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 2

After GMT parted with Voltas (who were our sole dealer) we focused on business with Ordnance Factories. GMT developed good rapport with Director General Ordnance Factories. (DGOF). The sales team identified Ordnance Factories in several locations and started visiting each one. GMT's Sales Engineer based at Calcutta started his regular visits to DGOF and developed good rapport and collected information in regard to expansion and new investments. DGOF tendered for a big Surface Plate of size 9000 x 1200 mm. This plate was required for Ordnance Factory Ambhajari near Nagpur.(OFAJ) They were setting up a factory for manufacture of large aluminum sections used for building bridges to transport arms and ammunition across river.

DGOF floated tender and we quoted and got the order from DGOF for the first time. 3 plates 3000 x 1200 matched and assembled mounted on special MS Fabricated Stand. A highly engineered product at that time. Plates were made mounted on stand duly assembled and scraped to the required accuracy. As per order the plate has to be inspected by DGS&D inspector. The inspector visited and inspected and accepted the plate for flatness accuracy. However, he said the plate has to pass for deflection test. Indian Standard for Surface Plate did mention deflection test. PV (GMT founder) accepted inspector's point and GMT made a Beam Comparator which is used for deflection test. This was designed and made strictly as per standard. The deflection was measured and our plate conformed to standard. PV was very impressed by the inspector of DGS&D, Mr. V. Subramaniam GMT used his services after his retirement and bought a number of standards for our library viz. IS and DIN.

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.

ADVANTAGES OF GRANITE SURFACE PLATES

ADVANTAGES OF GRANITE

1.	High degree of hardness (High quartz- high hardness)
2.	Low heat conductance
3.	Low temp sensitivity
4.	Non-magnetic
5.	Electrically Non-conductive
6.	Rust and acid resistance
7.	Matt surface, non-reflective surface
8.	Low water absorption
9.	High modulus of elasticity- Torsionally rigid, sag free, good slid's prop
10.	Dolerite - a better scratch resistance
11.	Modulus of elasticity - 26-86 GPa
12.	Compressive strength - 107 Mpa / 15600 PSI
13.	Water absorption - 0.07 - 0.31
14.	Density - 3g/cc
15.	Hardness - 6-7 Mohs scale
16.	Tensile strength 5 Mpa
17.	Co-efficient of thermal expansion - 6.1X10 -6/°C

It is  observed that fine-grained rocks have relatively higher density and hardness. They have higher resistance to scratch and are less porous. However stability of granite under varying temperature and humidity conditions is a major limitation even though the coefficient of thermal expansion is low compared to other engineering materials like cast iron and steel. If there is any small impact or scratch made over the granite surface plate, it results in crushing of localized zone and a broken piece or powder comes out without harming the surface accuracy. However in the case of cast iron or steel surfaces, under similar circumstances a bulge would result and the surface accuracy is affected and often these remain unnoticed by the naked eye.

The granite color alone is not an indication of the physical qualities of the stone. In general, the presence or absence of minerals determines the color of the granite and this may have no bearing on the qualities that make good surface plate material. There are pink, gray and black granites that are excellent for surface plates. However the consistency of several made from the same vein in a quarry can be unpredictable.this inconsistency is much less in pure black granite.

The aging qualities of these rocks are also excellent. This is conformed by a measurement carried out on a 1.6m X 1m surface plate kept in a metrology room immediately after its lapping and sparingly used over a period of four years. The variation in shape and the accuracy of this surface is negligible. Thus granite has been found to be a useful material for providing an accurate surface.