pre drilling for holes

[Luiz Fernando Pinto]

Hello, i made a hole with 10 mm diameter them the final diameter 11mm, my tool became like this and i didnt made the final hole, obviously. Is that because the relation of the diameters was too small?

 

[Tim1974]

Cheep drill bit ?
What material where you drilling ?
And what speed ?

 

[Luiz Fernando Pinto]

It´s not a cheep drill bit, it´s a dormer A002. And i thought that was a fake Dormer but it´s not. I alread taltked to Dormer and my outfitter.

So, i´m not sure what material it is, but it is a low carbor, i think. It´s a shame, but the previouly drill that I made were ok, for example, 8mm diameter.

It was about 500 rpm.

 

[Luiz Fernando Pinto]

Look why i thouth it was a fake Dormer tool, but it is not.

3 reasons.

1 - The chip that came whith the tool.

2 and 3 - A bad ending, at the chanfer edge and blurred letter.

Despite the photos, it's not a fake or cheap drill.

So, after all, that's why i am thinking it was the large pre drill hole
Or my lathe is too small... vibration, low robust, etc,... contributed to this.

 

[Tim1974]

Yer looks like it grabbed , I wouldn’t normally drill out so little (when possible)

 

[TonyM]

That does not look right even or especially for a second cut. It does not look overheated as I would expect with hard material which in any case would have shown with the 10mm drill. It definitely looks like a faulty drill bit.

 

[Tim1974]

yer your right tony looking at the pic agan on a bigger screen its not right at all ! unless the first drill work hardened the material ??? but yer you would see more heat , hmmmm wish i could run a file over the drill bit and see if its hard !

 

[Luiz Fernando Pinto]

Thanks a lot for the discussion. I will send the drill for my supplier,
he requested to send to him. Any new information i´ll post it here.

 

[Nick Hulme]

10mm pilot for 11mm final?
That's most of your problem right there, running it at 500rpm with 0.5mm engagement compounds the mistake as it will rip the edges off a drill bit more often than not, a 5mm pilot would be better.
This is not a case of a drill fault, it's tool abuse ;-)

 

[tornitore45]

10mm pilot for 11mm final?
That's most of your problem right there, running it at 500rpm with 0.5mm engagement compounds the mistake as it will rip the edges off a drill bit more often than not, a 5mm pilot would be better.
This is not a case of a drill fault, it's tool abuse ;-)

What a ridiculous statement!

Holes are reamed with 0,3 mm diameter difference.
Holes are enlarged by a trifle all day long by the thousand, in hard material without any problem.
500 RPM for a 10 mm is actually a bit slow, which eliminates overheating.
Low carbon steel does not work harden appreciably, an can almost be drilled with a screwdriver.
The drill may be a fake after all, faker can print brand logos.
The ugliness of the end is a good case for a fake.
The drill may have slipped through the hardening process.

 

[Nick Hulme]

Holes are reamed with 0,3 mm diameter difference.

The only relevance of that statement is that a reamer is not a drill.

 

[mcostello]

Do it all the time with no problems. Don't buy extra fancy drill bits either.

 

[tornitore45]

Nick you need to learn how to learn from those that know more than you.
Mountains of experience say you are wrong, why do you insist in defending something wrong?
By the way, from the point of view of the reamer cutting into the hole the geometry is essentially the same and that is why a drill bit can cut into a hole slightly undersized just like a reamer. The difference is that a reamer has multiple flutes keeping a better center and cutting a rounder hole, something a drill bit may not do because is allowed to wander, but that difference is meaningless to the issue at hand.

 

[Nick Hulme]

I am endlessly amused by you, please do keep it up

 

[tjwal]

I agree with Nick. The pilot hole shouldn’t be much bigger than the web of the final drill. Whether that caused the problem or not I don’t know.
John

 

[tornitore45]

Yes I am a funny guy. Please tell me what evidence you have to support your rambling about drilling. Again people drill with little stock removal all the times, you seems to be the only one incapable of doing so. Because... you are too pompous to learn.

 

[tornitore45]

1 - The chip that came whith the tool.

The picture shows flute that look like were machined with an hatchet.
What could possibly be additionally wrong with that tool.

 

[TonyM]

Tornitore is absolutely right. It's common practice to double drill for a better sized finished hole and certainly 1mm is not too little to remove for a finishing cut.
That drill has the cutting edge and the rest of the surface removed exactly as if the material being cut was harder than the drill. It is not burnt which indicates to me that the drill is not hard and I would hazzard a guess is not even HSS.

 

[Richard Carlstedt]

Late to the party, but I have seen similar drill damage to the flutes when the drill
was accidentally run in reverse.
Enlarging holes with minimal increases is common in industry, but feed rate
becomes more critical as the drill wants to pull due to the helix angle
Rich

 

[Luiz Fernando Pinto]

Late to the party, but I have seen similar drill damage to the flutes when the drill
was accidentally run in reverse.

It was not reverse mode, i never use this way.