Notes on using the Sherline screw-cutting attachment on a Unimat-3.
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Here are some details of how I made adapters to use the Sherline
screw-cutting attachment on my Unimat-3.  The key is to use the attachment
points and leadscrew drive slot on the Unimat that were intended for the
power feed accessory.

Four main parts must be built:

    1.   An arbor fits on the lathe spindle in place of the drive pulley
         and holds the Sherline drive gear and handwheel.
    2&3. A sleeve (with pressed in coupling) is clamped in a bracket.
         This assembly fits into the leadscrew hole on the left end of
         the lathe bed and attaches to a threaded hole in the headstock.
         The Sherline gearbox clamps to the sleeve.
    4.   A shaft fits inside the sleeve and attaches the Sherline gearbox
         to the leadscrew.

Two sheets of (crude) drawings, showing the above parts, are included.
Notes on construction and use follow.

By the way, no modifications were made to any of the original Unimat or
Sherline parts - so the attachment can still be used on a Sherline lathe.

FIRST STEP: Carefully study the instruction manual for the Sherline
screw-cutting attachment, available at:

    www.sherline.com/3100inst.htm


Parts List (doesn't include metal stock)
----------
10-32 x 1" allan head capscrew (to fit bracket)
10-32 x 3/16" allan head capscrew (to locate shaft in sleeve)
10-32 x 3/16" setscrew (to fit handwheel)
M6 x 22 allan head capscrew (to attach bracket to headstock)
4-40 x 1/8" pan head screw (fits arbor, key for gear and handwheel)
3/32 dia x 3/16 roll pin (to fit shaft)


Construction notes
------------------

Mount arbor directly on lathe spindle to turn 9/16 dia.

Shaft can be made from 5/16 dia CRS.  Turn down end for press fit into
short piece of 3/8 dia CRS that has been drilled through 9/32 - loctite &
press together, then face assembly to length.

Drive slot in shaft is easy to make with a hack-saw and file, if shaft
is first drilled 1/8" in lathe.

Make sleeve a bit long (say 2-1/4"), then assemble arbor with drive gear,
bracket, sleeve & Sherline gearbox with gears.  Mark sleeve length and
finish to length.

Put one of the large washers from Sherline kit on arbor before installing
4-40 screw with loctite.


Usage notes
-----------

Can be used with motor in place - just remove spindle pulley.

To disengage, loosen 10-32 screw in sleeve and pull shaft partially.

I can install (or remove) the complete adapter in less than 30 seconds,
after which the screwcutting attachment is installed exactly as per the
Sherline lathe.

Bracket & sleeve should remain assembled together permanently, and
can even be left in place while using the lathe (but belt guard can't
be closed).  In any event, the assembly can be removed in a few seconds
by removing the single bolt that attaches it to the headstock.

To cut inch pitches finer than 40tpi, make or buy a pair of 32 d.p.
gears, one 40t and the other 63t.  When used in place of Sherline's
primary gears (the first two gears in the train), these make the
Unimat 1.00mm pitch leadscrew effectively 40tpi.  (The exact pitch
is 25.4*63/40=40.005, which is an error of only 0.000125 per inch.)

Now set up the secondary gearing to cut one-half the desired pitch
(as per a Sherline lathe with inch pitch leadscrew).  For example,
when set to 32tpi, using the 40/63 primary gears will give 64 tpi.
You can use this method to cut threads up to 80 tpi.