Re: [bolger] RE:Back to lexan
Been out of town. When you look at the point of the bit, straight down, you
will note that, one, it is not a point, two, that the "line in the middle is at
a slight angle towards the left. Sharpen the bit so that the line is straight
(zero rake) or slightly angled to the right (neg rake)
Catching up on my email I notice there has been another plywood discussion.
For info of those of you who live where there are Menard's, I noticed last week
that they had plywood label Luann or maranti. What was most likely the Luann
was the normal stuff, but what was probably the maranti had many more plys
and looked exactly like the maranti I bought from Noah's. They only had this in
3/8" and 3/4" however, no 1/2", and the 1/4" was the same 3 ply as always.
The 3/8" was on sale for $20.49 a sheet.
I sharpen drill bits by hand all the time but I don't know what you
mean by negative rake. Is it possible to describe it? Thanks.
Mike
[Non-text portions of this message have been removed]
will note that, one, it is not a point, two, that the "line in the middle is at
a slight angle towards the left. Sharpen the bit so that the line is straight
(zero rake) or slightly angled to the right (neg rake)
Catching up on my email I notice there has been another plywood discussion.
For info of those of you who live where there are Menard's, I noticed last week
that they had plywood label Luann or maranti. What was most likely the Luann
was the normal stuff, but what was probably the maranti had many more plys
and looked exactly like the maranti I bought from Noah's. They only had this in
3/8" and 3/4" however, no 1/2", and the 1/4" was the same 3 ply as always.
The 3/8" was on sale for $20.49 a sheet.
I sharpen drill bits by hand all the time but I don't know what you
mean by negative rake. Is it possible to describe it? Thanks.
Mike
[Non-text portions of this message have been removed]
I figured you'd have your answer by now, but since I didn't see it, ...
Positive rake is what's normally put on a drill bit. It forms a wedge in
the material which causes splitting just in front of the edge. In brittle
materials this leaves microscopic cracks which will grow in time.
Zero rake or negative rake "cut" by scraping; i.e. the cutting edge meets
the material at 90 degrees or more.
Keep the speed down so that there's no adhesion between the bit and the
material.
One of GE's master machinists showed me once that he "blunted" the edge of
all his drills, but he had massive drilling machines to apply the added
pressure needed.
Roger
derbyrm@...
http://derbyrm.mystarband.net/default.htm
Positive rake is what's normally put on a drill bit. It forms a wedge in
the material which causes splitting just in front of the edge. In brittle
materials this leaves microscopic cracks which will grow in time.
Zero rake or negative rake "cut" by scraping; i.e. the cutting edge meets
the material at 90 degrees or more.
Keep the speed down so that there's no adhesion between the bit and the
material.
One of GE's master machinists showed me once that he "blunted" the edge of
all his drills, but he had massive drilling machines to apply the added
pressure needed.
Roger
derbyrm@...
http://derbyrm.mystarband.net/default.htm
----- Original Message -----
From: "kakwariver" <kakwariver@...>
> -- Inbolger@yahoogroups.com, RKAMILS@a... wrote:
>> There is nothing special about bits for plastic except that they
>> have what is called a negative rake. Anyone who has a grinder
>> and has learned how to re-sharpen their drill bits can do this.
>> You are also better off drilling non-Ferris metals such as brass,
>> bronze, etc., with bits sharpened with a negative
>> rake. Positive rake bits tend to catch as they come out the
>> backside. With a hand electric drill this can cause the drill
>> to give such a wicked twist that you can injure your wrist.
>> Bob
> I sharpen drill bits by hand all the time but I don't know what you
> mean by negative rake. Is it possible to describe it? Thanks.
> Mike
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-- Inbolger@yahoogroups.com, RKAMILS@a... wrote:
mean by negative rake. Is it possible to describe it? Thanks.
Mike
> There is nothing special about bits for plastic except that theyhave what is
> called a negative rake. Anyone who has a grinder and has learned howto
> re-sharpen their drill bits can do this. You are also better offdrilling
> non-Ferris metals such as brass, bronze, etc., with bits sharpenedwith a negative
> rake. Positive rake bits tend to catch as they come out thebackside. With a hand
> electric drill this can cause the drill to give such a wicked twistthat you
> can injure your wrist.I sharpen drill bits by hand all the time but I don't know what you
> Bob
mean by negative rake. Is it possible to describe it? Thanks.
Mike