CHAPTER VI
OVAL TURNING
Oval work as a problem in turning will be found to be a very good one as well as interesting to the pupil. It brings in the principle of the oval as used in ordinary shop practice; (arcs from points on the major and minor axes). For thick heavy ovals the off-centering is very slight, while for long, thin ones the off-centering is greater. The measurements given on Plates A-III--1-a, b and A-III--2-a, b will give a good idea of approximate distances to be used.
While the tool operations are much the same as in other spindle turning there is one notable difference. The design must be worked out by eye, because of the nature of the work no caliper measurements can be made for depth of cuts.
To get the best results the stock of oval turning should be cut square or slightly rectangular in cross-section and about 3" longer than the model to be made. The thickness of the stock should be about ⅛" greater than the major axis of the oval wanted.
The centers are located in the usual manner after which perpendicular lines are drawn from the sides, passing through the points of the centers. From the ends of one of these, perpendicular lines are extended lengthwise of the stock (on opposite sides) meeting the corresponding perpendicular at the other end of the stock. These lines form the ridge of the oval. On the other perpendiculars, the points for off-centering are laid off, measuring the required distance on both sides of the center point.
With a ⅛" drill bore holes ¼" deep at each of the off-centering points as well as the original center. This will insure the lathe centers penetrating the stock at the proper point. The stock is then placed in the lathe, using two corresponding off-center points as centers.
With the lathe running at third speed turn down the stock to the horizontal line forming the ridge of the oval, excepting for a distance of about 1¼" at the ends. The stock at the ends is necessary for the off-centering and, if cut away, will spoil the centering for the other side, especially at the live center end. The stock is then changed to the other off-center points and the second side is cut down to the line.
All measurements are then laid out and the design is cut, changing the stock in the lathe when necessary. Care should be taken that the sharp ridge left on the work forms a straight line the full length of the stock. After the design has been finished, the stock is centered on the true center and a very thin cut is taken the full length of the object to remove the sharp corners. The model is then sandpapered while the lathe is running very slowly.
CHAPTER VII
DUPLICATE TURNING
Under the head of duplicate turning have been classified only such models as clearly indicate the necessity of making two or more articles to complete the model or set of articles desired. But it is not intended to convey the idea that other models may not be made in duplicate as in many cases it is very desirable and even preferable that they should be made that way. Whatever the problem may be the suggestions offered at this point may be applied effectively.
Whenever two or more models are to be made identically alike there are always two possibilities of inaccuracies that will render the work dissimilar: First, inaccurate measuring both for length and points of new diameters and also on the new diameters themselves; second, a variation in the curved surfaces either on long convex or concave cuts.
The first difficulty can be overcome to a great extent by the use of a measuring stick. This stick should be made of any soft wood. It should be straight on one edge and about the thickness of an ordinary rule. On the straight edge lay off very carefully measurements for length, shoulders, beads, concaves and all points where calipering for new diameters will be necessary. Insert at each point measured a small brad which has been sharpened at both ends, leaving the end protrude about ⅛". Care should be taken that all brads protrude the same distance.
After the stock has been turned to the largest diameter, the stick is held in the position of the rule while measuring and the points are forced against the revolving cylinder, thus scoring it. This stick can be used as many times as the model is to be made and the measurements will always be the same.
To avoid dissimilar curves it is well to cut out a full sized templet of the model to be made. This templet can be made of any thin, stiff material, preferably light sheet iron. In some cases it will be necessary to make the templet in several pieces in order to help facilitate the tool operations.
The use of this templet will not only be a help to getting all curved surfaces the same, but will also check up on the various new diameters on the model. The cylinder should never be in motion while the templet is being used.
CHAPTER VIII
FINISHING AND POLISHING
To get a high and lasting polish on wood, the work must be first sanded so as to be perfectly smooth. In addition to this, open grained wood, such as oak, must be properly filled with a wood filler. If properly sharpened tools have been used very little sanding is required, and then worn sandpaper should be used as it does not cut into the work as new paper cuts. Remember sandpaper is not to be used as a tool in cutting down stock when working to dimensions. In using old sandpaper run the lathe at a moderate speed to avoid burning the wood, especially on square or round fillets. Keep the edges of the work sharp and do not wear them round. In using new sandpaper use a fine grit (00 or 0) and move the paper from one end of the work to the other slowly, so that no scratches result on the surface of the work.
The work may be finished by one of two methods. In the first method as in finishing ordinary cabinet work, the pieces should be stained and filled. In applying filler, run the lathe at the slowest speed after the material has dried sufficiently to rub into the pores of the wood. If the highlights are to be brought out, as in the case of oak, stain and then give a light coat of shellac, and apply the filler after the shellac is dry. The shellac keeps the dark filler from staining the flakes of the oak darker, and the pores of the wood fill in as before. The pores become darker than the flakes, and at the same time a smooth surface is produced. After the filler has hardened the wood may be waxed or varnished.
The second method, or French polishing, is rather difficult to apply and requires a little skill. A close grained wood, like maple, will be found more satisfactory for the beginner. An open grained wood may be filled in the ordinary way, or the grain may be filled by rubbing into the pores of the wood a combination of shellac, rotten stone or pumice, oil and alcohol. Rotten stone is used for dark wood and pumice is used for light wood. The wood may be left in the natural or stained as in the first method. The mixture of shellac, rotten stone, oil and alcohol, is applied to the work with a pad made of cotton waste, wrapped in cheese cloth to keep it from sticking to the work. It should be about 1½" in diameter and ½" thick. Hold the pad over the mouth of a bottle of shellac and tip the bottle so that the shellac comes in contact with the pad. The shellac will remain clean in a bottle and will be handy. The mouth of the shellac bottle should be about 1" in diameter and should be dipped once. Do likewise with a bottle, having a mouth ½" in diameter, containing alcohol. This should be dipped twice allowing the alcohol to dilute the shellac. Then drop on a couple of drops of oil and rub over the pad evenly; this aids in distributing the shellac properly and keeps the pad from sticking to the work. A bottle may also be used for this. For the rotten stone use a pepper shaker so that it may be sifted on the work as needed.
When the mixture has been applied to the pad, hold the pad against the work lightly at first, until most of the moisture has been worked out of it, and then gradually increase the pressure until the pad is almost dry. In putting on the first coat, use more shellac and alcohol and just enough oil at all times to prevent the pad from sticking to the work. However, the pad should not contain as much shellac that it can be squeezed out with the fingers. When the pad is dry, another mixture is applied, and where open grained wood is used, rotten stone, or pumice stone, is sprinkled on the work to gradually fill up the pores and to build up a smooth surface. Run the lathe at a low speed, depending on the size of the piece that is being polished. Allow the first coat to dry before applying a second coat for, if too much is put on at any one time, the heat generated in the rubbing will cause the shellac to pull, and it will form rings by piling up. These rings may be worked out in two ways, either by a slight pressure of the pad on the rings or by cutting them with alcohol applied to the pad. If too much alcohol is used it will cut through the shellac and remove what has already been rubbed on. If at any time too much shellac is used it will pile up and form rings. Too much rotten stone will cut down the polish and by absorbing the mixture will leave the pad dry. If too much oil is used the polish will become dull after a day or two.
After the first coat has hardened apply the second, but use less shellac and more alcohol and just enough oil to prevent the pad from sticking. This may be done by dipping the tip of a finger in the oil and spreading it over the pad. The entire mixture should be so that only a dampness can be felt on the pad. As the process goes on less oil and shellac are used. All oil must be removed when applying the last coat, or the piece will lose its polish. All the pores should be filled, and no rings should be on the finished work. Where a natural finish is desired, apply a coat of boiled linseed oil twelve hours before the work is to be polished. This will bring out the grain and will also aid in applying the first coat; no oil need then be used in the first coat.
A great amount of practice and patience is required to get a first class polish. Polishing can only be learned by experience. Correct your troubles in properly proportioning the mixture. Never use too much shellac as it will build up too fast and will not harden, thus causing rings; or it will pull and catch to the pad, thus forming bunches. The purpose of alcohol is mainly to dilute the shellac and to prevent against putting it on the work too fast, but care must be taken not to use too much alcohol to cut the shellac entirely. The oil helps to distribute the shellac evenly, but it must be removed when finishing the last coat, or the polish will not remain. It also helps to keep the pad from sticking to the work.
It is impossible to obtain a polish that will be as lasting and rich by any method other than the one described. For success it is essential to learn the proportions of the mixture and to acquire skill in applying the materials by using exactly the right pressure and the right movement of the pad.
CHAPTER IX
FACE-PLATE AND CHUCK TURNING
Face-plate and chuck turning open an entirely new field of work from that taken up in previous chapters of this book. If handled correctly, it has much greater educational and practical value than cylinder turning. From the practical standpoint the field of work is broader and the models to be made are of much greater value. Aside from this, trade methods and practices can be applied and a broad insight into commercial work can be given the student.
In some details of chuck turning the tool operations already learned can be employed, but for the most part they are entirely different. In order to preserve the educational value of the work as brought out by skill and dexterity in handling tools, it will be necessary to use the cutting method wherever possible. In some instances that method will be impossible, and the scraping method must be used.
METHODS OF FASTENING STOCK
All the work thus far has been on models where the stock worked upon is held between the live and dead centers. In face-plate and chuck turning the work is done at the head stock only and the piece is supported by means of a face-plate, or chuck, that is fastened to a face-plate, which is screwed onto the end of the live spindle. There are three methods of fastening stock to the face-plate, and it depends upon the nature of the exercise or model to be made which method is used.
1. SMALL SINGLE SCREW FACE-PLATE. For all work that does not require deep cutting in the center, such as in towel rings, picture frames, etc., the small face-plate with a single screw should be used.
Note:--Should it be found difficult to keep the block from working loose and turning, it is a good plan to fold a piece of sandpaper, grit side out, and place it between the face-plate and the stock.
2. LARGE SURFACE SCREW FACE-PLATE. For all work that does not require deep cutting on the outside, such as exercises, jewel boxes, etc., as well as all large stock, and all stock from which chucks are to be made, the large face-plate with the surface screws should be used.
3. GLUING TO WASTE STOCK. A block of scrap wood is fastened to a face-plate the same as for a chuck and surfaced off square. The block from which the model is to be made is planed square on one side and glued to the block on the face-plate with a sheet of paper between the two. To separate the model from the chuck, after it is completed, place a chisel on the waste stock, 1/16" back of the glue joint at such a point as will bring the chisel parallel to the grain of the model, and strike lightly with a mallet. This will cause the paper to separate and the model to become free.
This method will be found very convenient epecially on models where the base is to be left straight. It will also be found to save much stock when working with expensive woods.
LATHE ADJUSTMENTS
To get the best results in face-plate or chuck turning there should be no end play in the spindle of the lathe. The spindle should always be tested out, and if any play is found, should be adjusted before attempting any work. It is almost impossible to make a true cut when such a condition obtains.
POSITION OF TOOL REST
For all face-plate and chuck turning the tool rest should be kept as close to the stock as possible, the same as in spindle turning, regardless of the angle it may be set. Vertically, the rest in most cases should be sufficiently below the center of the stock to bring the center or cutting point of the tools used, when held parallel to the bed of the lathe, even with the center of the stock. This last condition will necessitate adjusting the height occasionally when changing from large to small tools.
CHAPTER X
TOOL PROCESSES IN FACE-PLATE AND CHUCK TURNING
B-I--1-a. Straight Cuts
1. ROUGHING OFF CORNERS. (¾" GOUGE.) FIG. 14. The tool rest is set crosswise to the bed of the lathe and parallel to the face of the stock.
Place the gouge on the rest with the handle well down. Roll the gouge to the left until the grind which forms the cutting edge is perpendicular to the stock. The point of contact should be slightly below the center or nose of the tool.
The handle of the gouge is then swung well to the back of the lathe or to the operator's right. The gouge is then pushed forward into the stock and to the left, making a shearing cut. The cut should not be too heavy. The starting point for this cut should be a line which will indicate the largest diameter or circle that can be made from the block.--This cut should be repeated until the corners are removed from the block.
To complete the cutting of thick stock it will be found necessary to change the tool rest to an angle of 45° with the bed of the lathe.
Fig. 14.
When hardwood is being turned it is sometimes advisable to saw the block almost round with a compass saw or bandsaw, if one is to be had. Should this be done the preceding steps are omitted.
The tool rest is then placed parallel with the lathe bed and a roughing cut is taken with the gouge the entire thickness of the block.
The lathe should be run on second or third speed until the corners are removed, and then changed to first speed.
2. CALIPERING FOR DIAMETER. The true diameter is then calipered the same as in spindle work.
3. SMOOTHING CUT. A smoothing cut is taken with a skew chisel the same as in spindle work.
Fig. 15.
4. ROUGHING CUT ON THE FACE. (¾" GOUGE.) FIG. 15. The rest is now placed parallel to the bed of the lathe and slightly above the center of the spindle. Place the gouge on the rest on its edge with the grind toward the stock and parallel to the face to be surfaced. The nose of the gouge is the cutting point.
The handle is then raised and the cutting point is forced toward the center. A very thin shaving should be taken. If the gouge is allowed to roll back so the grind above the cutting point comes in contact with the wood it is sure to catch and gash the wood.
5. SMOOTHING THE FACE. (SMALL SKEW CHISEL.) FIG. 16. For all work up to 3" in diameter, the surface may be smoothed by using a small skew chisel in the same manner as in squaring the ends of Stock in cylinder work. (Step 6--Exercise A-I--1-a, Straight Cuts.)
For larger work, place the chisel flat on the rest with the toe next to the stock and the back edge of the chisel parallel to the face to be surfaced.
The point of the chisel is then forced toward the center of the stock, using the straight back of the tool as a guide against the finished surface. Only a very thin cut should be taken at a time.
Fig. 16.
Note:--While this operation may be termed a scraping cut, it will be found to be much easier on the tool than if the cutting edge were held flat against the work as in other scraping cuts.
The surface of the work should be tested for squareness by holding the edge of the chisel or a straight edge across the face.
LAYING OFF MEASUREMENTS
In laying off measurements on the face of the stock a pencil compass or dividers should be used. Set the compass or dividers to one-half the diameter of the circle wanted. While one point is held at the exact center of the stock, which is easily located while the stock is revolving, the other is brought in contact with the revolving stock until a circle of the correct diameter is marked.
Fig. 17.
Should the center of the stock be cut away, rendering this method impossible, the following method may be used: Set the compass or dividers to the exact diameter wanted. Place one point in contact with the stock a little to one side of the required line on the part that is to be cut-away. Bring the other point to the stock and see if it touches the line first made. If not, move the first point until the two points track in the same line.
Fig. 18.
The rest should be set at the exact center for measuring.
All measurements on the edge of the stock can be made with pencil and rule as in cylinder turning.
B-I--2-a. Shoulder Cuts
1. EXTERNAL SHOULDERS. FIG. 18. The surplus stock at each successive shoulder is roughed out with a ¾" gouge, keeping well outside the finished measurements. The gouge for this work is held in the same position as described in B-I--1-a, Step 1, for Roughing Off Corners.
Fig. 19.
2. For the finishing cut a small skew chisel is used, and the process is the same as that used in squaring ends of stock. Both the vertical and horizontal shoulders can be handled easily by this method. Fig, 19.
3. INTERNAL SHOULDERS. For internal shoulder cutting the same methods may be used for roughing out and cutting the horizontal shoulders, but for the vertical or base shoulder it will be necessary to use the scraping process. (See "Use of Scraping Tools.")
B-I--3-a. Taper Cuts
Taper cutting will not be found hard as the gouge and skew chisel are used in the same manner as described in B-I--1-a, Steps 4 and 5. After the stock has been roughed away with the gouge to the approximate angle desired, a smoothing cut is taken with the skew. Care should be taken that the skew chisel is held at the exact angle of the taper desired.
B-I--4-a. V Cuts
V cutting will also be found easy as the tool process is exactly the same as that used in spindle turning. Exercise A-I--4-a. Fig. 20.
B-I--5-a. Concave Cuts
Place the ¾" gouge on the rest with the handle parallel to the bed of the lathe. Roll the gouge on its edge and swing the handle so that the grind is perpendicular to the stock with the nose of the tool as the cutting point.
Fig. 20.
Force the gouge forward into the wood. As soon as the cut is started, the handle is lowered and swung to the left; (if cutting the left side of the concave) at the same time the tool is rolled back toward its original position. This movement brings the cutting point farther down on the lip and the grind, resting on the side of the cut, will force the gouge sidewise and will form one-quarter of the circle. Fig. 21.
Fig. 21.
This cut is continued from alternate side until the concave is nearly to size. The cut should be tested with a templet before the finishing cut is taken.
B-I--6-a. Convex Cuts
Rough out the stock between the beads with a parting tool.
Hold the edge of the gouge on the rest with the handle, parallel to the bed of the lathe, to make the nose the cutting point.
Swing the handle to the left so that the grind will form a tangent to the bead at its highest point.
The gouge is then forced into the stock and to the right; at the same time the handle is swung to the right; keeping the grind tangent to the bead at the point of contact. Fig. 22. This cut is continued until the base of the bead is reached.
B-I--7-a. Combination Cuts
As in spindle turning, a combination exercise should be given at this point to provide an opportunity for studying out the best methods of working the various cuts just described into a finished product.
USE OF SCRAPING TOOLS
When scraping is to be employed, it should be done with only those tools that are made for that purpose, i.e., Square Nose, Round Nose, Spear Point, Right and Left Skew. The handling of these tools will be found easy. The only point to remember is that they should be held flat on the tool rest and parallel to the bed of the lathe when in use.
In general practice the ordinary skew chisel should not be used as a scraping tool, for the cutting edge is not sharpened to withstand the heavy strain required by such work. Should it be necessary, however, to use a skew chisel as a scraper, the tool should be held so that the top grind is parallel to the bed of the lathe while in use.
INTERNAL BORING
In roughing out the center for Napkin Rings, Jewel Boxes, etc., the quickest method is to work it out with a small gouge.
Place the gouge on the rest parallel to the bed of the lathe, having the point even with the center of the stock.
Force the gouge into the wood until a hole is bored to the depth required. If the hole is deeper than 1", remove the tool often and clear out the shavings in order not to burn the point.
In order to enlarge the hole to the proper size the point of the gouge is pressed against the left side of the hole a little above the center and a shearing cut is taken. To obviate the danger of the tool catching, all cuts should start from the back of the hole and proceed toward the front.
Fig. 22.
B-III--8-a. Sphere
After the sphere is turned as nearly perfect as is possible when working between centers (Steps 1 to 4) it is cut free from the waste stock and is centered in a chuck.
The chuck is made of any soft wood and should be cut in the end grain, which will insure equal pressure on all sides. Equal pressure cannot be obtained if the Chuck is cut in cross grain wood, owing to the tendency of side grain to give more than the end grain. The sphere should be forced into the chuck with slightly over half protruding. Very thin cuts should be taken and the sphere should be revolved one-quarter turn after each until true. As the sphere becomes smaller during the cutting, it will be necessary to cut the face of the chuck down and bore the hole deeper and smaller in order to keep more than half of it protruding at all times.
To remove the sphere tap the chuck lightly with a hammer just above it, at the same time pull out on the sphere.
CHAPTER XI
SPIRAL TURNING
Spiral turning is a subject that has received very little attention by most schools in which wood turning is taught. Spiral work is seen in antique furniture and also in the modern furniture of the present day. It seems that it takes the wheel of fashion about a century to make a complete turn, for what our forefathers neglected and destroyed the people of the present day value and cherish.
Spiral work gives excellent practice in shaping and modelling wood. It brings into play the principle of the helix as used in cutting threads, etc.; and its form, size and shape may be varied according to the taste of the individual. As in threads so in spiral work we have single and double spirals, and their form and proportion depend upon their use and application in furniture making. A variation of the spiral may be made in several ways: First, by changing the number of turns of the spiral on a straight shaft; second, by running a spiral on a tapered shaft; third, by changing the shape or form of the spiral itself; and fourth, by making more than one spiral on a shaft. It is uncommon to see ten or twelve spirals running around a single shaft.
Some of the forms of the above types are fully taken up and explained in the work that is to follow.
PLATES B-V--1-a, B-V--1-a’. SINGLE SPIRAL. STRAIGHT SHAFT
To work out a single spiral for a pedestal proceed as follows:
1. Turn a cylinder 2¼" in diameter. Make the ends slightly larger in order that the design may be turned on each, after the spiral has been worked out.
2. Lay off spaces 2-1/16" apart on the cylinder while the spindle is turning in the lathe and divide each of these into four equal parts. Each one of these large spaces represents one turn of the spiral. A good proportion is slightly less than the diameter of the cylinder; thus the diameter of the cylinder equals 2¼" and the width of the space 2-1/16".
3. On the cylinder parallel to the axis draw lines A-A B-B C-C D-D. These lines should be 90° apart as shown in the top diagram (Plate B-V--1-a’). Line D-D is on the other side of the cylinder as shown in the top and middle diagrams.
Fig. 23.
4. Start on line A-A at point X, circle 1, and draw a line connecting it with line B-B on circle 1’. Then connect B-B on circle 1’ with C-C on circle 2 and so on until a spiral has been drawn the entire length of the cylinder. This line will form the ridge of the spiral as shown in the middle diagram.
5. Next begin on line C-C at circle 1, and draw a line connecting it with D-D on circle 1’ then to line A-A on circle 2, and so on as before. This spiral represents the center of the groove or the portion which is to be cut away. This is not shown in the diagram because more or less confusion would be caused with the line representing the ridge of the spiral.
6. Begin on line C-C at circle 1, and saw to a depth of ¾". Saw the entire length of the cylinder leaving about 1½" at the ends. Do not follow the line here, but switch off gradually and follow circles 1 and 15, so as to allow the spiral to begin and end gradually and not abruptly.
7. Rough out with a knife or chisel by cutting on both sides of the saw cut. Then use a wood rasp to finish shaping out the spiral. When properly shaped out allow the lathe to turn slowly and smooth with sandpaper by following the spiral as the lathe turns.
|
Fig. 24. |
Fig. 24-a. |
Fig. 25. |
8. Cut the design on both ends of the cylinder and polish.
PLATES B-V--2-a, B-V--2-a’, B-V--2-a’’;. SINGLE SPIRAL. TAPERED SHAFT
To lay off a single spiral for the electric lamp shown in Figs. 24 and 24a proceed as follows:
1. Select your wood and bore a hole through it. Plug the hole and center the piece in the lathe. This insures getting the hole exactly in the center, and it will not be cut into while the cutting of the groove of the spiral proceeds. A groove may also be cut in two pieces of stock and glued together to form a hole through the stock.
2. Turn a cylinder 2½" in diameter, tapering it to 1½" at the one end; this part should be 12⅛" long. Both ends should be left larger than 2½" as the lower and upper designs must be cut here.
3. Let the spindle revolve in the lathe and draw circles as shown in the layout (Plate B-V--2-a’). The number of circles will vary with the taper. Since seven turns are needed in the present spiral, 28 circles will be necessary--four circles for each turn of the spiral as shown in the middle diagram. A good proportion to follow is to measure the diameter of the spindle at circle 2 and lay off this distance from circle 1 to circle 3. Then measure the diameter at circle 4 and lay off this diameter from circle 3 to circle 5 and so on until all circles have been made. Then divide these large divisions into four equal parts.
4. Draw four lines the entire length of the spindle, each 90° apart as shown by the heavy lines in the middle diagram. The heavy circles of the same diagram represent the complete turns of the spiral.
5. Lay out the line representing the ridge of the spiral as shown in the middle diagram. Begin on circle 1, where the straight line crosses it, draw to circle 1’ at the point where the next straight line crosses it, then to 2--2’--3--3’ and so on until the end is reached. This forms the ridge of the spiral as shown in diagram 3. Next it may be more convenient to draw another line representing the groove. In this case begin at point X in the middle diagram, opposite the point where first started, and continue in the preceding manner, making this line parallel to the other line.
6. Saw on the line last made, being careful not to saw too deeply. The depth must be ¼" less than half the diameter of the spindle where the cut is made. This saw cut forms the groove of the spiral. The groove is then cut out by hand with a chisel or knife, by working down the wood on both sides of the saw cut. After the spirals have been roughed out, a rasp is used to finish shaping them. The work is then sandpapered smooth, while the spindle is revolved slowly in the lathe.
7. Cut designs on the ends of the cylinder and polish.
PLATES B-V--2-b, B-V--2-b’. DOUBLE SPIRAL. TAPERED SHAFT
To work out a double spiral for the electric lamp illustrated in Fig. 25 proceed as follows:
1. Turn up the spindle in the usual manner. Since the base of the shaft is larger than the top, the spiral must also be in proportion and lines A-A’, B-B’, C-C’, D-D’, and E-E’, are drawn around the shaft. To get the approximate spacing from circles A-A to B-B measure the diameter at A-A’ plus about 3/16" and lay off from A-A’ to B-B’. Then take the diameter of B-B’ plus about 3/16" and lay off from A-A’ to B-B’. Then take the diameter at B-B’ plus about 3/16" and lay off from circle B-B’ to C-C’ and so on. If the shaft is tapered more, a different proportion must be used. Also if it is desired to have the twist wind around the shaft three times, a variation must be made in the number of circles.
Fig. 27.
2. If it is desired to have the twist wind around the shaft twice, draw circles 1-1’, 2-2’, 3-3’, and 4-4’ and the spaces will grow proportionately smaller at the small end.
3. Draw four lines running lengthwise on the spindle and 90° apart as shown in the midde figure in heavy lines (Plate B-V--2-b’).
4. Begin at A and draw a curved line to where the 90° line crosses circle 1-1’. From there extend the line to where the next 90° line crosses circle B-B’ at point B’. Continue in this manner until the other end of the shaft is reached. Begin at A’ and draw a line on the opposite side of the shaft. These two lines running around and along the shaft form the grooves while the portion in between forms the beads of the double spiral.
5. Saw to the desired depth, being ¼" less than half the diameter at the point where cut. With a chisel or knife form the grooves and beads. It is necessary to be careful about not ending the grooves too abruptly. (See point 6 in Plates B-V--1-a, B-V--1-a’.) Smooth with a rasp and sandpaper while the lathe is revolving slowly.
6. Cut the design on the ends and polish.
PLATES B-V--3-a, B-V--3-a’. DOUBLE GROOVE SPIRAL. STRAIGHT SHAFT
To work out the double groove spiral for the magazine holder illustrated, proceed as follows:
1. Square up the stock to 1⅜". Center carefully and turn the design on both ends as shown, in the upper diagram (Plate B-V--3-a’). Turn the cylinder between the top and bottom, making it 5½" long and 1⅜" in diameter.
Fig. 26.
2. Divide the cylinder into two equal parts. Each part represents one revolution of the spiral.
3. Divide each half into four equal parts as shown in the top and center diagrams (Plate B-V--3-a’), 1-1’, 2-2’, 3-3’ and so on. The proportion of the distance between these circles should be one-half the diameter of the cylinder.
4. Draw lines A-A, B-B, C-C, and D-D, parallel to the axis of the cylinder 90° apart.
5. With a band 3/16" wide of any substantial material (preferably a narrow strip of tin or a watch main spring) begin on the line A-A at circle 1, and connect circle 1’ at line B-B, and then connect circle 2 at C-C, and so on until the spiral is made the entire length. Mark on both sides of the 3/16" band so as to keep the spiral parallel.
6. Next begin at the line C-C where circle 1 crosses it and connect from here to 1’ at B-B. Proceed as in Step 5, as shown in the center diagram.
7. Now erase the extreme ends of the spiral near circles 1 and 5, and deviate from the original spiral and follow the circles in a more parallel direction so as to allow the spiral to begin and end gradually and not too abruptly. Refer to the lower diagram for this.
8. Cut out portions of wood between the bands previously marked around, as shown in the lower figure. The wood should be cut out with a knife so as to leave the corners sharp on the narrow bands. The portion cut out should be a semi-circle and can be sanded by making a spindle a little smaller than the distance between the bands and fastening sandpaper on the spindle. Place in the lathe and hold the spiral on the sandpaper cylinder at an angle so that the spiral will fit. Turn gradually and the sandpaper will smooth up the portion between the bands and true it up. At the ends where the grooves are smaller, use a smaller stick around which sandpaper has been wound and work out by hand.
9. It is well to cut straight down, about 1/32" deep, along the lines marking out the narrow bands. Then the wood will not be so likely to split while removing the stock which forms the grooves between the bands.
10. Cut out the mortises in the square portions which have been left at both ends. Make the frame work for the sides and cane. Glue together and polish.
Note:--By making the posts smaller and using the same construction for a side a nice looking book stall may be made. The proportions for the posts are the same as mentioned in Step 3.
[Transcribers note: There are 142 line art illustrations after this point in the book. See the Classification of Plates for all of them.]