Report of a turning topic (1993)

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From a carpenter/cabinetmaker I got an order to turn and twist 6 columns of oak, dimensioned  1500 mm.(58 inch) x 80 mm.(3,5 inch) diameter.  These columns were meant to be decoration parts on a great wall cabinet in a pub. This job took great strenght of my knowledge and experience as well as the possibilities of my lathe.

It was the challenge what made me decide to accept this order. 
  I had to deal with several problems.
 
  1. The capacity of my lathe is about 950 mm.
  2. With this length of columns I probable would need a steady center, which I don't have.
  3. Because making twists is mainly handwork and very time consuming, I had to think about a construction with which I, at least for a great part could route these twists.
  4. Another reason here was, the order came just a few days before my vacation and should be ready before I left.
  5. Until now, my experience with making twists was almost none.
  To start with the last problem, my experience with making twists was limited by making one single copy of  a chair leg. Turning wasn't the problem, but I never made a twist before. As I told before, I'm a self taught turner and I learned turning from books and videotapes. By studying these books and especially tape number 6 from Dennis White, where he explains and demonstrates the making of different types of twists, I was able to make that chair leg and now these columns.
Also a great help was the article in Woodturning nr.19, "carving on turning" by Chris Pye, where  he explains making barley twists.
  The capacity of my lathe.
I had to extend the bed bars to create a distance between centers of at least 1500 mm. Because this extension should be for one time use only, I kept it very simple. With some small wooden beams of the same dimension as the bed bars, which are 70 x 40 mm, I extended my lathe. With another two small beams I clamped it all together with bolts and F-clamps. The end of the extension bars were supported with a piece of 40 mm thick plywood which had the right length.With this construction it wasn't possible to slide the tool rest over the full length of the column, so I had to reverse them after turning halfway.
  Turning the columns.
When I accepted this order, I presumed I would need a steady center. But for the reason that I didn't have  one, I had to make one. I first tried to turn without it and discovered that it was possible to turn the columns without a steady center when I made light cuts in the midsection of the column. There was a light flattering of the wood, but this wasn't a problem because little unevenness would disappear with making the twists. Turning was done with the roughing gouge only and then coarse sanded whit a 5" sanding pad in a drill. During turning it was necessary to support the tailstock with some beams between the walls of my workshop  to stop it from shaking.
 
  Constructing a routerlathe.
Turning was the easiest part, but now I was standing for the more challenging and difficult task of making  the twists. By accepting this order I presumed this had to be done all by hand. Since this would be a very time consuming occupation, I took a better look at pictures of routerlathes and the principles of these  constructions. In contrast of what I was thinking first, the principle of such a construction wasn't that intricate. After some sketching and calculating I invented a very simple construction which could easily be built on to my lathe. Just like the extension of the bed bars, this construction also was meant for one time use only, so I used cheap chipboard to make a router carriage.
On this carriage the router could slide over the whole length over the workpiece. 
The router is moved by a 2 mm steel wire, connected on one side of the router and guided over some wheels underneath the lathe simultaneously with the router movement, the workpiece also has to rotate. To achieve this combination of movements I replaced the driving pulley by a cylinder on which he steel wire is winded around. So, standing on front of the lathe the router is sliding above the column and the steel wire is connected on the right side of the routerbase. From here the wire is guided to a wheel at the right end of the carriage, down over the second wheel underneath the extension bars to the third wheel at the left side under the lathe. This third wheel is placed right under the cylinder on the driving end. The wire goes up, wound around the cylinder, further guided over the fourt wheel, right above the cylinder and at the left side of the carriage, back to the left side of the routerbase. With a wire tightener the steel wire is tighten up. Next to the cylinder I placed a handwheel, turning this wheel does rotate the column and simultaneously moves the router.
  Calculation of the diameter of the cilinder.
 

The diameter of the cylinder on which the wire is winded around, determines the distance of router movement in relation with the rotation of the column. The outer ridge that winds around the twist is called the bine. The distance between two bines in a straight line, is called the Pitch. I decided to make the distance of the pitch one and a half times the diameter of the column. To define the diameter of the cylinder I made the following calculation.

Diameter of the column =   80 mm.
The pitch is 1.5 x 80     =  120 mm.
This means that the circumference of the cylinder also has to be 120 mm.
The formula for calculating a circumference is 3.14 x diameter. The circumference is known, so I reversed  the formula. 
The diameter of the cylinder is, 120 : 3.14 = 38.2 mm.

 
  Routing the columns.
Routing was done in several stages with different routing bits. As I have a light-duty router (900 watt) with a 8 mm. collet I couldn't use heavy cutters which match the pattern. So, I started with a 8 mm. straight bit to route a groove with the right depth. Next, with a 45 degree bit I took away the sides of this groove, so I had a big V-groove with a flat bottom. Hollowing the bottom of the groove and rounding over the top edges was done with a cove bit. Rounding over the top edges with a cove bit is not really practical, but I didn't have a alternative. With several light cuts I got close as I could get to the desired pattern. For every next cut I had to readjust the router, which was done by holding the router steady and turn the workpiece by slipping the steel wire.
Now I was facing the physical heaviest part of the job, rasping and sanding the twists. Rasping and coarse sanding was done with the lathe stationary. The following stages of sanding with grits up to 220, was done with the lathe running at low speed.

The whole operation was done in about 40 hours, I worked four and half day on it  and I had to delay my holliday for one day.
Done.

 

So, after finishing this job I closed my workshop without cleaning it first and took a well deserved vacation.