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Published byOswald Blake Modified over 8 years ago
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Hole Types & How To 4 main types of holes: Clearance Hole Tapped/Threaded Hole Countersunk Hole Counterbored Hole
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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
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Threaded Holes Threaded holes are used to fasten parts together
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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
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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
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Example Find the TDS for a ½”-13 UNC thread TDS = D – 1/N TDS = ½” – 1/13 TDS = ½” – 0.0769 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
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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
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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
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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!
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