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Posted by Trevor Jones on April 14, 2008, 9:04 am
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Dave99 wrote:
> wrote:
>
>
>>If you're saying what I think you might be saying, the angle is called
>>"lip angle". If you set the bit down on its cutting edge, it's the
>>clearance angle from the cutting edge to the back of the edge, right?
>
>
> Right... I did some searching and I've now seen it referred to as
> "Drill Lip Relief Angle". So 'Relief Angle', 'Lip Angle'... I guess
> all the same thing, right? All I know is that all the ones I've tried
> with a sharp angle there don't do what I want, and the couple I have
> that have the very modest angle do... So that must be the difference.
>
> Dave
Not really all the same thing.
The angle you see when you hold the drill, at the tip, from one lip to
the other, is the lip angle. The amount of drop behind the cutting edge
when it is cutting, is the relief angle,or clearance, and the angle on
the front of the cutting edge, in relation to the material, is the rake
angle.
All three can be modified to some extent to improve (or not) a drills
cutting characteristics.
If you can find an Industrial Arts textbook there is a better than
decent chance that the various angles are explained, with a decent diagram.
For average use, 59 degrees per side (118 degrees included angle) has
been settled on as the "best", but depending on the material, anywhere
from 30 degrees per side to 70 per side are around.
The relief or clearance, controls the maximum amount of material that
the drill can cut in a revolution, and the rake is adjusted to adjust
for the material, as much as it can be, whithin the limits of the helix
angle of the bit.
Some of the older Popular Mechanics Shop books had some really usefull
diagrams for drills, among other usefull info.
Cheers
Trevor Jones
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Posted by Larry Jaques on April 14, 2008, 9:26 am
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On Sun, 13 Apr 2008 21:59:17 -0700 (PDT), with neither quill nor
>wrote:
>
>> If you're saying what I think you might be saying, the angle is called
>> "lip angle". If you set the bit down on its cutting edge, it's the
>> clearance angle from the cutting edge to the back of the edge, right?
>
>Right... I did some searching and I've now seen it referred to as
>"Drill Lip Relief Angle". So 'Relief Angle', 'Lip Angle'... I guess
>all the same thing, right? All I know is that all the ones I've tried
>with a sharp angle there don't do what I want, and the couple I have
>that have the very modest angle do... So that must be the difference.
The higher the angle, the easier they are to chip on tough material.
By Jove, I believe you've got it! Carry on.
--
It is better to wear out than to rust out.
-- Bishop Richard Cumberland
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Posted by Dave99 on April 29, 2008, 2:36 pm
Please log in for more thread options Well, I tried taking some bits to a local shop that claimed they knew
how to do what I wanted... but I got the bits back and all they did
was copy the 118 angle onto the other bits. Would anybody happen to
know of anyone in the Los Angeles area that actually knows what
they're doing when it comes to sharpening? There has to be somebody
out there that knows what a lip angle is.
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