Plotting Curves

Now that I have a new scanner/printer (aaaarghh!!), I am able to continue the drafting series, although the images may vary a bit as I work out the bugs in my new tool.

Below is a three view sketch of a basic chair top design. It shows two posts as they emerge from the seat. To start, I thought that it would be best to have the posts be straight, to determine their basic limits.



As I covered in previous posts, information is taken from one drawing to the next to create the three views. When I design a chair, I work from some basic limits. For instance, I generally know where in space that I want the crest to sit, and you can imagine that the points on the end of the posts in each drawing would be in contact with the crest at that point.


Well, that being the case, it may not matter if the posts are straight or curved, as long as the top points are at the correct spot to support the crest at the chosen position. So for fun, let's throw in some curves. Initially, I like to focus on the front view, although it might change later based on the results in the other views. This curve is a bit extreme for an actual chair, but I thought that it would help to illustrate the point.

One very important factor to note about the chair that I am drawing, is that the curve that I am going to draft still sits in the sight line plane. In other words, just like the straight post, when viewed from above, the post will look like a straight line, so the overhead view won't change as I plot the points.
Below, you can see that I've plotted a point to start the side view.



I do this by selecting a point on the front view of the post and drawing a line horizontally to the side view. Then I project a line vertically from that same point and then "refract" it back down to the side view. Where they meet is my new point. It's fun to watch the curve emerge as I plot more points.


And here's the finished curve, truly a bit extreme!


Now with the side view apparent, it would be a good time, if making an actual chair design, to adjust the side view and then plot the points back to the front to see how to possibly temper this intense curve. In this instance, the side view is extreme because of the limit that I set in the beginning that the overhead view remain straight. Getting into curves that lie in a tilted sight plane is a bit heady for this example, and frankly, it makes my head spin.

Now, this is all fine and dandy, but if I was actually making a form to bend this curve, the information to shape it isn't apparent in this drawing, after all, the actual curve isn't seen fully in the front or side view. What we need is a profile of the curve, or in other words, the view from the side of the sight line.

I figured out this method years ago and then promptly forgot how I'd done it! With my recent renewed interest in drafting my curvaceous chair, I rediscovered the method.

Basically, we want the view that the creepy eyeball in the image has. So by extending lines at 90 degrees to the post in the overhead view and refracting them at 1/2 the angle of the sight line of the post, we can begin the same process that we followed before to get the side view of the curve.


Below is the resulting curve. Hopefully you can imagine that if you rotated the curve that I plotted on the right, it would be the same as what you see in the other images.


Sitting down, working this out and thinking this way has help me understand more of the geometry involved in the chairs that I am making and the factors that I can control to make them more beautiful and comfortable. While it may seem like too much of a throwback to a time passed, to me, it's just like the time spent making chairs by hand, time well spent.

New Happenings

Recently I got a counterbore from Morris Tools in Tennessee for my arm to stile joints. Boy does it make a difference.


I used to first drill a "shoulder" with a large forstner type bit and then finish it with a smaller bit for the actual mortise. It wasn't impossible to line them up, but it took some doing. Once I reground and sharpened the cutting spurs on the counterbore, it drilled a gorgeous joint and the alignment was a non issue. Below is the finished mortise.


Also on the tool front, I've been meaning to mention that while in Atlanta, I noticed that Highland Woodworking carries the diamond profile parting tools in the 1/8th inch size. Folks have contacted me looking for this elusive creature after I posted that it was my preferred size for turning but especially for the way it works with my caliper. The smaller cutting edge means less vibration and resistance but still cuts a wide enough kerf to easily measure.

I'm not sure what it says about me, but one of the most exciting and fun things to enter life here is our new ice cream maker. It's of the old wooden bucket variety (but with a motor, sorry galoots) and we've been putting it through its paces. It fits perfectly with our plan to have our goat milking in the spring. After vanilla, we decided to try mint chip, but no extract and green food coloring for us, I found a recipe and headed to the garden to pick the mint. Yes, Sue is still mad that I put mint in the garden, we'll never be rid of it!
Below is the mint steeping in the milk.

Here is the finished custard.

And into the freezer.

And the finished ice cream (actually, I probably stopped a bit short, but it froze in the freezer fine)


By the way, half of the sweetener in the mix is maple syrup from last spring, just one more reason to look forward to next years sugaring season.

Come to Life

It's always fun to see a project from drawing to completion, and this week with Alan Gensamer, we did just that. The drawing above is scaled so that 3/16" equals 1". Below is the finished piece.



Other than a mishap with drilling the arm (I foolishly veered from the drawing and paid the price of bending another arm!), the piece went very smoothly. Here's Alan getting it all together.


I haven't forgotten the curved stretchers, their drying in their forms. Below is a new (to me) bending method. I was getting some trouble with separation where the turnings narrow and expose endgrain, so I thought that I'd finally found a place to use a strap.



Not only did the strap work nicely controlling the separation (just a little in the center), but it pulled the piece to the form very evenly. My handy Irwin clamp (spreader) put so much force on the piece that the texture of the strap is embedded in the surface of the stretcher!

I've been asked about a million times about using straps in bending, and honestly, I've never found the need. I know that some very tight radii or thick bends could call for a strap, but the "normal" bends in my chairs have always bent just fine. I attribute this mostly to using straight grain white oak and hickory and shaving carefully along the fibers. I'll be knocking this piece together this week (hopefully), but today will be slow, Alan and I put in 7 days and I'm whipped!