Screw holes? How to create and what tools do you use? Today we will discuss this topic: counterbore and countersunk.
Counterbore and countersunk. What are the differences?
The “counterboring” is a mechanical process which consists in a cylindrical hole with a flat bottom which wides in turn another coaxial hole. This mechanical process is made by a “counterbore” a special tool. But when do you use a counterbore? Usually it is used when the head of a fixing element should not coming out from the surface of the piece you’re working on. In addition it is used to create on a boarder not perpendicular to the hole, a perpendicular seat for a cylinder head screw.
The difference of flaring from the spot having a largement of the tapered bore and not cylindrical. The recess is used to create receipts (or premises) of the screw heads. Why? In order to don’t make them protrude from the surfaces of machined parts once inserted. The “countersinking” can have variable inlet angles. (from 60 ° to 180 °) At 180 ° for the right fixation flat heads of different types. In addition the angle is determined by taking the opposite edges of the opening part.
Countersinks. Such measures in accordance with DIN 74-1?
Specifically, the measures of the countersunk of three cutting edges (DIN 335) are indicated for the fixation of screws according to DIN 74-1.
So for a correct coupling between the screw and mechanical component it is appropriate that the flaring is 90. Obtainable easily with the appropriate countersink.
Counterbore. Standard size or not?
The counterbores are created:
- With standard dimensions for various diameters of screws
- With non-standard dimensions in relation to the size of the screws.
In both cases there is a tip (called “pilot”) of the fixing screw diameter that is essential in ensuring the coaxiality:
- In the first case: the pilot is all in one with the tool and allows to center the counterbore of holes with only diameter.
- In the second case: the counterbore can fit pilots of different diameters, being able in fact to perform counterbores with the same diameter of the screw holes with a different diameter.
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