History of GMT - Surface plates and Bed Plates - Part-4

Bed Plates were developed where the plate design is different to that of standard surface plate. There was no change in ribbing. Bed Plates are kept side by side with a gap of 3 mm. The plates are offered in grade2 and grade3 accuracies. The plates are mounted on special Cast Iron stands. Depending upon customer needs stands are supplied with 600 mm above floor level or can be kept in a pit so that plate is in floor level.

Unique feature of the special plates are foundation arrangement, erection and commissioning. At our works the plates are matched and assembled and scraped to the required accuracies, They are dismantled and dispatched to the customers works. Fabricated stands are dispatched as a single piece wrapped in hay and gunny. 

 GMT bed plate - size - 6000X4000 mm (consists of 4000x1500– 4 Nos)

Foundation plan sent well in advance to the customer with instruction to prepare the foundation, size of foundation bolts, and other important details specified in drawings and documentation. On confirmation from customer that foundation is ready with our stand in position our team will visit customer site and erect and commission the plate, Minor touching up by scraping is done at customer end to ensure accuracies are maintained as per our inspection report.

I remember Vikram Sarabhai Space Centre, Trivandrum were so impressed with the design, stability and strength of our Special Surface Plate size 6000 x 1200 mm,  2 other divisions also bought similar sizes. When asked why not use the plate which is already available. The  Department Heads said that the plate looks so impressive they budgeted for their requirement and raised purchase requisition as a single tender and ordered for the same.
 

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.

History of GMT - Surface and Bed Plates - Part-3

Although our prices were high, we were securing a number of orders from Defence and Public Sector due to the ribbing design of our surface plates. The rigidity of the plate and capability to match and assemble surface plates together also worked in our favour. Notable users:

• Vikram Sarabhai Space Center 
• Nuclear Fuel Complex

We developed Portage Layout Table for precision measurements. Bendix US were making Layout Marking Machine. Bajaj Tempo and Hindustan Motors wanted such Tables. Size of the table 4000 x 2500 mm consists of 8 nos. 1000 x 1250 mm plates matched and assembled. The table top will have precision slots 12 mm width 250 mm pitch distance on length and breadth of the table. Bendix arm will travel on the slot manually. The plate is mounted on speciall. low height CI legs so that the height of the table from floor is max. 500 mm....to be continued

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.

History of GMT Surface Plates-Part 1

GMT commenced manufacture of Cast Iron Surface Plates, as per BS 817-1957. After supply a number of Surface Plates we had problems in quality of castings due to Plate ribbing which were diagonal as per BS. P.Venkat Raman then studied DIN 876-1963, and found it has orthogonal ribbing and made new pattern for Surface Plate as per DIN. This ribbing pattern had distinct advantages in making castings. The plate is also quite rigid due to its ribbing pattern.

To be continued....

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-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 Metrology bed plates and special products

Large Size GMT Cast iron bed Plate Size: 6000X4000 mm (consists of 4000x1500– 4 Nos)

Cast Iron Bed Plates Size : 7000 X 500 X 250 mm Cast Iron Bed Plate  Size : 4000 X 1250 mm Cast iron Matched surface plates Size : 4000 X 3000 mm (3000 X 1000 – 4 Nos) Cast Iron Bed Plate Size : 9000 X 350 mm (3000 X 350 – 3 Nos) Cast Iron Matched Surface Plate Size : 6000 X 3000 mm (3000 X 1000 – 6 Nos) Cast Iron Matched Surface Plate Size : 4800 X 2400M (2400 X 1200 – 4 Nos)

GMT Special Applications Granite Metrology Products

Granite bonded with metal has resulted in specials for many applications. Apart from complete range of standard granite and cast iron metrology equipment, including Surface Plates, Master Square, Tri Square and cubes, GMT also manufactures custom built special application metrology products.

Some of the applications include master square for alignment of machining center, Large size Granite Plate, Granite Base Structure for Contact Lens Grinding Machine, Run out Measurement System, fine pitch accuracy granite table, Granite structure for image processing machine etc.

Granite Best Suited for Metrology:
GMT has a metrology division located at Hosur, Tamil Nadu. This region is home to large deposits of world famous Indian black diabase granite. Indian black granite is best suited for metrology application. Granite Surface Plates are made from granite selected with great care at the quarry, by our experts.The uniform distribution of light and dark constituent minerals of this granite, result in a homogenous surface ideal for measurement reference.The following are the representative properties of our granites.
Texture : Fine. Specific Gravity : 3.08.Hardness :Scleroscope over 90. Modules of Elasticity : 9.0 to 12.0 x 10 Moisture of absorption : Nil.

GRANITE FOR SURFACE PLATES

In geological terms more commonly used, rocks for surface plates are Granite, Diabase / Dolerite and Gabbro. Granite consists of a fairly coarse grained aggregate of quartz and feldspar with small quantity of black or white mica. More often granite is identified by shades like black, grey, pink, etc,. The other and rather more commonly used rock for surface plate is the Diabase or Dolerite.

The properties, which help in selecting a rock for manufacture of surface plates, are hardness, density and the grain size. Uniformity of grains and structure is also a good feature. In general fine-grained Dolerite has better scratch resisting property than harder grey granites,and this has been confirmed by scratch test using a sharp diamond.

Another important property of rocks is the density. The compressive strength of a rock increases with an increase in the density. This higher density rocks have generally smaller grains and lesser porosity. Dolerite stays ahead in this category with very fine and smaller grains when compared with other igneous rocks. Diabase / Dolerite is a variety of a stone type known as Gabbro.

While it is closely related to granite, it is not the same. Dolerite lacks several of the minerals (such as quartz and mica) which give granite its distinctive grain structure. The lack of quartz means that Dolerite is slightly less resistant to wear than the hardest granite. However, this is offset by the lack of mica, which is very soft, and tends to flake out of granite plates, leaving pits. Dolerite is denser than granite, weighing about 190 lbs. per cu.ft. While most granite weigh between 160-170 lbs. per cu.ft.

Dolerite is less porous and more stable, which means that a smoother and more uniform surface finish can be achieved. It can used for multi-dimensional, very high-accuracy applications that require a very smooth, stable surface like angle plates, parallels, master squares, straight edges and so on.

BEING LESS POROUS, IT ABSORBS LESS MOISTURE THAN GRANITE AND THEREFORE WARPS LESS.

A medium to coarse-grained intrusive igneous rock composed of potassium and sodium rich feldspar, quartz, minor plagioclase, and small amounts of ferromagnesian minerals such as biotite or hornblende. It is the intrusive equivalent of rhyolite.
When we inspect granite specimen it shows orange to pink feldspar, white plagioclase, grey quartz with minor dark mafic minerals. Another form of coarse-grained granite consisting of white feldspar, grey quartz and black biotite it also contains an inclusion of dark metamorphic rock.

AVERAGE CHEMICAL COMPOSITION OF GRANITE (From Handbook of Physical constant)
Oxide	Weight
SiO2	70.18
TiO2	0.39
Al2O3	14.97
Fe2O3	1.57
FeO	1.78
MnO	0.12
MgO	0.88
CaO	1.99
Na2O	3.48
K2O	4.11
H2O+	0.84
H2O-	0.03
P2O5	0.19

MAJOR INGREDIENTS OF GRANITE
Quartz	38.8%
Orthoclase	16.7%
Albite	28.3%
Anorthite	9.2%
Corundum	0.3%
Hyperthene	4.3%
Ilmenite	0.6%