Hole Types & How To 4 main types of holes: Clearance Hole Tapped/Threaded Hole Countersunk Hole Counterbored Hole

Clearance Hole A clearance hole is used to allow a bolt or screw to pass through the part – this allows the bolt to thread into another part or a hex nut Most clearance holes are drilled between 1/64” to 1/16” larger than the fastener diameter depending on the amount of clearance required for the application

Threaded Holes Threaded holes are used to fasten parts together

Creating Threaded Holes Most commonly a three part process: Centre drill the hole Drill a hole at the proper Tap Drill Size (TDS) Tap the hole using the correct type of tap

TDS (Tap Drill Size) The TDS corresponds to the minor diameter of the thread size you require TDS can be found using a Sizing Chart or by using the following formula: TDS = D – 1/N

Example Find the TDS for a ½”-13 UNC thread TDS = D – 1/N TDS = ½” – 1/13 TDS = ½” – TDS =.4231” A full drill bit set will come with fractional drill bits as well as lettered and numbered drill bits, each having their own specific size

Countersunk Holes A countersunk hole is used when a fastener must be flush with the surface of the part In this case, a Flat Head screw is used An Imperial C-Sink is 82 degrees A Metric C-Sink is 90 degrees

Counterbored Holes A counterbored hole is used when the fastener must sit beneath the part surface, but a stronger fastener is required such as a hex head bolt or a socket head cap screw

Deburring Tips A quick and effective way to debur a hole is to use a countersink Put a countersink in the drill press and bring it down until it just touches the part, you should end up with a slight chamfer on the edge or your holes, but no sharp edges or burrs!