dull drill bit or really hard aluminum?

[BTL-A4]

I was drilling a 1/4" hole into what I think is 6061 aluminum plate (1/8" thick) with a standard drill bit using a little 3 in 1 oil for lube/coolant and got an entry hole that looked as shown on the left and an exit hole that looks as shown on the right.

What caused this? Dull bit? It was very hard to pull the drill press handle while drilling. Could the aluminum be really hard? Not actually sure what type it is; this was a scrap piece.

There was wood under the piece I was drilling and this smoked and burned.

 

[Robby321]

Junk bit...6061 aint tough..

 

[Old Man Roger]

My guess is a dull bit, but I guess if the drill press has multiple speeds, you may have it set too fast and clogged the bit.

 

[rlitman]

My guess is a dull bit, but I guess if the drill press has multiple speeds, you may have it set too fast and clogged the bit.

Agreed. Look at the cutting surfaces, and see if there's aluminum built up on it. You may be able to pop it off with a scribe.

 

[MoonRise]

Ah, you discovered the friction-heated thermally induced forging process.

AKA, a dull drill bit. Which instead of actually drilling the aluminum, heated it up and thus softened it and then you 'mooshed' it into a hole shaped hole while pushing some of the hot softened aluminum out the back of the aluminum sheet/plate.

Or you had the bit spinning 'backwards', although on most drill presses that is not all that easy to do, so maybe you had a left-hand drill bit spinning 'forward' in the drill press, and then it did the get-hot-and-mush-the-aluminum event.

 

[nbpt100]

Ah, you discovered the friction-heated thermally induced forging process.

AKA, a dull drill bit. Which instead of actually drilling the aluminum, heated it up and thus softened it and then you 'mooshed' it into a hole shaped hole while pushing some of the hot softened aluminum out the back of the aluminum sheet/plate.

Or you had the bit spinning 'backwards', although on most drill presses that is not all that easy to do, so maybe you had a left-hand drill bit spinning 'forward' in the drill press, and then it did the get-hot-and-mush-the-aluminum event.

I know someone who will run the bit backwards to drill holes in plastics.

He claims it works better. I never did but i did see him do it and it worked.

 

[larry_g]

That would be a cockpit error...

I'd suggest that you study up a bit here; http://neme-s.org/2005 May Meeting/drills.pdf

lg
no neat sig line

 

[jeepinerdeep]

One more vote for super dull.

You pretty much just forced a piece of round bar through the work piece.

 

[OccupantRJ]

Hint: when you are attempting to drill a hole and hear squealing noises and see no chips, you are not drilling, just rubbing. The bright side is that you are learning valuable information in your endeavor that could help you later in some way.

 

[Robby321]

I know someone who will run the bit backwards to drill holes in plastics.

He claims it works better. I never did but i did see him do it and it worked.

Not the way. Ya DULL the cutting edge with a carbide stone to a flat, and go slow so don't crack

 

[Lwel9226]

I'd suggest that you study up a bit here; http://neme-s.org/2005 May Meeting/drills.pdf

lg
no neat sig line

Someone should make a sticky out of this information...

THANK YOU . . . .
Lynn W

 

[bugnut]

definitely dull, probably running to slow should have been turning about 3000 rpm

 

[jmarkwolf]

Moonrise has got it right.

 

[Bretny]

Did you hve the same spindle speed as if you where drilling steel? You should be running the drill faster than if it was steel.

 

[BTL-A4]

Ah, you discovered the friction-heated thermally induced forging process.

AKA, a dull drill bit. Which instead of actually drilling the aluminum, heated it up and thus softened it and then you 'mooshed' it into a hole shaped hole while pushing some of the hot softened aluminum out the back of the aluminum sheet/plate.

Or you had the bit spinning 'backwards', although on most drill presses that is not all that easy to do, so maybe you had a left-hand drill bit spinning 'forward' in the drill press, and then it did the get-hot-and-mush-the-aluminum event.

This is my new favorite process!

 

[BTL-A4]

It was a right-hand drill going forward.

According to my chart, the RPM is supposed to be 6,112. Here's the math: cutting speed x 3.82/dia of bit=RPM. So 400 (cutting speed of aluminum with HSS) x 3.82/.25=6,112. I set it for less, about 4,000 RP, which seemed high to me. I have chart on my drill press that indicated a speed of about 4,000 so that's what I used.

I'm pretty sure the bit was dull. I use a 1/4" drill quite a bit, so that's shouldn't be a surprise. I just didn't think to look at it before I chucked it up.

The bit had aluminum on it that I picked off with a blade. I'll try and remember to post a picture.

 

[BTL-A4]

Hint: when you are attempting to drill a hole and hear squealing noises and see no chips, you are not drilling, just rubbing. The bright side is that you are learning valuable information in your endeavor that could help you later in some way.

Yes, I should have stopped when all I saw was smoke and it was really hard to press the drill into the material. I thought maybe the aluminum was just really hard. Lesson learned!

 

[OccupantRJ]

Hint: as a reference, a step pulley Bridgeport mill spindle does not even go above 2,720 rpm. 600- 800 rpm would have drilled that hole just fine with a properly sharpened bit. Wd40 works well as a machining fluid on aluminum. I also don’t like gathering up chips slung halfway across the shop using higher speeds.

 

[danielbuck]

1/4" drill through 1/8" aluminum should just punch right through. definitely a dull bit.

I'll second using Wd40 for drilling aluminum, but for a few holes through 1/8" thick material I probably wouldn't even bother with any oil.

 

[bullnerd]

Yes, pics please.

This thing has to be pretty dull! Did you drill concrete with just before the aluminum? lol!

I've seen it done in a shop I worked at in an electronics company.

BTW, if all your drill bits are dull, the drill dr works great with a little practice.