Expanding Round Table

Construction Blog: Page 2
Center Column Lathe Turning

I knew it would be quite some time before my machine shop could get any of the mechanical components ready for me, and without them, I couldn't begin working on the upper section of the table. So I decided to work on the pedestal first. This is the opposite approach I took 10 years ago, but back then, I didn't design the pedestal until after the whole upper table was finished. This time around, the entire table was fully designed and documented before I even ordered a single component.

Center Column Glue-up

I started out with a plank of rough-sawn Mahogany 13" x 2-1/2” x 12’. The plank was so heavy that I could only lift one end at a time to get it to the Radial Arm Saw (RAS) to cut it into more manageable lengths before planing. The finished blank was to be 5 layers thick from this board, so I first glued up the outer boards (picture to the right). Since the gluing surface was 240 sq. in. I was concerned about getting sufficient clamping pressure and used as many clamps as I could fit. (Ya think Norm would ever use this many clamps? If it is not obvious from the picture, I am a strong opponent of the whole "starving a joint" myth.)

After the first two glue ups (shown above) were completed, I cut them to width and length. However, before cutting them to length, I re-squared the sliding table on the tablesaw to ensure that the cuts were true. I realized early on that I would not be able to square the ends of the final glue up due to its size, so this was the last chance I had to make things square.

To get better glue joints on the center boards, plus to reduce the weight, I split the center board so there is a 2.5 x 2.5 inch hollow core. To make sure that all of the ends lined up, I used the new Festool Domino tenon joiner to register the ends to be flush. (You'll read much more about this tool later.)

This last glue-up is shown to the right. The top and bottom pairs are from the previous glue-ups, and these were glued to the middle pair. From this picture you can see how well the ends lined up.

Knocking Down the Corners

After the glue-up, I knocked down the corners as much as I could with the tablesaw. I drew the circle on the turning blank to make sure I didn't cut too much. Obviously that wasn't anything I needed to worry about afterall. This was the deepest I could cut, and it was no where near deep enough to bring the corners down to a turning radius.

It Won't Turn Very Fast!

The sheer massiveness of the turning blank isn't really obvious until you see it mounted on the lathe. Well now you know why I took the time to install the VFD on the lathe! This lathe is one of the heaviest tools in the shop, and the turning blank makes it look puny.

To mount the blank, I installed a face plate to the headstock end, and a piece of plywood to the tailstock end. Yes, I mounted a spindle turning with a faceplate. There is no way I was going to turn something this large with just a live-center holding it to the lathe. If this thing cut-loose, it would mash me against the back wall like a bug!

For those readers that are not familiar with lathe turning, I am adding the names of all the major parts in the picture to the right.

Because the turning blank almost touches the bed of the lathe, I needed to trim it nearly round before I could rotate it. I used a powered hand planer to round the corners. After rounding the first corner, I had to remove the blank from the lathe just to rotate it to the next side.

After rounding all four corners, it was time to spin the lathe. I discovered that the turning blank was so heavy that I had to reprogram the VFD for a higher starting torque just to get this spinning without stalling the motor. (I am glad I spent a few bucks more to get the programmable VFD.) Needless to say, I kept the speed pretty low until I was sure the blank was reasonably balanced.

My Roughing Gouge Can Go Around Corners

Shortly after turning on the lathe, I realized that I could not get the banjo to fit between the blank and the lathe bed. (The banjo is shown in the next image below.) So I decided to use a makeshift tool rest clamped to the front of the lathe bed. The concept was good, but I was too impatient and mounted the tool rest too far away from the turning. I hadn't gotten very far before the gouge caught in the turning.

Needless to say, it was a bit of an eye-opener, and it had me on edge for the whole rest of the turning. (Just in case you didn't know, that tool is supposed to be straight.)

After my failed attempt at making an outrigger tool rest I decided to work inward from the ends until I can get the banjo under it. This idea was going well for the tailstock-end of the turning, but then I realized I didn't even have enough clearance at the headstock (between the headstock and the turning) to install the banjo at all. The only way I could begin turning at the headstock end was to retry the idea of a freestanding tool rest. This time I used the frame from a roller stand as a tool rest and braced it with wood to make it rigid, yet movable to keep it close to the turning. I Very Carefully roughed out the headstock end enough to get the banjo underneath.

Even with the ends turned down, the center was still too thick to move the banjo from side to side, so I had to remove it from the lathe whenever I wanted to switch to the other end of the turning. I had the original column design created in SolidWorks and created a dimensional drawing from the model to show me the major diameters and where to place them. Unfortunately, I discovered that I don't have a caliper large enough to mark these diameters. So instead, it took longer, but I shaped the profile by eye. In the end, this was better because I was able to balance the curves on-the-fly for a more aesthetic shape.

From the basic shape, I did some reshaping for aesthetics and then finished the two ends (top and bottom). Even the final turning was still a little hairy because the only tool rest I own is the 12" straight one, and several areas of the profile forced me to have the gap between the tool rest and turning larger than desired. Memories of my bent gouge flashed through my eyes more than a few times, and having a tool catch at this point would have been catastrophic.

I have really come to appreciate the mass of my Oliver lathe during this project. I've had a lengthy discussion on the "Old Iron" discussion forum, and no one can identify the age of this lathe because none of the castings are typical for an Oliver Model 159. I've come to realize that this lathe weighs much more than a standard 159 even without my extended bed because all of the castings are thicker than normal.

Here is the final column after sanding. I am pleased with the shape and transitions.