Free Next Day Delivery
on orders over £59 ex vat*

Expert Technical Team
Get advice on 01924 869 615

Same Day Despatch
On orders placed up to 5.45pm


Spot Drills vs Centre Drills

Tom Beaumont

Product Training Manager

18 years engineering experience, specializing in 3 & 4 axis CNC milling, turning and horizontal boring.

Before drilling a hole or preparing to use a live (revolving) or dead centre on a lathe, it’s common to use a spot drill or centre drill to ensure accuracy for the drill or centre. Spotting drills and centre drills may have similar characteristics, but they are intended for two different purposes.


In this blog I will help to differentiate between the two and help you make the right choice when selecting the best tool for your application.

What are Centre Drills?

A centre drill has a slightly different geometry than a spot drill, they are shorter, with a tapered, or cone shaped end that is much smaller in diameter than the shaft of the drill. The smaller diameter is used as guide and creates clearance for the tip of lathe centre. A centre drill can also be used as a countersink to allow countersunk screws to sit flush with the surface.

Centre drills are mainly used to create a hole in the centre of a workpiece. This hole will act as a guide/support for a revolving or dead centre and in some case a starting point for the hole to be drilled with a larger drill diameter.

Centre drills come in two common types, Type A (DIN 333-A) this has 60-degree chamfer and Type B (DIN 333-B) that has two chamfers, a front 60 degree and secondary 120-degree chamfer. Centre drills are commonly available in Metric or BS (British Standard Imperial) sizes.

Why Use a Centre Drill?

A centre drill (which can be made from HSS or Carbide) can be used to drill a starter or guide hole in many different material types such as cast iron, aluminium, copper, steel, and stainless steel. Centre drills have a short and stubby design, this eliminates the risk of deflection making them the perfect tool for pre-drilling applications. When pre-drilling for a lathe centre, accuracy is key as the hole will ultimately keep the job aligned and stable during the machining process.

There are several advantages to using a centre drill:

  • Supports workpiece: Centre drilled holes can be used work holding tools to support the workpiece in a lathe.
  • Creates starting point: Centre drills can be used to create a starting point for a larger hole. This helps to prevent the larger hole from wandering and eliminates deflection.
  • Countersunk holes: Centre drills can be used as a countersink tool to allow fasteners to sit flush with the surface.

 

 

What are Spot Drills?

Spot drills are used to create a small indent prior to drilling with a twist type drill, the indent acts as a location point and guide for a larger diameter drill to follow minimising the risk of deflection. Spot drills differ slightly from centre drills as they are usually on a nominal shank and do not have the smaller pilot diameter that a centre drill has.

Unlike centre drills, spot drills can be used for multiple applications such as spot drilling, chamfering, countersinking, V grooving and engraving. They are available in HSS or Carbide with different point angles, most commonly 90° or 120°.

 

 

 

Why use a Spot Drill?

As mentioned above, a spot drill has multiple uses, the main use is spotting prior to drilling, this process increases the accuracy of the secondary drill. If the drill being used is not self-centring, then spot drilling is a must as it will minimise the risk of drill wander. Spot drilling will improve tool life and improve surface roughness. It’s worth noting that self-centring drills do not require spot drilling. 

There are several advantages to using a spot drill:

  • Accuracy: Spot drills are very accurate, which helps to ensure that the final hole is in the correct location.
  • Prevents wandering: Spot drills help to prevent the secondary drill from wandering.
  • Reduces heat: Spot drills create less heat than regular drill bits, which helps to prevent work hardening prior to drilling.

 

 

How to Choose Between a Spot Drill and a Centre Drill

Centre drills are first choice for predrilling when using revolving or dead centres in the tailstock on manual or CNC lathe.

The spot drill is a good tool to have in your arsenal, its function is no longer limited to the drilling of pilot holes. In addition to this, it is possible to use them as a chamfer mill and various angles are available. The angles can be 60°, 90°, and 120° and can be used for a wide range of processes, including:

  • Spotting
  • Engraving
  • Chamfering 
  • Deburring of edge

The best way to choose between a spot drill and a centre drill is to consider the following factors:

  • Purpose: What are you using the drill bit for? If you are simply creating a small, precise hole, then a spot drill is a good option. If you need to support the workpiece in a lathe or create a starting point for a larger hole, then a centre drill is a better choice.
  • Material: What material are you drilling? Spot drills and centre drills are available in both HSS and carbide. Both will drill a variety of materials. 
  • Size: What size hole do you need to create? Spot drills and centre drills come in a variety of sizes. Choose a drill bit that is the same size or slightly larger than the hole you need to create.
  • Machine: Are you machining on a lathe or a milling machine? If a lathe, then both options are suitable. However, on a milling machine, a spot drill is recommended.

 

 


Summary

In conclusion, Spot drills and centre drills are both useful tools for creating holes in metal. However, they have different purposes and advantages. Spot drills are more accurate and help to prevent the secondary drilling cycles from wandering. Centre drills are used to drill support holes in the workpiece for a lathe centre and create a starting point for a larger diameter hole. The best way to choose between a spot drill and a centre drill is to consider the purpose of the drill bit, the hole size you require and what machine you are working on.

 

For expert advice on choosing the right drill for your application, please contact our technical team on 01924 869 615 or email salescutwel.net.

 

Shop tools for spotting & centring...

Spot Drills

Excellent for Steel, Stainless Steel and Aluminium whilst also suitable for Hardened Steel up to HRc55, Titanium & Cast Iron.

Centre Drills

Range of HSS metric and imperial centre drills which create an accurate centre hole to locate
a live centre.

Drill Chucks

Drill Chucks for general drilling applications & suitable for use with both HSS & Carbide Drills.