the diameter of the shaft at the point where the center
straighten a shaft, however, always be sure the leading
rest will be used. Carefully align the center rest on this
petty officer of the shop is informed of the operation.
Use the following steps to straighten a shaft:
3. Mount the undamaged end of the shaft in a
1. Mount the shaft between centers in a lathe. If the
4-jaw chuck and "zero in" the shaft near the jaws of the
shaft is too long, mount it on rollers.
chuck Use soft jaws or aluminum shims to prevent
2. Clamp a dial indicator on the compound rest,
damage to the shaft surface.
locate the area of the bend, and measure how much the
4. Position the previously set center rest under the
shaft is bent (runout). To determine the area of the bend,
shaft so the center rest is between the chuck and the
run the dial indicator along the shaft longitudinally. The
damaged end of the shaft.
greatest variation of the pointer from zero indicates the
bend area. With the dial indicator set at this point, rotate
5. Cut off the damaged portion of the shaft.
the shaft and note the amount of fluctuation of the
6. Face, center drill, and drill the end of the shaft.
pointer. This fluctuation is the amount of runout. Mark
The diameter of the hole should be about 5/8 of the
the longitudinal position of the bend and the high side
diameter of the shaft; the depth of the hole should be at
of the bend with chalk or a grease pencil.
least 1/2 times the hole diameter.
3. Remove the shaft from the lathe and place it on
7. Chamfer the end of the shaft liberally to allow
a hydraulic press. Place a V-block on each side of the
space for weld deposits.
bend area and turn the shaft so the high side is up. Move
the press ram downward until it touches the shaft. Set
8. Make a stub of the same material as the shaft.
up a dial indicator so that the contact point contacts the
The stub should be 1/4 inch larger in diameter and 3/8
high side of the shaft as near to the ram as possible.
inch longer than the damaged portion of the shaft plus
the depth of the hole drilled in the shaft. This provides
4. Carefully apply pressure on the shaft with the
ample machining allowance.
ram. Watch the pointer of the dial indicator to determine
how much the shaft is "sprung" in the direction opposite
9. Machine one end of the stub to a press fit
the bend. When the indicator reading is 0.002 or 0.003
diameter of the hole in the shaft. The length of this
inch greater than the amount of runout, release the ram
portion should be slightly less than the depth of the hole
in the shaft. (A screw fit between the shaft and stub can
be used instead of the press lit.)
5. Set up the shaft between centers and check again
as expiained in step 1. Repeat steps 2, 3, and 4 until the
10. Chamfer the shoulder of the machined end of
runout is decreased to within acceptable limits.
the stub the same amount as the shaft is chamfered.
If the first attempt produces little or no change in
11. Press (or screw for a threaded fitting) the stub
runout, spring the shaft further in the second operation
into the shaft and have the chamfered joint welded and
to overcome the elasticity of the shaft so that it bends in
the required direction. It's better to make several tries
12. Mount the shaft with the welded stub back in
and gain a few thousandths of an inch at a time than to
the lathe, and machine the stub to the original shaft
do it in one or two tries and perhaps bend the shaft too
dimensions provided by the drawing or blueprint.
fur in the opposite direction.
Stubbing a Shaft
You can repair the damaged ends of shafts by
To repair valves, you must have a knowledge of the
removing the bad section and replacing it with a new
materials from which they are made. Each material has
"stub" end. Always check to see if your type
its limitations of pressure and temperature; therefore,
commander allows stubbing of shafts. Use the
the materials used in each type of valve depend upon
following steps to stub a shaft:
the temperatures and pressures of the fluids that they
1. If a blueprint is not available, make a drawing
of the shaft showing all dimensions.
Valves are usually made of bronze, brass, cast or
2. Begin with a piece of scrap stock (spud) of the
malleable iron, or steel. Steel valves are either cast or
same material as the shaft. Use a lathe to machine it to
forged and are made of either plain steel or alloy steel.