 

[Dave Hoskins]

That math killed my brain, Darren! But I can answer this for sure from personal observation. Some rockers are round and some are more oval. Not sure what determines which one to use, but most I have seen are oval. But, those are all wood rockers made from pecan and cedar. Now I know that is no help, but I just had to throw my two cents worth in.

 

[Bill Arnold]

I've never built a rocking chair, but I did repair one for a neighbor several years ago. It had runners that were rectangular in cross-section; taller than they were wide. They also flattened out a bit on the back ends to help keep the rocker from turning over if one were to get a bit wild. They were much like most I've seen.

The following is a good read but also includes some math, so watch out.

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

 

[Bill Arnold]

Of course, there's always this:

 

[Bruce Haugen]

I've never built a rocking chair, but I did repair one for a neighbor several years ago. It had runners that were rectangular in cross-section; taller than they were wide. They also flattened out a bit on the back ends to help keep the rocker from turning over if one were to get a bit wild. They were much like most I've seen.

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

I’ve made a couple, but borrowed from existing rockers, so I can’t tell you the radius.

The last was for our grandkids. I made the rockers 6” longer in back and with a straight section on the end to try to prevent someone tipping over. Our two year old grandson finally did it. My son wasn’t concerned about it, only if he kept doing it. Must’ve been all he needed was one time because he hasn’t done it again.

 

[Dave Richards]

I think generally the rockers have to be part of an ellipse rather than circular. I just finished plans for a client for a craftsman style rocker. The rockers are 32 in. long overall, 1-3/16 in. thick, and the high point of the inner curve is 2-1/4 high.

 

[Darren Wright]

Thank you all for the links and info, I've got some reading to do.

 

[Ryan Mooney]

I'm liking the catenary curve just because I think they're cool with no supporting evidence that it's in any way practical for a rocking chair.

 

[Darren Wright]

I've been working on drawings to figure out a radius, which I think around 52" should work, so will work on a template for those.


It looks like my challenge is in attaching the runners to the chair. The original rocker was a swivel base that as inset into the bottom of the chair. That is where the real structure of the chair lies. The chair is somewhat "Rib" framed, like a guitar, around the base area, so there are only 1/2" and 1" ribs all around the base to really attach to.



I'm thinking I'll frame up a box to attach to the area the old base attach to bring it out to the bottom of the chair, then attach a larger piece of 1/2" plywood the shape of the bottom of the chair to that, then runners with some cross supports to the plywood.