This is a great project for experience turners. It goes beyond a standard bowl with the challenge of working out of round. The same principles can be used for natural edge.
Step 1: Squaring Up the Blank
The blanks that I got were close to square but not quite perfect. After selecting one edge, I used a combination square to make my marks. You could also use a diagonal check to make sure is square. Then I cleaned up the edges on the band saw. A table saw or a drop saw would probably be idea but work with what you have.
Step 2: Mounting It on the Lathe
Normally I would use a screw chuck however with the forstner bit, I can drill a hole for the chuck. This will allow me some minor adjustments to make sure all corners line up. I have it semi tight in the chuck and tap the low corners. Spin it by hand to make sure the blank is true. Then tighten the jaws for a firm hold.
Step 3: Turning the Underside
Warning: Turning square or natural edge is more dangerous. With the uneven edges, if you slip, it will likely draw blood.
After marking out the size of the foot, start removing some of the waste with pull cuts. I like starting on some solid timber and moving to the outside. That way you get easier consistency with the cut. (pic 2 and 3)
Keep removing waste and define the foot. I clean up the edges of the foot with a skew. That gives a fairly clean cut. I enjoy adding some detail of a 3 v-grooves. The set is a simple touch that adds another element. (Pic 4-7)
When most of the material is roughed out, resharpen the tool and finish with an even flowing push cut. This will give the best finish. Try and do it in one cut with a sweeping motion. If you do it in multiple, rub the bevel and pick up the cut again. Looking at the profile on a flat spot, it should be a consistent curve with no flat spots. You can hold a ruler up to it and if the ruler is in contact with 2 spots, its not a perfect curve. There should be a similar angle the entire way.
Sanding is one of the parts that is most dangerous. Sand the middle section like you would any other bowl. The wings is the more interesting part. That I do with a palm sander. Its the safest way with out shredding your fingers. You can sand a little bit of the wings on the lathe as long as most of the pressure is on solid timber. I sand with 120, 180, 240 and 400 grit with both by hand and on the palm sander
Step 4: Turning the Inside
Warning: Keep fingers behind the tool rest. Easiest way not to get cut by the spinning wings. Even be careful when moving to turn the lathe off. That one is from past experience.
Start with a few cuts just on the outside of the solid section into the middle when you are no longer cutting air. A few cuts should be stepped down. The reason it should be stepped is if you try to flush is up from that direction, you are likely to get a catch. A cut from the other direction should clean that up.
Picture 2 shows the ghosting created by the spinning wings. You can see the tool as the timber spins. The key to get a consistent thickness of the wings is to keep the bevel parallel with the underside of the wings. I like to keep the bowls at a 5mm thickness.
To get the wings even, you cant take it all to the 5mm thickness straight away. It needs to be done incrementally to reduce chatter. Pictures 3, 4 and 5 show this. You can use calipers to get the thickness but I like working from touch as you pick up little bumps that may be harder so see in the calipers.
After the wings are done, you can start removing the bulk of the middle. It will be flatter but there should still be a flowing curve. Like the outside, you still dont want flat spots. Once again I like adding 3 v-groves. It just adds a little more character to the bowl. The ratio that I like is the middle ring should be 1/2 of the total diameter (opposing corners). The other groves I make 5mm from the center one which also ties into the thickness.
Sanding is done in a similar way to the underside with care. The concave shape however means you can not use the palm sander. I use a 50mm soft backed pad on a drill. With a sharp bevel rubbing cut, there should be no tear out to sand. If you sand too much, that can distort the shape
Step 5: Sand the Edges
There were still band saw marks so I used the disc sander and then the palm sander to clean the edges. Use a ruler to measure the corner to corner and then the sides to make sure it still has its true shape of a square. Then arise the edges to take away the shape edges.
Step 6: Finishing
A trick with purple heart as a timber is after turning, it can brown a bit. To get the colour back into it, leave it in the sun and you will see the colour come back. Shouldnt take too long.
Like most of my projects, I spray it with satin lacquer using a gravity fed gun. 3 coats with a cut back in between the 2nd and 3rd.
Step 7: Quick Video of Me at Work
Sometimes a video can show a bit more of the process. Good luck and keep turning