How to Use Counterbores
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Description
A counter-bored hole has two diameters; a large diameter that is big enough to fit the screw head and the smaller diameter houses the shaft of the screw.
Benefits of having a counter-bored hole are:
• A smooth, clean surface is sustained when a large fastener is needed
• A counter-bored hole allows for a part to be fit into tight clearances without needing the extra room of a bolt head
Safety
• A short-sleeved shirt, long pants, closed toed shoes and eye protection are required while operating machinery.
• An operator should not wear gloves or jewelry.
Steps to Using a Counterbore
| Set-up | |
|---|---|
| 1. Select the desired screw size. | |
| 2. Determine the proper pilot drill bit and counterbore bit size from Table 1. | |
| Counterbores are located in the fifth drawer down in Cabinet #3. Pilot drill bits are located on-top of Cabinet #3. | |
| Counterbores are located on the left side of the drawer next to the center drills. | |
4. Inspect drill bit and counterbore for jagged or broken edge - Seek mentor if broken or jagged.
Purchasing new bits: Msc: 1-800-645-7270 www.mscdirect.com McMaster: 1-562-692-5911 www.mcmaster.com |
| Procedure | |
|---|---|
| 5. With proper drill bit selected, drill through hole to pilot size, oil liberally. | |
| 6. Mount counterbore in mill, drill press, or lathe and adjust speed according to Speed Chart. Select head depth to screw size using Table 1.
Note: These are suggested starting speeds, not necessarily the correct speeds. | |
| 7. Cut counterbore to head depth indicated in Table 1, oil adequately. | |
| 8. Remove any chips or burrs caused from counterboring. This can be done with a deburring tool or a chamfer bit. | |
| 9. Insert the screw into the hole to ensure a proper fit. |
