Jet ZH Series Troubleshooting guide

Operation and Maintenance Instructions
ZH Series Large Bore Lathes
Models GH-2680ZH; GH-26120ZH
Model GH-2680ZH shown
For ZH-Series Lathes Parts List and Electrical Diagrams, see document M-321860-1
JET
427 New Sanford Road
LaVergne, Tennessee 37086 Part No. M-321860
Ph.: 800-274-6848 Revision C3 08/2018
www.jettools.com Copyright © 2017 JET

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1.0 IMPORTANT SAFETY
INSTRUCTIONS
1. Read and understand the entire owner’s manual
before attempting assembly or operation.
2. Read and understand the warnings posted on
the machine and in this manual. Failure to
comply with all of these warnings may cause
serious injury.
3. Replace the warning labels if they become
obscured or removed.
4. This lathe is designed and intended for use by
properly trained and experienced personnel
only. If you are not familiar with the proper and
safe operation of a lathe, do not use until proper
training and knowledge have been obtained.
5. Do not use this lathe for other than its intended
use. If used for other purposes, JET disclaims
any real or implied warranty and holds itself
harmless from any injury that may result from
that use.
6. Always wear approved safety glasses/face
shields while using this lathe. Everyday
eyeglasses only have impact resistant lenses;
they are not safety glasses.
7. Before operating this lathe, remove tie, rings,
watches and other jewelry, and roll sleeves up
past the elbows. Remove all loose clothing and
confine long hair. Non-slip footwear or anti-skid
floor strips are recommended. Do not wear
gloves.
8. Wear ear protectors (plugs or muffs) during
extended periods of operation.
9. Do not operate this machine while tired or under
the influence of drugs, alcohol or any
medication.
10. Make certain the switch is in the OFF position
before connecting the machine to the power
supply.
11. Make certain the machine is properly grounded.
12. Make all machine adjustments or maintenance
with the machine unplugged from the power
source.
13. Remove adjusting keys and wrenches. Form a
habit of checking to see that keys and adjusting
wrenches are removed from the machine before
turning it on.
14. Keep safety guards in place at all times when
the machine is in use. If removed for
maintenance purposes, use extreme caution
and replace the guards immediately after
maintenance is complete.
15. Check damaged parts. Before further use of the
machine, a guard or other part that is damaged
should be carefully checked to determine that it
will operate properly and perform its intended
function. Check for alignment of moving parts,
binding of moving parts, breakage of parts,
mounting and any other conditions that may
affect its operation. A guard or other part that is
damaged should be properly repaired or
replaced.
16. Provide for adequate space surrounding work
area and non-glare, overhead lighting.
17. Keep the floor around the machine clean and
free of scrap material, oil and grease.
18. Keep visitors a safe distance from the work
area. Keep children away.
19. Make your workshop child proof with padlocks,
master switches or by removing starter keys.
20. Give your work undivided attention. Looking
around, carrying on a conversation and “horse-
play” are careless acts that can result in serious
injury.
21. Maintain a balanced stance at all times so that
you do not fall or lean against moving parts. Do
not overreach or use excessive force to perform
any machine operation. Never force the cutting
action.
22. Maintain a balanced stance at all times so that
you do not fall or lean against moving parts. Do
not overreach or use excessive force to perform
any machine operation. Never force the cutting
action.
23. Use the right tool at the correct speed and feed
rate. Do not force a tool or attachment to do a
job for which it was not designed. The right tool
will do the job better and more safely.
24. Use recommended accessories; improper
accessories may be hazardous.
25. Maintain tools with care. Keep cutting tools
sharp and clean for the best and safest
performance. Follow instructions for lubricating
and changing accessories.
26. Do not attempt to adjust or remove tools during
operation.
27. Never stop a rotating chuck or workpiece with
your hands.
28. Choose a low spindle speed when working
unbalanced workpieces, and for threading and
tapping operations.
29. Do not exceed the maximum speed of the
workholding device.
30. Do not exceed the clamping capacity of the
chuck.

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31. Workpieces longer than 3 times the chucking
diameter must be supported by the tailstock or a
steady rest.
32. Avoid small chuck diameters with large turning
diameters.
33. Avoid short chucking lengths and small
chucking contact.
34. Turn off the machine and disconnect from power
before cleaning. Use a brush to remove
shavings or debris — do not use your hands.
35. Do not stand on the machine. Serious injury
could occur if the machine tips over.
36. Never leave the machine running unattended.
Turn the power off and do not leave the
machine until moving parts come to a complete
stop.
37. Remove loose items and unnecessary work
pieces from the area before starting the
machine.
38. Do not operate the lathe in flammable or
explosive environments. Do not use in a damp
environment or expose to rain.
Familiarize yourself with the following safety notices used in this manual:
This means that if precautions are not heeded, it may result in minor injury and/or possible
machine damage.
This means that if precautions are not heeded, it may result in serious injury or possibly even
death.
WARNING: Some dust, fumes and gases
created by power sanding, sawing, grinding,
drilling, welding and other construction activities
contain chemicals known to the State of California
to cause cancer and birth defects or other
reproductive harm. Some examples of these
chemicals are:
•lead from lead based paint
•crystalline silica from bricks, cement and other
masonry products
•arsenic and chromium from chemically treated
lumber
Your risk of exposure varies, depending on how
often you do this type of work. To reduce your
exposure to these chemicals, work in a well-
ventilated area and work with approved safety
equipment, such as dust masks that are
specifically designed to filter out microscopic
particles. For more information go to
http://www.p65warnings.ca.gov/ and http://www.
p65warnings.ca.gov/wood.
WARNING: This product can expose you to
chemicals including lead and cadmium which
are known to the State of California to cause
cancer, and phthalates which are known to the
State of California to cause birth defects or other
reproductive harm. For more information go to
http://www.p65warnings. ca.gov.

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2.0 Warranty and Service
JET warrants every product it sells against manufacturers’ defects. If one of our tools needs service or repair, please
contact Technical Service by calling 1-800-274-6846, 8AM to 5PM CST, Monday through Friday.
Warranty Period
The general warranty lasts for the time period specified in the literature included with your product or on the official
JET branded website.
•JET products carry a limited warranty which varies in duration based upon the product. (See chart below)
•Accessories carry a limited warranty of one year from the date of receipt.
•Consumable items are defined as expendable parts or accessories expected to become inoperable within a
reasonable amount of use and are covered by a 90 day limited warranty against manufacturer’s defects.
Who is Covered
This warranty covers only the initial purchaser of the product from the date of delivery.
What is Covered
This warranty covers any defects in workmanship or materials subject to the limitations stated below. This warranty
does not cover failures due directly or indirectly to misuse, abuse, negligence or accidents, normal wear-and-tear,
improper repair, alterations or lack of maintenance. JET woodworking machinery is designed to be used with Wood.
Use of these machines in the processing of metal, plastics, or other materials may void the warranty. The exceptions
are acrylics and other natural items that are made specifically for wood turning.
Warranty Limitations
Woodworking products with a Five Year Warranty that are used for commercial or industrial purposes default to a
Two Year Warranty. Please contact Technical Service at 1-800-274-6846 for further clarification.
How to Get Technical Support
Please contact Technical Service by calling 1-800-274-6846.Please note that you will be asked to provide proof
of initial purchase when calling. If a product requires further inspection, the Technical Service representative will
explain and assist with any additional action needed. JET has Authorized Service Centers located throughout the
United States. For the name of an Authorized Service Center in your area call 1-800-274-6846 or use the Service
Center Locator on the JET website.
More Information
JET is constantly adding new products. For complete, up-to-date product information, check with your local distributor
or visit the JET website.
How State Law Applies
This warranty gives you specific legal rights, subject to applicable state law.
Limitations on This Warranty
JET LIMITS ALL IMPLIED WARRANTIES TO THE PERIOD OF THE LIMITED WARRANTY FOR EACH PRODUCT.
EXCEPT AS STATED HEREIN, ANY IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE EXCLUDED. SOME STATES DO NOT ALLOW LIMITATIONS ON HOW LONG AN
IMPLIED WARRANTY LASTS, SO THE ABOVE LIMITATION MAY NOT APPLY TO YOU.
JET SHALL IN NO EVENT BE LIABLE FOR DEATH, INJURIES TO PERSONS OR PROPERTY, OR FOR
INCIDENTAL, CONTINGENT, SPECIAL, OR CONSEQUENTIAL DAMAGES ARISING FROM THE USE OF OUR
PRODUCTS. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF INCIDENTAL OR
CONSEQUENTIAL DAMAGES, SO THE ABOVE LIMITATION OR EXCLUSION MAY NOT APPLY TO YOU.
JET sells through distributors only. The specifications listed in JET printed materials and on official JET website are
given as general information and are not binding. JET reserves the right to effect at any time, without prior notice,
those alterations to parts, fittings, and accessory equipment which they may deem necessary for any reason
whatsoever. JET®branded products are not sold in Canada by JPW Industries, Inc.
Product Listing with Warranty Period
90 Days – Parts; Consumable items
1 Year – Motors; Machine Accessories
2 Year – Metalworking Machinery; Electric Hoists, Electric Hoist Accessories; Woodworking Machinery used
for industrial or commercial purposes
5 Year – Woodworking Machinery
Limited Lifetime – JET Parallel clamps; VOLT Series Electric Hoists; Manual Hoists; Manual Hoist
Accessories; Shop Tools; Warehouse & Dock products; Hand Tools; Air Tools
NOTE: JET is a division of JPW Industries, Inc. References in this document to JET also apply to JPW Industries,
Inc., or any of its successors in interest to the JET brand.

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3.0 Table of Contents
1.0 IMPORTANT SAFETY INSTRUCTIONS.......................................................................................................2
2.0 Warranty and Service.....................................................................................................................................4
3.0 Table of Contents...........................................................................................................................................5
4.0 Specifications.................................................................................................................................................6
5.0 Dimensions and mounting hole centers.........................................................................................................8
6.0 General description and nomenclature..........................................................................................................9
7.0 Unpacking....................................................................................................................................................11
7.1 Contents of the Shipping Container .........................................................................................................11
8.0 Installation....................................................................................................................................................12
8.1 Leveling the lathe .....................................................................................................................................12
8.2 Completing installation.............................................................................................................................12
8.3 Chuck Preparation....................................................................................................................................13
8.4 Break-In Period ........................................................................................................................................13
9.0 Maintenance/Lubrication ...............................................................................................................................14
9.1 Coolant Preparation .................................................................................................................................16
10.0 Electrical Connections................................................................................................................................16
10.1 Conversion to 460 Volt Operation ............................................................................................................17
11.0 Basic Controls............................................................................................................................................18
12.0 Operation ...................................................................................................................................................20
12.1 Tool Setup..............................................................................................................................................21
12.2 Spindle Speed........................................................................................................................................21
12.3 Feed and Thread Selection....................................................................................................................21
12.4 Thread Cutting........................................................................................................................................22
13.0 Adjustments ...............................................................................................................................................22
13.1 Chuck Jaw Reversal...............................................................................................................................22
13.2 Gib Adjustments.....................................................................................................................................22
13.3 Tailstock Adjustments ............................................................................................................................23
13.4 Gap Section............................................................................................................................................23
13.5 Belt Adjustment and Replacement ............................................................................................................24
13.6 Brake Strap ............................................................................................................................................24
13.7 Friction Clutch Adjustment .....................................................................................................................24
13.8 Aligning Tailstock to Headstock .............................................................................................................25
13.9 Spindle Bearings....................................................................................................................................25
13.10 Speed Control ......................................................................................................................................25
13.11 Lead Screw ..........................................................................................................................................26
13.12 Apron Feed Clutch ...............................................................................................................................26
13.13 Tool Post..............................................................................................................................................26
13.14 Cross Slide Nut Adjustment .................................................................................................................27
13.15 Shear Pin Replacement .......................................................................................................................27
13.16 Steady Rest Adjustment.......................................................................................................................27
13.17 Follow Rest Adjustment........................................................................................................................28
14.0 Troubleshooting the ZH Series Lathes.......................................................................................................29
15.0 Lubrication Schedule and General Maintenance.......................................................................................30
16.0 Reference Tables.......................................................................................................................................31
16.1Inch Lead And Feed.................................................................................................................................31
16.2Special Inch Lead And Feed....................................................................................................................32
16.3 Speed Selection Lever Positions............................................................................................................33
17.0 Electrical – 230 volt to 460 volt Conversion...............................................................................................33
18.0 Change Gear Diagram...............................................................................................................................34

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4.0 Specifications
Model Number................................................................................GH-2680ZH.........................................GH-26120ZH
Stock Number ....................................................................................... 321860..................................................321890
General Capacities:
Maximum Swing over Bed.........................................................26” (660mm)......................................... 26” (660mm)
Maximum Swing over Cross Slide.......................................16-1/2” (420mm)...................................16-1/2” (420mm)
Maximum Swing Through Gap..................................................34” (870mm)......................................... 34” (870mm)
Length of Gap........................................................................7-7/8” (200mm)....................................7-7/8” (200 mm)
Distance between Centers ......................................................80” (2030mm)..................................... 120” (3050mm)
Width of Bed..............................................................................16” (405mm)......................................... 16” (405mm)
Motors and Electrical:
Main Motor.............................................................................TEFC Induction.....................................TEFC Induction
Horsepower.......................................................................10 HP (7.5kW)...................................... 10 HP (7.5kW)
Phase............................................................................................... 3 PH......................................................3 PH
Voltage............................................................230/460V (prewired 230V)....................230/460V (prewired 230V)
Full Load Amps........................................................................25.4/12.7A.............................................25.4/12.7A
Cycle ...............................................................................................60 Hz.................................................... 60 Hz
Feed Motor......................................................................................Induction............................................... Induction
Horsepower................................................................................... 1/2 HP...................................................1/2 HP
Phase............................................................................................... 3 PH......................................................3 PH
Voltage............................................................230/460V (prewired 230V)....................230/460V (prewired 230V)
Full Load Amps........................................................................2.85/1.65A.............................................2.85/1.65A
Cycle ...............................................................................................60 Hz.................................................... 60 Hz
Coolant Pump Motor........................................................................Induction............................................... Induction
Horsepower................................................................................... 1/8 HP...................................................1/8 HP
Phase............................................................................................... 3 PH......................................................3 PH
Voltage............................................................230/460V (prewired 230V)....................230/460V (prewired 230V)
Full Load Amps........................................................................0.54/0.27A.............................................0.54/0.27A
Cycle ...............................................................................................60 Hz.................................................... 60 Hz
Power Transmission..................................................................... v-belt (x 4).............................................v-belt (x 4)
Controls circuit...............................................................................110V A.C...............................................110V A.C.
Lamp circuit.....................................................................................24V A.C. ...............................................24V A.C.
Indicators circuit.............................................................................110V A.C.............................................. 110V A.C.
Headstock and Spindle:
Spindle Bore..........................................................................4-1/8” (105mm).....................................4-1/8” (105mm)
Spindle Mount..........................................................................D1-8 Camlock.......................................D1-8 Camlock
Spindle Taper with Sleeve.......................................113mm Dia. 1:20 / MT-5....................... 113mm Dia. 1:20 / MT-5
Number of Spindle Speeds........................................................................ 12..........................................................12
Range of Spindle Speeds.....................................................36 to 1600 RPM....................................36 to 1600 RPM
Distance Floor to Spindle Center (approx.) ..............................................46”.........................................................46”
3-Jaw Scroll Chuck:
Load Capacity........................................................................ 661 lb (300 kg)......................................661 lb (300 kg)
Inside Diameter ............................................................5-11/16” (145mm)................................5-11/16” (145 mm)
Carriage:
Maximum Compound Rest Travel........................................5-1/2” (140 mm)....................................5-1/2” (140 mm)
Maximum Compound Rest Swivel................................................+/- 90 deg..............................................
+/- 90 deg.
Maximum Cross Slide Travel............................................14-1/16” (358 mm)................................ 14-1/16” (358 mm)
Maximum Carriage Travel .......................................................65” (1650mm)..............................106-1/4” (2700 mm)

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GH-2680ZH GH-26120ZH
Gearbox:
Number of Longitudinal Feeds................................................................... 51..........................................................51
Range of Longitudinal Feeds..... 0.0020 – 0.094 in./rev. (0.051-2.39mm/rev)............0.0020 – 0.094 (0.051-2.39mm)
Number of Cross Feeds ............................................................................ 40..........................................................40
Range of Cross Feeds ............... 0.0010 – 0.040 in/rev. (0.027-1.02mm/rev)..............0.0010 – 0.40 (0.027-1.02mm)
Number of Inch Threads............................................................................ 48..........................................................48
Range of Inch Threads..................................................................30-2 T.P.I...............................................30-2 T.P.I
Number of Metric Threads......................................................................... 22..........................................................22
Range of Metric Threads.................................................................1-14 mm................................................1-14 mm
Number of Diametral Threads................................................................... 24..........................................................24
Range of Diametral Threads...........................................................56-4 D.P................................................56-4 D.P.
Number of Modular Threads...................................................................... 18..........................................................18
Range of Modular Threads..............................................................0.5-7mm................................................0.5-7mm
Leadscrew Pitch......................................................................1/2” (12.7mm)....................................... 1/2” (12.7mm)
Tailstock:
Tailstock Spindle Travel .............................................................6” (150mm)........................................... 6” (150mm)
Tailstock Taper......................................................................................MT-5..................................................... MT-5
Maximum Tailstock Cross Displacement.............................+/- 0.40” (10mm)...................................+/- 0.40” (10mm)
Other:
Small Steady Rest Capacity.........................................3/4” – 5” (20-125mm)............................3/4” – 5” (20-125mm)
Large Steady Rest Capacity.......................................4” – 9.5” (100-240mm)..........................4” – 9.5” (100-240mm)
Follow Rest Capacity....................................................3/4” – 4” (20-100mm)............................3/4” – 4” (20-100mm)
Coolant tank capacity............................................................... 3.4 gal. (13L).........................................7.1 gal. (27L)
Overall Dimensions ..............................137-13/16”L x 53-1/8”W x 58-1/16”H.... 177-5/32”L x 48-1/32”W x 58-1/16”H
(3500 x 1350 x 1475 mm) (4500 x 1220 x 1475 mm)
Approximate Net Weight..................................................7932 lbs. (3595 kg)................................8010 lbs. (3630kg)
1Values are emission levels, not necessarily to be seen as safe operating levels. Since workplace conditions vary,
this information is only intended to allow the user to make a better estimation of the hazards involved.
The specifications in this manual were current at time of publication, but because of our policy of continuous
improvement, JET reserves the right to change specifications at any time and without prior notice, without incurring
obligations.

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5.0 Dimensions and mounting hole centers
Figure 1
Lathe Size 80 inch
(GH-2680ZH) 120 inch (GH-26120ZH)
A 2560mm(100.8 in.) 3565mm(140.4 in.)
B 3500mm(137.60 in. ) 4500mm (177.2 in.)
C 1721.5mm (67.8 in)
Table 1

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6.0 General description and nomenclature
Figure 2 – General Description (GH-2680ZH shown)
The ZH series lathe operates on a centralized gear
system. The motor power is transferred through
four v-belts to a shaft, which in turn transmits the
energy through a multi-disc friction clutch and
various gear pairs, to the spindle. The clutch also
controls the spindle’s direction of rotation. Through
clutch disengagement, the operator can stop the
spindle without turning off the motor, which will
prolong the life of the motor.
Bed and Stand
The lathe bed (A) is made of cast iron with low
vibration and high rigidity. Two precision-ground v-
slideways (B), reinforced by supersonic fre-quency
hardening, offer precision guidance for the
carriage. The main drive motor is mounted in the
stand (C) below the gearbox.
(The GH-26120ZH model has three stands: left,
center, and right).
Headstock
The headstock (D) is cast from high grade, low
vibration cast iron. In the head, the spindle is
supported at three points; by a cylindrical roller
bearing at the front and a tapered roller bearing
and ball bearing. See section 11.0for detailed
explanation of controls. The electrical box is
mounted to the rear of the headstock.
Feed Gearbox
The gearbox (E) is made from high quality cast iron
and is mounted to the left side of the machine bed.
This lathe adopts a three-axle sliding common gear
mechanism, together with thread selection change
mechanism, and doubling mechanism, which
enable it to cut a comprehensive range of metric,
modular and diametral pitch threads, thus
eliminating the need for gear changes except
where special threading is required.
Carriage
The carriage assembly is composed of the Apron,
the Saddle, the Cross Slide, the Compound Rest,
and the four-way Tool Post.
Apron (F).Quick travel of the Apron for
positioning is accomplished by means of a bed-
mounted rack and pinion, operated manually by
the handwheel on the front of the apron, or
automatically by the feed direction handle (P),
which has a rapid traverse (Q).
Saddle (G). The saddle is made from high
quality cast iron and rides along the v-ways.
Cross Slide (H). The cross-slide is mounted on
the saddle and used for cross feed operations.It
moves on a dovetailed slidewhich can be
adjusted for play by means of the gibs.

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Compound Rest. The compound rest (I), which
is T-slotted and mounted on the cross slide, can
be rotated 360°, allowing tapers to be turned.
The compound rest travels on dovetailed ways,
with adjustable gibs.
Quick Change Tool Post. The tool post (J) is a
turret design, mounted to the compound rest. It
holds up to one tool.
Tailstock
The tailstock (K) slides on a v-way and can be
locked at any location by a clamping lever. The
tailstock has a heavy duty quill with a No. 5 Morse
Taper and etched graduation scale. The tailstock
can be offset for taper cutting, and bearings can be
adjusted for drag along the ways.
Leadscrew and Feed Rod
The leadscrew (L) and feed rod (M) are mounted
on the front of the machine bed. They are
connected to the gearbox at the left and are
supported by bearings on both ends.
The leadscrew is used only for threading functions.
This maintains its accuracy and prolonged service
life.
Spindle Direction Control Axle(N)
Spindle rotation can be reversed by simply moving
the control lever (O) mounted at the right of the
carriage. (Allow spindle to come to a stop before
reversing.)
Travel Stops
Six stops (R)can be moved to any position along
the travel setting rod, and are secured in place
using socket head screws. The convex surface of
the stop contacts a limit switch on the underside of
the apron. The travel setting rod can be rotated on
an eccentric into six positions to modulate the
contact between stops and limit switch.
A carriage stop (S) is also provided for manual
carriage operation.
Steady Rest
The ZH series lathes are provided with small and
large steady rests (T). A steady rest serves as a
support for shafts on the free tailstock end. The
steady rest is mounted on the bedway and secured
from below with a bolt, nut and locking plate.
Follow Rest
The traveling follow rest (U) is mounted to the
saddle, and thus follows the movement of the
turning tool. Only two fingers are required as the
place of the third is taken by the turning tool. The
follow rest is used for turning operations on long,
slender work pieces. It prevents the work piece
from flexing under the pressure of the cutting tool.
Work Lamp
Adjustable halogen lamp (V) with independent
on/off switch.
Coolant Nozzle(W)
Fully adjustable gooseneck; flow is regulated
through a valve lever at its base.
Foot Brake(X)
Activates a braking strap at the motor for
emergency stopping of all lathe functions.
Chuck Guard (Y)