Instructions

have come a long way at becoming a good machinist. You
will find erasers aren’t much good and no one has come up
with a good “putting on” tool when it comes to metal parts.
Complex parts are very difficult to make. When you are
making one off “one-of-a-kind” parts, don’t worry about
how long it takes. Spend your time planning and checking
so you don’t have to start over.
When a rotary table is put on a vertical mill, you end up with
a machine that is theoretically capable of reproducing itself.
Of course, the size of the rotary table has to be considered,
and the Sherline table would be too small to accomplish
this on a full-size milling machine. But having a rotary
table means the capabilities of your mill will be greatly
expanded, and only the size of the part and the ingenuity
of the operator will govern the complexity of the part. The
purpose of these instructions is to give you an insight into
properly using this accessory. An inexpensive calculator
with trig functions is a must for complex jobs.
FIGURE 4—Sherline’s tilting angle table (P/N 3750) is
designed to hold the rotary table and allows it to be tilted
to any angle from 0° to 90°.
Standard milling machine setups usually involve aligning
the work with the table and then with the spindle. This is
easily accomplished because the table can be accurately
moved with the handwheels.
Dealing with Backlash
When working with a rotary table, the term “backlash”
must also be used. Backlash occurs in all rotary tables and
exists between the worm and worm gear just as it does in
a leadscrew, so it must be considered. In the case of this
particular table it amounts to .2° to .3°. Setting the worm
any closer to the gear will cause excessive drag and wear.
The smaller the diameter you are working with, the less
the backlash error will effect you. When working on a
diameter of 1" (25.4 mm), the total backlash will be less
than 0.002" (0.05mm), but at 4" (100 mm), the error could
be as high as 0.010" (.25 mm). (See the “Maintenance”
section on page 13 for instructions on adjusting the worm
gear backlash and Page 3 for the paragraph on setting the
electronic backlash compensation.)
When the rotary table is used with the right angle attachment,
backlash has to be considered in a different way if an
“off balance” fixture is mounted. As the out-of-balance
fixture is being lifted against gravity, the backlash remains
normal, but after the fixture goes past top dead center, the
off-balance fixture will pull the backlash to the opposite
side. This could give you an error equal to the backlash.
This is around .2° and must be considered. I realize this is
an unusual occurrence, but it is a tough one to find, which
is why I mention it. If you believe this is a possibility,
hold the backlash in the correct direction after the move
is complete and tighten the lock. Of course you could also
add a counterbalance to eliminate this problem.
Using the Mill and Rotary Table as a Lathe
A machinist working with miniature tools may find it useful
to use the rotary table to turn large diameter parts. The CNC
table can be set to run continuously and diameters can be
formed with end mills rather than lathe tools.
Locking the Table When Making a Cut
If you are using the rotary table to cut a gear, the table
lock should be used during the cutting process; however,
I don’t believe it is necessary when cutting a small, fine
pitch gear. As soon as you lock the table you stand a chance
of forgetting to unlock it before attempting to advance the
table. This would result in losing your place, because the
stepper motor system has no way of recording whether or
not it moved. When doing repetitive machine operations
you have to be very methodical. Let your mind wander and
you stand a good chance of screwing it up. If you make
this type of screw-up, all is not lost if you took the time to
write the exact handwheel setting down at the start so you
can start over from exactly the same place. This is good
insurance before starting a series of cuts.
Precautions Regarding Hot Chips and Coolant
Care should be taken to prevent hot chips from landing
on the computer and burning into the keypad. Also, the
electronics can be damaged if the motor is flooded with
coolant. Sherline’s one-year warranty does not cover this
kind of damage because it is caused by misuse. The extension
cord between motor and controller should be used to keep
the computer at a safe distance.
FIGURE 5—A demonstration of CPR or Cutter Path
Radius.
Making Allowances for Cutter Diameter
A close look at Figure 5 will start making you aware of the
complexities of working with a rotary table. Unless you
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