[Beginningwoodworker]

Mahogany Kitchen Stool Project

Well, here we go. I have been working on the design and preparation of this project for 3 years. The final prototype was just completed.



This is my second prototype. The first one was a quick (that is a relative term) mock up to see if I had the size correct. I built this out of scrap 2×4s and screws. Pieces were only roughly shaped. After building this, we determined that it was about a half inch too tall.



The second prototype was built as a prelude to actual construction. Each stool has 42 mortise and tenon joints. Several of them are angled and others are on curved parts. By making a full prototype, I have a scale pattern to verify the layout of each piece before I cut into my lumber.



Also, I get a chance to make mistakes and learn. I ended up missing on three or four dimensions and had to patch parts up. I have chosen to form the curved parts by laminating thin strips. The two curved boards on the back formed very well, but the 5 slats did have some spring back. I'll need to adjust the form or move to thinner strips. Stay tuned on that one.

Finally, I get one last chance to check my design choices. In this case, my wife and I felt that the slats on the back were spaced a little too far apart. It ended up crowding the gap to the legs. I changed the design and moved the slats a little closer together.

I'll outline how I intend to proceed with this blog. I'll post updates on the construction as I go. Woodworking is a spare time activity for me. Weeks may go by with only a little activity. I'll post a few "flashback" entries where I will cover my design process.

I'll also keep a log of construction hours. This will not include design or prototyping time.

Cutting rough stock : 2 hrs
Cutting legs to width and thickness: 4 hrs 20 min
Cutting thin stock for seat back laminations: 3 hrs

Total so far: 9 hrs 20 min

Nice looking stool.

 

[Beginningwoodworker]

Begin Rough Cutting

Back in early November, I went to my favorite lumber yard and started looking at what kind of wood to use. I was interested in mahogany, but wanted to check out my options. They had some very nice ribbon mahogany. I went home and gave it some more thought. The next weekend, I made the plunge.



I had only one problem, I kept seeing pieces that looked too nice to pass up! I ended up with way more than I needed for this project. I can rationalize it that I saved gas by not making an extra trip You can see 3 fir 2×4's on top of the stack. They ended up being the material for my prototype.

Even though I had plenty of material, I took it as a challenge to try to get the most use out of each and every board foot. I spent way too much time on this, but I packed in the pieces in the most compact cut layout I could. Here is the result after 3 or 4 iterations on my CAD system.



I'm hopeful I will end up with only small blocks of scrap and a big pile of sawdust!

Fast forward to last weekend. I finally was able to start cutting the legs. Here is where I ended up.



I got the width and thickness rough cut and then ran them through my planer. I learned something about my dial calipers. I bought a nice one with resolution down to 0.001 inches. The resolution makes it nice to know exactly what dimension I am at. On the other hand, I don't need to worry about being off by 0.001 or 0.002 inches. If I can't see the difference when I hold two pieces up to each other, I am happy.

Current time log:
Cutting rough stock: 2 hrs
Cutting legs to width and thickness: 4 hrs 20 min
Cutting thin stock for seat back laminations: 3 hrs 15 min
Prepping laminations: 15 min

Total so far: 9 hrs 50 min

I love Mahogany wood.

 

[Beginningwoodworker]

Preparing Lamination Strips

There are three curved parts in each stool. These are formed by gluing up thin strips to create a thicker laminated part. The three parts are:

1. Seat Back - 7/8" thick (formed with 5 or 6 strips)
2. Back Rest - 7/8" thick (formed with 5 or 6 strips)
3. Slats - 3/8" thick (formed with 3 or 4 strips) (5 per stool)

As I plan the construction, I start to realize that I have 6 stools with 7 curved parts each. That works out to 42 glue ups. Each one requires a full day for the glue to cure. I do have three different forms, but this is still a lot of time - 30 glue ups are for the back slats. I need to get the glue up process started first. I can work on shaping the other pieces while the glue dries on the laminated parts.

The 7/8" thick parts were prototyped with 6 layers. They formed fine with no spring back. I prefer to use fewer, thicker strips and end up with one less glue joint. I'll be testing out the first glue up with 5 strips and see how it goes.

The 3/8" slats were prototyped with 3 layers. There was some spring back that made it difficult to align parts for assembly. I need to reduce the spring back. My plan is to try to modify the form and test it with another prototype glue up.

The wood for the laminations was resawn off the Back Leg stock. I ended up with pieces about 1/2" thick and 3 5/8" wide. They were long enough to provide two pieces for the glue up. I then resawed these to give me 2 long strips. Now I am up to 4 pieces for the glue up.



I figured I would share some of the things I do when resawing. First I use a 7 1/4 inch thin kerf blade. The kerf is only 1/16". This helps me get the most out of each piece. If the board is too wide, I need to stay with one of my larger blades. I do not have a zero clearance insert (yet), so I use a long scrap of thin plywood and clamp it to my saw table. I raise the blade through the plywood and I end up with a temporary zero clearance solution. Finally, I use a marking technique to keep track of which board each pair of strips came from.

I use my hand saw and make a set of marks across the end of the board.



In this case I have marked this piece as belonging to stool number 4. By angling the marks, I can return the two pieces to the same orientation as before the resaw cut. Each stool has 2 boards (one for the Seat Back and one for the Back Rest). I mark the second board for stool number 4 with 4 cuts, but I place them in a different spacing.

I now have strips of wood that can provide 4 pieces for my glue up, but I need 5 or 6. Fortunately, my strips are wider than I need. When I rip them to the desired width, I have two narrow pieces left over. In the case of the Seat Back, these two narrow strips can be glued together. This way all the wood comes from the same board and I should be able to keep the colors matched.



Once I let the glue dry and clean up the piece, I have 3 strips of wood. Each is long enough to give me two pieces for a total of 6 parts for the lamination.



The strip on the right is the glued up one. The Back Rest is wider. As a result, my left over pieces are not wide enough to make the third strip.



In this case, I have added a third piece of left over stock to make the strip wide enough.



This entry is long enough. I'll cover more later.

Current time log:
Cutting rough stock: 2 hrs
Cutting legs to width and thickness: 4 hrs 20 min
Cutting thin stock for seat back laminations: 3 hrs 35 min
Prepping laminations: 2 hrs 20 min
Glue up Laminations: 35 min

Total so far: 12 hrs 40 min

Great start!

 

[Beginningwoodworker]

Laminating Seat Back and Back Rest

Once I have my strips sanded to thickness, I can cut them and get the five pieces I need for gluing. I have enough material for six so I'll have a strip left over. There are a couple of cases where I ended up with damage on part of a strip and that sixth piece was nice to have.

First, I sort my six long strips and find which end I want to have in the final part. I look for color, grain direction and any character that I might want to have on the outer faces. Then I mark for cutting. I use the inner form and rock it along the strips to get the length.



I then set aside one piece and cut the last two to length. Next, I spend a few minutes and sort and re-arrange the pieces. I am looking for the two nicest surfaces to be on the outside as well as have uniform color and grain direction on the top edge. This can take several tries before I find a combination I am happy with. I then mark the pieces to make sure I keep the orientation unchanged.

Now it is time to apply glue. I use yellow wood glue - it has a fairly slow set up time and that is a good thing for this operation. I just use a piece of cardboard to get an even coat.



I coat one face and make sure the entire surface is coated and fairly even. I can see wood grain through most of the glue. If I have too much, I transfer it to the next surface to be glued.



One thing that you do NOT want to do is glue your piece to the fixture. To prevent this, I use a piece of stretch wrap (from the kitchen). Then I put the stack into the fixture and start to draw it together.



The fixture has two arcs offset by the thickness of the part. These arcs were cut carefully to ensure that I would get even pressure along the glue joints. After the first clamp is at its limit, I add two more clamps. As I draw these two in, the first clamp comes off.



The outer form of the fixture is set up to be a jig for cutting the tenons. As a result, they are short and do not pull the ends in to the inner fixture. So I add C-clamps on each end.



After getting all 6 clamps tightened, I set the assembly aside for 24 hours. I have two fixtures - one for the curve at the back of the seat and one for the curve at the top of the back rest (you can refer back to a picture of the prototype here). The two pieces have a different radius.



I checked the spring back after when I unclamped the first part. There was about 1/16 of an inch at the center. I used 6 laminations in the prototype and there was less than half that much. I like fewer glue joints , so I will live with this much spring back.



My first glue up had a little too much glue. The squeeze out wicked onto the face of the part. I used less on the rest of the parts and never had this issue again. It only took a little sanding to remove the squeeze out.



On one piece, I had a swirl in the grain that looked cool. It was on two of my parts so by placing one on the inner face and the other on the outer, I could give the illusion that the swirl went all the way through the part. Unfortuantely, the part on the outer surface broke during clamp up. I had to unclamp, unwrap, remove the broken part, retrieve my spare 6th part, rearrange for grain and color, clean the glue off the new outer surface and reclamp. It was a bit of scramble, but it all worked out.





After unclamping, I trim the part to width and length. I am very pleased with how these parts are turning out. The glue lines are hard to find and the parts are very uniform.



Here is a shot of eleven of the twelve parts. It has taken a while to get this far, but I am pleased with my pace.



Current time log:
Cutting rough stock: 2 hrs
Cutting legs to width and thickness: 4 hrs 20 min
Seat Back and Back Rest
> Cutting thin stock for laminations: 3 hrs 35 min
> Prepping laminations: 8 hrs 40 min
> Glue up Laminations: 3 hr 50 min
> Trim Laminated Parts: 2 hr 25 min

Total so far: 24 hrs 40 min

Looks good.