Sunday, August 23, 2015

At Long Last: The Rocking Chair is Done!

After over a year of planning, preparation, and building (plus the birth of my son and sudden lack of shop time), at long last the Boston Rocker project comes to a close!

A lot has happened between my last post in March and now. My son is more curious about the world than ever and growing by leaps and bounds! My free time remains at an all-time low, however, and that means scant little time in the shop. However, I managed to get a decent chunk of time in recently, and have completed one of the biggest projects I set out to do: my son's Boston Rocker.

The Arms

In my previous post on the rocking chair, I had just completed the roughing of the back spindles and mounting into the top crest, in addition to the front roll of the chair seat. All that remained was the arm spindles and the arms themselves.

Off-cuts from one arm, which started out as a solid block of
Possibly the second most harrowing set of cuts I've made for this project were in the arms. Like the crest, I started from a 16/4 block of solid walnut with a pattern traced onto it which I printed from my Sketchup plan. Having completed the top crest, I was a bit more confident in my ability to cut a good arm though, and sure enough, all went very well. I put on my ¼" bandsaw blade and went to town on the wood. I started first with the overall shape of the arm top-to-bottom, and then flipped each arm 90° and cut out the taper from the sides down to the back of the arm where the arm meets the back spindles. Lots and lots of sanding, and we have two very nice arms.

Rough fit of everything with the arms.
The spindles for the arms were quick to make, based on the plans. Spinning some wood on my lathe, I knocked out four spindles, two straight for the interior, and two stylized with beads in the middle for the fronts. Fitting the spindles required me to drill angled mortises into the arms, which I was able to easily do thanks again to the patterns I made from my model. A power drill and a ½" Forstner bit did the trick, followed by some reaming to taper the mortises to fit the tenons I turned.

Dry-mounting the arms, I was able to figure out where on the back spindles I needed to chop out to provide a mortise for the arms to slip into. Clamping the spindles down, I used my drill press to eat out most of the mortises using a Forstner bit, and straightened the mortises with my chisels, testing the fit as I went along.

Putting it all together, I now had what looks like a rocking chair, if only very rough! I'm home free! All that's left to do is sand, stylize, finish, and glue! I thought.


Taking all my spindles back to the lathe, I added in the final stylized details from my plan which give the chair its nice, old look. With that done, it was time to sand everything like crazy, then apply some finish. I opted to finish all the parts separately, rather than put together, as this would make getting into all the nooks and crannies of the chair much easier. Plus, the spindles can all be finished on the lathe in a few minutes!

The finish I chose was a simple garnet shellac. Nothing more, nothing less, just easy. Shellac is a very friendly finish to use, goes on easy, can easily repair spots, and rubs out nicely. Plus, it's completely non-toxic when dry, something I feel is very important if my son is going to be anywhere near it. The shellac gave the wood a beautiful warm, golden glow and really brought out all the details in the grain. Simply beautiful!

Next step: gluing!

Gluing, Take 1

Before I started gluing the chair in earnest, I decided to run some experiments. Since this was the first time I was using this particular kind of joinery (tapered mortise and tenon), and also the first time using hot hide glue, I figured this was a good idea to avoid ruining the actual chair.

Off to the finishing room with a few off cuts and some quick spindles, shaped similar to the spindles of the chair. I got my glue nice and hot, spread it on the tenon, mated the tenon into the mortise, and waited 24 hours to let the glue set. Then, I clamped the piece down, and gave it my all to try and break the joint.

Glue-up experiments.  These were the successful ones.
Turns out my all was very little. Putting my leaning weight up against the spindle was all that was needed to break the joint. Crap! That means if I were to try and glue up the real chair, it would hold together just long enough to look pretty, and collapse the first time anyone sat in it!

OK, don't panic! We can fix this, right? Just gotta figure out what kind of joint I need to make this work, and then how to make that joint out of what I have. Thus began a long series of experiments. I tried wedging the joints (both blind and through). I got this to work once, but not reliably enough to apply to the chair, and it meant driving the spindles through the seat of the chair. I wasn't quite prepared to do this yet.

I did some more reading on tapered tenons and mortises, and came to realize something important. My tenons were strictly tapered, not cylindrical in any way. This allowed me to adjust the angle of insertion easily, but also made a very loosely-fitting joint, especially to lateral pressure. Second, traditional tapered tenons are tapered only on the shoulders, not for the whole tenon. The joint itself is essentially a dowel joint, straight and cylindrical. This makes it strong and tight fitting, but also allows the feature of being driven in further with use.

With this in hand, I worked up a few more experiments. This time, all of the joints were strong, and the wood broke long before the glue joint did. Bingo!

Gluing, Take 2

Start straight, then taper!
OK, so how do I apply this to my existing parts? I had only gone ¾" into the seat of the char (which is 1 ¼" thick), so I had room to dive deeper. I decided to straighten out the tenons to ½" diameter (which matches the Forstner bit I was using). Then, I cut an additional ¼" for the tapered shoulder. Meanwhile, I drilled further into the mortises, bringing them to just over 1" deep. With these modifications, my spindles fit tight and strong! It resulted in a net reduction in height by about 2" over the whole chair, but sitting in the (now perfectly stable, unclamped) chair, I didn't notice the difference.

I needed to clean up the spindles to blend in the new shoulders, so some more lathe work and some refinishing work, and this was completed in a couple days.
With all this done, I heated up my glue, got my finishing room nice and toasty warm to give me as much open time as possible, and went to gluing.

In the End

After letting all the glue dry and set for 24 hours, I gave it the pressure test. I sat on it gently, then harshly, then backwards. I stood up on it, jumped on it. I picked up the chair by all spindles and parts alone. Everything held together beautifully as one solid piece! The rocking action is smooth, the seat is comfortable, and it looks absolutely beautiful! It now has a place in my son's room, right next to his crib.

Now if I can just get him to sleep... ■

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