This bowl is titled experimental since I've taken on a type of woodturning I've never done before. Yet I documented the process enough to be sure I could pass on to you, the reader, enough insight for you to make one of your own!
This bowl is made by turning a whole piece of log on its side, and this presents the woodturner with many obstacles to overcome, starting with the mounting of the log to the lathe, and ending with the fact that the bowl will present two large knots (which are the center of the log, a part of the wood we try to avoid mostly in woodturning for its tendency to crack while drying), with a few more surprises between those.
The skill level you will need for this project is low to medium, and it has just a few more points to be aware of while turning than your normal bowl turning technique.
Step 1: Mounting Your Log
Since this turning will be done on a whole log, instead of what we turners call "a blank", it presents a few unique problems to overcome. Branches, uneven bark and the general shape of the log might prevent us from simply mounting the log and spin it freely.
First, if the length of your longest diagonal on your log is longer than the swing of your lathe (mine is a 12 inch swing lathe), you will need to trim the edges of the log so it will spin without hitting the lathe bed.
Next we need to find the center of the log by width and length (using one of two rulers), once we decide which side will be our top (that side will get tapped with the drive center) and which is our bottom (will be held by the tailstock with a live center), we can tap our drive center into the log (some like to flatten a spot for this, or even drill a small indentation using a forstner bit, but if the bark is not too thick, you can just hammer the drive center to it well and make sure it grabs wood).
As you can see in the pictures above, I had some problems with a few of the branches hitting the front facing motor cover, but a few strokes with an axe and some sawing took care of those. I finish by giving the log a test spin to see nothing hits the motor and the lathe bed, and we're ready to move to the next step.
Step 2: Shaping the Outside
Using a bowl gouge exclusively on this entire project (except for a couple of uses I had for the paring tool) makes the job of turning the outside of this bowl easy. We will make a conical shape that will show in the best possible way the "wings" of the bowl made from the high points of the log vs the low points. once the "top" of our bowl is fairly round we can go on to shape the rest of the bowl, ending with the foot of the bowl, where we will turn a tenon so we could reverse mount the bowl into the chuck.
Step 3: Creating the Tenon
In order for us to be able to hollow out the bowl we will need to create a tenon on the bottom of the bowl for us to grab on to with our chuck. Using the parting tool I prepare the surface for the tenon by making a flat spot on the bottom of the bowl, then using a caliper to measure the tenon width I cut it flat against the bottom.
Step 4: Filling in the Cracks
After giving the bowl a light sanding using 80 grit sand paper, we will take the time to fill in the knots, small spots of rot and cracks we have all around the bowl. I chose to the CA glue (super/krazy glue) and used coffee grind as the filler, since I didn't want to "hide" those features but make them even more pronounced against the bright grain of the wood.
By creating a small mound with the coffee grind, I can drop a few drops of CA onto the center and mix it until I get a putty like consistency which I can use to fill in the voids. I even used the same paste to fill in some worm holes that I located near the "sting" of the bowl.
After the CA/coffee putty has dried and hardened, I'm using some power sanding with my homemade sanding pads and 5 cm (2 inches) wide velcro backed sanding paper circles, from grit 80 to 400, to smooth the bowl all over and get it ready to be finished on the outside.
Step 5: Finishing the Outside
After the outside of our bowl is sanded down to 400 (for project I'm leaving with a natural edge and a matt oil finish I will sand up to 400, no more), I can start applying my choice of finish, in this case, mineral oil. Now, the oil are using will do a few different things. It will condition the wood, slowing down the drying process greatly, which is good, since it means there is a good chance the knots which are the center of the log will not crack and knots tend to do when drying. It will displace some of the water in the cells of the wood, making it more stable, and it will give our wood a stronger color, and will make the grain "pop" out.
Applying the oil will show you very clearly the difference between end grain and cross grain, as when you will apply the oil on the end grain part (the center knot of the wood) you will see it soak up really clearly, any oil placed on it at the start will quickly be absorbed, while the end grain, absorbing some, while leaving most of the oil floating on the surface. This is what we want to achieve in the end grain sides as well, for the oil to soak in until it floats on the surface, that is when we know the wood is saturated,
Once the whole bowl is soaked and no more oil penetrates the wood, wipe off the excess with a clean paper towel.
Step 6: Flipping the Bowl Over
Once the outside of the bowl is done, we can replace the drive center with our chuck, and mount the bowl to it using the tenon we've created before. As you can see from the second picture, I am using my tailstock for support and to give the wood equal pressure while I tighten the jaws of the chuck, after which I remove the tailstock completely, in preparation for hollowing of the bowl. Bring your tool rest all the way to the bowl's face, but mind you, if you have any branches (like this piece has), make sure they don't hit the tool rest, or the banjo, while spinning.
Step 7: Hollowing the Bowl
Although a crucial step in the process, this one is so straightforward, a good look through the images will give you all the information you need!
As you can see from the image progression series above, I started on the two small branches I had on the surface of wood, once those were taken down, I started pulling from the center out (a pull cut is a little bit cleaner than a push cut, at the relatively low surface speed the center of any vessel has), first taking out the barks, and than starting to dig well into the wood. I leave the edges of my bowl to the end to prevent stresses on the side walls of the bowl as the narrow profile is being created.
What I like the most about working with uneven wood surface, like this bowl, is that for a long time into hollowing the inside of the vessel, you can see clearly with your own eyes the width of the walls in the ghost image created from looking at something spinning which is not whole, Like you being able to see the bowl gouge cutting inside the bowl in one of the pictures. Of course that later on, when the walls are already high, I will use a caliper, both to gauge the depth of the bowl, and both for the widths of the walls using a special curved caliper.
Notice how I position my tool rest in the last couple of images, to allow me to cut along the walls of the bowl with as little space as possible between the wood and the gouge. This will prevent the gouge from vibrating and creating marks on the walls of the bowl which will be problematic to sand even later.
Step 8: Finishing the Inside
Dealing with the cracks and knots on the inside of the bowl is exactly the same as the outside, only this time I'm using fine sanding dust as a filler. The dust mixed with CA glue works perfectly to fill in any holes I can find in the wood.
Once the glue is dry I can power sand the whole of the inside to the bowl, all the way to 400 grit, much the same as the outside, some done by hand to make sure the curve of the bottom of the bowl is sanded down correctly.
I finish up by applying once again a good amount of mineral oil, again, until the wood doesn't soak up the oil any more, and then I wipe the excess with a clean paper towel to finish up.
Step 9: Parting the Bowl Off
Now my bowl is done, both inside and out, I can use my parting tool again to start parting the bowl off the lathe. Slowly I chip away the wood at the base of the bowl, angling my tool upward into the bowl so I will have a ring of wood as the low point around the edges of the bottom of the bowl, while the rest of it will be "lower" than the sides, so I know my bowl will always sit flush against any surface.
I stop before the bowl is completely parted and I finish parting the bowl using a saw. Later on I sanded the rough surface of the bottom of the bowl down using my power sanding pads, as seen before.
Step 10: Enjoying Your Work
And the bowl is done! I hope you didn't nick your fingers or hand on the spinning bowl wings, as that happens a lot, and if you had any "special" feature survive the turning (note the "sting" I had created from a branch that was luckily situationed in my log), consider yourself lucky, as those add a lot of character to the bowl.
Mind you I lost small pieces of bark turning this bowl. This is mostly avoided by applying a bead of CA along the border of the bark and wood all around the bowl, but since I didn't do this step in this project, it is not shown. Just be mindful of that technique and use it when needed.
Thank you for taking the time to read this Instructable!!