CHAPTER V
TOOL PROCESSES IN SPINDLE TURNING
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.
[Ill.u.s.tration: Fig. 4.]
Roll the gouge over slightly to the right so that it will make a shearing cut instead of a sc.r.a.ping 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 3/4" from the dead center end. Work back another 3/4", 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.
[Ill.u.s.tration: Fig. 5.]
2. THE SIZING CUT (SMALL GOUGE). FIG. 5.
Set the calipers to the required diameter of the cylinder.
With a small gouge held in the right hand sc.r.a.pe grooves about 1" apart, holding the calipers in the left hand perpendicular to the cylinder and measuring the cuts as they are made. The sc.r.a.ping should continue until the calipers will pa.s.s easily over the cylinder. It will be well while sc.r.a.ping to work the handle of the gouge a little from side to side so that the nose has more clearance. This will prevent the piece which is being turned from chattering or vibrating.
The calipers will be slightly sprung by coming in contact with the revolving stock but this error in diameter will be removed by the finishing cut which removes these marks from the finished cylinder.
3. THE SMOOTHING CUT (LARGE SKEW).
FIG. 6. Lay the skew chisel on the rest with the cutting edge above the cylinder and at an angle of about 60 to the surface.
Slowly draw the chisel back and at the same time raise the handle until the chisel begins to cut about 1/4" to 3/8" from the heel. The first cut is begun from 1" to 2" from either end and is pushed toward the near end. Then begin at the first starting point and cut toward the other end. One should never start at the end to make a cut as there is danger that the chisel will catch and cause the wood to split or that the chisel will be torn from the hands.
The first cut takes off the b.u.mps and rings left by the gouge, and takes the stock down so one can just see where the sc.r.a.ping 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.
[Ill.u.s.tration: Fig. 6.]
4. TESTING FOR SMOOTHNESS. In testing for smoothness place the palm of the hand, with the fingers extended straight, lightly on the back of the cylinder opposite the tool rest. This position will avoid any possibility of the hand being drawn in between the cylinder and the rest.
[Ill.u.s.tration: Fig. 7.]
5. MEASURING FOR LENGTH (RULE AND PENCIL). FIG. 7. Hold the back edge of the rule in the left hand and place it on the tool rest so that the front edge is almost in contact with the revolving cylinder.
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.
In case several measurements are to be made, as in some of the following exercises, the rule should not be moved until all are marked. This will insure more accurate work than if the rule be changed several times.
6. SQUARING ENDS (SMALL SKEW AND PARTING TOOL). FIG. 8. This operation is done with the toe or acute angle of the 1/2" or 1/4" skew chisel.
Place the chisel square on the tool rest. Swing the handle out from the cylinder so that the grind, which forms the cutting edge, next to the stock is perpendicular to the axis of the cylinder. The heel of the chisel is then tipped slightly from the cylinder in order to give clearness. Raise the handle and push the toe of the chisel into the stock about 1/8" outside the line indicating the end of the cylinder.
Swing the handle still farther from the cylinder and cut a half V. This will give clearance for the chisel point and will prevent burning.
Continue this operation on both ends until the cylinder is cut to about 3/16" in diameter.
The remaining 1/8" is then removed by taking very thin cuts (about 1/32") holding the chisel as first stated. After each cut is made the end should be tested for squareness by holding the edge of the chisel over the end of the cylinder.
[Ill.u.s.tration: Fig. 8.]
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.
In large cylinders where considerable stock has to be cut away in order to square the ends, time will be saved by sizing the ends down with the parting tool to within 1/8" of the desired line, leaving enough stock at the base of the cuts to still hold the cylinder rigid while cutting on the ends.
[Ill.u.s.tration: Fig. 9.]
For this operation hold the parting tool on the rest with the cutting edge parallel to the axis of the cylinder and the lower grind tangent to the cylinder. Lift the handle and force the cutting edge into the wood; at the same time push the chisel forward to keep it at the proper tangency.
7. CUTTING OFF (SMALL SKEW). FIG. 9.
After both ends have been squared cut away stock, at both ends, to leave just enough to hold the cylinder from separating from the waste ends.
With the chisel held in the right hand in the same position as in squaring the ends, and the fingers of the left hand around the stock to catch it, slowly force the point of the chisel into the stock at the live center end, until it is cut free and the cylinder stops in the operator"s hand. Too much pressure should not be used in this operation or it will cause the cylinder to twist off instead of being cut, and will leave a ragged hole in the end.
The dead center end, which has been scored heavily before cutting off at the live center, is then removed by holding the grind of the chisel flat on the end of the cylinder. The latter is revolved by hand until the stock is cut away.
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 s.p.a.ce permits) or the parting tool (in narrow s.p.a.ces) rough out surplus stock, keeping 1/16" away from the lines indicating shoulders.
4. Caliper to the diameter of the second step.
5. The shoulders are cut down as described in "Squaring Ends, Step 6, Straight Cuts."