A Course In Wood Turning.
by Archie S. Milton and Otto K. Wohlers.
PREFACE
This book is the outgrowth of problems given to high school pupils by the writers, and has been compiled in logical sequence. Stress is laid upon the proper use of tools, and the problems are presented in such a way that each exercise, or project, depends somewhat on the one preceding. It is not the idea of the writers that all problems shown should be made, but that the instructor select only such as will give the pupils enough preliminary work in the use of the tools to prepare them for other models following.
The related matter on the care of the lathe and tools, the grinding of chisels, the polishing of projects, and the specific directions and cautions for working out the various exercises and projects with the drawings, make the book not only valuable for reference, but also as a cla.s.s text to be studied in connection with the making of projects. The drawings show exact dimensions and are tabulated in the upper right-hand corner in such a way that they may be used in a filing case if desired.
At least two designs are shown for each model, and these may be used as suggestions from which students, with the aid of the instructor, may work out their own designs.
The book has been divided into two parts: (A) Spindle Turning, and (B) Face-Plate Turning. The same order is followed in each part; the related information is supplied where required as the pupil progresses.
Part A takes up the following: (I) Exercises; (II) Models, involving the same tool processes, only in a somewhat different degree; (III) Oval Turning, explaining the use of two centers; (IV) Duplicate Turning, where identical pieces are turned.
Part B is arranged as follows: (I) Exercises; (II) Models, which are an application of cuts in exercises that involve only face-plate work; (III) Models, which require chucking; (IV) a.s.sembling Exercises, involving spindle turning, face-plate work and chucking; (V) Spiral Turning, showing the method of turning a spiral on the lathe.
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.
CHAPTER I
INTRODUCTORY
Wood turning has had a definite place in the commercial world for a great many years. It is used in various forms in making furniture and furniture parts, building trim, tool parts, toys, athletic paraphernalia and many other useful and beautiful articles in common use.
When properly taught in the schools it is one of the most valuable types of instruction. It appeals to pupils more than any other type of manual work, as it embodies both the play and work elements. It is very interesting and fascinating and, in the hands of a skilled instructor, is readily correlated with other work.
Wood turning gives a pupil preliminary experience necessary in pattern making and machine shop work. It brings into play the scientific element by demonstrating the laws governing revolving bodies. In bringing the chisel into contact with the revolving surface, the mathematical principle of the "point of tangency" is ill.u.s.trated. Excellent tool technique is developed in wood turning as on the exactness of every movement depends the success of the operator, and any slight variation will spoil a piece of work. This brings in a very close correlation of the mental and motor activities and also gives the student an opportunity for observing and thinking while at work. When his tool makes a "run" he must determine the reason and figure out why a certain result is obtained when the chisel is held in a given position. Certain cuts must be fully mastered, and it takes a good deal of experience and absolute confidence in one"s self in manipulating the tools before it is possible to attempt skilful work. If sc.r.a.ping is allowed the educational value of the work is lost.
In wood turning a vast field for design and modeling is opened, and art and architecture can be correlated. The pupil will see for himself the need of variety in curves and must use his judgment in determining curves that are so harmonious and pleasing that they will blend together. If properly taught the beauty in the orders of architecture can be brought out in the making of the bead, fillet, scotia, cove, etc.
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.
Success in turning depends on the following:
1. Care of lathe, tools, selection of materials.
2. Study of the scientific elements of-- a. Revolving bodies.
b. Points of tangency.
c. Study of results by reasoning and observing.
3. Development of technique and exactness.
4. Correlation of mental and motor activities.
CHAPTER II
THE LATHE
The sizes of turning lathes are given as 10", 12", etc. These figures denote the diameter, or size, of the largest piece of work that can be turned on them. The measurement is taken from the center point of the live center to the bed of the lathe (usually 5" or 6") and is one-half the diameter of the entire circle. The length of a lathe is determined by the length of a piece of work that can be turned. This measurement is taken from the points of the live and dead centers when the tail stock is drawn back the full extent of the lathe bed. Fig. 1 shows a turning lathe with sixteen princ.i.p.al parts named. The student should learn the names of these parts and familiarize himself with the particular function of each.
CARE OF THE LATHE
The lathe should be oiled every day before starting. At the end of the period the lathe should be brushed clean of all chips and shavings, after which it should be rubbed off with a piece of waste or cloth to remove all surplus oil. All tools should be wiped clean and put in their proper places. If a student finds that his lathe is not running as it should, he should first call the attention of the instructor to that fact before attempting to adjust it; and then only such adjustments should be made as the instructor directs.
SPEED OF THE LATHE
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.
[Ill.u.s.tration: Fig. 1. - Wood Turning Lathe]
TO FIGURE THE DIAMETER OF PULLEYS
Suppose a motor runs 1500 R.P.M. and is fitted with a 4" pulley. Suppose also, a main shaft should run 300 R.P.M.
Then, 1500 : 300 :: x : 4; Or, 300x = 6000, x = 20, or the diameter of the large pulley on the main shaft.
Suppose again that a line shaft runs 300 R.P.M., and a counter shaft 600 R.P.M. The counter shaft has a pulley 4" in diameter. The pulley on the line shaft must then have a diameter of 8".
300 : 600 :: 4 : x; Or, 300x = 2400, x = 8"
Suppose the cone pulley on the counter shaft runs 600 R.P.M.; a lathe spindle runs 2200 R.P.M., when connected with the small cone pulley which has a diameter of 3". The large cone pulley has then a diameter of 11".
600 : 2200 :: 3 : x Or, 600x = 6600; x = 11"
RULES FOR FINDING THE SPEEDS AND SIZES OF PULLEYS
1. To find the diameter of the driving pulley:
Multiply the diameter of the driven by the number of revolutions it should make and divide the product by the number of revolutions of the driver. (20 x 300 = 6000; 6000 1500 = 4"--diameter of motor pulley.)
2. To find the diameter of the driven pulley:
Multiply the diameter of the driver by its number of revolutions and divide the product by the number of revolutions of the driven. (4 x 1500 = 6000; 6000 300 = 20"--diameter of the driven pulley.)
3. To find the number of revolutions of the driven pulley: