History of GMT - Manual chucks-conclusion

HMT Kalamaserry and HMT Bangalore are still buying our Hand Operated Chucks. They are fitted on their NH 22, NH 26 AND L 45 Lathes.

We tried selling chucks in the US. We supplied to Leblond Makino who were making manual lathes in 1987 in Singapore. Swamy (former Marketing Director-GMT), PV (Founder-GMT), Leela(present Chairperson-GMT) and I met Mr.K.S.Shankaran who was in charge of US sales. But unfortunately in the US they use scroll chucks. Their approach was use and throw and did not give much importance to long life.

Over a period of time manual chucks were replaced by Power Chucks. However, GMT Manual Chucks are still preferred for machining certain components.

About the author : Shri. K Jagannathan - Executive Director – Sales & Marketing, GMT.
Sri.K.Jagannathan is synonymous with lathe chucks in the Indian machine tool industry. He has been with Guindy Machine Tools for over 5 decades. His vast experience and immense knowledge of workholding products is evident in some of the most complex workholding solutions provided by GMT.  

History of GMT - Manual Chucks - India Pistons story

GMT chucks proved very successful in machining auto liners made of CI Castings. India Pistons one of the leading manufacturer of liners had machining problems. PV suggested certain changes in liner casting so that the special jaw to suit our chuck will ensure firm grip on the liner during machining. 

India Pistons were very happy with the chucks performance and recommended our chuck to all their subcontractors and we sold a number of our 3B 250 mm chucks with special jaws....

About the author : Shri. K Jagannathan - Executive Director – Sales & Marketing, GMT.
Sri.K.Jagannathan is synonymous with lathe chucks in the Indian machine tool industry. He has been with Guindy Machine Tools for over 5 decades. His vast experience and immense knowledge of workholding products is evident in some of the most complex workholding solutions provided by GMT. 

History of GMT - Manual Chucks - Part-1

Voltas were the selling agents for GMT chucks. Several initiatives were taken by GMT to help them to sell chucks especially to ordnance factories and BHEL, Tiruchy. This included demonstration of GMT chucks on their lathes. Chucks were given to CMTI and HMT R&D for testing. They inspected our chuck for gripping power and compared the same with Forkardt and Reishauer. Their report were very encouraging. In terms of gripping force GMT chuck was far superior to Forkardt and Reishauer.

GMT Manual Chuck

However, selling GMT chucks against scroll design proved to be a challenge. Without running down the scroll design we were focusing on our chuck's gripping force for machining castings, forgings, aircraft alloys and wherever intermittent cuts on components were the need. The chucks were recommended for gear driven lathes namely HMT H 22, H 26, LB 17, LB 20, LB25 and German, Czech and American gear driven lathes. Full Horse Power could be utilized on the machine using our chuck for machining. This selling point caught the attention of customers and we sold GMT chucks to many industries initially with Voltas and later by direct selling in 1972 after our agreement came to a close with Voltas.

Sri.K.Jagannathan

About the author : Shri. K Jagannathan - Executive Director – Sales & Marketing, Guindy Machine Tools Limited.
Sri.K.Jagannathan is synonymous with lathe chucks in the Indian machine tool industry. He has been with Guindy Machine Tools for over 5 decades. His vast experience and immense knowledge of workholding products is evident in some of the most complex workholding solutions provided by GMT.

GMT Eccentric compensating chuck

GMT Eccentric compensating chuck is used for machining forgings and black bars between centres on copy turning lathes. GMT Eccentric compensating chucks are supplied with special cover at extra cost. This special cover fitted on the chuck in lieu of spring loaded centre to ensure that the chuck works as a self-centering type.

GMT Eccentric compensating chucks are supplied with spring loaded centre. The function of this spring loaded centre is to ensure that the component rests against its face. GMT Eccentric compensating chuck is essentially designed where the component is usually located between two centres. 

 One on the chuck body and one on the tail stock of the machine. Since the line of centres is defined, concentricity is guaranteed, but the function of the jaws is that they are designed to adjust and accommodate the lack of concentricity between the centre line of the component and its outside diameter.

The chuck has floating wedge for compensation and is operated by power - hydraulic or pneumatic rotating cylinder or by an electro mechanical actuator. In this chuck, gripping is achieved through a radially floating wedge. This wedge floats to the required extent in the body of the chuck to compensate the irregularities in the roundness of the component.

The chuck body and wedge are designed to withstand heavy cutting loads. The floating wedge is capable of withstanding high operating forces. The floating wedge with its mechanical advantage, converts the operating force into a high clamping force.

Construction

The body is of forged steel. The guide ways are hardened and ground. The chuck body is suitably recessed to remove large amount of material. The floating wedge and base jaws are made from nickel chrome steel, casehardened and ground on all working surfaces. 

The base jaws are guided in the deep, wide, hardened slots in the body, which provide the ample bearing area necessary to withstand the forces resulting from high gripping forces. Provision has been made for manual lubrication of the sliding surfaces periodically through grease nipples. Serrations are provided on the top face of the base jaws.

GMT Power operated pneumatic chuck

 

Power Operated Pneumatic Front end Chucks are designed to utilise in full, the spindle bore for bar/pipe work. This design avoids rear mounting of the actuating cylinder and necessary draw bar connections. The chuck can be mounted on the lathe spindle with an adaptor flange as needed. The actuating cylinder is built into the chuck. The stationary air distribution system with the ports to supply air to the respective sides of the piston is mounted separately on the chuck.

These chucks are available in various sizes ranging from size 160mm Ø to 1000 mm Ø. The chucks are offered with standard jaw stroke of 4.2mm to 12mm and extended jaw stroke of 19mm to 25.4mm. The extended jaw stroke to hold pipes, casings and tool joints.

For holding long oil pipes, one chuck is mounted on the front end of the spindle, and one chuck at the near end of the spindle. Power Operated Pneumatic Front end Chucks have twin non-return valves, which prevent the clamping air from returning through the port unless air is let in on the other side of the piston. This ensures retention of clamping force even when the air supply is switched off. The maximum operating pressure of the chuck is at 10 bar pressure.

Principle of Operation
Power Operated Pneumatic Front end Chuck has two special rubber seal rings on the distributor assembly. The special seal ring is compressed when the chuck is pneumatically actuated to facilitate opening and closing of chuck jaws. Once the job is clamped due to venting of the air supply, the special seal rings lift to ensure rotation of the chuck. This design eliminates wear on the special seal rings.

Construction
The chuck body is made of forged medium carbon steel. The guideways are flame hardened and ground. The wedge and base jaws are made of nickel chrome steel; case hardened and ground on all working surfaces. Serrations are provided on top face of the ground base jaws. The various radii on the hard jaws in conjunction with serrations are designed to grip a wide range of job diameters.

Electro Pneumatic Control Unit
Each GMT Power Operated Pneumatic Front end Chuck is supplied with an Electro Pneumatic Control Unit. This control unit consists of Lubro Control Unit, Electrical Contactors, and Fuses and in addition, solenoids for interlocking with the main spindle.
Push button or foot operated switch is supplied with the Electro pneumatic Control Unit for actuating the chuck.

Features :

• Power operated pneumatic front end chucks are designed to utilise in full, the spindle bore for bar/pipe work.
• This design avoids rear mounting of the actuating cylinder and necessary draw bar connections.
• The actuating cylinder is built into the chuck.
• The stationary air distribution system is mounted separately on the chuck.
• Power operated pneumatic front end chucks have twin non-return valves.

GMT universal ball lock chucks

GMT universal ball lock chucks (UBLC) are designed to clamp components and ensure face butting. Ball Lock Chucks have certain distinctive advantages over wedge and lever type chucks. Jaw movement is achieved by sliding and swivel of the base jaws, which are amply proportioned.

This results in less wear, less bearing pressure and less stress concentration in the jaws when compared to same sizes of wedge or lever type chucks. 

Apart from the radial clamping forces, these ball lock chucks provide an axial force to pull the component against the butting face. This is achieved as the jaw movement is along an arc. Wedge, base jaw, spherical aligner, spherical bushes are made of Nickel Chrome Steel, case hardened and precision ground on all working surfaces.

Eccentric compensating type of ball lock chuck is essentially designed where the component is usually located between two centres, one on the chuck body and one on the tailstock of the machine. Since the line of the centres is defined, concentricity is guaranteed and the ball lock chuck design allows adequate freedom for the jaws to adjust and accommodate the irregularities of the job before full clamping force is applied.

Features :

• Positive pull back action against jaw face after clamping due to spherical movement.
• Positive sealing to prevent entry of chips.

GMT UBL chucks are offered in 2 versions:

• Self centering
• Eccentric compensating

Recommended torque for jaw screws

Recommended torque for jaw screws should be applied while tightening the top jaws with master jaws.

Use screws of reputed make only. (Eg. TVS, Unbrako). Length of the screw should be as per GMT standards. Write to esales@gmt.co.in for a free electronic copy of GMT PHNC Instruction Manual.

RECOMMENDED TORQUE

                          SCREW SIZE                                                      TIGHTENING TORQUE

                                        M8                                                                         39 Nm

                                       M10                                                                        77 Nm

                                       M12                                                                       110 Nm

                                       M16                                                                       220 Nm

                                      M 20                                                                       400 Nm


Important Instructions:
If you use screws that are  longer than recommended size, the top jaw will not clamp with master jaw, as the clamping screw will rest at the bottom face of master jaw T-Slot. This will result in master jaw breakage.If the soft-jaws are purchased from outside source, ensure that the jaws meet GMT standards.

Click here for further information and instructions on chuck maintenance. or visit our website www.gmt.co.in

Chuck Lubrication: General Guidelines

Your lathe chuck is really a consumable. It wears with use. In addition, chuck wear results primarily from  lack of lubrication and improper usage and application. Burrs, coolant, chips, poor chucking practice all contribute to the problem. These can be overcome to a large extent by proper maintenance and lubrication. Poorly lubricated chucks wear out faster and become unsafe for use. Chucks can easily lose 50% of their normal gripping force and accuracy if not properly lubricated.

Frequency schedule for lubrication

Because of the widely differing job conditions, it is difficult to recommend a standard frequency schedule for lubrication. Lubrication once per shift with grease gun can be taken as a general standard norm.

Recommended Grease

All GMT Chucks are factory lubricated with GMT recommended grease and are ready to use.GMT chucks are provided with dust cover for better protection.

Under clean operating conditions, GMT chucks can be operated up to 10,000 cycles without dismantling & re-lubrication. To ensure extended service life and maximum performance ,every chuck should be dismantled ,cleaned and re-lubricated periodically.

Dismantling Frequency:
A new chuck must be dismantled after completion of  10,000 cycles.Then periodically after completion of every 20,000 to 25,000 cycles. If C.I castings are machined continuously , dismount once in a month regardless of no. of cycles. While applying grease by grease gun, slide the master jaw through full stroke (clamping and de-clamping) to ensure uniform distribution of grease on sliding surfaces.

Important Tip : The life of the chuck is considerably extended when it is well lubricated.

For more information, please visit our website www.gmt.co.in