A counterbore are a process for creating a cylindrical hole with a flat bottom; a counterbore is used to allow a fastener’s head to sit flush with an surface of the material. A counterbore is different than a countersink. A countersink create a V shaped conical hole.
A counterbore creates a wide cylindrical hole with a flat floors. Using a countersink for a fastener with a flat bearing surface will cause the fastener to wobble within the hole. This will prevent the fastener from tightening correct.
How to Make a Counterbore
A counterbore should of been used for tightening the fastener when the fastener have a flat bearing surface. To counterbore, three measurement must be made: the measurement of the pilot hole, the bore diameter, and the depth. The pilot hole is where the screw shank will enter the material.
The bore diameter is the wide diameter of the counterbore tool. This measurement must be larger than the diameter of the fastener head. The depth is how far the counterbore tool will enter the material.
This measurement must be taken to ensure the fastener head will sit flush with the surface. If the depth is measured incorrectly the fastener head may stick out of the surface or sit to far below the surface for a wrench to be able to turn the fastener heads. The sequence of operations for counterboring include measuring the dimensions and drilling the pilot hole.
The pilot hole must be drilled first. If the operator drills the bore diameter first the counterbore tool may wander off of the center of the material. This will create an oval shaped hole instead of a circular counterbore.
The type of material will affect the counterboring process. For example, if the material is stainless steel, the tool will work harder and the metal will work harden. Slower speeds and cutting fluid will be used when counter boring in stainless steel.
If the material is aluminum, it will gall. The aluminum will smear within the tool. A Forstner bit can be used to counter bore in hardwood as the grain may tear when using other cutting tools.
A Forstner bit will shear the wood fiber and will not tear the wood. To successfully counter bore the material, calipers must be used to measure the dimensions. The fastener head must flush with the materials surface.
When perform correctly the result will be a smooth plane where the fastener head is level with the materials surface. By following the correct measurements and following the correct sequence of operations the counterbore will create a seamless transition between the fastener and the materials surfaces. Its important to make sure you’re measurements is accurate so the hole dont look bad.
Youll also need to check that the hole is deep enough to accommodate the moddern fastener heads. Dont forget that metal will work harden if you use teh wrong speed. Its alot easier to do it rite the first time.
