Drill bits - wrongly marked!

the watchman

Hi All,
Came across this today.
Firstly I have to hold my hands up and say that most of the time I do buy the cheap drill bits from those pound shops, as an amateur they do me just fine.

I wanted to replace one that was worn out (see pic). It said on the shank that it was a number 5 and under that it was marked 3 sixteenths (sorry cant type fractions).

However I ended up buying a set from a more reputable outlet but they still were a cheap range.
I found that the new drill bit marked No.5, 3/sixteenths was much smaller than my old one. On close inspection I realize that the new one is correctly marked and the old cheapy is incorectly marked.

Never came across this before so thought I would put it out there.
They'll be hundreds now saying it happens al the time lol:D

chuck eastwood

Silly question but are you measuring the shank or the boring tip

the watchman

chuck eastwood wrote: »

Silly question but are you measuring the shank or the boring tip

It's a good question chuck, so I need to try and clarify.
I am not measuring the length of the drill bit but the general width of the shank and/or the tip. I am clearly not an expert on these matters but the fact remains that the two drill bits in question, one old and one new have exactly the same specification markings on them ie No.5 and 3 sixteenths and yet are clearly totally different sizes.
If you used both drills to drill two holes the new drill would make a much smaller hole ie. 3 sixteenths and the other (old cheapo version) a bigger hole, not sure of the size, I guess around 3/8ths.

I think I've got that right. If I have does this happen often?.

antiskeptic

the watchman wrote: »

It's a good question chuck, so I need to try and clarify.
I am not measuring the length of the drill bit but the general width of the shank and/or the tip. I am clearly not an expert on these matters but the fact remains that the two drill bits in question, one old and one new have exactly the same specification markings on them ie No.5 and 3 sixteenths and yet are clearly totally different sizes.
If you used both drills to drill two holes the new drill would make a much smaller hole ie. 3 sixteenths and the other (old cheapo version) a bigger hole, not sure of the size, I guess around 3/8ths.

I think I've got that right. If I have does this happen often?.

The drills you have are masonary items by the looks of it. Which means the shank diameter isn't the size of the hole being drilled. The tip of the new drill, you can see, has little 'wings' which increase the diameter to the marked size: 5mm (metric) or 3/16th (imperial - that's how you type a fraction btw ). The shank is made smaller than the tip to allow the debris created by the drilling to more easily pass back along the shank as you progress down the hole.

What's probably occurred is that the tip of your old drill has worn away/broken off - and all you're left with is a blunt-tipped shank. It'll still drill a hole in masonary but that hole will be a shank diameter one - not a marked size one.

the watchman

Hi lads,

Antiskeptic you would be right if the old one had broken or worn down as you mentioned but I just checked and took new pics.
New pics of both drills together. The big one is the old one and unbroken.
I think they explain things better than I can.
As I said before both have same spec stamped on them.

kitser

the old one looks like 5/16

amiable

the watchman wrote: »

Hi lads,

Antiskeptic you would be right if the old one had broken or worn down as you mentioned but I just checked and took new pics.
New pics of both drills together. The big one is the old one and unbroken.
I think they explain things better than I can.
As I said before both have same spec stamped on them.

You need to get a calipers and measure them yourself. You should never rely on what is written on a drill. Check twice Drill once