3.5" Lathe Thread Cutting Attachment

3.5" Lathe Thread Cutting Attachment
3.5" Lathe Thread
Cutting Attachment
P/N 3100
Purpose of the Thread Cutting Attachment
One of the big advantages of having a lathe is that it gives
you the ability to  cut threads. In reality you do not normally
cut threads on a manual lathe if they could be done with
low cost taps and dies. The reason you cut threads is to
produce non-standard threads for which you don’t have
taps and dies. The second important reason is to produce
a thread that is true or concentric with the centerline of the
part. If we put threads on the Sherline spindles and chucks
with taps and dies it would be impossible to produce 10%
of our tools with acceptable runout. You will also find that
when you start designing and building special parts you’ll
often need to use non-standard threads to work within the
constraints of your design. For example, if you needed a
0.900" diameter, 24 TPI (threads per inch) thread, a tap and
die could cost more than your lathe and take weeks to order.
Sherline offers a unique and versatile thread cutting
attachment for its lathe. This low cost attachment enables
you to machine 46 different unified thread pitches (Pitch
range from 80 to 5 threads per inch) and 28 different metric
thread pitches (Pitch range from .25 to 2.0mm). What’s
more, it allows you to cut them as either left hand or right
hand threads. Ten optional gears with odd tooth counts
are available for even more pitches. The lathe tool can, of
course, be ground to cut any of the various thread forms,
and any of these various pitches or thread forms can be cut
on any pitch diameter you desire. This versatility enables
you to machine any standard or non-standard thread you
might desire as long as it is within the size limitations of
the lathe.
The attachment consists of 15 hobbed metal gears, mounting
bracket, engagement mechanism and 4.00" (102 mm)
handwheel. Threads are generated on the Sherline lathe
by gearing the spindle to the lead screw. As the spindle
is rotated with the handwheel mounted on the headstock
spindle, the tool will advance an amount equal to the ratio
of the gears. When the tool has completed its movement,
you simply stop cranking, back up the tool and turn the
spindle in the opposite direction until the tool is past its
starting point, reset the tool and you’re ready for the next
pass. It’s a simple as tapping! By using a 127-tooth gear
(supplied), true metric threads can be cut on an inch lathe
(Model 4000, 4400 or 4500) or true inch threads can be cut
on a metric lathe (Models 4100, 4410 or 4530).
An Introduction to Thread Cutting in the Real World
After designing and putting the enclosed screw cutting
attachment into production, I sat down and started reading
what other people had written about cutting screw threads
before writing my own instructions. It amazed me that I
had been able to cut threads all these years knowing so
little. How and why I was able to do this is going to be
the subject of my instructions. There are plenty of books
available at any library to go into additional detail on the
subject if required, but my instructions are based on using
sharp pointed 60° tools and cutting threads for your own use.
The reason other books go into such great detail on the
precise methods used commercially is that they are telling
you how to cut threads from specifications for other
people. They must have exact methods and standards to
make sure that a bolt made in California will screw into a
nut manufactured in New York. Fortunately, we have the
tremendous advantage of having both pieces at hand and
we can just “keep cutting ‘till they fit.” It’s as simple as
that! You simply select the proper gears from the chart; put
in a 60° threading tool and have at it.
A point to ponder about thread cutting is how a lathe
produces a thread. It doesn’t matter whether it is a 20" or
a 3" lathe. The principle is the same. The leadscrew that
drives the saddle is geared directly to the spindle. When
the spindle turns, the saddle moves. If they were geared
one to one, the pitch cut would be the same as the pitch of
the lead screw. On Sherline’s 3.5" lathe, this would be 20
Threads Per Inch (TPI). If we turned the lead screw 180°
while we turned the spindle 360° (by using a 20 tooth to a
40 tooth gear arrangement) we would cut 40 TPI. Please
note that we did not have to consider the diameter of the
stock. The only requirement is that the major diameter is
at least twice the depth of the thread plus enough material
to support these threads while cutting them. One gets used
to hearing a diameter called out with the threads, such as
1/4-20, 6-32, 10-24, etcetera, but while it’s unusual to think
of 40 threads per inch cut on something 2" in diameter, in
some cases it may be entirely practicable to do so.
It may interest you to know how a metric thread can be
cut on a 3" lathe that has American National screw threads
on its leadscrew. The 127-tooth conversion gear does this
by driving the leadscrew at a ratio that converts 20 TPI to
1 mm. Consider 100T on the spindle driving a 127T. The
SHERLINE PRODUCTS INC. • 3235 Executive Ridge • Vista • California 92081-8527 • FAX: (760) 727-7857
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ratio is .7874 to 1. The leadscrew has 20 TPI: .050" P x
.7874 = .03937" = 1 mm.
Figure 1—Component parts of a thread cut with a sharp pointed
60° Vee tool.
MAJOR DIAMETER— Largest diameter of the thread of
either the screw or the nut.
MINOR DIAMETER— Smallest diameter of the thread of
either the screw or the nut.
PITCH DIAMETER— The theoretical diameter that falls
on a point where the thread width
and the groove width are the same.
PITCH (P)— The distance from point to point
measured parallel to the axis. Metric
threads are always expressed in
LEAD— The distance a screw thread advances
axially in one turn. On a double lead
screw, the lead is twice the pitch.
NOTE: The same methods can be used in figuring dimensions
for American (inch) or Metric screw threads.
1 mm = .03937"
Pitch (Metric) x .03937" x .758 = depth of screw thread in inches
Take the time to familiarize yourself with component parts
of the screw thread from Figure 1. The pitch diameter is
the important one to consider. Before going on, let’s take
the time to really understand why. The pitch diameter
determines how a screw or thread will fit, not the major
diameter. Suppose you were cutting 20 TPI and the major
diameter was .010" undersized and the pitch diameter was
correct. About the only thing wrong would be that the flat on
the point of the thread would be a little wide, but it would
still have approximately 75% of its strength and work well.
Now let us suppose we cut the pitch diameter undersized
by .010". We would end up with a nut that fits so loose
and a thread that was so weak that we would have to
scrap it. This is where “cutting to fit” comes in. You can
compensate for some pretty bad errors on the major and
minor diameters by having the pitch diameter correct. To
get it correct, all you have to do is to keep trying it for size
as you cut. Don’t ever take the part out of the chuck to try
it because it would be next to impossible to re-chuck it in
exactly the same place. However, the entire chuck, along
with the part, could be removed from the lathe to try it for
size. Don’t force anything when trying the part for size,
because you might move the part slightly in the chuck, and
really “screw things up.”
Why have I made such a point about having the major or
minor diameter wrong and still making the part work? Read
on. You’re probably thinking I must really be a “hacker”
if I can’t cut a diameter within .010". Well, the problem
in many cases, is not how close you can cut to a diameter,
but what the diameter should be.
Example: Your buddy just heard you bought a nice, shiny
new lathe complete with a screw cutting attachment, and
like all good friends he immediately goes to work trying to
figure out how you and your new lathe will be of some use
to him. It doesn’t take him long! He has a camera that he
tried to repair himself last year, but lost an important part.
Of course the missing part has metric threads, but that’s
a “snap” for a Sherline lathe. A quick check with a thread
gauge indicates that it has 0.9 mm Pitch. No problem, yet. It
is an internal thread, so you will have to cut a screw to mate
with it. Here’s the problem: What is the major diameter?
You can measure the diameter of the hole, but you can’t be
assured that the thread form is perfect and that this is really
the minor diameter. You can only assume that it’s close.
Now take this dimension and add to it twice the depth of
the thread, which should give you the major diameter. To
get the depth of one thread, multiply the Pitch x .6. (Note:
Pitch x 1.2 + Minor Diameter = Major Diameter). Total
depth of thread using a sharp pointed 60° tool = P x .65 =
.036" x .65 = .023".
The constant .6 is not used to figure depth of an external
thread, it is just one used to get you in the “ball park” in a
situation such as this.
At least we have a fairly reliable place to start now and can
probably get one cut that will work on the first try. Always
keep track of the total depth of cut in case it comes out
undersized. At least you’ll know how deep not to cut it on
the second one!
The example I gave you was one of the more difficult
situations you may run into, not only because you had to
do the job for free to keep a friend, but also because you
had very limited information from which to work.
Usually, you will be cutting both the screw and nut. This is
a case where two wrongs can almost equal one right. You
can rectify any error you may have made in cutting the first
one by compensating for it in the mating part.
Left-hand threads can be cut as easily as right-hand threads
on a lathe; the only difference being the addition of an idler
gear that reverses tool movement so that it travels left to
right instead of right to left.
It’s hard to appreciate just how much money an inexpensive
lathe like this with a screw cutting attachment can save you
until you have had to have a special part made that doesn’t
have a standard thread size. Even though there may be taps
or dies available, a single left-hand 1-32 set would probably
cost half as much as your entire thread cutting attachment.
P/N 3100, Pg. 2 OF 8
What I have tried to do in these opening remarks is to
show that screw cutting is really easy, and to give you the
self-confidence it takes to do any job well. Too often, good
craftsmen are stopped from venturing forth because the
only information available shows the technically perfect
way to do things rather than the simple, practical methods
everyone really uses.
Thread Cutting Conversion Kit
This kit has been engineered to add additional versatility to
your lathe. With this attachment, a wide variety of threads,
both right-handed and left-handed can be produced. Most
American standard and metric threads may be cut with
equal ease and precision. The accompanying charts list the
entire range from which you may choose. (See Figure 5.)
Conversion Instructions (Refer also to Illustrations)
1. Carefully drive the furnished small sheet metal screw
into the hole located in the spindle that extends from
the left side of the drive pulleys. Use a proper size
screwdriver for this operation and avoid installing the
screw at an angle since it must seat squarely against the
spindle. After driving, remove the screw and dress down
any “burr” that is raised around the edge of the hole. A
small, fine file is suitable for this. Next, slide two thin
spacer washers over the tube and against the pulley.
Reinsert the sheet metal screw and tighten firmly.
2. Remove the headstock. Locate the exposed flat head
socket screw in the top of the bed a loosen it a few turns.
3. From below, remove the cap screw under the base
directly below headstock. Note how may washers (if
any) are used with this screw. (Normally a 4000-series
lathe does not require any washers and a 4400-series
lathe uses one washer.)
4. Grease the sliding shaft with the flats on both ends and
slide it into the leadscrew support (situated directly
below the pulley). Be sure the end with the small flat
enters first. Now slide the fixed shaft with a single
flat into the leadscrew support. To guarantee that the
shaft is fully inserted and engaged, rotate it one or two
revolutions while applying gentle inward pressure to
Figure 2
Side view, thread cutting attachment installed
the end of the shaft.
5. Replace the screw from Step 3, making sure that the
point of the screw goes into the machined groove in
the shaft. Make sure also that any washers that were
on this screw are still in place. Check that the shaft is
free to rotate. If the shaft binds, first double check to
assure that the end of the cap screw is registered in the
groove of the fixed shaft and then add an extra washer
under the screw head if needed so it doesn’t go in quite
as deep. Retighten the flat head socket screw in the bed
and replace the headstock.
6. Pull out the black plug on the front of the lathe base
below the name plate and slide the remaining shaft
(with handle) into the hole with the handle facing
upward. It may be necessary to rotate the shaft about
30° each way to get it to completely seat and register
with the sliding shaft.
NOTE: If insertion or movement of the engagement lever
is difficult, try loosening the two screws on the bottom of
the machine that hold the bed to the base. Move the bed
slightly until a good fit occurs.
7. It may be necessary to deburr parts for smooth
NOTE: The section below entitled “Cutting A Thread for
Practice” uses the example of cutting a 28 pitch right-hand
thread on a 1/4" diameter piece of stock. The following
numbers are based on that setup.
Example: Setting up to Cut a Typical Thread
Refer to the chart (Figure 5) and select the type of thread
to be cut. As an example, we have chosen an American
standard, 28 TPI, right-hand lead.
Figure 3
Setup for cutting 28 Threads Per Inch
NOTE: Idler gear “E” is used for right-hand threads, idler
gears “F” and “G” are used for left-hand threads and are,
therefore, not used in this example.
Remove the motor assembly by removing the two socket
head cap screws that secure the motor mounting bracket
to the headstock and slip the drive belt off the pulley. (See
the Assembly and Instruction Guide that came with your
machine for more details if needed.)
Slide gear “A” (100) onto the spindle engaging slot with
the previously installed sheet metal screw head.
Install gear “B” (100) and gear “C” (20) onto the primary
support arm. The drive pin is used not only to drive the
“C” gear, but also to hold the “B” gear on the arm.
Install gear “E” (40) on the secondary support arm.
Slide the lower split end of the primary support
arm over the leadscrew support. Adjust until gear
“B” meshes properly with gear “A” (100). When
mesh is satisfactory, tighten clamp screw.
P/N 3100, Pg. 3 OF 8
Install gear “D” (28) and secure with a hex head screw and
small washer. NOTE: This screw only needs to be finger
tight and should not be used when it interferes with the
secondary support arm. Adjust the secondary support arm
and gear for proper engagement with the mating gears. When
satisfactory, tighten the retaining screw and pivot screw.
Install the crank wheel by it sliding it over the spindle.
Line up the slot with the protruding sheet metal screw head
and tighten down the crank wheel set screw using a hex
wrench. A few drops of oil on moving parts will be helpful.
Figure 4—Gear Setup Diagram for Example. NOTE: See Figure
7 on page 8 for a detailed setup drawing.
Cutting a Thread for Practice
I believe the time has come to “HAVE AT IT.” We will start
by chucking up a piece of aluminum and turning it to 1/4"
diameter. Let’s cut 28 TPI on it. Be sure to have a nut to
check it with. Looking at the chart we see we need a gear
“A” (100T) on the spindle, driving a gear “B” (100T), that
is attached to the gear “C” (20T), driving the lead screw
gear “D” (28T), using the idler gear “E” (40T) that mounts
on the swing arm. The gears should mesh so they run “free”
and have a reasonable amount of backlash. NOTE: All
gear trains have some “backlash” and it will not affect the
quality of the thread, but it does have to be allowed for.
This is why the tool has to be backed out before the lathe
spindle is reversed.
Over 90% of the threads cut on a lathe of this type will
have a pitch less than .070, and be less than 3/8" long.
Now and then you may have to cut a fairly course thread
(more than .070" pitch), and it is a good idea to “rough
out” the thread by moving the tool post slightly to the left
between passes. This keeps the tool from having to cut on
both sides of the thread at the same time. On a standard
lathe, the tool is advanced by the compound rest which
is set at 29°. This allows only one side of the tool to cut
and lessens the load considerably. The final cut is then
taken with the crosslide being advanced to “clean up” the
thread. We can get the same effect by moving the tool post.
When cutting fine threads you can get away with cutting
“straight in”. The crank drive gives you the “feel” and a
precise method of stopping needed in single-pointing fine
threads. Cranking the spindle counter-clockwise gives you
reverse. This allows you to cut the entire thread without
disengaging the leadscrew.
Establish the depth of the first cut by bringing the tool in
to the point where it just touches the part surface. Write
down the dial setting. Now engage the leadscrew lever. The
leadscrew may have to be turned back and forth a little while
applying slight pressure on the lever in order to get it to
CUT. With the tool moved past the end of the part, advance
the tool inward .003" for first cut. Turn the spindle counterclockwise until the desired length of thread has been cut.
Back the tool out until it is completely clear of the part.
Crank the spindle clockwise until the tool is at the original
starting point. Advance the tool to its last point plus .002".
I’ve always found it useful to write these dial settings down
too. It is amazing how fast you can forget one! Now take
the second pass by cranking the spindle counter-clockwise.
The amount the tool should be advanced from this point
on should be governed by the amount of force it took the
last pass. The cut will get progressively heavier each time
the tool is advanced. Remember, you can’t ruin your part
by taking too light a cut. To figure what the total amount
the tool should be advanced if you are using a sharp “vee”
form tool (standard form of tool used in single pointing
threads) simply multiply the pitch times .758.
Example: Pitch of 28 TPI = 1/28
Pointed tool depth = P x .758 = 1/28 x .758 = .027
If you are not too good with math and don’t like to do it,
just keep cutting and looking at the flat on the top of the
thread. When the flat is 1/8 the pitch, the nut should fit.
Either way, check it long before you think it is finished to
be on the safe side until more experience is gained. The
last two passes should be repeats of previous dial settings
to clean up threads. Not too hard was it? No matter what
type of threads you may cut, the basic method will remain
the same.
Cutting Internal Threads
Internal threads are very seldom cut full depth. To figure
the hole size you should start with, take the pitch of thread
you are cutting and multiply it by 1.083. Then subtract the
resulting number from the major diameter. To figure the
total depth using a sharp pointed 60° tool, multiply the
pitch by .65.
EXAMPLE: To cut an internal 1.5-28 TPI:
Major Diameter = 1.5"
P = 1/28 = .036"
Major Diameter - (P x 1.083) = Hole Size
1.500" - (.036" x 1.083) = Hole Size
1.500" - .039 = 1.461"
Hole size = 1.461"
Cutting Double Lead Pitches
A double lead thread could be cut by picking change gears
that are one-half the pitch and indexing the “A” gear 180°
after cutting the first thread to depth. NOTE: There isn’t
any way to check a double lead until it is completely cut,
therefore, the depth must be figured mathematically. It has
always been fun for me to do jobs like this, not necessarily
because they were needed, but just to see if I could do it!
P/N 3100, Pg. 4 OF 8
Screw Cutting Operation Review
(Read detailed instructions before proceeding.)
1. Turn or bore stock to proper diameter.
2. Remove the motor assembly from the lathe by
unscrewing the two socket head cap screws that hold
the motor bracket to the headstock.
3. Install the 60° brazed tip carbide thread cutting tool in
the tool post.
4. Place the tool bit at the starting point of the thread and
set it for a .003" depth of cut.
5. Engage the lever at the base of the lathe by turning the
handle clockwise. Turn lead screw handwheel back and
forth slightly until full engagement occurs.
6. Turn the spindle crank handwheel until the tool bit has
traveled the full length of your intended thread.
7. Back the crosslide out to clear the tool from the thread.
8. Turn the crank handwheel backwards until the tool bit
has traveled past the starting point of the thread.
9. Return the crosslide to its original position and advance
it an additional.002" in depth.
10. Repeat steps 6, 7, 8, and 9 until the full thread depth
has been cut. Using cutting oil will make cutting easier
and will give a better finish.
Notes Regarding Using the Threading Attachment
with a Digital Readout
To keep the drive gear from scratching the tachometer decal
on your pulley, make sure the shim washers (P/N 31050)
are in place to space the shaft gear away from the pulley.
Then adjust the drive gear so that it is centered or slightly
off-center away from the pulley so that it can’t contact the
decal. As an alternative, a piece of thin steel shim stock
could be cut like a large washer and inserted between the
gear and the pulley for protection.
Note also that the addition of DRO handwheels to your lathe
will cause the long leadscrew to be moved slightly to the
right. This will require the use of a slightly longer sliding
shaft when using either the thread cutting attachment or the
P/N 3001/3011 power feed. When purchasing a DRO for
use with a machine using either of these attachments, be
sure to mention that you have these attachments. You will
be supplied with a longer version of the P/N 15090 sliding.
The longer shaft is P/N 81509 should you need to order it.
Thank you,
Sherline Products Inc.
*Notes on Cutting Certain Thread Pitches
(Refers to chart on following page.)
Cutting left hand threads coarser than 20 T.P.I. and right
hand threads pitch 5 through 9 T.P.I. will require that you
remove the shaft from the 100-tooth gear and press it in to
the 50-tooth gear. These are threads that wouldn’t normally
be cut on a machine of this size. If you don’t wish to switch
gears and shafts, an extra gear and shaft can be ordered
from the replacement parts list to eliminate this problem.
On threads with pitches 5 through 9 T.P.I. you will encounter
a problem with interference between the handwheel and
the 40-tooth gear. A spacer should be made to keep the
handwheel mounted out toward the end of the spindle to
eliminate this interference. This also occurs when making
a 1.0 mm pitch thread on the 4100 metric lathe.
Coarse threads in steel
Threads cut with a pitch coarser than 16 T.P.I. or 1.5mm
begin to push the maximum capabilities of a small lathe
when cut full depth into steel. You may have to slightly move
the tool post occasionally so the entire thread form isn’t
being cut at one time. Pitches coarser than this can be cut
into plastic and wood with no problems. Large pitch threads
are also used with multiple lead threads. For example: a
20 T.P.I. double-lead thread would need a 10 T.P.I. setup
and a cutting tool that would form a 20 T.P.I. thread form.
Cutting Inch Threads on a Metric Lathe and Metric Threads
on an Inch Lathe
INCH LATHES—The chart on the next page assumes that
you have an inch lathe. You can cut metric threads on your
inch lathe by using the chart on the right side of the page.
METRIC LATHES—If you have a metric (P/N 4100 or
4410) lathe you will need to substitute a gear to use the
chart. When cutting inch threads on a metric lathe, substitute
a 127 tooth gear for the 100 tooth gear listed in column
“A.” (Note that you will only be able to cut threads from 5
TPI to 40 TPI.) When cutting metric threads on the metric
lathe, substitute the 100 tooth gear for the 127 tooth gear
listed in the column for gear “B.”
P/N 3100, Pg. 5 OF 8
Figure 5—Gear Selection Chart for Thread Cutting Attachment
NOTE: This chart lists gears
used with the inch version of the
lathe. For use with metric lathes
Gear E
see the note ** below the chart
Gears F and G used
used for RH
for alternate gearing.
threads only
for LH threads only
80 50
76 50
72 50
68 50
64 50
60 50
56 50
52 50
48 50
1002024 402630
44 50
1002039*4028 22
1002037*4026 28
1002035*4028 26
1002033*4028 30
1002031*4028 26
1002029*4026 30
1002027*4026 30
1002025*4026 30
1002023*4026 30
1002021*4026 30
19 RH
100403830-- -
19 LH+
502038 --3022
18 RH
100403630-- -
18 LH+
502036 --2834
17 RH
100403430-- -
17 LH+
502034 --2830
16 RH
100403230-- -
16 LH+
502032 --2830
15 RH
100403032-- -
15 LH+
502030 --2826
14 RH
100402830-- -
14 LH+
502028 --2630
13 RH
100402630-- -
13 LH+
502026 --2430
12 RH
100402430-- -
12 LH+
502024 --2630
11 RH
100402230-- -
11 LH+
502022 --2630
10 RH
100402030-- -
10 LH+
502020 --2624
50403630-- -
50403230-- -
50402830-- -
50402430-- -
50402030-- --
* See notes on page 80 for cutting left hand threads with a pitch coarser than
20 T.P.I. and for cutting right hand threads with a pitch of 5 through 9 T.P.I.
Gear E
used for RH
threads only
Gears F and G used
for LH threads only
.25 50
.3 50
.35 50
.4 50
.45 50
.5 100
.6 100
.7 100
.8 100
.9 100
1.0 RH50
127402030-- -
1.0 LH
1272020 --2624
1.1 100
127362038-- -
127382036-- -
127402030-- -* Gears marked with an asterisk and highlighted in a grey box are not
included in the standard set but can be purchased separately.
**METRIC LATHES—To use this chart with the model 4100 or 4410
(metric) lathe, use a 100-tooth gear in place of the 127-tooth gear (“B”
gear) when cutting metric threads and a 127-tooth gear in place of the
100-tooth (“A” gear) when cutting inch threads. Press the shaft out of
the 127-tooth gear and into the 100-tooth gear. Inch threads finer than
40 T.P.I. cannot be cut on the metric lathe.
NOTE—Gear “E” or “F”
and “G” are idler gears and
are used to transmit power
and control direction
of rotation only. See
drawings on page 7 for
more detail of how gears
are actually installed on
the support arms.
NOTE—When cutting right hand threads, Gear “E” is used in the vertical
slot of the secondary support arm, part number 3103. When cutting left
hand threads, gear “F” is used in the vertical slot and gear “G” is used
in the horizontal slot and gear “E” is not used.
P/N 3100, Pg. 6 OF 8
Figure 6
Exploded View
Thread Cutting Attachment
NOTE: Gears shown are for example only. For other combinations,
see accompanying charts (Figure 5).
**3115 Gear Shafts are press fits in 3111 and 3127 Gears.
NOTE: Ask for part number 81509 instead of 15090 if using the threading
attachment on a lathe equipped with a Digital Readout. 81509 is slightly longer.
Parts list, Thread Cutting Attachment
Primary Support Arm
Secondary Support Arm
Small Shim Washer
Large Shim Washer
Gear Bushing
Gear Drive Pin
10/32 X 3/8" Set Screw
Sheet Metal Screw, Pan Head, No. 6 X 3/16", Type A
100 Tooth Gear, 56 Pitch (W/ Notch)
100 Tooth Gear, 56 Pitch
10-32 X 1" Skt Hd Cap Screw
10-32 X 3/8" Skt Hd Cap Screw
10-32 X 5/8" Skt Hd Cap Screw
No. 10 Washer
Gear Shaft
20 Tooth Gear, 24 Pitch
22 Tooth Gear, 24 Pitch
24 Tooth Gear, 24 Pitch
26 Tooth Gear, 24 Pitch
127 Tooth Gear, 56 Pitch
28 Tooth Gear, 24 Pitch
30 Tooth Gear, 24 Pitch
32 Tooth Gear, 24 Pitch
34 Tooth Gear, 24 Pitch
36 Tooth Gear, 24 Pitch
38 Tooth Gear, 24 Pitch
40 Tooth Gear, 24 Pitch
50 Tooth Gear, 56 Pitch
Sliding Shaft
Sliding Shaft O-Ring
Engagement Lever
Fixed Shaft
10-32 x 3/8" Flat Head Socket Screw
Optional 24 Pitch gears are available for cutting odd numbers of T.P.I., where the last two numbers
before the final zero(s) in the part number represent the number of gear teeth. Available are sizes
31210, 31230, 31250, 312700, 31290, 31310, 31330, 31350, 31370 and 31390.
P/N 3100, Pg. 7 OF 8
Gear Installation on Primary and Secondary Shafts
(Illustration shows gears for 20 TPI RH and LH setup)
4" Drive handwheel shown
removed so gears can be seen.
Spindle pulley
Primary Support Shaft
Gear A (Spindle)
Gear B
Secondary Support Shaft
Gear C
Gear E
Engagement shaft and lever
Gear D (Leadscrew)
Figure 7a—Gears A, B, C, D and E installed for cutting a right-hand thread
Gear A (Spindle)
Gear B
Gear C
Gear F
Engagement shaft and lever
Gear G
Gear D (Leadscrew)
Figure 7b—Gears A, B, C, D, F and G installed for cutting a left-hand thread
P/N 3100, Pg. 8 OF 8
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