Turning long slender spindles on a wood lathe is a challenging task which can result in poor finishes due to vibration and chatter. Results can be improved when the stock is stiffened to reduce work piece deflection from tool pressure or compressive forces from the tailstock. Steady rest can provide this support, but are not practical when using a lathe duplicator. One method of stiffening the work piece is to hold it firmly on both ends and place it in tension. As a result, longer and thinner spindles can be turned with better results.
My solution for holding work pieces in tension combines a Chuck with Spigot Jaws on the headstock with a Collet Chuck, Live Center and Drawbar on the tailstock.
Step 1: Tools
A. Beall 1 1/4"-8 Collet Chuck with ER-32 Collet to fit the stock
C. Oneway Live Center with 5/16" all-thread drawbar, washer and wingnut
Headstock Chuck with Spigot Jaws
Note: This method could also be accomplished with two Beall 1 1/4"-8 Collet Chucks. I initially purchased the collet chuck for another purpose to fit my headstock, not the tailstock. The main benefit of the Spigot Jaws Chuck is holding and turning the rough stock while cutting the tenons.
Step 2: Sizing the Stock
Pictured above are 60+ blanks I turned into spindles. I started with 7/8" square hickory blanks of various lengths (18" - 24") that were trimmed to an octagon to reduce the amount of stock to remove, as well as to allow the cutting of a 1/2" tenon on each end using a Veritas Dowel and Tenon Cutter. The tenons were cut by mounting the blanks in the Spigot Jaws of the chuck and running the lathe at a very slow speed. The board attached to the Tenon Cutter rest against the bed of the lathe, and provides support while cutting the tenons. This made easy work of the blanks...like sharping a large pencil.
Step 3: How It Works
One end of the stock is firmly mounted in the Spigot Jaws of my headstock chuck. The tailstock is moved into position, and the tenon is placed in the collet chuck and tightened with a spanner wrench. The tailstock is locked down, and the wingnut of the all-thread drawbar is tightened. Next, the ram is retracted in order to place the work piece in tension. Tighten the wingnut again to firmly seat the chucks morse taper in the tailstock.
Placing the stock in tension stiffens it, thus reducing the amount of vibration from tool pressure and/or the compressive forces generated by the tailstock ram.
As seen in the photos above, this method is capable of exerting 100 lbs of force on the blank without either chuck slipping. While using this setup, I probably wasn't exerting more than 15 or 20 lbs of tension on the work piece, but this is only a guess.
More information about calculated and experimental results of different work piece mounting methods can be found at the American Association of Woodturners (AAW) written by Dennis J Gooding, "AN ENGINEER’S LOOK AT TURNING SLENDER WOOD SPINDLES".
Step 4: Results
The photo of the lathe duplicator shows an example of spindles being turned between centers. The results were unsatisfactory because it seemed to produce a lot of chatter. As a result, I was motivated me to try this technique.
I was able to turn 60+ chair spindles (18" - 24") with a finished diameter of 5/16" (8 mm) near one end. These were made using a lathe duplicator. The finish required some sanding, but overall the results were great. Turning thin spindles with a hand tool using this technique should yield good results as well, as Dennis J. Gooding confirmed in his article.
Instructions for building my duplicator seen above can be found at Wood Lathe Duplicator With Angle Grinder.
One thing I noticed after turning very thin pieces (5/16" or 8mm) the spindles behaved like torsion springs. With the lathe stopped and the work piece in both chucks, I could twist the collet chuck a few degrees and release it which resulted in a slight oscillation axially for a very short period of time. I cannot say for certain how this affected my results, but the 2 lb 6 oz (1.07 kg) weight of the collet + collet chuck + adapter probably affected the results one way or the other. I hoped to reduce this affect while turning by cutting the thinness section last, and placing the thinness section closest to the headstock.