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Off-center and Off-axis turning- A Complex ZigZag Finial

July 18, 2013

It´s always exciting to try something new with turning and one avenue I had never tried had been off-center turning.  I have some long range plans of using off-center turning to enhance some sculptural and monumental turnings but first I needed to explore some of the basics.

Some of you know Paul Hedman from our Fargo-Moorhead Turning Club.  He is making a name for himself nationally with his innovative and creative turning, often eccentric.  He and I did a joint workshop in my shop in Winter 2012.  I had admired his work and we had often spoken of the mechanics of eccentric chucks, and his increasingly sophisticated series of chucks.

Then at the Turning Symposium in St. Paul in the summer of 2011, I saw one of the new generation of Escoulen eccentric chucks and I knew I had to have one.

The Escoulen eccentric chuck surrounded by some of its various "work-holders."

The Escoulen eccentric chuck surrounded by some of its various “work-holders.”

You can look at the Chucks Plus website to see more information on the chucks.  They are definitely expensive ($500 for the basic chuck and another $250 for the ball attachment) but I have found them to be very well designed and made to allow lots of creative turning.  What I like best about them is:

  • A variety of ways to hold the wood, but mostly with a cup chuck, a nice solution wth end grain/spindle oriented wood
  • the ability to use the ball joint to change the axis of the wood in fairly repeatable ways
  • and also to slide the work off center.  I like best to combine those two methods
  • the ability to slide the weights to balance the work for good turning speed and minimum chatter.  That makes for good quality of finish in the final turnings.

My first goal was to design and turn some new finials for some hollow vessels that I was turning.  I wanted to start with Paul Hedman´s design and make them even more thin and angular.  The following video will show the process I used to turn those finials and also a few of the finished designs.  You can look at the following video from a TV broadcast that shows two kinds of eccentric turning.

I used either hard sugar maple for light colored wood or Rosewood for dark colored.

I have a great stash of rosewood that I keep for just such projects as this.  In about 1994 I found a dining table at Goodwill store in St. Paul. MN.  It was rickety, with bad joints in all the 6 chairs but the table was solid.  Best of all the wood was Walnut and Rosewood.  I quickly cannibalized the chairs for parts and have used that Rosewood for many projects since.  From its color and grain, I believe that it is Indian Rosewood.

I cut the wood to a size that seems appropriate, with the wood perhaps  1 inch by 1 1/2 inches to allow me to swing the wood on its axis and still have enough wood.  Like many fragile looking turning projects, goblets and even thin-sided bowls, they can be done only by leaving enough wood close to the chuck to support the turning further away from the chuck and then slowly and gradually thinning the wood closer to the holding point.  It gives the work a magical quality that people can´t imagine how such thin and fragile work was created and supported.

Mark the centers of the rectangular piece, hold it between centers and roughly soften the corners of the piece.  I don´t want it round because I am using a rectangular cross section piece to allow zig zags all on one axis.   The most important task between centers is to create an accurately shaped spigot to pound into the cup chuck.  I learned from Paul Hedman that a 1/4 inch final spigot size is very versatile- fine enough to look good on a delicate finial but also sturdy enough to support a large one.

One of the new techniques I learned in this process is how to adapt an open end wrench to be an accurate cutting tool for spigots.  The Escoulen chuck includes a measuring gauge for accurate spigots, but by using an open end wrench, you can both cut and measure with the same tool, always a more accurate operation.  To adapt a wrench, buy or find an open end wrench of the right size (which helpfully is just a tin fraction larger than the specified size) and sharpen the top flange of the wrench.

For short and small finials the spigot can be the 10 mm spigot, but for larger and longer ones the 22 mm is suggested for more support.  For the larger ones it also makes sense to make the spigot longer for more support, perhaps just over one inch.  Be sure to flatten and undercut the face that will abut the chuck.  There are two problems I have had to deal with when I finally pound the spigot into the chuck.  First, it´s difficult to pound it in straight enough that the right angle face of the work piece fits tightly against the chuck.  When it doesn´t, I drip some thick super glue in the gap between the chuck and the work piece to add rigidity to the joint. 

The other problem is hard to describe.  It is a complex dance of adjustments to swing the ball joint side to side and also offset the work piece to put it in good cutting position.  You might find watching the short video most helpful to understand this.  But it is essential that the orientation of the work piece, especially if it is rectangular in cross section and not square, be pounded into the chuck in a way that lines up with the holes in the chuck and allows the swing in the correct plane. 

There are four adjustments you need to make, and if you set up the process well, you may only need to make two of them with each swing of the zigzag finial.

First, the swing of the ball.  You can read more in the Escoulen chuck material about how the set screws control the movement of the ball.  Three pointed set screws tighten into machines depressions in the ball to either point the ball perfectly straight, or if only one of the pointe set screws is tightened, then they allow rotation of the ball on a single plane from that center point.  The other three set screws, which are flat as they meet the ball, lock in whatever on or off axis position is chosen.

The second adjustment is the degree to which the whole assembly is shifted off-center.  That means loosening the two hex heads and then using the set screw in the edge of the chuck to move the center.  There is a a scale in millimeters which is helpful but not too precise.

Third, you will need to rotate the assembly.  There are three set screws to the left of the ball that have indexing marks around their collar.  You will be loosening and rotating this collar with every zigzag.  This rotation means that the off-center adjustment in step two may only need to tweaked.

Fourth, the further the assembly is off-center or off axis, the more the weight may need to be shifted to balance the turning and allow higher turning speeds.  That is done by loosening the set screws on two of the weights, but the weight that is on the opposite side of the chuck from the shifted assembly should stay where it is.  The other two can be shifted, all the way up against the third weight if you are out past 20 mm on the scale or in between if the shift is only 5-10 mm.  You may need to experiment and see if this adjustment can smooth out the vibration and allow higher turning speeds.  You can buy even heavier auxiliary weights to add to the standard weights, which may be particularly necessay if you were turning bowls or vessels on this chuck.

Then I start my turning of the finial. Depending on the height, I will do it in 4-7 steps, in each case swinging the finial as far to each side as I can. With each swing, there are three actions that need to take place.  First, loosen the three set screws and swing the work piece as far over as possible.  I like the effect of the most radical swing possible, but you may need to work up to that.  Then you will shift the work piece to the side so that you will be turning where you want to be.  I keep the tail stock close at hand to be able to see where the center line of the lathe really is.

Carefully spin the work piece by hand to make sure that your tool rest does not touch.  That may mean some considerable overhang and you may need to move the tool rest closer during each turning step.  I have a 3/8 gouge that I like to use.  It is short and sturdy, fine High Speed Steel in a metal handle that gives it extra weight and rigidity.  You will need to use your very finest bevel-rubbing turning technique to get a good surface and be very careful of your hand placement.  Be very careful.

As you come to the last section, you will want to finish the finial in the straight-on position so that the finial will stand straight on the top of the hollow vessel or whatever article you intend to add this to.  I learned from Paul Hedman to put a 1/4″ spigot on the end of the finial with a 1/4″ wrench modified to be an accurate sizing cutter.  Now, go and do it.OLYMPUS DIGITAL CAMERA

OLYMPUS DIGITAL CAMERA

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