Thomas Canfield
02-10-2013, 8:56 PM
I will be doing a demo for my local club, Hill Country Turners, over in Kerrville Thursday. I have made a little outline of talking points and am posting here for any comments if you have any idea of additional things to discuss. Time will be somewhat limited and I like to take a green section to rough turn and then also remount a dried green turned piece. I plan to mount the dried piece first when I have sharp tools since sharpening during demo may not be possible. I will either be using a section of Cherry Laurel (if not too wet and slinging sap) or some Texas Ash for the demo.
TURNING A NATURAL EDGE BOWL
A loose definition of a natural edge bowl is a bowl turned from a log segment with the bark side as the rim of the bowl. It can be either with or without bark, and the time of year that the tree was cut will have a major impact on the ability to retain the bark. Wood cut in the late summer and fall have a better chance to retain the bark that wood cut in the early spring and early summer with extra sap. The first step is the selection of wood and the desired shape. A long oval can be turned from a section that is longer than wide, that is a 12” long section of a 8” log for example. A “round” bowl would need to be turned from a larger diameter log than the length and still the rim will be oval. Green wood also turns easier and is often used turning to final thickness and allowed to “warp” with some additional work later done to get a flat of sitting bottom.
Basic steps after wood has been selected are:
1. Mount on lathe with bark side toward headstock. I usually use a 2 ¾” Forstner bit to get a flat spot for either the worm screw in chuck or a 2 ½” faceplate , but you can also use a 2 or 4 prong drive center in a 1” drilled hole, and then the tailstock against the flat side of the section. The section should be balanced using a band saw to round up if balance is an issue for smaller lathe. Extra care should be used with position of the tool rest and hand position due to the wings and any air gaps.
2. Turn the outside and form a tenon with dimple (live center has done this if used). You need to cut from the bark toward the bottom to prevent pushing off the bark, and a sharp tool is required to prevent a lot of tear-out on the end grain since there is a lot of air gap near the bark outer limit. The remainder of the bowl outside is turned in normal manner from center toward outside. I prefer a tenon with dimple since I can remount later between center and true up the tenon to return if turned rough, and also to be able to turn off tenon using a jam chuck with pad. Sand the outside if turning to final dimension and hand sanding will be required at the end of the wings. With the lathe not turning, a random orbital sander can be used on the tips
3. Reverse the piece and install the tenon in the chuck. I use the live center on larger pieces until getting down to a full circle cutting of deeper. A sharp tool is required when getting near the finish diameter of the bark edge to prevent tear-out where the problem is magnified due to the air gaps and soft bark tissue. Again, extra care should be used with position of the tool rest and hand position due to the wings and any air gaps.
4. The interior needs to be turned down in stages, down to bottom of bark, and possible multiple stages on the lower due to the flexibility of the wings. Continue turning to the bottom using a sharp tool for the final cuts.
5. Sanding the interior wings needs to be done with the lathe off either by hand or using a small powered sander with foam pad. Sanding the lower interior can be done in the normal manner being careful of the wings.
6. After final sanding, the natural edge bowl is then reversed and using a jam chuck* and pad inside and the live center in the bottom dimple, the tenon can be reduced to a nub and that area sanded prior to the hand removal of the nub. I use a flush cut saw with plastic shield against the bottom to cut off the nub and then work down the remaining raised section with chisel and/or sanding.
7. *Caution – the wings add extra height requirement for the type of jam chuck used. That might be a consideration in deciding the height of the natural edge bowl that you can turn.
Tom Canfield 2-10-13
TURNING A NATURAL EDGE BOWL
A loose definition of a natural edge bowl is a bowl turned from a log segment with the bark side as the rim of the bowl. It can be either with or without bark, and the time of year that the tree was cut will have a major impact on the ability to retain the bark. Wood cut in the late summer and fall have a better chance to retain the bark that wood cut in the early spring and early summer with extra sap. The first step is the selection of wood and the desired shape. A long oval can be turned from a section that is longer than wide, that is a 12” long section of a 8” log for example. A “round” bowl would need to be turned from a larger diameter log than the length and still the rim will be oval. Green wood also turns easier and is often used turning to final thickness and allowed to “warp” with some additional work later done to get a flat of sitting bottom.
Basic steps after wood has been selected are:
1. Mount on lathe with bark side toward headstock. I usually use a 2 ¾” Forstner bit to get a flat spot for either the worm screw in chuck or a 2 ½” faceplate , but you can also use a 2 or 4 prong drive center in a 1” drilled hole, and then the tailstock against the flat side of the section. The section should be balanced using a band saw to round up if balance is an issue for smaller lathe. Extra care should be used with position of the tool rest and hand position due to the wings and any air gaps.
2. Turn the outside and form a tenon with dimple (live center has done this if used). You need to cut from the bark toward the bottom to prevent pushing off the bark, and a sharp tool is required to prevent a lot of tear-out on the end grain since there is a lot of air gap near the bark outer limit. The remainder of the bowl outside is turned in normal manner from center toward outside. I prefer a tenon with dimple since I can remount later between center and true up the tenon to return if turned rough, and also to be able to turn off tenon using a jam chuck with pad. Sand the outside if turning to final dimension and hand sanding will be required at the end of the wings. With the lathe not turning, a random orbital sander can be used on the tips
3. Reverse the piece and install the tenon in the chuck. I use the live center on larger pieces until getting down to a full circle cutting of deeper. A sharp tool is required when getting near the finish diameter of the bark edge to prevent tear-out where the problem is magnified due to the air gaps and soft bark tissue. Again, extra care should be used with position of the tool rest and hand position due to the wings and any air gaps.
4. The interior needs to be turned down in stages, down to bottom of bark, and possible multiple stages on the lower due to the flexibility of the wings. Continue turning to the bottom using a sharp tool for the final cuts.
5. Sanding the interior wings needs to be done with the lathe off either by hand or using a small powered sander with foam pad. Sanding the lower interior can be done in the normal manner being careful of the wings.
6. After final sanding, the natural edge bowl is then reversed and using a jam chuck* and pad inside and the live center in the bottom dimple, the tenon can be reduced to a nub and that area sanded prior to the hand removal of the nub. I use a flush cut saw with plastic shield against the bottom to cut off the nub and then work down the remaining raised section with chisel and/or sanding.
7. *Caution – the wings add extra height requirement for the type of jam chuck used. That might be a consideration in deciding the height of the natural edge bowl that you can turn.
Tom Canfield 2-10-13