Workholding definitions

accuracy

The accuracy of a chuck/expanding mandrel measured in mm TIR is comprised of two components:

• The distance between the centerline of the machine spindle and the centerline of the workholding device.
• A random variation about the centerline of the workholding device caused by conditions built into the chuck such as internal friction and sliding fits.

actuator
A device that clamps the chuck or expanding mandrel through the aid of pneumatic or hydraulic cylinder.

chuck
A chuck is a specialized type workholding device usually used to hold a rotating workpiece (such as the bar or blank in the headstock spindle of a lathe)

clamping cylinder
See actuator.

collet
A collet is a holding device—specifically, a subtype of chuck—that forms a collar around the object to be held and exerts a strong clamping force on the object when it is tightened, usually by means of a tapered outer collar to grip the work piece. 

collet chuck
A device that uses a collet for workholding. 

compensating chuck
A chuck in which the jaws individually locate their gripping diameter without altering the position of the workpiece.

 

crank Shaft Machining Chuck

A special power chuck designed for crank shaft Eccentric Turning and milling operations. This chuck can be tailor made to suit machine. Crankshaft is held between centres of RH and LH chuck. Aligning jaw of the chuck facilitates job clamping. Chucks are actuated by hydraulic cylinders. 

dead length
The action of gripping a workpiece without changing its axial position and uses the face of the spindle as its locating surface for the inner collet. 

diaphragm chuck
A chuck that uses the deformation of a flexible material to grip a workpiece and is ideal for thin walled components. Diaphragm chucks are primarily used for light accurate turning, fine boring, facing and grinding operations.

 

expanding mandrel
A workholding device which is used for internal diameter clamping of component to machine in a single setup

 

face driver
Face Driver allows roughing and finishing operations completed in one clamping and you will able to machine the entire length of the workpiece in one operation.

 

first operation chuck
A workholding device designed to grip on unmachined castings, forgings or bar stock.

 

fixture
A work-holding or support device used to securely locate or support material, workpiece or a tool during machining operations ensuring that all parts produced using the fixture will maintain conformity and interchangeability.  Usually custom designed to hold a specific workpiece. 

indicating band
A diameter on the chuck body designated for measuring runout of a chuck.

 

mandrel
see expanding mandrel

 

master jaw
The moving part in a chuck to which the top jaw is mounted. 

pull-back chuck
This Chuck is ideal for the finishing operation, it simultaneously grips and pulls the piece part back against a workstop. The Radial pull back function of the chuck ensures a positive resting of the component after clamping 

repeatability
The repeated accuracy of chucked workpieces, especially the workpieces with a relatively higher length/diameter ratio used for production of duplicate parts.

retracting jaw chuck
A chuck which grips shafts for turning the complete length by retracting jaws into the chuck face to allow the area previously gripped to be machined. Either a face driver or expanding arbor provides the torque when machining the area previously gripped by chuck jaws.

 

rotational part
A piece part symmetrical about a central axis.

 

second operation chuck
A workholding device designed to grip on previously machined surfaces.

self-centering chucks
A self-centering chuck, also known as a scroll chuck in which all jaws move to or away from the workpiece and maintain on common center.

 

self-contained
A Chuck with an integral or built-in pneumatic or hydraulic power cylinder.

 

soft jaw
Top jaw blank that can be machined to specific dimensions Soft jaws are mounted to the master jaws.

 

top jaw
The component that clamps the workpiece and is mounted on the master jaw.

History of GMT -1960-70

Years 60 to 70 GMT were busy in manufacture of Cast Iron Surface Plates. In 1963 we signed agreement with Berg for the manufacture of Manual Chucks. As the development of Manual Chucks were in process Surface Plates orders were coming in from Voltas. Then we received a big order (about 152 plates) for size 1500 x 1200 from HAL Nashik through Voltas. As we needed more space to produce Surface Plates we shifted to Pallikkaranai. Foundry operations were in Guindy. After executing the order for HAL Plates order in flow dropped drastically from Voltas.

Development of Power Chucks and Lapping Machines were taken up. We had become very skilled in the scraping process This was a strong base to commence SPM building activity which we took up  when  complete drawings were given by the buyers. Lucas TVS particularly gave us a breakthrough in the manufacture of Coil Winding Machine, Riveting Machine and Conductor Cropping Machine for automobile coils. SPM's for Sundaram Abex for brake shoe machining, Sundaram Fasteners, Wheels India (Flash Cutting Machine) and Grindwell Norton (Grindwell Norton was on an island called Mora reached by boat. From Gateway of India) were made in early 70s.

 SPM manufactured for TVS

This decade saw a lot of SPM’s manufactured by GMT.

GMT history - part 4 - Hand operated chucks

PV was looking for a chuck design which is far superior than the Scroll Type. Although Reishauer and Forkardt manual chucks were available by import at that time their design were different and manufacturing them were difficult as it involves special machines which cannot be used for any other operation except for making components for these chucks.

Berg chuck with worm and worm wheel design

Through Voltas PV imported Berg Chuck from Germany. On a study of its design he found the chuck is unique because of its worm and worm wheel design and steep rise and fall of cam. This design has high mechanical advantage for machining castings and forgings. In those days castings and forgings were so uneven on outer surface during machining intermittent cuts will emerge. To deal with such machining parameters high gripping force chucks are the only answer.

Voltas were representing Gildemeister Germany who are manufacturers of Multi Spindle Chuck and Bar Autos. Berg Germany were associated with Gildemeister for work holding. In 1963 GMT signed agreement with Berg for the manufacture of Manual Chucks…the rest is history

GMT-history-part-3-manufacture of surface plates

When PV started GMT he wanted to make Bench Lathes similar to the designs of South Bend USA. This design appealed to him and he felt it would be useful as a training lathe to train operators. He purchased 3 machines: one bench lathe and two lathes which he installed in PREWO and used for jobbing.

PV displaying GMT Cast Iron Surface Plate at an exhibition in the early 60’s

 

The Bench Lathe was stripped completely drawings were taken, patterns were made for Bed and castings were also made. After machining, the Bed scraping had to be done. He was looking for a Surface plate as a master for scraping. At that time Praga were the only Indian manufacturer of SurfacePlates. They were quoting long delivery. He therefore decided to look at standards for Surface Plates as per BS 817- 1957.After getting into the manufacture of Surface plate for internal use he was approached by Voltas to manufacture and supply Surface Plate to them. They will be the selling agents. PV therefore abandoned Lathe project and fully focused on Surface Plate manufacture and signed selling agreement with Voltas.

Today, GMT is the most respected brand among the surface plate manufacturers in India.

GMT – The beginnings – Part-2

The factory used to be lit by tube lights, the floor was dark with oil and coolant soaked in from innumerable spills from the hundreds of trial assemblies of special purpose machines, and the air was redolent of the smells of machine oil, coolant and grease. 

Purchase of part for machines was a HUGE challenge.Nothing was available locally in Pallikaranai and all parts had to be purchased from Mount Road or George Town

and the excitement of each installation merited heated discussions and arguments, with with the whole team wanting to know everything about the machine design,the commissioning problems and the customer feedback.

Voltas were our sales agents. This gave us access to the industrial markets in India. When we parted with them, we established our own network by carrying a chuck in a box from customer to customer. PV*, Jagannathan**, LSM*** have trudged for miles carrying an Hand Operated Chuck in a suitcase to demonstrate and sell. In the old days one just walked into any establishment and expect to be welcomed with warm hospitality and friendship and a willingness to learn. Today one has to fix an appointment and cross the “security barrier” before one can meet a prospective user.

The dedication and the perseverance of our sales team paid off with GMT establishing itself as the most reliable brand for chucks in the Indian market.

*PV – P.Venkat Raman, Founder, GMT

**K.Jagannathan – currently the Executive Director-Sales & Marketing, GMT

***LSM – L.Subramaniam – currently the General Manager, GMT