Burl Bowl For New Woodturners
Burl Bowl For New Woodturners
Burl wood is some of the prettiest wood in the world. It’s twisted and multi-directional grain give a fascinating activity to the surface of the wood. Burls usually come from large knob-like projections from along the tree trunk. These irregular growths are usually caused by a fungus. Very twisted and irregular growth patterns can also be obtained from the roots of trees.
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Burl bowls make a very good project for the beginner turner. Because the wood is so beautiful, it is not necessary for the novice turner to create the most difficult turning to have a very nice artistic result. How to Acquiring Burl
Usually the easiest way to acquire a nice piece of burl wood is from your wood supplier. The wood will already be sawn to a convenient size and kiln dried. Because the wood is sawn and dried it is easy for you to look at it an get an idea of the woods potential beauty. The way that I usually acquire my burl wood is with a chain saw. I have two large walnut tree stumps in my back yard that sometimes gives me very attractive burl-like wood.
Use of Wet Wood
In this article I will be using a very wet and irregular shape walnut root to make a burl bowl. The bowl will be rough turned. It will then be taken off the faceplate, quick dried and returned to the face plate. The dried bowl will then be returned and finished.
Getting the Bowl Round The first step is to get the piece of burl reasonably round before you put it on your lathe. The rounder the timber is the less wear and tear there will be on you and your lathe. If your burl came from a wood supplier, it very likely will be flat on at least two sides. Decide where to put the center of your bowl and then use your compass to draw a circle. Use your band saw to cut your burl round. If your burl came from a chain saw you will need to decide where the bowl is inside the block of wood. This may require a few minutes of studying to select the best orientation of the timber. Fix the wood so that you can safely cut a flat surface that will be the bottom area of the bowl. Now mark a circle on the timber with chalk. You can use a compass or any large circle that you have that is the correct size. Use your chain saw to make the piece of timber as round as you can.
Mark the center of your burl timber on both the tail stock side and the head stock side. If the timber came from a wood supplier you can do this with a pencil. For my piece there was so much soft bark and dirt that I had to mark the centers with a gouge going through the center of a large faceplate.
Mount Timber Between Centers
Next mount our timber between centers on your lathe. You will be using a spur drive on the headstock side and a live center on the tail stock side. Position the timber and bring the tailstock into position. Orient the timber so that the bottom of the bowl is against the tailstock. You will prepare this area to accept a face plate. If your timber came from a wood supplier and is flat on both sides this step is not necessary. Once the timber is made round, you will mount a face plate on the timber that was facing the tailstock. The bowl is then turned around and the faceplate is mounted on the head stock.
Lock the tailstock onto the ways so that it can not slip backward. This is very important for safety reasons. Advance the live center into the timber so that it is held firmly. Lock the live center so that it can not come lose. Position the banjo so that you are able to make cuts at the tailstock. Rotate the timber by hand to make sure that it does not hit the banjo or the ways. Set the speed of your lathe to its lowest speed. My starting speed for this project was 125 RPM. Your lathe probably will not go that slow.
Turning The Burl Round
Using a bowl gouge or a roughing out gouge start working on the tailstock area. Start working the timber round. Start from the tail stock area and make the timber run true. Once you have it true, you can rub the bevel of your bowl gouge and make nice cuts with out the tool "bumping" up and down. With the bevel rubbing work outward making larger and larger areas round. This is a slow process and you must be patient and careful. As you move your bowl gouge from the tail stock area toward the middle it is very likely that you will have "a semi-visible" area of wood. In real life the rough edges are just a "a semi-visible" blur. Carefully cut this away making sure that you do not allow this projection of timber hit you or grab your tool.
Make the entire piece of timber round using your bowl gouge or large roughing out gouge. You will slowly work your way toward the head stock. At this point you are not trying to shape the bowl, you are just turning the timber true. As the timber becomes truer and truer you can increase the speed of your lathe. Be careful to always keep the lathe speed below the vibration point. By the time I had my piece of timber true I had increased my RPM to about 250. If your lathe will not go this low speed it may be necessary for you to use smaller pieces of timber that are more in balance. It is necessary to constantly check your tailstock and advance it into the wood when necessary. My wood was very soft and I had advanced the live center about 3/4 of an inch before I had the piece round. If you do not keep pressure on the live center the spur drive will eventually spin free and not turn the timber.
Using you bowl gouge, prepare a slightly concave area a little larger diameter than your face-plate.
Attaching The Faceplate
The face plate must be securely attached to you timber so that it does not come lose during the turning process. There are 3 things that you can do to make sure that the face plate does not come lose.
First most faceplates have hole for 4 screws. This is inadequate. Drill 4 additional holes in between the ones from the factory. This gives you 8 holes. Some faceplates have a hole in the center. This hole is very helpful in getting the faceplate centered to the timber. This gives you either 8 or 9 holes for your wood screws.
Second use a large enough screw to secure the timber. This means that you will need a supply of different size hex head #8 metal screws. The hex head is good because they do not strip out like Phillip’s Head screws. The #8 metal screw is good because the large fins of the screw grab a lot of wood and have a lot of holding power.
The third thing that you can do to keep your faceplate attached is to use your tail stock when ever possible. This means that the only time that the faceplate is working by itself is when you are hollowing out the inside of the bowl.
Since my piece of timber was quite heavy I used a one inch hex head screw. For smaller bowls I would use a 3/4 inch or 1/2 inch screw. I like to make a small starter hole with an awl to make it easier for the screw to go in.
Shaping The Exterior Of The Bowl
Mount the timber using the faceplate on your lathe. Bring the tail stock up and secure it tightly. Advance the live center into the timber and lock it into place. This is a important safety precaution.
You are now at the point where you get to start using you artistic abilities. Look at the wood and start thinking about what shape you would like to make. An open bowl like a fruit or salad bowl is a good simple project that can give very nice results. Cut an exterior shape that you like. The Roman ogee is a classical shape that is very popular. Since my timber was very wet it was necessary to only rough turn it at this stage. It would have to be dried before I could make my final cuts. Use your bowl gouge to shape the exterior. Cut the area at the face plate down to about 1 inch larger diameter than you want your final bowl to be. Adjust your banjo constantly so that it is always close to the area that you are working. Start shaping the exterior of the bowl. Use a small gouge to shape the foot of the bowl. When you have working room it is good to use the bowl gouge from the small base plate area to the larger diameter of the bowl. In this way you can rub the bevel of the tool and be cutting on supported wood grain at the same time.
Hollowing Out the Interior
Now that the rough outer shape is completed it is time to cut the interior. Remove the live center and attach a Jacob’s chuck bit into your live center. A Forstner bit makes a very nice center hole. This hole in the center of the bowl will make it much easier to hollow out your bowl. Decide how deep the hole must go. I mark how deep the screw holes go from my face plate then add about 3/8 to 5/8 of an inch for the thickness of the bottom. Mark this place on the exterior of the bowl. Then holding the drill in front of the bowl place a piece of tape to mark the desired depth. I use duct tape on the drill bit to mark how deep I want to go.
Adjust your lathe speed to about 200 to 300 RPM. Turn the lathe on and slowly advance the drill into the center of the bowl. Remove shavings often so that you do not over heat your drill bit.
Next use your bowl gouge to start hollowing out the bowl. Come in about 1/2 inch from the outside rim and start making cuts going toward the center hole that you drilled. In this photograph the RPM is about 200. The timber is very wet and the bowl gouge is sharp. Even with this slow RPM nice shavings were produced. Again adjust your banjo so that it is close to the timber that you are cutting. Cut the bowl to an even thickness of about 3/4 to one inch. The larger your wet bowl is the thicker it needs to be. This is because the bowl will warp during the drying process. After the bowl is dried you will put it back on the lathe and re-true both the outside and the inside. If your initial thickness is not adequate the outside will meet the inside.
Since the bowl has to be dried and returned, it is not necessary to make smooth finish cuts. Mark the face plate and the bowl before you take the face plate off so that you can remount to the same holes. I usually use a red marker for this.
Quick Drying the Bowl
A wet turned bowl can be quickly dried by using a microwave oven and a regular stove. This is a technique that I developed a few years ago after I read an article about why bagels get soggy when you heat them in the microwave. The microwave heats the water in the bagel but does not drive the water out. A regular oven will drive the moisture out of the bagel.
I decided that a good fast technique for drying timber would be:
- Rough turn the bowl
- Heat the bowl in the microwave
- Dry the bowl in the regular oven
This technique has worked very well for me, and is in fact my favorite drying technique. It is fast and easy. The only significant problem is that your spouse may complain about the smell in the kitchen.
Heat the bowl in the microwave until it is quite warm to touch. The time required for this will very depending on the size of the bowl, the water content and the size of the microwave. Usually 3 to 5 minutes is required. During this time turn your regular oven on and set the temperature to 300 degrees F. When the bowl has been heated in the microwave, remove it with two pot holders and transfer it to the oven. Leave the oven door cracked at the top so that air can circulate and drive the moisture out of the wood. Set the timer in the oven for 30 minutes and let it cook. I then like to put it back into the microwave to reheat the moisture again. I then put it back in the oven for another 30 to 120 minutes.
This gives a very good and rapid drying. The only area that might still be moist is the thick base. You will turn most of this away when you reverse turn the bottom of the bowl. This technique is not as gentle to the wood as slowly letting it dry for 6 months. It will make cracks open up a little wider. Since you are working with burl wood that has cracks and multi-directional grain this will only accentuate the beautiful cracks and flaws in the wood.
Remount The Bowl
Remount the bowl on the face plate. Use the marks that you made so that you align with your original holes. Because the bowl has warped during the drying process most of the holes will not match perfectly. First place two screws that line up with the long grain of the bottom. These two screws will line up the best. Then place the remaining screws. Mount the faceplate and bowl on the lathe. Next bring the tailstock up and lock it into position. Use a flat nose live center if you have one to put pressure on the inside of the bowl. If you only have a pointed live center place a small piece of plywood between the live center and the inside of the bowl. The live center gives a lot of protection and saves a lot of wear and tear on your wood screw holes.
Re-true the outside of the bowl. The bowl will be warped so you will have to remove wood to get it round again. This wood is now hard and dry. Make sure that your bowl gouge is sharp. I sometimes mark the bowl with chalk to see where I need to do additional turning. The chalk shows up well when the bowl is turning and I know when I have removed enough timber because all the white has disappeared.
You are now going for a very smooth final shape. If you want you can use your skew to make little groves in the outside of your bowl as accent lines. Next reposition the banjo so that it is close to the rim of the bowl. Hand rotate the bowl to make sure it turns freely. Now true the lip of the bowl. Notice that a flat nose live center is applied to the inside of the bowl to secure it and add safety.
Returning The Inside Of The Bowl
It is now necessary to remove the tailstock and rely totally on the wood screws. Using your bowl gouge re-cut the inside wall of the bowl. Reposition your banjo so that it is always close to the area that you are cutting.
If the bottom of your bowl is flat you will need to use a round nose scrapper to cut the bottom of the bowl. The curve of the round nose scrapper must be small enough to fit in the curve as the bottom meets the side of the bowl. For final cuts tilt the scrapper at about a 30 to 45 degree angle so that you can make very gentle slicing cuts. Check to see that you have a very smooth surface on the entire inside of the bowl. Mark any imperfections with chalk then make very fine cuts with your scrapper to make the entire inside very smooth. The chalk is marking areas inside the bowl that need smoother final cuts. This chalk can be seen well while the bowl is spinning. When all of the white is gone your probably have removed the imperfection. It is important to take your time here and do a good job. This will save you a lot of sanding time latter.
Filling Cracks And Flaws
You have the artistic choice to decide what you want to do about the cracks and flaws in your burl wood. Very often you will chose to leave the flaw to accentuate the beauty of the wood. If you want to fill the flaw, super glue and very fine saw dust from your ways is the most popular technique. This give excellent results and is the most popular technique for getting rid of small cracks in the timber.
Another technique for handling cracks is to fill them with some contrasting material using super glue as a binder. Turquoise is a popular choice. Other possibilities are brass or copper fillings or colored sand. Colored sand must be treated very carefully because it is so hard. I was not satisfied with the results from this treatment and wished that I had use saw dust instead.
No matter how fine your cuts you will want to do some sanding. As you learn to do finer and finer cuts you will use less and less course sand paper. Use a course enough sand paper to remove the final scratches from your cutting. Then progressively use finer and finer sand paper. I like to use both hands at the same time so I often sand both the inside and the outside at the same time. Sand to about 220 to 400 grit. Use some sort of dust extraction or filtration to protect yourself form the dust.
I like to apply some type of finish while the bowl is still on the lathe. There are several advantages to this. First it can save you a lot of hand rubbing. Second the finish can high light a flaw while you can still do something about it. At the present time I am using wipe on polyurethane. I wet the timber with the polyurethane on kitchen paper. I make sure that all the timber is completely wet. Then I turn the lathe on a low speed and with a dry kitchen paper thoroughly dry the bowl. I like the way it works and it gives a nice satin finish. The bowl is now finished except for reverse turning the bottom.
The last step is to reverse turn the bottom of the bowl. There are several ways to hold the bowl so that you can turn away the bottom of the bowl including: cutting a spigot from soft wood, using a vacuum chuck, or using jumbo jaws on a 4 jaw chuck. In this case I used the jumbo jaws on a 4 jaw chuck. Mount the jaw on the chuck and again bring the tailstock forward with blunt live center. Lock into place and apply very light pressure from the live center. This will prevent you from throwing the bowl as you cut the bottom.
Use your skew to true up the bottom of the bowl. Then cut out the screw holes with the skew or small gouge. Shape as much of the bottom of the bowl as you can with the tailstock in place. Carefully use your skew to cut off the small nub that meets your live center. Stop the lathe and move the tailstock away.
This is the most dangerous stage of the process. The bowl is only lightly held by the jumbo jaws. Any heavy cut on the outside diameter can cause the bowl to come lose and go flying. This can hurt both you and the bowl. Make very light cuts with your skew. Add concentric rings if you like. Sand the bottom of the bowl. If possible place a vacuum hose close to the bowl to remove saw dust. This can prevent a lot of health problems. Finally apply finish to the bottom of the bowl.
Turning an open bowl with burl timber can be a very fun project. You will end up with a beautiful bowl while you learn a lot, and have a lot of fun. Once you get a taste of turning burl timber you very likely will like to try your hand at doing a closed form.