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In Taper-Lok fastener removal the hole always has to be reamed to the next oversize in order to restore the correct interference. During the PoC testing the depth of cut was optimized to reach the best compromise of force required to sever the head (which was done by chiseling it sideways after cutting), and hole enlargement as a result of driving the taper out; vs. cycle time and electrode life.
Cut depth (from top of head) varied from 0.150” for short grip-length 3/16” fasteners to 0.200” for 5/16” fasteners, with times in the 15second to 35 second range. These times and depths were significantly greater than traditional e•drill head-side removal, with electrode life typically being 1/3 of typical life. Cuts were refined to enable fracturing of the stem approximately 2/3 down inside the grip-length, which when punched out resulted in hole opening of only a few thousandths of an inch, well within the cleanup of a first oversize.
When on-site, and upside down under the wing, there were also challenges in holding the gun still for these longer cycle times, and water leakage from between the tightly spaced fasteners was also a challenge. However, approximately 100 e•drill removals resulted in zero damage, and the client considered the other challenges were insignificant compared with the challenges and cycle times for traditional drilling. The client was more than happy, especially considering that this kind of removal was not what the product was designed for.