A new correspondent recounts an insightful development of a specialized cutting tool:

“The requirment was to enlarge the size of a hole in the enclosed shell of a tube bundle assembly of a boiler.

“To fulfill the challenge ahead, a specialized cutter was made, and the purpose was resolved successfully.

Process challenge

"Since the job was performed on-site and in enclosed conditions, there were the following constraints:
"1) As the inner part of the shell was inaccessible, it was necessary that the chips should not fall on the inner side of the shell during the process of enlarging the hole size from Ø16 mm to Ø 25mm.
"2) The modifications were to be carried out on site, and from outside of the shell-tube bundle assembly.
"3) The tubes were not to be damaged during the modification process.

Operational sequence

"1) The tool is to be located at the center of the existing hole in an outlet distributor shell, from the O.D.
"2) When the pilot of the cutter enters the hole, a spring-operated stopper will be pushed inside.
"3) The cutter will begin to enlarge the hole from Ø16 mm to Ø25 mm. The pilot will prevent the chips from falling on the inner side.
"4) The spring-operated stopper will be pushed out when the balance drill depth is 2 mm.
"5) The spring-operated stopper will prevent the end disk (last chip) from falling inner side when the drilling process is completed.
"6) When the tool is pulled back after the process, the last chip (end disk) will be pulled out. After discarding the end disk, similar procedure to be carried out for remaining holes."

K.S. Rao is affiliated with L&T Heavy Engineering - India.