If you screw a wood screw into a thinner squared lumber or in the edge area of a piece of wood, it can quickly happen that it spreads or splits. You should therefore pre-drill the wood to avoid this and to prevent damage to the workpiece. By pre-drilling the wood screw has more space in the material.
The diameter for pre-drilling depends not only on the diameter of the screw used, but also on the type of wood used. For example, hardwood is predrilled with a different diameter than softwood.
If you want to screw two pieces of wood together, you must specify the following. Pre-drill the wood to be mounted (drilling diameter = thread diameter of the wood screw). Bring both pieces of wood into position and mark the second piece of wood with the drill. Now you can pre-drill the second piece of wood. You can find the correct drill diameter in the table - Pre-drilling wood screws - below.
For hardwood hardwoods, a larger drill is used to pre-drill the diameter than for softwood softwoods. Here is a list of the most common types of wood.
Hardwood: oak, beech, maple, walnut, birch, alder, ash, cherry tree
Softwood: fir, spruce, larch, pine, Douglas fir
The following table gives an overview of which drill bit diameter should be used for pre-drilling. This depends on the external thread diameter of the wood screw used and the type of wood used for the workpiece.
|3 mm||2 mm||2 mm|
|3,5 mm||2 mm||2 mm|
|4 mm||2,5 mm||3 mm|
|4,5 mm||3 mm||3 mm|
|5 mm||3 mm||3,5 mm|
|6 mm||4 mm||4 mm|
|7 mm||4,5 mm||5 mm|
|8 mm||5 mm||6 mm|
|10 mm||6,5 mm||7 mm|
|12 mm||7 mm||8 mm|
* All information without guarantee.
There is a rule of thumb for the drilling depth and the pre-drilling of wood. For softwood you pre-drill about half the screw length, for hardwood you should pre-drill about 2/3. In order not to drill too deep, a depth stop at the drill helps or one marks the depth at the drill with some adhesive tape.
So that the wood screw can develop its full carrying power, the thread should be countersunk approx. 2/3 into the workpiece.
No matter which wood screw you use, when you pre-drill you never make a mistake. With softwood, however, in some cases you can do without pre-drilling and save time.