CNC Tooling Spot Drill Centre Drill

CNC Tooling Spot Drill Centre Drill

Category : Tooling Useful Stuff

CNC Tooling

Spot Drill Centre Drill Spot The Difference

Now if you already know then:


You don’t need to waste your time reading all this bollocks.

CNC Tooling

Spot The Difference

Now Let’s Talk About Centre Drills

They come in various sizes designated by a BS number.

BS1 to BS6

BS6 being big.

Anyway BS1 is 1/8″ diameter and BS6 weighs in at a massive 5/8″and a government health warning.

CNC Tooling

There is only one reason why you would use a centre drill and that is if you require clearance for a centre.

CNC Tooling

If you have a long part and you wish to support it with a tailstock then you need clearance for the point of the centre.

If you used a spot drill the point would touch before the sides.

CNC Tooling

If the part is going to be ground then it will most likely be held between two centres.

CNC Tooling


CNC Tooling

Now the big problem with centre drills is that in order to clear the point of your centre they have to have that little point (pilot) on the end.

And these little bastard break off. Oh and if your turret on your lathe is not aligned properly, you got no chance.

A BS1 centre drill has a pilot that’s just .64mm in diameter!!!!!

As soon as it makes contact you’ll see it wandering aimlessly around like a drunk teenager in Birmingham on a Saturday night.

Carry on now and it will snap off and if your having a shit day it will lodge itself in the part. You’ll need a neutron bomb to get it out.

So let’s move on and stop talking about these annoying little beasts.

Rule Number 1 only use them if you have to.

Rule Number 2 only use them if you really have to.

Rule Number 3 only use them if you really really have to.

CNC Tooling Spot Drills

Now these again come in various sizes a much bigger range from 2mm to 20mm and you get a 120 degree point or a 90 degree point.

B & Q are great for all kinds of DIY products (free add). But whatever you do don’t use the drills for serious engineering.

CNC Tooling

Shelves, building kitchen units, making the misses a Jewelry Box. They are fantastic, but not if you want to be a serious grown up engineer and play with the big boys.

So lets bin all the shitty cheap HSS drills and buy some decent stuff. Oh by the way don’t blame me if your boss says “dream on”

Why Am I Saying This

Well because modern drills are amazing.

They hold accurate size.

Don’t need a spot drill.

Really super fast.

Last longer.

Oh did I mention they are bloody expensive.

Centre Drill

Now with HSS drills you can buy thousands of em for a fiver and still have change to buy Robbie Williams concert tickets.

Authors Note

Please don’t read any of my articles if you like Robbie Williams, it means your a twat. Now Robin Williams, that’s totally different. Don’t you just love “Mrs Doubtfire” my favourite film.

Drills Drills More About Drills

But good quality modern drills are expensive. The good news is they easily pay for themselves. You need to treat them carefully because if they are carbide then they can chip and smash easily. You know in that James Bond movie where he is disarming a nuclear bomb? Well treat them like that and you’ll be just fine.

CNC Tooling

Anyway that’s not what this article is about.

CNC Tooling Centre Drill

A centre drill has a 60 degree point which is not good to start a drill. With a spot drill you can get a 120 degree point which is roughly the same as your drill point so it gives the drill a great start.

The drill won’t wander but if you heed my advice and use a super duper new drill then it will drill perfectly without any spot drill.

Spot Drill Last

I would always  use good quality CNC Tooling.

Use a good quality modern drill and then use a 90 degree point spot drill after to chamfer your holes.

This means you can rapid the spot drill right into the hole and then feed in just a tiny amount to create the chamfer.

Spot Drills The Good Bit

You can deburr with a spot drill. Just program it to go around your shape and put a nice clean chamfer around you part.

CNC Tooling Conclusion Spot Drill Centre Drill

Always use good quality CNC Tooling

Use a centre drill only if you have to.

Make sure your turret is aligned on a CNC Lathe.

Centre drills are for centre locations on long or ground parts.

Centre drills are for grinding between centres

Spot drill can be same angle as drill.

Spot drill after drilling.

Use spot drills to deburr parts.


If you have been affected by any of the issues in this post or need CNC Counselling then contact me.

If you want to learn to program CNC Milling Machines

Look no further Contact CNC Training Centre

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