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Tip
#56
Lathe Turning
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Other
Special Techniques
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Figure
12-53.
Small workpieces can be turned by mounting them on a
screw center. Be sure there are no chips between the
workpiece and the screw center's front face.
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There
are many special techniques that can be performed on the lathe.
Let's take a look at some of the simplest:
Screw
Center Work
Workpieces that are too small to be mounted on a faceplate
or not long enough to be fitted between centers can be set
up for turning by using a screw center (a device that is mounted
on the Mark V main spindle). Find the center of the workpiece
and start a hole for the screw by using an awl or by drilling.
Mount the workpiece by threading it on the screw center (Figure
12-53). The technique makes it possible to shape small
items like drawer or door pulls, finials or small posts (Figure
12-54).
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Figure
12-54.
Turning is accomplished in normal fashion. On jobs ilke
this it's best to use carbide-tipped tools since they
have smaller cutting profiles than conventional tools.
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Figure
12-55.
Extra-long lathe projects can be produced if you turn
separate pieces and then connect them as shown here.
Click on image to see larger view.
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Extra-Long
Work
When a
project is longer than the spindle capacity of the lathe,
it can be turned as separate pieces that are then joined in
the manner shown in Figure
12-55. The tenon on the one piece can be formed while
the part is on the lathe. Drill a matching hole in the mating
piece; then put the parts together with glue. Use a Iockwedge,
if you wish, to reinforce the joint.
The same
idea applies when you join a faceplate turning to a spindle
turning (Figure
12-56).
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Figure
12-56.
The same idea will work when you need to connect a spindle
turning to a faceplate turning. Click on image to see
larger view.
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Figure
12-57.
When a large diameter is required in one area of the
turning, either (A) reduce the stock or (B) build up
the stock. Click on image for larger view.
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Glued-Up
Stock
When a large diameter is required in one area of the turning,
two methods are used to prepare the stock (Figure
12-57). In one, start with oversized stock and use a jointer
or bandsaw to reduce the stock before it is mounted on the
lathe. Warning: Glue the stock and leave it clamped for at
least 24 hours prior to turning.
In the
other, glued blocks are used to build up the larger diameter.
The mating surfaces must be perfectly flat and true for a
perfect joint if the final turning is to resemble a solid
piece of wood.
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Figure
12-58.
Make a large turning block by laminating pieces of stock.
The laminations can be of contrasting wood.
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When solid
stock large enough for a deep bowl or similar project is not
available, stock may be glued together (Figure
12-58). Or rough-cut rings may be glued onto a solid base.
This method saves a lot of material since the cutout discs
may be used in other ways. Figure
12-59 shows rings cut for a project that will have straight
sides. If the sides are to slope or taper, the rings should
vary in size. The important thing is a good glue job so the
stock will hold together with just a faint line showing on
the finished item.
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Figure
12-60.
You can get interesting inlaid effects if you prepare
a turning blank by gluing together pieces of contrasting
wood. It's not easy to do, but try to visualize the
end result.
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Figure
12-59.
Speed up shaping a deep bowl by gluing precut rings
to a solid base.
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You can
produce intriguing lathe projects with an inlaid appearance
when you prepare the base stock by gluing together pieces
of contrasting wood. The initial blocks can be prepared for
either spindle turning (Figure
12-60) or faceplate turning (Figure
12-61). The blocks won't look like much to start; the
appealing effects occur when the turning is complete. It's
not easy, but try to visualize the results as you plan the
initial block assemblies.
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Figure
12-61.
The same idea applies to faceplate work. A good glue
job is critical.
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Figure
12-62.
Here are other ways you can prepare stock for split
turning. Oval moldings and even quarter-rounds are possible.
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Select
wood not only on the basis of color contrast, but also for
similarity in density. Good combinations to try are maple
with rosewood, and holly or birch with cherry, walnut, or
mahogany.
Split
Turnings
Split turnings are lathe projects that end up as half-round,
shaped columns. Using the paper-glue-joint method shown in
Figure 12-62,
two pieces of wood will produce identical half-round mold-ings.
Four pieces of wood, paper-glued to a central core piece,
will separate as elliptical moldings. Four pieces of wood,
assembled as a solid block, will become four pieces of quarter-round
molding. Warning: Glue the stock and leave it clamped for
at least 24 hours prior to turning.
Procedures
like this are useful when a special molding is needed or when
you need a particular hardwood molding that isn't available.
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Figure
12-63.
You can prepare stock this way when you need a lathe
turning with a center hole such as a lamp base. Click
on image to see larger view.
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Through
Holes
The two methods shown in Figure
12-63 can be used to prepare stock for projects like lamp
bases before the material is mounted for lathe turning. Cut
grooves in the center of the stock. A groove about 7/16" wide
by 7/32" deep in each piece will do for lamp cords.
Glue the
pieces together and use keys to plug the opening at each end.
When the turning is complete, open the grooves by boring holes
at each end of the turning.
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Figure
12-64.
The drill chuck grips the bit. The workpiece, while
turning, is quill fed against the bit to form the hole.
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Accurate
center holes, of limited length when using conventional bits
or much deeper when working with extra-long bits or extension
bits, can be formed by mounting the drill chuck on the tailstock.
Figure 12-64
shows the technique being used to form a socket hole in a
small candle stand. The procedure is the opposite of normal
boring. Here, the drill bit is stationary; the workpiece turns.
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Figure
12-65.
Construction details of an indexing device, (A) guide
pin holder, and(B) indexing disk. Click on image to
see larger view.
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Indexing
Some lathe projects, like wheel hubs, require radial holes
that are equally spaced about their circumference. A good
way to do such work accurately is to use an indexing device.
The plans for one that you can make and which is mounted on
the Mark V's upper auxiliary spindle is shown in Figure
12-65. Make the guide pin holder first. Then drill holes
in the power plant cover and mount the holder as shown in
Figure 12-66.
Drilling holes in the power plant cover will not damage the
machine. You must situate the holder so the guide pin and
the spindle have a common vertical centerline.
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Figure
12-66.
The guide pin holder is mounted this way. Drilling mounting
holes in power plant cover will not damage the machine.
Be sure the guide pin and the auxiliary spindle have
a common vertical centerline.
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Figure
12-67.
The indexing disk is mounted on a faceplate which locks
on the upper auxiliary spindle. When the disk is engaged
by the guide pin, lathe-mounted work will be held in
a fixed position.
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The indexing
disk, which is the control that positions a project for drilling,
is made next. After the disk is cut out and rounded, mount
it on a small faceplate. Then secure the faceplate on the
auxiliary spindle (Figure
12-67). Push the guide pin forward so it will mark the
disk. This will establish the radius of the circle on whose
circumference the guide holes must be drilled. Make a layout
and drill the holes. The plans suggests a spacing of 22-1/2°,
but you can increase or decrease it.
A typical
use for the indexing device and a drill guide are shown in
Figure 12-68,
where the hub for a wheel is being drilled for spokes. For
example, if the hub is to have eight spokes, lock the indexing
device at any point and drill the first hole. Turn the indexing
device 45°, lock it with the pin, and drill the second hole.
Turn the indexing device 45° for each hole until all are drilled.
If the wheel needed four spokes, the device would be turned
90° to establish each hole position.
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Figure
12-68.
A typical appilcation for the indexing device. It positions
work so radial holes can be equally and automatically
spaced. The drill guide keeps the bit square to the
workpiece.
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Figure
12-69.
Construction details of the drill guide. Click image
to see larger view.
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The drill
guide, made as shown in Figure
12-69, is mounted in the tool rest arm and positioned
so the bit will be square to the work and so its point will
be on the work's horizontal centerline.
Indexing,
as shown in Figure
12-70, can also be used to gauge the spacing of surface-drilled
holes. The drill guide can do double-duty. When you position
it correctly, it will act as a stop to gauge hole depth.
Turning
Small Components
Model makers will find a dowel turning fixture almost indispensable
for small turnings like head-lights, wheel hubs, rims, capstans,
deadeyes for boat and automobile models, and for making components
for miniature furniture.
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Figure
12-70.
The indexing device and the drill guide can also be
used to automatically space surface holes. The drill
guide can also serve as a stop to gauge hole depth.
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Figure
12-71.
A dowel turning fixture makes it easy to turn small
parts from dowel stock.
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A good
feature of the dowel turning fixture, shown in Figure
12-71, is that it allows mounting of a long piece of dowel
that is gripped for turning with the drill chuck that substitutes
for the usual drive center. The bolt acts as a tool rest.
The table to which the fixture is clamped, or the power plant
is moved to position the dowel for each new turning. The dowel
doesn't have to be cut until several individual parts have
been formed.
To make
the dowel turning fixture follow the plans in Figure
12-72. The plans show three sizes of holes, but you can
accommodate other sizes of dowels merely by drilling additional
holes.
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Figure
12-72.
Construction details of the dowel turning fixture for
1/4 ", 3/8", and 1/2" dowels. Additional holes for other
sizes of dowels can be drilled. Click on image to see
larger view.
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Figure
12-73.
The bolt, which is part of the dowel turning fixture,
serves as a tool rest. Apply paste wax to the dowel
so it can turn with minimum friction.
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Figure
12-73 shows the relationship between the dowel turning
fixture and a turned dowel. It's a good idea to coat the dowel
with paste wax to minimize friction where the dowel turns
in the block.
The dowel
turning fixture can also position tiny work for concentric
drilling. If the work is very tiny, it can be gripped in a
router chuck locked on the main spindle.
Turning
Ovals
The most important part of turning a cylinder into an oval
shape is the initial layout on the ends of the stock.
First
make an accurate template for locating the true center and
the two off centers (Figure
12-74). If the ridge line is located first, it is easy
to position the template at the ends of the stock and mark
the centers with an awl.
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Figure
12-74.
You can turn cylinders with an oval cross section if
the work is shaped while it is mounted on off centers.
These drawings show the procedure to follow. Click on
image for larger view.
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Turn
the work on true center until it is round. Remark the ridge
line.
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Figure
12-75.
When the oval is complete, use sandpaper to smooth the
project and to remove the ridge line. The shape of the
oval will depend on how far apart you space the off
centers.
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Mount
the work on one of the off centers. Turn it until the cut
nears the ridge line. Now it's round on one side, oval on
the other.
Mount
the work on the remaining off center; turn it down to the
ridge line. Now the work is oval. Sand it as illustrated in
Figure 12-75.
Turning
Spirals
Spiral forming is classified as a lathe job even though most
of the work is done by hand. It is started by mounting stock
between lathe centers and turning it to a cylinder.
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Figure
12-76.
This is the kind of layout you must use to prepare stock
for spiral forming. Click on image to see larger view.
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Layout
of the spiral divisions is shown in Figure
12-76. First mark off the length of the spiral. Divide
this into equal spaces, each approximately the diameter of
the cylinder. Draw four lines along the length of the stock,
connecting common perpendicular diameters at each end. Now
divide each space into four equal parts and, with a heavy
piece of paper as a guide, pencil-mark diagonal lines across
each one as shown.
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Figure
12-77.
To form spirals: (A) Use a keyhole saw or backsaw to
cut on the spiral line. (B) Start the shaping with a
round file. (C) Continue the shaping by using a square
file. (D) Finish the shaping with a half-round file.
Then work with strips of sandpaper to achieve final
smoothness. Click on image to see larger view.
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Now follow
the sequence detailed in Figure
12-77. Use a saw to cut along the spiral line to the depth
needed (Figure
12-77A). This depth is easily controlled if a keyhole
saw is used. If a backsaw is used, clamp a block of wood to
it to act as a depth guide. Next use a round file to form
a groove to the depth of the saw cut (Figure
12-77B). Open up the groove with a square file (Figure
12-77C). Shape it with a half-round file (Figure
12-77D). Use sandpaper to do the final shaping and smoothing.
Back to
Introduction
Back to Faceplate Turning
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