Point cuts and point thinnings of twist drills for metal cuttingJanuary 11, 2018
In addition to the point cut, there are also various point thinnings on twist drills. Learn what decisive influences they have on the drilling process.
As a matter of principle, the point cut allows guidance during drilling. Without the point cut, drilling would not be possible in the first place.
In contrast, the different point thinnings improve centering in the material.
There are various point cuts and point thinnings according to DIN 1412. Depending on the type of application, hard or rather soft materials, different point cuts and point thinnings are used.
We present six of them in more detail with the areas of application as well as advantages and disadvantages.
Shape N: Helical point normal ground
Applications: for all normal drilling work in steel, non-ferrous metal, and plastic.
Advantages: powerful main cut, resistant to impact, and lateral forces. Simple manual grinding possible.
Disadvantages: broad cutting edge requires considerable pressure.
Shape A: Cut chisel edge
Applications: for all normal drilling work in steal using drills for drilling into solid materials with larger drill diameters.
Advantages: good centring when starting to drill, as the length of the chisel edge is reduced to 1/10 of the drill diameter, and fewer pressure is required.
Disadvantages: additional regrinding work.
Shape B: Cut chisel edge with corrected major cutting edge
Applications: for drilling high-density steel (e.g. manganese steel), hard spring steel, thin workpieces, and drilling out.
Advantages: resistant to impact, one-way load, and lateral forces. Does not catch in thin workpieces.
Disadvantages: high pressure required, tendency to slip, extra work involved in regrinding
Shape C: Split point
Applications:for drills with very strong cores, for particularly tough, hard materials, and for deep-hole drills.
Advantages:very good chip removal (heat removal), very good centring, low feed force.
Disadvantages: extra work involved in regrinding.
Shape D: Ground for grey cast iron
Applications: for drilling grey cast iron.
Advantages: good centring, low feed force, good heat removal.
Disadvantages: perfect grinding only possible by machine.
Shape E: Centre point
Applications: for drilling sheet-metal and soft materials, for blind holes with flat bottoms.
Advantages: good centring, minimal formation of burrs when through-drilling, precise drilling in thin sheets and pipes, does not catch.
Disadvantages: sensitive to impact and one-way loading. Perfect grinding only possible by machine.
The function of the point cut is to guide the twist drill while drilling. The function of the point thinning is to improve the centering in the material.
Depending on the application you will need different point cuts and point thinnings.
In addition to the standard point cuts and point thinnings, special cuts designed for special applications can be seen again and again.
These two components are only one part that is important for the different fields of application. All components of a twist drill and their functions will be presented in one of the following articles.
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