Expanding Round Table

Construction Blog: Page 3
Colonnade Turning and Fluting

Preface: I actually started turning these columns before turing the center column, and this was before I started documenting my work. However, I didn't finish these columns until later. That is why I wrote about them after the center column, and also why there are fewer pictures. 

Wood Preparation

For the eight fluted columns around the outside of the pedestal, I wanted to make sure that the wood grain and color was consistent, so I hand picked a mahogany plank large enough to get all of the columns from the same board. I started out by planing a 12-foot long by 14-inch wide by 2-1/2-inch thick plank of mahogany. I think it weighed at least 150 pounds. After surfacing the plank, I cut it into more manageable segments and jointed and ripped them into 4-1/2 inch wide pieces for glue-up (3 rips per segment).

This plank of wood was more than I needed for the columns, but because two of the resulting pieces had visible structural defects in the grain (cleaving grain), I decided to cut the entire plank into turning blanks, resulting in 5-more pieces than I actually needed. This would give me enough material to make 2-1/2 extra columns. Instead of throwing away the two flawed pieces, I decided to use them as a “machine-setup” column. In other words, this was a sacrificial column that I could ruin in the process of setting up subsequent machining, but it would never be used beyond that. The other pieces also gave me one extra good column as a spare just in case something went wrong, which of course, it did!

I got into quite a “groove” turning these columns, and the round blanks were coming out extremely accurate and consistent. However, since this is before I started taking pictures, this topic is rather dull and boring, so I will skip ahead a couple of steps and dive into the fluting task. This is when I began documenting my progress. 

I forgot that I had this picture, but it is the only one I have of the unfluted columns. I set all of the columns out on the floor just to get an idea of the scale and design of the pieces to make sure that what I was visualizing during the design was how the actual parts would look.

Indexing Ring

I knew that the best way to flute the columns was to keep them mounted on the lathe and run the router on rails over them, but my Oliver lathe was not easily adaptable for indexing the turning every 30 degrees. So I decided to create a sled for the shaper. This didn’t work. The first column went OK, but the second column went south. Since I had only one spare column and couldn’t afford to ruin another one, I decided to take the time to make a router carriage for the lathe.

It took a while to figure out how I could make an accurate indexing ring without altering my vintage Oliver lathe. I removed the bell housing from the reeves drive, inverted the hand wheel, and screwed the indexing ring onto the back of the hand wheel. I slotted the indexing ring so I could run a bolt through the ring and into the original mounting hole for the bell housing. I later discovered that the big handscrew from my shaper’s fence fit the bolt hole. This made changing the index a lot easier. It doesn't look very pretty, but it sure worked well.

Router Carriage

The router carriage for the lathe was actually easy. I already had the base of the carriage built years ago to hold my drillpress to make a large set of hollow spiral columns. It uses bearings as wheels and is captive between the steel rails of the lathe bed. I mounted my Festool OF1400 router to an aluminum sheet and mounted that to the carriage.

I positioned the router so the carriage would hit the lathe's headstock at the top of the flutes. To control the bottom position of the flutes, I used the tailstock as an adjustable stop. I could change the position of the end of the flutes by increasing or decreasing the extension of the live center.

To flute each column, I locked the indexing ring into one slot. I then moved the carriage toward the headstock and plunged the router down into the column. I then rolled the carriage to the side until it hit the base of the tailstock. With each single flute complete, I had to remove the hand-screw, rotate the index ring to the next slot, and repeat this 12 times for each column. It was mind numbing redundant work, but with this setup, it was error-proof.

I skipped ahead in my pictures, but this image shows the fluted columns after they were completed. The octagon in the center is part of the base, which is discussed on the next page. You'll notice that I still have not removed the plywood scrap from the top of the center column. I won't remove this until I am ready to assemble the base just in case I need to re-mount it in the lathe.