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Metal Drill Bits


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#1 e~shot

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Posted 21 June 2013 - 11:08 PM


I'm very new to this subject, trying to learn new things with my drill press :)

 

Hrawk as given me very good suggestions on countersink, center drill bits etc... so, I searched for it, found these useful videos.

 

Metal drill types

 

 

Center Drill

 

Twist Drilling

 

Countersinking & Chamfering a Hole

 

Reaming

 

Counter-boring a Hole

 

Spotfacing

 

Tapping

 

 

 

 

 

 



#2 ash

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Posted 22 June 2013 - 01:01 AM

I have a few issues with the info in the first video.

 

  • The standard twist drill bits he's showing work fine or wood, metal or plastic. Like any knife, sharpening is part of the game, so there's no need to have different bits for each material in most cases
  • "Titanium" drill bits aren't made of titanium, they're made of high speed steel with a coating of titanium-nitride. Once that wears off the cutting edges it's no better than a normal HSS bit.
  • It's not just the tip that does the cutting, its the conical edges that go from the middle to the outside of the drill bit. If there is vibration or you're unsteady, the spiral edges will cut, making your hole oversized, not exactly round or not in the same place you started it.
  • "Cobalt" drill bits are not made of cobalt, it's just high speed steel with a higher than normal cobalt content with allows them to hold their edge under heavy loads, high temperatures and therefore survive drilling very hard materials.
  • The blue-tipped bits he showed are for masonry, not metal or wood.

 

Centre-drills are indeed awesome. They are very rigid and increase your chances of starting your holes where you need them. Beware of two things - being so rigid, the small tip can break off unexpectedly if you drop them or push them too hard. We broke a lot of them in high school! Secondly, don't go deeper than the conical section. They are just for starting off your holes, not for going right through. Normal long drill bits are flexible and not really self-guiding. Wood is not very consistent, so it will let the drill bit wander its way through if the opportunity arises.

 

Brad point drill bits are the best for wood, but not suitable for metal. Self-starting and self-guiding. No always easy to find. Standard conical tip bits can be reground to brad point if you know what you're doing.

 

Hole saws and Forstner bits can be used to rough shape a slingshot frame if you don't have a bandsaw/scrollsaw/jigsaw. I'll demonstrate another time.

 

More thoughts later.


Edited by ash, 22 June 2013 - 01:48 AM.


#3 e~shot

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Posted 22 June 2013 - 01:20 AM

Thanks for clearing up Ash.



#4 ash

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Posted 22 June 2013 - 01:28 AM

Third video - perfect.

 

A centre-punch hasn't been mentioned yet, but is important, especially when drilling metal by hand. The tip of a drill bit isn't pointed, it has a tiny flat spot left behind in sharpening. This can cause the bit to skate over the surface when you're trying to start your hole. The answer is to centre-punch your spot so that the flat tip of the bit can locate itself in the dimple and stay there. On metal, you need a proper hard punch that can take a hammer hit like this:

 

 

centre_punch.jpg

 

On wood, the same punch will work, but i prefer to use an awl and press it in by hand:

 

301-6060-lg.jpg

 

Soft plastics can benefit from either of the above. On hard plastics the metal punch could crack the plastic and the awl might not go in far enough, but starting with a small drill or centre-drill should be pretty easy without a punch mark.

 

~ Centre punches are really a lathe tool, but they can make life easier for drill press or hand drill users. The reason the short, rigid centre drill is so important on a lathe is that you can't centre-punch the exact spot, so you go with the super rigid bit that can't be flexed and pushed off-centre by the tiny bumps and ridges in the work piece. You just need it to "spot-drill" as in Video 3.

 

~ Then you can go with a small pilot drill - I usually use 3mm or 1/8" - followed by your final size.

 

~ If you're drilling bigger than 3/8" or 10mm, the flat tip may be bigger than your pilot hole, so an intermediate hole half-way between your pilot and final sizes would be a good idea.

 

~ Don't forget to peck-drill as per Video 3. This is the key to clean holes.

 

~ If you're drilling right through your piece, have it pressed flat against another sacrificial piece of wood, which you can drill right into. This will help avoid the underside of your workpiece from chipping out.

 

NB, these tips are with regard to normal conical tip twist drills. Brad point drill bits and Forstner bits don't need pilot holes in most cases.


Edited by ash, 22 June 2013 - 01:46 AM.


#5 ash

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Posted 22 June 2013 - 01:43 AM

Two thumbs up for the second guy's videos. 

 

Extra for experts: http://en.wikipedia.org/wiki/Drill_bit

 

Here's a brad point (aka spur point) bit for wood or soft plastic: 

 

endgrain.jpg

 

Here's a Forstner bit, best for flat-bottomed, large diameter holes in wood and soft plastic The toothed ones seem best, but plain ones are ok. Run them slowly.

 

Forstnerbit600px_1_7.jpg



#6 e~shot

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Posted 22 June 2013 - 02:04 AM

Two thumbs up for the second guy's videos. 

 

Extra for experts: http://en.wikipedia.org/wiki/Drill_bit

 

Here's a brad point (aka spur point) bit for wood or soft plastic: 

 

endgrain.jpg

 

Here's a Forstner bit, best for flat-bottomed, large diameter holes in wood and soft plastic The toothed ones seem best, but plain ones are ok. Run them slowly.

 

 

Yes... locally it is bit expensive but already got a good deal on ebay,



#7 e~shot

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Posted 02 July 2013 - 07:31 PM

This site looks interesting



#8 e~shot

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Posted 14 July 2013 - 07:15 PM

51010.jpg

 

Bolt extractor

 

 



#9 Imperial

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Posted 15 July 2013 - 12:44 AM

 

Hole saws and Forstner bits can be used to rough shape a slingshot frame if you don't have a bandsaw/scrollsaw/jigsaw. I'll demonstrate another time.

 

 

ive done that in the past.  hole saws are a lil costly though. 



#10 Dr J

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Posted 15 July 2013 - 08:57 PM

I have found that if a bit of tape is placed on the underside of the hole being drilled, it prevents blowouts.




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