For a lathe center, choose a center drill designed to make the required support seat. For locating a subsequent drilled hole, a spot drill is the more direct choice in the center drill vs spot drill comparison, provided the drill and machine manufacturer recommend spotting for the setup.
Center Drill vs Spot Drill: Key Differences
A conventional combined center drill makes a pilot hole and a conical seat for a lathe center. A spot drill makes a small locating feature for a following drill. Some operators also use center drills for spotting, but the pilot geometry and the following drill’s engagement need attention.
| Feature | Combined Center Drill | Spot Drill |
|---|---|---|
| Primary purpose | Prepare a workpiece for support by a lathe center | Locate a subsequent drilling operation |
| Typical feature made | Pilot hole and conical seat | Small locating divot |
| Geometry to check | Pilot and seat must suit the intended center | Point angle must suit the following drill |
| Other use | Sometimes used to spot hole positions | Spotting may be unnecessary for some drills |
Center Drill: Uses and Tradeoffs
A conventional combined center drill has a small pilot and a wider conical cutting section. The pilot provides relief for the tip of the lathe center, while the conical section forms its seat. One common instructional example uses a 60° seat for a matching 60° center; check the tools you’re using rather than assuming that angle applies.
The combined tool suits work that needs a center seat, and it can also be used to spot hole positions. For spotting, its pilot changes the shape of the starting feature, so check whether that feature and the way the following drill will engage it are compatible with the operation. You can find our Center Drill in the product catalog.
Spot Drill: Uses and Tradeoffs
A spot drill makes a small locating feature where a subsequent drill will enter the workpiece. It suits a drilling operation when spotting is recommended for the drill and setup. Spotting isn’t necessary for every drill, so check the drill and machine manufacturer’s recommendations, especially when using a self-centering drill.
Point-angle compatibility matters. If the spot angle is smaller than the following drill’s point angle, the outer cutting edges may contact the work first and experience shock loading. Follow the tool manufacturer’s guidance for the actual drill and setup.
A spot drill also has limits on irregular or inclined surfaces: spotting alone may not keep the hole in the correct position. For a lathe center seat, select a center drill suited to that center.
Which Drill Should You Choose?
Choose a center drill if:
- You need a pilot and conical seat for a lathe center.
- You’re considering spotting with a center drill and have checked its pilot geometry and compatibility with the following drill.
Choose a spot drill if:
- You need a locating feature for a subsequent drilling operation and spotting is recommended for your setup.
- You can select a spot geometry that suits the following drill.
Before starting, check the intended center or following drill, the tool geometry and the machine manufacturer’s recommendations.
FAQ
Can a Center Drill Spot Holes?
Yes. Some operators use center drills to spot hole positions. Check how the pilot-shaped feature will engage the following drill before using one for that operation.
Is Spot Drilling Always Necessary?
No. Whether you need to spot depends on the drill and setup. Follow the drill and machine manufacturer’s recommendations, particularly for a self-centering drill.
Can a Spot Drill Make a Center Seat?
Choose a center drill suited to the lathe center when you need a support seat. A spot drill’s primary purpose is to locate a subsequent drilled hole.