Poignard
Well-Known Member
Exactly! A blunt drill can neither cut nor scrape.
I have drilled acrylic successfully using a masonary drill or a straight-flute drill.
Drilling acrylic
- Thread starter Neeves
- Start date
Exactly! A blunt drill can neither cut nor scrape.
I have drilled acrylic successfully using a masonary drill or a straight-flute drill.
William_H
Well-Known Member
I am not sure how this negative rake works. However looking closely at a drill bit you find that it has 2 inclined plane cutting edges. Just like a wood plane. Now on a wood plane you can have a very fine angle to the wood such that it takes off a small amount of wood off or you can set the blade to an aggressive angled deep cut. Mostly the angle is set something like 30 degrees to give best cut speed. This aggressive cut angle can pull the blade into the wood possibly more than you want such that it gives a rougher finish.
So it is with a drill bit in acrylic that the aggressive cut angle of the 2 cutting edges can pull the bit into the acrylic almost like a wood screw drawing into wood and stressing the wood apart. Acrylic may not take this stress and crack.
The answer is to not blunt the edges of the bit but grind them down so that the angle of attack of the edge to the acrylic is much finer so it is more inclined to cut out the material rather than dig in. (and don't use too much pressure) ol'will Whether it is actually necessary is another question. You may wish to take your chances.
So it is with a drill bit in acrylic that the aggressive cut angle of the 2 cutting edges can pull the bit into the acrylic almost like a wood screw drawing into wood and stressing the wood apart. Acrylic may not take this stress and crack.
The answer is to not blunt the edges of the bit but grind them down so that the angle of attack of the edge to the acrylic is much finer so it is more inclined to cut out the material rather than dig in. (and don't use too much pressure) ol'will Whether it is actually necessary is another question. You may wish to take your chances.
VicS
Well-Known Member
I need to drill some holes (3-5mm) in 5mm acrylic. At the back of my mind is the idea I need to use blunt drill bits - is this correct? If it is correct - what is meant by blunt. I have lots of blunt drill bits- which I would need to sharpen if I was drilling steel - are these sufficiently blunt or do I need to grind some blunt.
I have this idea sharp drill bits cause acrylic to crack.
All of this seems counter intuitive.
Jonathan
I believe some of the advice in this thread regarding the way in which the drill bit should be ground is wrong.
Take a look at this page http://www.plasticsmag.com/features.asp?fIssue=Sep/Oct-01
