This .pdf document is bookmarked Operating Instructions and Parts Manual 20-inch Disc Grinder Models J-4421-2 and J-4421-4 JET 427 New Sanford Road LaVergne, Tennessee 37086 Ph.: 800-274-6848 www.jettools.com Part No.
1.0 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.
2.0 Table of contents Section Page 1.0 Warranty and Service ..................................................................................................................................... 2 2.0 Table of contents ............................................................................................................................................ 3 3.0 Warnings ........................................................................................................................................
3.0 Warnings - Misuse of this machine can cause serious injury. - For safety, machine must be set up, used and serviced properly. - Read, understand and follow instructions in the operator’s and parts manual which was shipped with your machine. When setting up machine: - Always avoid using machine in damp or poorly lighted work areas. - Always be sure machine is securely anchored to the floor. - Always keep machine guards in place. - Always put start switch in “OFF” position before plugging in machine.
3.2 General Electrical Cautions This machine should be grounded in accordance with the National Electrical Code and local codes and ordinances. This work should be done by a qualified electrician. The machine should be grounded to protect the user from electrical shock. sizes for branch circuits or electrical extension cords according to the following table is recommended: 3.
4.0 General Specifications The JET Model J-4421 20-inch diameter disc grinder is a high production, rapid stock removal tool. The stock removal rate is controlled by the amount of pressure the operator applies to the work piece and the grit of the abrasive sheet mounted on the drive disc. By using different grit values and materials, a wide range of materials can be ground and an equally wide range of surface finishes achieved.
5.0 Machine set-up 5. Use the two leveling bolts on the rear of the base to level the grinder. Shim under the anchor positions as needed to level the grinder. 6. Secure the grinder to the floor using the anchors. 5.1 Grinder set-up 1. Uncrate the grinder and remove it from its shipping skid. 2. Remove the table raiser crank which is taped to the grinder and install the crank on the raiser shaft, securing it with the set screw in the crank. 3.
4. Reestablish power to the service branch for the grinder. 5. Turn on the grinder using the ON/OFF switch and observe the direction of rotation of the drive disc. It should be turning CLOCKWISE when viewed from the front. If it is turning clockwise, the grinder is correctly connected and can be placed in service. If the disc is not turning clockwise, the electrical connections are hooked up backward and need to be corrected. 3. Locate the cut-out coil which is under the switch.
2. Always allow time for the disc to come fully up to motor speed before contacting the workpiece to the disc. This gives you a chance to check for possible wheel wobble (looseness of the disc or motor, or damage from some earlier operation) before working against the disc. 3. This is a very powerful and aggressive grinding device which operates at high surface speeds. Therefore, you always want to support the workpiece while using the work table.
working voltage (due to start-up of larger machines on the electrical branch or other fluctuations in line voltage) the switch automatically trips OFF. The switch will not activate the machine while it remains in overload condition. If the switch trips off, wait 3 to 5 minutes for the overload relay to automatically reset. To restart the machine you should remove the workpiece from the table and turn the switch ON, again. Then wait for the motor to come up to full speed before continuing your grinding.
Figure 10: Achieving accurate angles using a machinist’s protractor Figure 11: Use of the miter system 7.5 Using the miter system 8.0 Recommended abrasives The miter slot in the table allows you to use a miter gauge to grind angles on workpieces. Use the following procedure: 1. Put the table in a level position. Use the table tilt mechanism to adjust it, if necessary. 2. Loosen the lock knob on the miter gauge. 3. Adjust the miter gauge to the angle you want to cut. 4.
Silicon carbide While discs may be available for 20 inch grinding, this material is not recommended for use on the ModelJ-4421 because a water coolant/lubricant is typically required for effective use of this material. Application tip While the 20 inch grinder can mount the full range of grits available – from 24 to 400 – the most efficient production and the longest abrasive disc life can be achieved when the production manager is aware of the capabilities of the grits offered.
10. Press firmly against the full surface of the disc. The idea here is to be sure the grinding disc makes full contact with the drive disc and is laying absolutely flat on the disc surface. 6. Loosen the four bolts which hold the motor to the stand. 7. Slide the motor toward the rear of the stand while pulling the drive disc and hub toward the front of the stand. This is a combined effort. The disc and hub can be separated from the motor shaft only if you perform these two operations at the same time.
22. If the drive disc does not have a grinding disc installed on it – install a disc now, using the instructions in sect. 9.1 Removing and replacing grinding discs. 10.0 Lubrication Since the grinder operates in an environment of high amounts of dust and grit, most lubrication would simply pick up the grit and cause increased wear to the machine and its parts. Therefore, the primary method of keeping the machine working surfaces in good order is KEEPING THE MACHINE AS CLEAN AS POSSIBLE.
11.1.
11.1.2 J-4421 Motor and Trunnion – Parts List Index No Part No Description Size Qty 1 ................ J-5644311G .............. Base ........................................................................ ...................................... 1 2 ................ 5644321 .................... Column .................................................................... ...................................... 1 3 ................ J-5644331G .............. Support Bracket ..................................
Index No Part No Description Size Qty 60 .............. 5644961 .................... Worm Gear .............................................................. ...................................... 1 61 .............. 5644971 .................... Spring Pin ................................................................ Ø4 x 20 mm .................. 1 62 .............. 5644981 .................... Shaft ........................................................................ ............................
Index No Part No Description Size Qty 119-5 ......... 5646003 .................... Pointer ..................................................................... ...................................... 1 119-6 ......... 5646004 .................... Roll Pin .................................................................... Ø3 x 6 mm .................... 1 119-7 ......... 5646005 .................... Stop Link .................................................................. ............................
11.2.1 J-4421 Foot Brake – Exploded View 11.2.2 J-4421 Foot Brake – Parts List Index No. Part No. Description Size Qty 1 ................ J-4421-001 ................ Foot brake................................................................ ...................................... 1 2 ................ J-4421-002 ................ Bracket..................................................................... ...................................... 1 4 ................ TS-0207021 ..............
12.0 Electrical Connections – J-4421 427 New Sanford Road LaVergne, Tennessee 37086 Phone: 800-274-6848 www.jettools.
