10 July 2012
Bailey & Mackey’s Darex XT3000 sharpener investment cuts costs
A 1st Machine Tool Accessories supplied US-made Darex XT3000 bench-top sharpener is restoring the split point cutting edges on a step drill at the Birmingham factory of Bailey & Mackey, and has proved equally capable of regrinding the chisel point on jobber drills.
In a three-step process taking a couple of minutes, the pressure, vacuum and temperature gauge, switch and transducer manufacturer, Bailey & Mackey, reports the Darex XT3000 returns worn step-shank drills to as-new condition, even when they have been burnt or chipped on the tip. It has also eliminated the expense of having bits resharpened off-site.
The company traditionally employed step drills with split point geometry on its eight CNC lathes and four machining centres. Such tools do not wander when entering the cut, so a centre drilling operation can be avoided, improving productivity.
The Darex XT3000 is able to restore the split point cutting edges on a step drill at any angle from 118 to 150º and is equally capable of regrinding the chisel point on a jobber drill. At Bailey & Mackey this type of bit was until recently used exclusively on manually-operated, pull-down machines for drilling through bushes which prevent the tool's tendency to deviate from centreline on entry. Now, these lower cost tools converted to split point geometry are used for CNC drilling of brass, which accounts for 80% of Bailey & Mackey's throughput, and also for aluminium and plastic components.
Jobber drills are reground with split points even before they have been used if they are destined for a CNC machine. Sometimes they are similarly ground for use on manual drilling machines as the tools penetrate faster and with lower force, so the operator needs to apply less effort.
"However, the company's production engineer, Alan Boylin, advises that care be taken because if an excessive amount of the web behind the cutting edges is removed and the point is too sharp, a jobber drill is prone to wear and breakage. Conversion of tip geometry from chisel to split is thus a compromise and is mastered with experience.
He adds: "Hand resharpening of drills is inconsistent without long practice and difficult for inexperienced operators to get right, whereas the Darex machine is quick to use and delivers dependable results every time."
"Machine operators here are responsible for inspection and for resharpening their own drills when necessary. It takes 10 minutes' instruction and a little practice to become fully proficient with the process."
Two holders are provided with the XT3000, capable of retaining drills ranging in diameter from 3 to 12 mm and from 12 to 21 mm. Built-in CBN wheels grind the high speed steel drills, although diamond wheels can be specified if a user wants to sharpen carbide twist drills.
It is worth noting that in this application, free-cutting brass is being machined for the majority of the time, leading to relatively low drill wear, yet even here payback on the Darex sharpening machine is just 18 months. If, however, tough steels and exotics are routinely cut, requiring much more frequent drill tip refurbishment, payback time for the machine would be much shorter. Diamond wheels are also available for sharpening solid carbide twist drills.
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