What is the primary distinction between a bowl gouge and a spindle gouge? Looking through the pictures of various gouges on woodturning supply websites, I see some bowl gouges ground straight across, some ground swept-back with a fingernail profile, some ground with a steep angle, and some ground with a shallow angle. I see the same diversity in the spindle gouges. So what makes a bowl gouge a bowl gouge and a spindle gouge a spindle gouge?
The major difference between a bowl gouge and a spindle gouge is the shape and depth of the flute. The flute of a spindle gouge is circular and shallow, while the flute of a bowl gouge is a modified open U-shape.
For spindle work, the grain of the wood is always parallel to the axis and the grain orientation does not change as the work turns. The chisel is always cutting downhill and the cutting action is across the grain. Most of the work is less than 3" in diameter which allows chisels to be shallow and thinner in cross-section because the spindle gouge does not need to be supported for long distances over the tool rest.
Bowl turnings are mounted on a faceplate or a chuck, which usually orients the wood so the grain is perpendicular to the turning axis. Whenever possible, the work is turned from the face. The grain direction will vary and is changing continuously as the work turns. Some end grain tearout is inevitable, but a narrow gouge, freshly sharpened and with a smaller nose radius, will minimize tearout.
Bowl gouges are frequently ground in various configurations with variations in the profile and bevel length. The preferred cut with a bowl gouge is a bevel rubbing cut. What determines the grinding angle for a bowl gouge is the type of bowl you are going to make and whether you will still be able to maintain bevel contact. You will see from the four illustrations in Diagram A (taken from Allan Batty’s booklet Woodturning Notes) what determines the angle for grinding the tool.
Fig. 1 – As this is a shallow type of bowl, there are no restrictions placed on the gouge by the wall of the bowl,
therefore none placed on the angle of the tool.
Fig. 2 – With this bowl, the wall restricts the gouge movement. As the depth does not exceed the radius, an angle of 45° would be ideal to maintain bevel contact throughout the cut.
Fig. 3 – Here the restriction becomes greater as the depth of the bowl has now exceeded the radius which, in turn, would require a shorter bevel angle of approximately 55°. This would allow the bevel to contact right to the bottom of the bowl.
Fig. 4 – Now the depth has increased even further, which requires an even shorter angle, in this case approximately 60° to 65°, to allow successful bevel contact.
You can see that the determining factor is the type of bowl you want to make. An angle between 45° to 55° would be a good working compromise.
For most work, the bowl gouge will extend further over the tool rest than a spindle gouge will (as illustrated in the figures in Diagram B). This requires a heavier bar of steel with more mass to overcome or reduce vibrations.
In normal use of these bowl gouges, one will cut as well as the other and both will produce excellent results. Turners will use different profiles, bevel lengths, and bevels swept back or ground with a steep angle. All are trying to make a bevel rubbing cut using a sharp tool with a flat or slightly hollow ground bevel. Most gouges are sharpened as shown in Diagram B or are modifications of these grinds.
I am relatively new to woodturning (about 2 years now). Most of my recent work has been with faceplate turning and almost all of my material is green wood. I have great success with it and am having a wonderful time, but I am frustrated by the occasional checking that sometimes occurs. At times, the piece is nearing completion and a check appears. Thus far I have been resigned to cutting out the portion that is checked (if possible). But sometimes the entire piece is lost. Is there anything I can do to prevent checking once work on the blank has begun? Can checking be reversed?
It is difficult to present a definite way to dry roughed-out bowls, because so many variables may determine procedure or success. Some of the variables are: air temperature; humidity; wood stability; moisture content of wood; figure or grain such as crotch, stump, or burl; open or closed grain; density or weight; sapwood or heartwood; plain sawed or quarter-sawed; tension in the wood, etc.
It is not my intention to deal with these in detail. However, here are a few conclusions based on years of working or turning green wood.
1. Partially seasoned wood (below 35% moisture content) is easier to dry than freshly cut, very wet wood.
2. Quarter-sawed wood is more stable and less likely to warp than plain or flat sawed wood.
3. Open grain woods are easier to dry than dense, close grained woods.
4. Fruit woods are difficult to dry, and the sapwood needs to be removed during the roughing-out process.
5. Don’t turn or try to dry blanks that have the heart center in them. They will crack or check most of the time.
6. Burls are much easier to dry.
7. Crotch wood or stump wood is more difficult to dry than plain or quarter-sawed woods from other parts of the tree.
8. The harder and denser the wood, the slower it must dry and more care must be taken.
9. Direct sunlight causes more problems than heat or low humidity.
Once the bowl is roughed out, it must be taken care of or it will probably crack. Treatment of roughed-out bowls may be accomplished in a number of ways, but the objective is to slow down the moisture evaporation from the wood, particularly in the end grain areas, so the inside wood dries at about the same rate as the outside wood. If any signs of checking or cracking show up, immediately put the roughed-out bowl in a plastic bag and close it loosely, so a little air and moisture can move out. The checking will stop, usually in a few days, and the surface openings in the bowl usually close together and are no longer noticeable.
Roughed-out unseasoned bowls should be kept in a cool area, on the floor if possible, and away from heat and sunlight. These precautions will help greatly to reduce or eliminate most problems with cracking. Some partially dry, open-grained woods may be dried without further treatment.
1. Coat the bowl inside and out with green wood sealer.
2. Coat the end grain areas with green wood sealer and leave the flat grain area uncoated.
3. Coat the end grain area with paste wax and leave the flat grain area uncoated.
4. Put the bowl in a box and cover it with shavings.
5. Place the bowl in a plastic bag and every two or three days take it out and let the surface moisture evaporate. Turn the bag inside out and put the bowl back in it. Repeat every two or three days until the moisture no longer collects inside the bag. Then leave the bowl out of the bag to finish drying. This method is usually necessary for dense, hard woods which are difficult to dry.
I have used double-faced tape on several occasions for turning plates. The problem is in removing the turning from the faceplate. What is the best way to remove and separate the turning from the tape without damage?
One way to turn bowls or plates without screw holes is to use cloth-backed, double-faced tape to secure the wood blank to the faceplate. If the blank is true and in balance, double-faced tape will hold it to the faceplate during turning and finishing. I have turned many plates and platters 10" to 12" in diameter and 1-1/2" to 2" thick without any problem. For maximum holding power, make sure that both surfaces (the faceplate and the wood blank) are flat, clean, and dust free. Cover the faceplate with strips of tape, but don’t overlap the tape. Press the tape firmly to the faceplate before removing the backing from the tape. Center the wood blank and clamp it to the faceplate with firm, even pressure. This will ensure a strong bond. When you place the work on the lathe, give it a tug to make sure the bond is strong. When removing the finished piece, wedge a wood chisel between the wood and the faceplate. Exert slow, steady pressure and the tape will begin to stretch and then let go. Easy does it.
Do not use the double-faced tape on wet wood!
In the Winter 2007 edition of Woodturning Design, Dale suggests using oil to smooth out end grain. What kind of oil? How much? And does oil create problems with finish?
My first experience in seeing someone use oil on rough or bruised end grain areas of a bowl or platter was in 1982, when watching Ray Key smooth these areas. To refresh my memory, I called Ray this morning and we talked about this method, as well as to find out if anything new had come up in the last twenty years or so. There is nothing scientific about this method. Only experience shows that it works.
The oil of choice is a light viscosity mineral oil which can be purchased at a drugstore. The thin oil will penetrate deeper into the wood. The oil seems to soften the rigid fibers and allows the fibers to cut clean using a freshly sharpened gouge. Several applications of mineral oil may be necessary, depending on how deep the roughened area penetrates. Fresh oil and light shearing cuts should produce good results. The mineral oil works fine with oil type finishes, but will not work with lacquer or similar
surface coatings. Finishes which are shellac based, or
wax-finished work, will not go cloudy or discolor from the application of mineral oil.