Technical Information Hints on Use & Maintenance
Web Thinning
On most drills the web increases in thickness towards the shank with the result that, as the drill is shortened by repeated sharpening, the chisel edge will
become wider. As the chisel edge does not cut but forces the metal out of the way, too wide a chisel edge will result in more pressure required for penetration,
leading to greater heat generation and a resultant loss of life.
hold
HOLD original
ORIGINAL
THICKNESS
thickness
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Cutting Fluids
The use of cutting fluids is an advantage in most drilling operations and an essential in some. The two main functions of the cutting fluid are lubrication
and cooling. The purpose of lubrication is to reduce friction by lubricating the surfaces tool and work, to facilitate easier sliding of the chips up the flute
and to prevent the chips welding to the cutting edges. In production work, particularly when drilling deep holes, the cooling action of the fluid is often
more important than the lubrication. Overheating will shorten the life of the drill. Intermittent feed on deep holes, where possible, not only clears the
chips but permits more effective cooling.
Speeds
The speed of a drill is the rate at which the periphery of the drill moves in relation to the work being drilled. As a rule, with a drill working within its speed range for
a specific material, more holes between sharpenings will be achieved if the speed is reduced and less holes if the speed is increased. Thus, for each production run,
a speed must be established which will result in the highest rate of production without excessive breakdown time or drill usage. The factors governing speed are:
Component material, hardness of material, depth of hole, quality required, condition of drilling machine, efficiency of cutting fluid.
Feeds
The feed of the drill is governed by the drill size and the component material. As with speeds, an increase in feed will lessen the number of holes produced
sharpening but it is essential that a constant feed be maintained. If a drill is allowed to dwell, breakdown of the cutting edges will result.
Small Drill Feeds and Speeds
Deep Hole Drilling
When drilling deep holes, speeds and feeds should be reduced as follows:
Depth of hole
Speed Feed
3 times drill diameter 10 10
4 times drill diameter 30 10
5 times drill diameter 30 20
35 to 40 20
6 to 8 times drill diameter
462
Reduction percent %
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Breakdown of small drills can most often be attributed to two faults: speed too high and feed too low. A feed which will produce CHIPS not POWDER, coupled
with a speed compatible with the strength of the drill is essential for small hole drilling. Feeds must be based on thickness of chip, not mm/min, and speeds
adjusted accordingly. EXAMPLE: A 1mm drill is to operate at a feed of 0.013mm /rev, drilling steel. While the material may permit a speed of 30m/min or
9,500 RPM it is obvious that the drill could not withstand a load of 0.013mm feed at this speed; a penetration rate of 124mm/min. The correct procedure is
to retain the feed but reduce the speed to obtain a penetration within the capacity of the strength of the drill.