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Precision Center Punching Using Computer Numerical Control Machine

IP.com Disclosure Number: IPCOM000035637D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Reester, KA: AUTHOR

Abstract

When drilling small holes (0.5 mm diameter or smaller) in stainless steel on Computer Numerical Control (CNC) machines, 'work hardening' of the material occurs when using conventional 'hole spotting' methods. This process/tool minimizes the 'work hardening'.

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Precision Center Punching Using Computer Numerical Control Machine

When drilling small holes (0.5 mm diameter or smaller) in stainless steel on Computer Numerical Control (CNC) machines, 'work hardening' of the material occurs when using conventional 'hole spotting' methods. This process/tool minimizes the 'work hardening'.

An automatic spring-loaded center punch is a standard shelf item; however, it is not normally precise enough to achieve the desired results when used as is. The 'spot' made by the punch must be on location within 0.025 mm or the small drill will break as it deflects into the 'off center' spot. The following modifications to a standard automatic center punch were made: A) The knurled shank was ground to fit a standard Numerical Control (N/C) tool holder. B) The tip was ground concentric to the shank within 0.015 mm. C) The spring force on the tip was reduced by changing to a 'lighter' spring (behind the tip). D) The nose piece was rebuilt by adding a bushing to reduce the clearance between the nose and the plunger to a minimum, resulting in a 'slip fit' between the two pieces. E) Maximum 'runout' between shank and tip to be 0.05 mm.

The reworked center punch is mounted in a N/C tool holder. The holder is then mounted in the spindle of the CNC machine. With the spindle rotation off, the N/C program positions the workpiece and then detents the punch creating a 'spot' that is on location and has not been 'work hardened'. Accurate hole location and...