6. The new diameter or step is then trued up with a skew chisel in the same manner as a cylinder; except that in nearing the shoulder the chisel is pushed up on the cylinder until the heel, which is the only part that can be worked into the corner, becomes the cutting point. Fig.
10. In very narrow steps it will be advisable to use the heel entirely as a cutting point.
In spaces between shoulders, too narrow to permit the use of the skew chisel, very effective work can be accomplished by slightly tipping the parting tool sideways to allow a shearing cut to be taken with the cutting edge.
7. Where several steps are required on the same cylinder, each successive one is worked out as above described.
Note:--All preliminary steps in working stock to size, laying of dimensions, etc., in preparation for the exercise in hand, will be omitted in the following exercises:
Exercise A-I--3-a. Taper Cuts
[Illustration: 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 1/2"
or 3/4".
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.
[Illustration: 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.
The exact depth of the concave is then calipered in the usual manner as described before. A finishing cut is then taken after the cut has been tested with a templet.
[Illustration: 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 1/4" or 1/8".
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.
[Illustration: 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.