Project Tutorials

Helix

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This wood is fresh cut and warps as the turning progress. At times you may find that two sides of the bowl have a ridge left. If the difference is slight don’t worry about it as long as the grain is cut smooth without tearout. The ridge can be removed with power sanding later.

Sand the inside smooth. This is very important because a pencil is going to be pulled across the surface to make the mark for cutting the helix.

Make sure that the inside surface is a smooth continuous curve without any bumps.

I use a colored pencil with a blunt tip so it won’t break easily. With the lathe spinning at a slow speed, around 200 to 300 rpm’s, let the pencil find the center. If your lathe won’t go that slow you will need to go to its slowest speed and make your mark very fast. Pull the pencil down or to the side in a straight line quickly, maintaining contact with the wood. Stop the lathe and see what kind of mark you have made. If you have a mark that is 1 ½ to 2 full revolutions in the bowl from bottom to top that will work fine. Too many revolutions and the pieces will be hard to separate once cut. If it did not make a good mark the first time sand it away and try again until it does.

This is what your mark should look like. There are 1-½ revolutions from bottom to top. The easy part is over, now we need to make two more marks equally spaced around the inside by hand to match this one.

The index plate on the pulley assemble comes in handy for dividing the outer rim into three section. With the 48-hole plate on my Oneway lathe I move the bowl 16 holes at a time to mark the outer edge.

Set the tool rest close to the edge of the bowl and align the first mark with it. Index 1/3 around and make the next mark, another third around and make the last mark. There are now three equally spaced reference marks on the rim of the bowl. You can also use dividers to walk around the rim but if you are like me and only have six-inch dividers you will have to set them to make two steps for each mark. This bowl is 11” in diameter and the rim circumference is about 35”.

Hold a pencil against the wood and make some reference circles at steps from the rim to the bottom. The exact distance the circles are separated by does not matter; they are for reference marks only.

Using dividers to mark intersections at the reference circles. Walk the dividers from the original mark around the bowl in thirds and make a mark every 120 degrees so you have the three equally spaced marks.

Hand draw two more spirals to match the original using the marks at the reference circles. For me this is about the hardest part of this project.

With the spiral marks completed I drill the center with a bit so when I reach the bottom of the bowl during band sawing I can turn the blade inside the hole and cut back out. The depth drilled only needs to be a little more than the wall thickness of the bowl.