Rotary surface grinder gets new lease of life

When DK Holdings decided to get an existing rotary surface grinder rebuilt and upgraded to CNC, after discussing the project with a number of rebuild specialists, the company eventually selected IMTS

When manual grinding methods proved less than effective in holding tolerances on a fine annular step form required for a new style of diamond plated cutting disc, leading superabrasive producer DK Holdings in Kent, decided to get an existing rotary surface grinder rebuilt and upgraded to CNC.

After discussing the project with a number of rebuild specialists, the company eventually selected Rochester-based Industrial Machine Tool Services (IMTS) to carry out the work.

The fully rebuilt Abwood RG1 ring grinder, which now has a Fagor 102 CNC system, enables this special 'rivett' form to be accurately and repeatably ground on a range of discs to a tolerance of 0.12 mm and in a cycle time some 25% faster than before.

What's more, the upgraded machine has also de-skilled this grinding operation, improved surface finish levels and reduced scrap rates to zero.

IMTS wrote special software macros for the two main grinding cycles and provided on-machine training for the operator.

The project took just under three months to complete and the total cost was almost 30% less than the price of a new CNC rotary surface grinder.

The decision to go for a rebuilt machine was based on a number of factors as workshop manager Vic Williams explained.

"We looked at the possibility of buying a new CNC rotary surface grinder, but the high cost involved combined with the fact that the new product would only account for around 25% of the machine's workload convinced us that upgrading an existing model was the best option.

Another consideration was that the 28-year old ring grinder in question was in need of a rebuild anyway and so upgrading to CNC was an even more cost effective solution." After detailed consultation with IMTS's managing director Charles Thurston, the company placed the order for the Abwood machine to be rebuilt and upgraded.

DK Holdings has been manufacturing diamond and CBN superabrasive products since 1959.

Originally named Diagrit Electrometallics, it was amalgamated with Kendia Diamond Products in 1983 and the first letter of each company name was used to unify the two businesses.

Employing 120 people at its 50,000 ftý factory in Staplehurst, the company produces a wide range of superabrasive products which are widely used in the stone, reinforced plastics, engineering, woodworking and saw sharpening industries.

DK manufactures electro-plated and resin-bonded grinding wheels (in both diamond and CBN) as well as cutting blades, hole cutters, dressing tools, belts, pads and flexible discs.

It also offers a range of pneumatic and electric hand tools to power these tools along with floor restoration equipment, too.

The mechanically-actuated Abwood rotary grinder was delivered to the IMTS works in March of last year where it was completely stripped down.

All the major elements were examined for wear and tear, the slideways refurbished and key items such as bearings and seals replaced.

It was subjected to a full mechanical rebuild (to bring it right back to the original maker's specification) and was also modified to accept recirculating ballscrews for horizontal and vertical traverses and equipped with servo motors and a Fagor two-axis CNC system.

Special software was written by IMTS to provide two easy-to-use programs for plain ring face grinding and the production of the special 'rivett' form required on the periphery.

Interlocked guarding to CE standards was also provided.

EN 42 steel blanks for the diamond plated cutting discs are initially turned on a CNC lathe in batch sizes of up to 50 off before being transferred to the grinding section.

A family of five different discs are produced in sizes from 125 to 300 mm diameter and in thicknesses going from 0.5 to 1 mm.

Held by a magnetic chuck, the discs are finish ground on each side and the annular step (which can vary in size from 0.1 and 0.25 mm deep by 0.2 mm wide) is produced.

All grinding operations are under automatic control including dressing, although this is selected manually as and when required -- usually about twice a day.

Tolerances on the 'rivett' forms are within 0.12 mm for both depth and width and the flatness of the disc is within 0.05 mm.

Grinding cycle time is around 3 min per side.

The upgraded ring grinder was installed at DK Holdings in June of last year, on schedule, and it has been in constant use ever since on a single shift (8 hour) basis.

In use, the machine has simplified the grinding of diamond plated cutting discs, de-skilled the operation, increased productivity and improved quality and surface finish.

And as Mr Williams concluded: "The quality of the rebuild from IMTS is excellent and we would certainly consider using the company's services again on the grinding front." Established 20 years ago, IMTS offers a range of specialised grinding services.

This includes: complete machine rebuilds, partial rebuilds, CNC retrofitting, on-site service (for both manual and CNC grinders) and the supply of spare parts.

The company works closely with control manufacturers and has developed its own special grinding software.

IMTS also designs and manufactures a range of new grinding machines including the Rochester series of CNC cylindrical grinders and vertical creep feed surface grinders.

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