Tuesday, 9 October 2012

Bare Fence Posts & the Turnip of Destiny

Well, I finally got around to turning something.

This summer my wife and I spent most of our free time in July replacing the fence at the front of our house.  When it came to the front gate we wanted to fancy it up a bit. We talked about options like a trellis or lights or some fancy post caps but didn't really settle on anything.  So now the posts are bare on top and a lot taller than they really should be.

On the last weekend of July I attended the Saskatoon 2012 Wood Turning Symposium and saw a demonstration on how to do a barley twist by Beth Ireland.  Although I was impressed by the versatility of her method, inspiration didn't really hit me at the time.  It was only later that an idea of what to do with the gate posts started to form.

The image that eventually formed was that of a wooden candle flame.  Although I'm not 100% sold on the giant candlestick look for the gate posts it became one of those things I had to do.  Just to see if I could.

I started by creating a profile on my cad program and transferring it to cardboard as shown below.

When I turned the mahogany in the background to match the profile it came out like this.

I immediately christened it the Turnip of Destiny.  Yes I am a total geek.

Once the shape was achieved it was time to lay out the twist.  I started by making a copy of the template out  of thin plywood and using it to mark off longitudinal lines on the turnip.

My lathe has an indexing wheel on it with 36 positions, or every 10 degrees of rotation.  For every two lines you make you will get 1 helix, or twist, on your piece.  I used every second position, giving me 18 lines and 9 helix.  After marking the lines along the length I used the 1/2" increments on the first template to mark out the placement of the lines of latitude.  A quick spin of the lathe takes the line all the way around.

Once the grid was marked out I used a cardboard straight edge to mark the diagonals.

If you were making a reed (or rope) style twist you should mark the diagonals starting from all 18 of the long lines but because I planned to make a fluted twist I took a short cut and only marked 9 helix.

As the diameter of the turnip changes the angle of the helix and the space between them also changes.  This creates a cool effect as you go along.

Now it was time to pull out my weapons of choice to make the twists.  These were a Microplane Rasp with a round blade and a small riffler. 

I started with the rasp at the widest point of the turnip and worked my way downhill in both directions, trying to stay centred between the marked twists.

At the ends, where there is less room to work, I used the riffler.

When using the riffler it really pays to use as many of the teeth as possible.  Because it is curved you can fall into the trap of just using a small portion.  This cuts a few deep grooves, but then it slows down and looks like crap.  If you use a curving stroke though, you use all the teeth and, because of the random pattern, it cuts faster and leaves a cleaner surface.

The pattern starts to emerge.

After sanding, two finished fence post finials.

In the end, the hardest part of this project was trying to make the turnips match the template.  I really suck at making things match.  It actually took longer to turn them than it did to shape the twists.