3100 Sherline Thread-Cutting Attachment Instructions

3100 Sherline Thread-Cutting Attachment Instructions
SHERLINE
PRODUCTS
INCORPORATED 1974
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
SHERLINE PRODUCTS INC. ˆ 3235 Executive Ridge ˆ Vista ˆ California 92081-8527 ˆ FAX: (760) 727-7857
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5/29/09
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 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 Pitch
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" undersize 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 undersize 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.
What I have tried to do in these opening remarks is to show
that screw cutting is really easy, and to give you the selfP/N 3100, Pg. 2 of 8
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 the end of the shaft.
Figure 2
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 operation.
NOTE: The section below entitled “Cutting A Thread for
Practice” uses the example of cutting a 28 pitch righthand 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
GEAR
A
B C D E
TEETH
100 100 20 28 40
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.
Install gear “D” (28) and secure
with a hex head screw and small
washer. NOTE: This screw only
Side view, thread cutting attachment installed
P/N 3100, Pg. 3 of 8
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
engage properly. DO NOT DISENGAGE THE LEVER
UNTIL THE THREAD HAS BEEN COMPLETELY
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 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 theads 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.
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.
Joe Martin, President and Owner,
Sherline Products Inc.
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 see the note ** below
the chart for alternate gearing.
Gear E used for
RH threads only
Gears F and G used
for LH threads only
Gear E used for
RH threads only
Gears F and G used
for LH threads only
THREADS
PER IN.
GEAR
A
GEAR
B
GEAR
C
GEAR
D
GEAR
E
GEAR
F
GEAR
G
PITCH
(mm)
GEAR
A
GEAR
B
GEAR
C
GEAR
D
GEAR
E
GEAR
F
GEAR
G
80
76
72
68
64
60
56
52
48
44
40
39*
38
37*
36
35*
34
33*
32
31*
30
29*
28
27*
26
25*
24
23*
22
21*
20
19 RH
19 LH+
18 RH
18 LH+
17 RH
17 LH+
16 RH
16 LH+
15 RH
15 LH+
14 RH
14 LH+
13 RH
13 LH+
12 RH
12 LH+
11 RH
11 LH+
10 RH
10 LH+
9+
8+
7+
6+
5+
50
50
50
50
50
50
50
50
50
50
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
199**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100**
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
50
100
50
100
50
100
50
100
50
100
50
100
50
100
50
100
50
100
50
50
50
50
50
50
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
40
20
40
20
40
20
40
20
40
20
40
20
40
20
40
20
40
20
40
20
40
40
40
40
40
40
38
36
34
32
30
28
26
24
22
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
23
24
23
22
21
20
38
38
36
36
34
34
32
32
30
30
28
28
26
26
24
24
22
22
20
20
36
32
28
24
20
38
40
40
40
40
40
40
40
40
40
38
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
30
-30
-30
-30
-32
-30
-30
-30
-30
-30
-30
30
30
30
30
28
30
28
28
28
28
26
24
26
26
28
28
30
26
28
28
28
28
28
28
28
26
26
26
24
26
26
26
26
26
26
-30
-28
-28
-28
-28
-26
-24
-26
-26
-26
------
22
22
34
30
30
26
30
34
30
30
22
22
22
28
34
26
30
30
30
26
26
30
30
30
30
30
30
30
30
30
24
-22
-34
-30
-30
-26
-30
-30
-30
-30
-24
------
.25
.3
.35
.4
.45
.5
.55
.6
.65
.7
.75
.8
.85
.9
1.0 RH
1.0 LH
1.1
1.2
1.25
1.3
1.4
1.5
1.6
1.7
1.75
1.8
1.9
2.0
50
50
50
50
50
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
127**
20
24
28
32
36
20
22
24
26
28
30
32
34
36
20
20
22
24
30
26
28
30
32
34
35*
36
38
40
40
40
40
40
40
40
40
40
40
40
40
40
40
40
20
20
20
20
24
20
20
20
20
20
20
20
20
20
30
30
30
30
30
30
30
30
30
30
28
30
30
30
40
-40
40
38
40
38
38
38
38
38
38
36
30
28
26
26
24
20
28
28
28
28
26
24
24
20
20
-26
24
22
22
22
22
20
20
20
20
----
22
22
22
22
22
22
20
22
22
22
22
22
22
22
-24
26
26
26
24
24
26
26
22
22
----
+
See notes on page 5 for cutting left-hand threads coarser than 20 T.P.I.
and for cutting right-hand threads with a pitch of 5 through 9 T.P.I.
* 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
31090
31080
Figure 6
Exploded View
3100 Thread Cutting Attachment
31010
31050 (2)
31100
40900
31150 (2)**
31020
31040
31200
70
310 10*
311 5090
1
31030
40330
40340
40660
40510
31040*
15420
31060
(2)
40510
NOTE: Gears shown are for example only. For other
combinations, see accompanying charts (Figure 5).
15430
**31150 Gear Shafts are press fits in 31110 and 31270 Gears.
31320*
40660
40510
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
Part No.
31010
31020
31030
31040
31050
31060
31070
31080
31090
31100
31110
40340
40510
40330
40660
31150
31200
31220
31240
Description
Handwheel
Primary Support Arm
Secondary Support Arm
Small Shim Washer
Large Shim Washer (2)
Gear Bushing (2)
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 (3)
10-32 X 5/8" Skt Hd Cap Screw
No. 10 Washer
Gear Shaft (2)
20 Tooth Gear, 24 Pitch (2)
22 Tooth Gear, 24 Pitch
24 Tooth Gear, 24 Pitch
Part No.
31260
31270
31280
31300
31320
31340
31360
31380
31400
31500
15090
15420
15430
40900
Description
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
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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