Designing A Comfortable Chair - Part II

I mentioned in my previous post about a cool chair fitting rig described in Fine Woodworking issue #96 (Oct. 1992) titled "Design a Chair that Fits like a Glove" by Glenn Gordon.  I am designing a swivel office chair for a client.  I adapted the chair fitting rig in that article for a swivel chair:

The hardware for the swivel office chair dictates some parameters such as lean back (which is 3 degrees).

The part that I copied from the article is the back splat fitting assembly:

In the above photo we see how the assembly can be tilted back as necessary with the use of hinges.  However, a way is needed to support the assembly - the first photo above shows how the assembly is supported using plywood bolted to the sides of the side rails and a top piece that is clamped to support the back assembly.  It works, although there is a lot of weight overhanging the back of the chair which makes the chair want to lean back too easily when sitting.   Not sure how to get around that.

For the final chair, the back splat will meet and mortise into the top crest rail.  The crest rail will be proud of the back splat about 3/16" of an inch.  With the chair fitting rig I simulate this fact by clamping a 3/16" plywood to the top back support.  The goal is to make sure that the 3/16" bump does not end up digging into the client's back - very important since the Blacker House arm chair I built last year has this issue - the bottom of the crest rail digs into the back a bit and is not very comfortable.  Lesson learned!

Another question is what distance must the wheels be from the center for stability?  I drilled a couple holes so that I could test different distances for the wheels:

Designing A Comfortable Chair

This past spring I spent a fair amount of time on our new fence.  I live on a corner residential lot and the new fence wraps around 3 sides of our lot.  We went bird crazy and cut out barn swallows in the fence panels.  Actually, let me clarify.  My wife cut out the birds!  Here is one section of the fence:

Now imagine 36 sections of fence with anywhere from 2-5 bird cut outs in each section.  I still need to finish the 6 gates but that will be an ongoing process for now.  After finishing a small project for a client it is time to get back into the shop for my next project.

I am now working on a swivel office chair for a customer.  The chair will be inspired by the Green & Green blacker house arm chair. The back splat, crest rail, and the various ebony plugs and splines will borrow from the arm chair.  The base will use swivel office chair hardware with 4 legs dovetailed into the hardware.  No arms.

A year ago I built as close a reproduction of the blacker house arm chair as I could based on various photos I acquired here and there.  I think I got pretty close:

Now, I'll be honest.  The chair is not the most comfortable chair I've sat in.  Of course, chairs in many ways are like shoes and should be custom fit for each client.  When I sit in this beautiful chair I find that the bottom part of the crest rail digs into my back somewhat.  My first reaction is perhaps I need to make the entire back sweep farther to the rear, even though the chair back already has a pretty well defined rearward sweep.  Since the customer wants the back to be like the blacker house arm chair it is important that the back be comfortable for the customer as well as look beautiful.

There is an article in issue #96 (Oct. 1992) of Fine Woodworking titled "Design a Chair that Fits like a Glove" by Glenn Gordon.  The article has a very cool chair-fitting rig.  I may build one for this project.  In the meantime, I quickly hacked together this setup (I still need to attach the swivel base):

It is not nearly as fancy as the rig in the article.  Nonetheless, I find it pretty revealing.  The shape of the splat I borrowed from my couch.  The couch is a new Scandinavian style couch with great back support and curvature.  I took some 12 gauge electrical wire and shaped it to the shape of the back of the couch.  I then used the wire to quickly draw the curve on some 8/4 lumber.  It is a very good starting point.  I can move the  entire back forward or rearwards as well.

For the crest rail I've tried 2 orientations.  The first orientation is where the crest rail sweeps back following the curvature of the splat, similar to the blacker house arm chair:

The splat has nice lumbar support.  However, the bottom of the plywood crest rail sticks out which is very noticeable when sitting.   I tried moving the entire back forwards and backwards and I still experience the bottom of the crest rail digging into my back a bit.  Next I straightened the crest rail so it is more vertical and in line with the back of the splat rather than the front:

With this scenerio my back rests upon the entire crest rail rather than the very bottom of the crest rail - which I find more comfortable.  What kind of design follows from this?  Here is an absolutely beautiful chair designed and built by master craftsman Jeff Miller where the back of the chair sweeps forward at the top rather than rearwards as with the blacker house arm chair:

So I will explore the forward sweep in the context of the Green & Green design motif.

Green & Green Settee - Finished

Here is the Green & Green inspired entry-hall settee fully clothed just before delivery.  Fun project!

Green & Green Settee Part XVI

The last element for the settee are the rail brackets.  The joinery part has already been done and they now consist of rectangular pieces of cherry:

All that is left is the shaping and installation.  A trip to the bandsaw quickly gives them a recognizable form.

 

I use rasps, files, sandpaper to smooth the surface.  There's no right or wrong - just go with what looks good.  I also round over the lip.  I install a small dowel and it is now ready for installation:

The settee is ready for finish!  Although freshly sanded and prepared cherry is rather light and brownish and can be somewhat blotchy immediately after finishing, I sincerely believe no stain can match the natural patina of quality cherry over time.  I explained this to the clients and they agreed.  I knew of one fellow who wiped ammonia directly onto a cherry table.   Afterwords it was a toxic and somewhat scary thing that had to be neutralized.  It actually did accelerate the patina process but I had to wonder if all the ammonia actually got neutralized.  Not sure if I would want babies hanging around the table.  Fuming may work but I've read that this process takes quite a bit longer.  I'll defer to the natural process of light.

I don't have a photo of it, but I made a drop-in seat out of 12mm baltic birch plywood.

For finishing I use a tung oil / varnish wipe-on finish made by Old Masters.  I've used this product before and I'm quite pleased with the results.  There seems to be a bit more varnish in the blend and they use real tung oil.  I wipe on 4 coats and call it quits.  The customer wants a more natural look so I do not use too many coats.  Then off to the upholsterer.  The last blog will have a photo of the final result.

Green & Green Settee Part XV

After glue-up I went ahead and sanded the whole piece with 180 grit.  I'll spare you the gory details of sanding.  I had either handplaned or pre-sanded (120 and 150) most of the parts before glue-up, so this sanding phase wasn't too bad.  For a few spots I had to dip down to 150 to touch up a dinged area here and there.

Next I cut the groove for the crest rail ebony spline.  There is a bit of trepidation taking a router hand held to a nearly finished piece:

I have only a 1/8th inch wide groove cutter (it may actually be a biscuit cutter, not sure).  As you see in the photo, I had to make two passes to get the width I wanted.  Unfortunately, I had some tearout, so I had to widen the groove a bit to clear that out.  I went very slow and removed very little to remove the tearout, which produced only fuzz but no tearout at the problematic area the second time around.  Unfortunately, the groove is a bit wider than I wanted, but it still looks fine.  The problem I think is that I went the entire depth with the first cut.  Next time I will take multiple passes, with the first pass shallow to avoid tear out.

I used my bandsaw and small Jet 10-20 drum sander to make ebony splines.

It is not an exact 90 degree angle where the top spline meets the vertical spline so I had to fuss with the top of the vertical spline on a makeshift shooting board using shims of paper to change the angle:

After using a coping saw to remove most of the ebony, I use a small coarse sanding drum on a dremel to level the ebony to where I can finish with hand tools and sandpaper.  The small sanding drum is very aggressive and the process goes quite fast.   I have a vacuum hose underneath (not shown for some reason) in an attempt to capture most of that gnarly ebony dust.

I also tackle the plugs, using the same process as I did for the arms in an earlier post.  Before installing the plugs I wet the entire piece to raise the grain then sand with 220.  Sanding around plugs is not a lot of fun so better to do so before hand.

I install corner glue blocks inside the seat area.  Glue blocks add a tremendous amount of strength to the piece:

 

I see the light at the end of the tunnel!

Green & Green Settee Part XIV

Center Splat:

The center splat is nothing spectacular to look at.  It will be hidden by upholstery.  However, it will be visible from the back so I want the joinery looking nice.  The splat will have integral tenons and they will be flush with the front (which means there will be no front shoulder, only a back shoulder - this makes things a bit easier).

I had cut the mortise in the back rail long ago before glue up.  I need to cut the mortise in the freshly fitted crest rail.  First, I'll go ahead and remove part of the rabbet with a handsaw and shoulder plane.  While the mortises will be "centered" on both the crest rail and the back rail, it is pretty difficult to get perfect alignment.  Consequently, I'll put side shoulders on the bottom tenon and cut the tenon a bit narrow so I can adjust it side to side.  I will not be able to do that up top with the rabbet.

 

Ok, its time for the tenons.  One can take one of two approaches.  1)  treat one of the tenons as a straight tenon and the other as an angled tenon 2)  treat both as angled tenons.  Now, the former sounds like it would be easier, and perhaps it is a tad easier.  For example, one could treat the bottom tenon as a straight tenon and only angle the top.  But there is a big disadvantage.  Since the entire splat curves back quite a bit one would need a very thick board to make this work.  Also, the top tenon would end up compensating for all of the angle and we will probably end up with a weak tenon.

Option 2 is much more forgiving on the amount of wood required since we can angle the board.  Also, both tenons are angled but the amount of angle on each is not too bad.

First, I establish the relationship between the two tenons.  I put temporary floating tenons in each mortise and glue a piece of plywood to both:

 

The splat front will pretty much have the same shape as the rear posts.  So I use my rear post template to layout the shape.  Then I place the splat jig onto that layout to determine where the tenons will go.

In the photo above note that I have marked where the shoulder will be.

Ok, now I need to cut the tenons.  First, I need to know my angles.  I've learned long ago that if one wants to build chairs then one needs at least 2 bevel gauges - top/bottom, left/right, etc .  Starrett bevel gauges are excellent and well worth the few extra bucks.

I'll use my tablesaw to cut the tenons.  I have a high tech tenon jig (the Mach 7 Tenon Jig) with a perfect 90 degree face to which I will clamp the splat.  Given this fact,  I clamp my splat to a 90 degree surface.  I could use the Mach 7 Tenon Jig but I find it easier to clamp to my jointer fence, which is also 90 degrees (note that the splat has been milled flat and square).  Note that the splat jig is clamped to the workpiece.  After getting the angle for the first tenon, I carefully flip the workpiece and use the other bevel gauge to measure the opposite tenon, making sure that the splat jig stays firmly clamped and does not move.

 

 

Then I clamp it to the Mach 7 Tenon Jig:

Now, given a right tilt blade, there is a risk that the blade could ruin my Mach 7 Tenon Jig.  Fortunately, I have enough wood in front so that this does not happen.  In the photo above, I have cut the front face of the tenon.  I move my fence to the right and cut the back part of the tenon.  My table saw fence has a micro-adjust on it - which makes it easy to dial in for a nice fit.  Still, I leave it a hair thick and finalize the fit with a shoulder plane.  Note that the rear shoulder was rough cut with a bandsaw to allow me to test fit the tenon.

Once the tenon is fitted, with the same blade angle I cut the rear shoulder.

I go through the same process for the opposite tenon, using my other bevel gauge to set the saw blade.  I then cut and fit the other tenon.  Note that I am a bit conservative when cutting the shoulder.  I do not want to remove too much so that there is a gap between the shoulder and the crest rail.  So cutting the top shoulder may require creeping up to the final fit and a pass or two with a shoulder plane.

I bandsaw the front profile and here is the splat in its rough state:

To shape the splat I use a shoulder plane, rasp, spokeshave, sandpaper.  If one had a long belt sander this would work as well and faster - but the hand tool approach goes quite fast.  If the splat was wide or had a more complicated shape (i.e. a Chippendale style splat) then the hand tool approach would be the only option.

Here is the back where it meets the crest rail:

Before glue up I clean the ends of the crest rail with a sanding drum on my drill press.  I get very close but leave a smidgen which I can easily sand down flush with the rear posts after glue up.  The end flares out a bit - a thick 1/8" or so.  This gives it a nice look.

 

While I'm at it, I shape and glue on side cleats for the rabbet.  Later I'll glue on some strips at the bottom to complete the rabbet all around for the upholstery. 

If I build this again I will probably integrate the bottom rabbet into the rear rail rather than glue on cleats. However, for the sides I need to glue on cleats unless I go with lumber thicker than 8/4.

Green & Green Settee Part XIII

As much as I try to control the ebony dust via dust collection, it still gets everywhere.  I wash my clothes immediately and the next day enter the shop with clean clothes.  However, once I start working the cleanliness lasts about 2-3 minutes - tops.  I vacuum around as much as I can to get the dust removed.

Time for the crest rail!  It starts off as a slab of lumber - just over an inch thick.

 

I begin the shaping first.  My first template based on my drawing represents only half of the crest rail.  I create a full size template off of the half size template.  The template is extra long to allow for screws at the ends.  I will also create a rabbet in the crest rail.  At the location of the rabbet I throw in some extra short screws.  A 1/2" template can still flex and once I cut the rabbet those screw holes will disappear.

I use a rabbeting bit and go thru a series of bearings to get to a final rabbet 1/2" wide and 3/8" deep.  Fortunately, I had no major wood movement after doing so (unlike what happened to my front rail!).

Where the rear post meets the crest rail I need to remove the rabbet before cutting the mortise. (I am using a floating tenon - the rear post already has a mortise on top).   I mark the location and cut the shoulders with a handsaw.  Now, I am by no means a beginner with the use of the handsaw.  Nonetheless, I use it infrequently enough so that I do not trust cutting exactly to a line.  I leave a little meat and then use a chisel and pair to the line.  I place the chisel in the knifed scribe line and then gently tap with a hammer so that the chisel exactly follows the scribe line down the side of the shoulder.  Light tapping gives me a lot of control and excellent results.

After bandsawing the waste I then use a shoulder plane and a wide chisel to clean the area. I just check for a 90 deg surface vis-a-vis the front of the crest rail.  I'll fine tune the fit after cutting the mortise which will allow me to see how the crest rail actually fits on the rear post.

 

I take it to the multi-router and then cut the mortise.  I used a scrap piece of wood first to adjust the mortise location height before cutting the real mortise.

 

With my first fitting I was actually pretty darn close!

I had to use a shoulder plane to tweak the crest rail shoulder area to close a few very small gaps here and there.   

I've decided to quit here.  I'll write another post where I build the center splat which is worth its own post.  If you want to build chairs then the next post will be very worthwhile, as most traditional style chairs have curved splats.