MACHINING & MACHINERY
GUNDRILLS
UNISIG
UNISIG Drills Down to the Smallest Diameters
By Eric Krueger and Ryan Funk , Engineering Team , UNISIG
The modern gundrill is an engineering marvel , a well-designed piece of equipment that does one thing exceptionally well . A new gundrill will produce round , straight holes with enhanced cylindricity even at its deepest points . And it does all this while simultaneously providing a fine I . D . finish and excellent tool life .
Like all tools , gundrills wear out , typically after drilling around 1,000 ″. While a talented operator can still drill a hole with a worn gundrill , it will more often result in a loss of hole tolerance and finish at best . As gundrills wear , they require more thrust and torque while producing more run-out and experiencing greater drift . A dull cutting edge will produce irregular chips , which in turn cause spikes in coolant pressure – sure signs that failure is imminent .
Unlike some tools , gundrills are excellent candidates for resharpening . When performed correctly , the same gundrill can be resharpened to perform as well as a new drill as many as 8 to 10 times . The only significant difference between a resharpened gundrill and a freshly produced tool from the OEM is a slight back taper , an issue only for shops that require tolerances far beyond most manufacturers ’ needs – all other shops can simply account for the everso-slightly reduced tool diameter . Otherwise , the only visible difference will be seen in the length of solid carbide on the gundrill ’ s tip .
Even coated drills can be sharpened . Naturally , this will reveal the raw carbide on the face , but this does not impact performance . The coating will remain on the wear pads and continue to improve the gundrill ’ s size control and ability to leave behind a finished surface . Tool life will be impacted , but the only other option is having it fully resharpened and re-coated by the OEM , which will likely be less cost effective .
Manufacturers have several options for resharpening their gundrills . For specialized gundrills , such as twin-flute tools and those intended for ultra-highfeed applications with chipbreakers below a coating , resharpening is something that only a gundrill ’ s OEM can do . A local sharpening service will likely have the proper equipment , but this requires having redundant tooling and factoring in lead time and transportation costs .
However , both of these methods result in a loss of process intelligence . The grinding process can offer valuable information manufacturers can use to optimize their gundrilling applications . As a result , more manufacturers that use gundrills are choosing to resharpen their tools in-house .
The main risk of performing resharpening operations in-house is poorly sharpened gundrills . Without the correct tip geometry , gundrills do everything worse : size control , roundness , cylindricity , finish , chip control , straightness and depth all negatively impact workpiece quality and result in significantly diminished tool life . This will cause operators to reduce feedrates or change out tools more frequently to achieve the necessary tolerances and out of fear of catastrophic tool failure .
Modern gundrill grinding systems make it easy to avoid these consequences . For the greatest advantage , one needs the full system . That means a grinder , the appropriate gundrill fixture and equipment for calibrating and inspecting the drill tip .
A basic , high-precision manual tool grinder is used as a platform for these systems , though the length of some gundrills necessitates a reinforced table for sufficient accuracy . Choosing a fixture can be more complicated , as gundrills can be ground in two different ways . Sweep grinding leaves behind a gradual transition between elements of the tip ’ s geometry , while facet grinding creates distinct geometry . UNISIG typically recommends facet grinding , because the slight increase in tip strength produced by a sweep grind is outweighed by the repeatability and greater ease of inspection offered by facet grinds .
The final piece of advanced gundrill grinding systems involves a digital inspection camera capable of viewing and storing magnified images . Ideally , this will allow the user to perform measurements and identify flaws without taking the tool out of the fixture . In addition to allowing for highly precise grinding , this inspection is vital for process optimization .
Process optimization capability is the real added value conferred by performing gundrill resharpening in-house . Frequent inspection allows for the maximization of tool life . Shops become familiar with the wear patterns created by a given application and may find they are replacing gundrills too often . If a gundrill tip has even wear across its entire cutting edge , it could easily have many hundreds of inches of life left , something that will only become apparent with repeated inspections .
In-house gundrill resharpening also ensures that shops can obtain the best tip geometry for their given applications . Whether it is uneven or unexpected wear , or the sudden appearance of chips in the cutting edge , once a shop identifies an irregularity , they can then adjust speeds and feeds to optimize the process . The inspection equipment even makes working with tooling OEMs easier , since shops can send them a measurement set and picture of a tool when asking for advice on how to improve the geometry .
Further information on all machines and the complete UNISIG machine program is available at : www . unisig . com or follow the company on LinkedIn and Twitter (@ UNISIG ).
You will also meet us at the EMO 2021 show in Milan , Italy in Hall 2 , E38 from 4 .– 9 . October .
For further information , please visit www . unisig . com
88 PECM Issue 53