GriStar Series グライスター シリーズ プロのための自動工具研削盤

Regrinding drills on GriStar Series No.2 (Relief shape)

Sep. 11.2021

In this article, we will discuss the settings and parameters of the relief shape of cutting tools.


Relief Shape

In the case of drills, there are two general types of relief shapes: “Flat” and “Cone”.

Flat Relief

The escape surface is made up of flat surfaces. It is called “First Relief, “Second Relief” in order from the tip of the blade. Depending on the relationship between the angle of inclination (relief angle) of the relief surface and the tip angle (described below), the back of the blade may be higher when it is rotated, in which case, the “3rd Relief” may be added.

One of the advantages of the flat relief is that it is easy to secure a relief angle near the center. It is also easier to secure a larger relief angle than cone relief. It is also centripetal and stabilizes the hole accuracy. However, the merit is also a demerit as it is. The cutting edge tends to be thinner and there is concern about the strength of the cutting edge compared to cone relief.


Cone Relief

As you can see, it is a cone-shaped relief surface which is angled so that it goes down from the cutting edge to the back side. It is made up of only the first relief.

The advantage of cone relief is that it is easier to secure the hardness of the cutting edge compared to flat relief. It is also more advantageous than flat relief in terms of chamfer angle and surface roughness for Chamfer machining such as center drills, leading drills, and chamfer drills. However, depending on the setting of the tip angle and relief angle, it may be difficult to secure the relief angle near the center, and the centripetal force may be inferior than flat relief.



It is so called because its shape resembles a Brad.

The center part is protruding and the periphery is flat (180°). The advantage is that burrs do not easily appear on the work material. It is suitable for thin workpieces and counterbore processing.



There are shapes such as first cone relief to second flat relief and first flat relief to second cone relief. They are designed for optimum processing by incorporating the features of the flat and cone relief according to the purpose.


Chamfer (additional work)

Drills are made up of a twisted groove (rake angle of the cutting edge), a tip angle, and a relief angle, so the cutting edge of the outer periphery is inevitably weaker than that of the center due to its structure.

In order to secure the hardness of the outer periphery, chamfers are sometimes added to the outer periphery. It also helps to reduce burrs on the work piece.


About Tip Angle

Another important factor that forms the shape of the relief surface is the “tip angle”. There is a relationship between small tip angle to large tip angle and small thrust resistance to large thrust resistance. Depending on the rotation speed and times setting, it also affects the chip thickness. The most common values are 118° for HSS drills and 140° for carbide drills, but the optimum value varies depending on the work material.


About Blade Thick

In the GriStar series, there is a parameter called “blade thickness”. This is the width of the blade in parallel with the left and right blades. Please measure it with calipers before inputting it.

In some cases, it is written as a phase angle in the tool drawing. In that case, perform the following calculations and enter that value.

Blade Thick = Drill Diameter * Sin


Try Setting

Set the tip shape based on the above information and by looking at the tool to be resharpened and the tool drawing or instructions.

First, click on the “Tip Shape” tag at the top of the edit screen and select the relief shape from the list.
Next, enter the drill diameter, tip angle, and blade thickness.
Here are the general parameters for your reference.


ParameterHSS DrillCarbide Drill
Tip Angle118°140°
Relief Angle
(First / Second Relief)
Flat: 3°/ 25°
Cone: 8°
Flat: 10°/ 20-25°
Cone: 8°
Blade Thick*measurement needed*measurement needed
In the case of wave-shaped blade
Proper value will be diameter * sin(8°~10°)


In the next article, we will explain about thinning part.


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