Large drill bits - why so long?

[GrahamRounce]

Hi - I've been doing some drilling into steel with a 12mm hss bit, and of course it vibrated like anything - because it's 15cm long!
Why?
How many users are going to need to drill through 10cm of metal?! Very few, I bet. For the vast majority (correct me if I'm wrong), 99% of holes over about say 8mm diameter are probably less than a cm or two deep! Isn't a 15cm-long bit a waste of money and accuracy?
I've searched for shorter, stubbier ones but the few I've found are much more expensive, presumably because they don't make so many...
Is there a rational reason I've missed?
Thanks,

 

[Sideways]

Probably it's in the name - jobber drills - general purpose used for a multitude of jobs.
Drilling wood, plastics, non ferrous etc as well as steel.
Drill passing through another part before starting to drill.
Drill used in the tailstock of a lathe for full depth boring before or instead of using a boring bar.
Resharpenable many times over.

But stub drills are a great thing to have and worth buying in the sizes you use most in metal.
Boring on a lathe, jobber drills famously tend to wander so start off with a stub drill to get the hole properly centred and switch to jobber drills for depth once you have used up the reach of the stub drill.

 

[J-G]

Hi - I've been doing some drilling into steel with a 12mm hss bit, and of course it vibrated like anything - because it's 15cm long!
Why?
How many users are going to need to drill through 10cm of metal?! Very few, I bet. For the vast majority (correct me if I'm wrong), 99% of holes over about say 8mm diameter are probably less than a cm or two deep! Isn't a 15cm-long bit a waste of money and accuracy?
I've searched for shorter, stubbier ones but the few I've found are much more expensive, presumably because they don't make so many...
Is there a rational reason I've missed?
Thanks,

It's not just the depth of the hole that needs to be covered. Often it is more about the 'reach' and other issues

Over many years the 'Standard' has been developed - this is what is known as the 'Jobbers' drill standard, and, as you have discovered, the majority of drills produced are to this standard. This is beneficial as far as cost is concerned due to the number produced. The extra cost of Material is miniscule compared to the machine time & labour . . . .
[EDIT] @Sideways post has just popped up! and I concur with his comments.

 

[GrahamRounce]

Yes, I get that, but you'd think the long size would be the "special" rather than the default?!

 

[Phil Pascoe]

For most people total accuracy isn't necessary. You can drill shallow holes with a long bit but you can't drill deep holes with a short bit. It's pleasing most of the people most of the time.

 

[Ed Weber]

Yes, I get that, but you'd think the long size would be the "special" rather than the default?!

I agree
I also use stubby bits often.

 

[guineafowl21]

Blacksmith’s drills are what you need:

https://ffx.co.uk/product/Get/Ffx-Qq0108501180-5055945277760-Hss-Blacksmith-Drill-Bit-12Mm

Just drill a pilot hole about the width of the web on the 12mm drill. No need to step up in size endlessly.

 

[ChaiLatte]

Blacksmith’s drills are what you need:

A 12mm blacksmith's drill is somewhat of a contradiction in terms. The whole idea of a blacksmith's drill is that for sizes above 1/2" or 13mm, the shank size stays constant at 1/2" or 13mm no matter what the diameter of the cutting part. In the US, they are known as Silver and Deming drills.

 

[ChaiLatte]

Over many years the 'Standard' has been developed...

It was a little difficult to find. Jobber drills are BS328-1, of which I can find no online copy. However, this standard is paralleled in Indian Standard IS 5101 and in ISO 235 (which also covers stub drills).

https://law.resource.org/pub/in/bis/S01/is.5101.1991.pdfhttps://cdn.standards.iteh.ai/samples/64191/02902a376a3647aa97135468c592fa9f/ISO-235-2016.pdf

 

[deema]

If the drill ‘vibrated like anything‘ there is an issue with the setup or technique, as it shouldn’t. A few things it could be:
Drill is blunt
Drill hasn’t enough or no clearance.
Drill is ground off set, ie the point isn’t in the centre
Did you centre drill and then pilot hole to clear the centre where the drill doesn’t have any cutting tip?
Work piece not held rigid.
Drill / Chuck has excessive run out, you need a very accurate drill to drill metal without vibration
Insufficient pressure on the dill when drilling causing friction through rubbing blunting the drill.
Not Pecking to clear the swarf.
No lubricant
Drill is made of cheese and bending, ie not a quality drill bit.

I haven’t listed every cause, but the most likely.

 

[likeakite]

Deema may be on to something

 

[aforjeh]

Did you centre drill and then pilot hole to clear the centre where the drill doesn’t have any cutting tip?

I understood the rest of your list, but are you saying large bits don’t have cutting tips? Or it’s likely to be blunt at the tip, or at least blunter than a small pilot?

I don’t do much metal, and feel I might learn something here!

 

[ChaiLatte]

...Or it’s likely to be blunt at the tip...

Yes. Look up 'drill bit chisel edge'.

In the picture below, the small circle in the middle diagram is the bit that cannot cut, and has to bulldoze the material out of the way.

 

[stuart little]

Probably it's in the name - jobber drills - general purpose used for a multitude of jobs.
Drilling wood, plastics, non ferrous etc as well as steel.
Drill passing through another part before starting to drill.
Drill used in the tailstock of a lathe for full depth boring before or instead of using a boring bar.
Resharpenable many times over.

But stub drills are a great thing to have and worth buying in the sizes you use most in metal.
Boring on a lathe, jobber drills famously tend to wander so start off with a stub drill to get the hole properly centred and switch to jobber drills for depth once you have used up the reach of the stub drill.

Always use a centre drill first, on a lathe.

 

[Phil Pascoe]

I agree
I also use stubby bits often.

So do I, but long ones suit 90% of people 90% of the time - that's why they're the default.

 

[bushwhaker]

DIN 1897 - short metal drill bits.

 

[aforjeh]

Yes. Look up 'drill bit chisel edge'.

In the picture below, the small circle in the middle diagram is the bit that cannot cut, and has to bulldoze the material out of the way.

View attachment 164145

Huh - so a smaller pilot bit would also have a similar 'non cutting' tip, but it would be smaller and therefore have less bulldozing to do?

For the record I do pilot drill and work up to larger sizes but understood it as the process of removing material bit by bit that made it easier.. Although in practice it doesn't make too much difference, other than ensuring your pilot hole is large enough to fit the 'tip' in? i.e. I shouldn't expect great results if I just pick steps at random...

 

[likeakite]

If I'm drilling up to say 13mm, I'll centre drill first and then go up through sizes until I reach 13mm. Obviously the speed of the lathe/mill/drill needs to correspond to the bit size and material.

 

[TomGW]

I use ‘split point’ drill bits for metal. Definitely a better option.
https://www.performacut.co.uk/split-point-drill-bits

 

[AES]

I use ‘split point’ drill bits for metal. Definitely a better option.
https://www.performacut.co.uk/split-point-drill-bits

Agreed, but be careful. Especially on thin materials, split point drills tend to "grab" and "pull through" the job very quickly, often with disastrous results. For that reason IMO they should ONLY be used on a pillar drill -in a hand-held "pistol" drill you'll never be quick enough to hold them back as they start to grab.

But they do the job very well in a pillar drill.

Edit for a P.S. AND with the job securely held.