The Project Gutenberg EBook of A Course In Wood Turning
by Archie S. Milton and Otto K. Wohlers

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Title: A Course In Wood Turning

Author: Archie S. Milton and Otto K. Wohlers

Release Date: March 25, 2005 [EBook #15460]

Language: English

Character set encoding: ISO-8859-1

*** START OF THIS PROJECT GUTENBERG EBOOK A COURSE IN WOOD TURNING ***




Produced by Jason Isbell and the PG Online Distributed Proofreading Team

Transcribers note: Mis-spelled words in the original left as is. Below is a list of all known mis-spelled words kept from the original:

Table Of Contents - Classification of Plates
bowels - should be bowls
Chapter II - SPEED OF THE LATHE
centrificial - should be centrifugal
Chapter IX - METHODS OF FASTENING STOCK
epecially - should be especially
Chapter XI - SPIRAL TURNING
modelling - should be modeling
Chapter XI - PLATES B-V--2-b, b’
midde - should be middle

A COURSE IN WOOD TURNING

1919

PREFACE

The ultimate aim of this book is to give, through the exercises and problems, a thorough understanding of the principles of wood turning by gradually developing the confidence of the pupil in the complete control of his tools, at the same time suggesting harmonious lines in design which will lead to other ideas in designing problems.

TABLE OF CONTENTS

CHAPTER I

A feeling of importance is excited in a boy when he sees his hands shaping materials into objects of pleasing form. Wood turning properly taught awakens the aesthetic sense and creates a desire for the beautiful. The boy or man who has learned to make graceful curves and clean-cut fillets and beads will never be satisfied with clumsy effects which are characteristic in cheap commercial work, made only to sell.

CHAPTER II

The speed of the lathe should range from 2400 to 3000 revolutions per minute when the belt is on the smallest step of the cone pulley. At this speed stock up to 3" in diameter can be turned with safety. Stock from 3" to 6" in diameter should be turned on the second or third step, and all stock over 6" on the last step. The speed at which a lathe should run depends entirely upon the nature of the work to be done and the kind of material used. Pieces that cannot be centered accurately and all glued-up work with rough corners should be run slowly until all corners are taken off and the stock runs true. At high speed the centrificial force on such pieces is very great, causing the lathe to vibrate, and there is a possibility of the piece being thrown from the lathe thus endangering the worker as well as those around him. After the stock is running true the speed may be increased.

POINTS ON SETTING UP LATHE AND SHAFTING

CHAPTER III

The skew chisel is sharpened equally on both sides On this tool the cutting edge should form an angle of about 20° with one of the edges. The skew is used in cutting both to the right and to the left, and therefore, must be beveled on both sides. The length of the bevel should equal about twice the thickness of the chisel at the point where it is sharpened. In grinding the bevel, the chisel must be held so that the cutting edge will be parallel to the axis of the emery wheel. The wheel should be about 6" in diameter as this will leave the bevel slightly hollow ground. Cool the chisel in water occasionally when using a dry emery. Otherwise the wheel will burn the chisel, taking out the temper; the metal will be soft and the edge will not stand up. Care should be exercised that the same bevel is kept so that it will be uniformly hollow ground. The rough edge left by the emery wheel should be whetted off with a slip stone by holding the chisel on the flat side of the stone so that the toe and heel of the bevel are equally in contact with it. Rub first on one side and then on the other. The wire edge is thus worn off quickly as there is no metal to be worn away in the middle of the bevels. The chisel is sharp when the edge, which may be tested by drawing it over the thumb nail, is smooth and will take hold evenly along its entire length. If any wire edge remains it should be whetted again.

The parting tool is sharpened on both sides. This tool differs from the ordinary chisel in that it is between ⅝" and ¾" thick and only about ⅛" wide at the widest point, which is in the center of its entire length. The bevels must meet exactly at the center, or the widest point, and should make an angle of about 50° with each other. If the bevels do not meet at the widest point the tool will not clear, and the sides will rub against the revolving stock; the tool will be burned and will thus lose its temper. The bevel should be hollow ground slightly as then comparatively little metal need be removed when whetting.

CHAPTER IV

Take the live center from the spindle and with a wooden mallet drive the spur deep into the wood. Never drive the wood onto the live center while in the spindle because serious injury may be done the machine by such practice. When extremely hard wood is being used, it is a good practice to make saw cuts along the diagonal lines and bore a hole at the intersection, thus allowing the spur to enter the wood more freely. Oil the other end of the wood while holding it in a vertical position, and give the oil a chance to penetrate into the wood. Then replace the live center by taking the stock and center and forcing it into the spindle by a sudden push of the hand. The tail stock is then moved about ½" to 1" from the end of the piece to be turned, having the tail spindle well back in the tail stock. The tail stock is then clamped to the lathe bed. Turn the tail stock hand wheel until the wood is held firmly. Work the cone pulley by hand at the same time, so that the cup or dead center will be forced deeply into the wood, so deeply that the live center will not continue to turn. Now turn the dead spindle back until the live spindle begins to turn freely and clamp the dead spindle fast.

The operator stands firmly on the floor back far enough from the lathe to allow him to pass the tools from right to left in front of his body without changing the position of the feet. It may be found convenient to turn slightly, bringing the left side of the body a little closer to the lathe. In no case, however, should the tools be brought in contact with the body as the cutting operation from right to left should be accomplished by a movement of the arms alone and not the swaying of the body. (Fig. 3.)

CHAPTER V

Exercise A-I--1-a. Straight Cuts

1. THE ROUGHING CUT (LARGE GOUGE).

FIG. 4. Place the gouge on the rest so that the level is above the wood and the cutting edge is tangent to the circle or surface of the cylinder. The handle should be held well down.

Fig. 4.

Roll the gouge over slightly to the right so that it will make a shearing cut instead of a scraping cut. This rolling of the tool will also throw the chips from the operator.

Then lift the handle slowly, forcing the cutting edge deep enough into the wood to remove all or nearly all of the corners, at the end of the work which is being turned. This cut is begun about ¾" from the dead center end. Work back another ¾", moving toward the live center and make a second cut, and so on until the entire length of the cylinder is gone over. This method of removing corners should always be followed to avoid any possibility of breaking a large sliver from the stock, with consequent danger to the worker.

The tool may then be worked from one end to the other, getting a fairly-smooth, regular surface, slightly above the diameter required. However, do not begin on the very edge of the cylinder end. It is better to begin about 2" from one end and work to the other, and then reverse and work back.

The tool should also be held at a slight angle to the axis of the cylinder, with the cutting point always in advance of the handle.

The first cut takes off the bumps and rings left by the gouge, and takes the stock down so one can just see where the scraping to size was done. Then take the last cut and remove all traces of these, leaving the cylinder perfectly smooth and of the required diameter at each end. Test the cylinder for accuracy with a straight edge.

With a sharp pencil mark off the required length, starting from the dead center end. The first mark should be just far enough in on the cylinder to insure cutting past the point of the dead center. This will leave all surplus stock at the live center end where it is needed, because, if not enough stock is left at this end, there is danger of striking the live center spur with the tool and of injuring the chisel and perhaps the work.

This is an easy cut after it is mastered, but is one of the hardest to learn. Should the operator lose control of the tool and allow any part other than the point to touch the cylinder, a run or gashing of the wood will be caused.

Exercise A-I--2-a. Shoulder Cuts

1. Turn a cylinder to the largest diameter required.

2. Lay off measurements with rule and pencil.

3. With the gouge (where space permits) or the parting tool (in narrow spaces) rough out surplus stock, keeping 1/16" away from the lines indicating shoulders.

Exercise A-I--3-a. Taper Cuts

Fig. 10.

Calipering for New Diameters. For all diameters on tapers the calipers should be set 1/16" larger than the desired measurement in order to avoid working under size in the finishing cut which removes all caliper marks.

If the taper runs to the extreme end of the cylinder, as in Plate A-I--3-a, a parting tool should be used, instead of a gouge, to take off a very thin shoulder.

If the taper forms an internal angle as in Plate A-I--3-b, a gouge is used as in Step 2--Sizing Cut--Plate A-I--1-a.

In other cases where tapers connect with straight cylindrical shoulders it is best to turn the shoulders to size before working the tapers.

In cutting a long straight taper the skew chisel is used, much in the same manner as in ordinary cylinder work, except that at the start of each cut the heel must be the cutting point. This will avoid any chance of the chisel catching and drawing back and thus gouging the wood beyond the starting point. As soon as the cut is well under way the chisel may be pushed up on the cylinder so that the cutting point is a little above the heel. All cuts should be made from the highest point on the cylinder to the lowest and thus cut across the grain of the wood.

In making the cut, care should be taken to see that the chisel is not tipped to a greater angle than that of the taper wanted. Should that be done a hollow, or dished out, taper is sure to be the result instead of a straight one.

Exercise A-I--4-a. V Cutting

In cutting V's a small skew is almost always used and the cutting is done with the heel.

Place the chisel square on the tool rest so that the cutting edge is perpendicular to the axis of the cylinder. Draw the chisel back and raise the handle so that the heel is driven into the wood, thus scoring it. This cut should not be too deep or the chisel will burn. This scoring should be at the exact center of the V cut.

Swing the handle a little to the right and at the same time tip the chisel so that the grind, which forms the cutting edge, is at an angle of about 45° with the axis of the cylinder. The handle is then raised at an angle of 45° bringing the heel down to make a good cut. The chisel is then swung to the other side and a similar cut is taken. These cuts are continued, together with the center scoring, until quite close to the pencil marks. Test the angle before the finishing cut is taken.

It will be found best to have the V slightly greater than 90° at the base until the final cut is made, at which time it can be trued up.

The V should be tested with the square end of a rule. The cylinder should not be in motion while testing.

When angles other than 45° are cut, the cutting edge of the chisel should be tipped so that it is parallel or nearly so to the side of the cut desired.

A-I--5-a. Concave Cuts

The concave cuts as a rule will give the pupil considerable trouble at first owing to the fact that the grind, which forms the cutting edge and which must be held perpendicular to the cylinder at the start, is on the under side of the tool and cannot be seen. However, as soon as the correct angle of the tool is located, the cut will be found as easy as any. Concaves are usually made with a medium sized gouge either the ½" or ¾".

Place the gouge on the rest with the grind or cutting edge well above the wood. The tool is then rolled on its side so that the grind at the cutting point, which is on the lip of the gouge well below the center, is perpendicular to the axis of the cylinder. Fig. 11.

Slowly raise the handle to force the gouge into the wood. As soon as the gouge has taken hold, the tool is forced forward and upward by a slight lowering of the handle, while at the same time it is rolled back toward its first position. Care should be taken not to roll the chisel too fast or a perfect arc will not be cut.

Fig. 11.

By this triple action the grind, which comes in contact with the surface of the curve, forces the lip sidewise and cuts one quarter of a circle. Reverse the position of the gouge and cut from the other side in the same manner to form the other half of the semi-circle. The cutting should always stop at the base of the cut as there is danger that the tool will catch when cutting against the grain of the wood on the other side. Repeat this operation until within about 1/16" of the required size. At the end of each successive cut the tool should have been forced far enough forward and upward to bring the grind or nose of the chisel well out on top of the cut. Fig. 12.

A-I--6-a. Convex Cuts

The convex cut, or Bead as it is usually called, is generally considered the hardest cut to make.--The cut is made with the heel of a small skew chisel, usually the ¼" or ⅛".

After the cylinder has been marked off, rough out all stock between the beads with a parting tool. The base of the cuts is finished the same as described in Plate A-I--1-a, for shoulder cutting. With a sharp pencil mark the center of each bead to be made. This line is the starting point for all cutting.

Place the chisel on the rest, with the cutting edge above the cylinder and the lower grind tangent to it. Draw the chisel back and raise the handle to bring the heel of the chisel in contact with the cylinder at the line indicating the center of the bead. The chisel is then moved to the right (if cutting the right side of the bead); at the same time the chisel is continually tipped to keep the lower grind tangent to the revolving cylinder and also to the bead at the point of contact. Fig. 13. This cut is continued until the bottom of the bead is reached. It is well in turning a series of beads to work the same side of all before reversing to the other side.

Note:--The same principles employed in this exercise are also used in working out long convex curves such as are found in chisel handles, mallet handles, etc. The only exception is that in most cases the point of contact need not be the heel of the chisel but higher up as in ordinary straight work.

A-I--7-a--Combination Cuts

These exercises are so designed as to include one or more of each of the foregoing cuts. The student here is given an opportunity of combining these cuts into one finished product.

Fig. 13.

An analysis of the exercise chosen should be made to determine which of the various cuts should be made first, second, etc., in order to produce the exercise in the shortest time and with the least amount of tool manipulation.

After the student has mastered these cuts with a certain degree of skill and accuracy, he is ready to apply them in working out various models in Section II.

A-II--1-a. Chisel Handles

At this point it is well to state that the small end of all work should be turned at the dead center. In the case of chisel handles the socket or ferrule end is at the dead center where the stock can safely be cut away to permit the fitting of the ferrule or the socket.

After the stock is turned to a cylinder of the largest dimension desired, the taper, for the socket chisel, should be turned first and fitted to the chisel in which it is to be used. Then the rest of the handle is worked out. Ferrules should also be fitted in the same manner. A drive fit should be used for all ferrules.

A-II--2 and 3. Mallets and Gavels

The biggest source of trouble in these models is getting the handles to fit true. This is caused by not getting the hole in the head straight.

Turn the head to a cylinder 3/16" larger than the finished dimension. Then bore the hole perpendicular to the axis as near as possible, either by leaving it between the lathe centers or by placing it in a vise. The handle is then fitted into the head. A snug fit is necessary. If one side "hangs" or is lower than the other the centers are moved sufficiently to correct it. The head is then turned to exact size and finished.

CHAPTER VI

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.

CHAPTER VII

CHAPTER VIII

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.

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.

CHAPTER IX

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.

CHAPTER X

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.

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.

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.

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.

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.

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.

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.

Mirror (See Pages 299-301).

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

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. 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.

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.

[Transcribers note: There are 142 line art illustrations after this point in the book. See the Classification of Plates for all of them.]

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