Denny Wetter once again proved himself the ring master as he demonstrated turning wooden bracelets using segmented pieces, in much the same method used to make wooden bowls. As usual he starts with a drawing. The purpose of the drawing is to firm up the original idea for a bowl or bracelet and to determine initial lengths to cut the segments. Some trial software is available here :
http://woodturnerpro.com/downloads/76-trial-software-downloads-version-3-software-version-2-1-software.html
Other sources are available on the web, either for free, as a trial, or for licensing. Denny’s favorite pattern has twelve segments, and one may come close to finding segment lengths by drawing a circle slightly larger than the diameter of the base, all the way up to the diameter of the top of the bowl. Of course the diameter needs to be larger that finished dimensions, to allow some room to true up and turn the piece. Denny pads his diameters by at least ¼ “. His favorite is to use ¾“ thick stock, even using cutoffs of some unique wood species. A twelve sided segment will show segment joints that correspond to the hour marks on a clock, as a point of illustration. Where segments meet, the pieces form a 30 degree angle, meaning each piece is cut at 15 degrees.
Denny uses a custom made jig to insure the same segment length for each of the same segments on each layer. Progressing up the bowl from the bottom, the segments get longer to accommodate the lager diameter of the upper layers of the bowl. Also, Denny’s jig allows very small adjustment of the angle cut on the end of the segments. The angle adjustment can be a trial and error process until suitably tight wood joints are achieved, but an initial setting of 15 degrees is the place to start.
For those who have attended the Tampa Wood Show and watch the “Dubby” being demonstrated, that is an indicator of the repeatability needed to produce segments. Jerry Cole has placed a video on You Tube that can give a good indication of what is attempted in explanation here:
//www.youtube.com/embed/t8yiXydcQN4
Denny uses a zero clearance insert to help prevent chip out. After cutting, the pieces are gathered, glue applied, and the pieces are clamped with ordinary hose clamps (think radiator hoses) joined end to end until a sufficient length is reached. You may get lucky, after your first twelve test cuts, or like most common people, your angle may a little adjustment. Test cuts may be made on squared up scrap and later used as kindling if needed. A small variation can be concealed by gluing up two sets of six pieces—a half of the intended diameter, and then sanding the remaining mating pieces on a disc sander to make it fit! Mark both the top and bottom of each piece and place one half on top of the other and sand together, so that when the pieces are correctly aligned, any variation in sand angle of one piece will cancel out with the other. One may need to try this to see how it works. Glue will fill some gaps, but keep the gaps tight if possible.
Denny cautions that segmented bowl bottoms can crack and shrink with changes in humidity and through drying. An alternative is a bowl bottom made out of strips keeping most expansion in one direction. Use contrasting woods if desired. This bottom piece needs to be sanded flat.
The glued up segment pieces need to be flattened as well. Denny showed three methods. One way is to sand the pieces flat on the sanding disc, being careful to hold the entire piece against the spinning disc.
Alternatively mount a melamine work disc to a faceplate and hot melt glue the segmented diameter to the work disc and turn it flat or sand it flat using sandpaper glued to a flat working board. The third method is to mount the rough segment all the way against the face of the chuck and then flatten with the bedan tool. Also, pencil lines can be marked on all the segments and one can sand until all the lines are gone. In any case, put a straight edge against it and check it for flatness by looking for light between the piece and the straight edge.
Now, since this meeting is actually about turning wooden bracelets, but by point of illustration includes a generalization about cutting segmented bowls, Denny proceeded to show how to make bracelets. He begins with a 2 3/8” forstner bit at 500 rpm. He mounts the bit in a chuch in the tailstock and slowly advances it into the bracelet. (Lathe tip; remember to hold onto the chuck as it is being withdrawn as it is only held in place by the friction of a morse taper.) Then he cleans us the outside with a bedan. Next it is back to the inside with a round nose scraper. This first piece was made of contrasting cedar and pine and he sands the inside and outside. Then he removes the piece with a chisel against the hot melt glue.
The free piece is remounted on the expanding Nova chuck, or it can be mounted on a custom fitted nylon soft jaw accessory to the Nova chuck. Denny’s expanding soft jaw has a grove in it to hold the bracelet. Once mounted, he matches the other side. For this one he burned rings on the pine. Steel wire can be used to burn rings, but don’t hold the steel wire by wrapping it around your finger. Not only does it get hot, but a catch can pull your whole hand and more into the lathe.
Denny shared his secret of very thin bracelets. First one make rings as described, and then ¼“ thick sections are parted off. Hollow out just slightly wider than the parting tool. After the pieces come off the lathe, flatten the remaining part with a sanding board. Thin pieces can then be glued together in interesting patterns and turned to make up the bracelet.
Stay tuned next month for another lathe episode of “As the World Turns.”
Pictures and text by Andy DiLorenzo