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Posted by BottleBob on August 28, 2008, 3:19 pm
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To All:
This is from a post I made some years ago it amc. I thought the
readers in here might enjoy a break from all the political trash
talking. <g>
Now let me just add that before my test I was of the opinion that
centerdrilling was more accurate than spotdrilling.
==================================================================
I did a little test today on my day off. In a piece of 6061 I
center drilled 4 holes with a .125 piloted center drill .1 deep at 2000
rpm and 5 IPM. Then I spot drilled another row of 4 holes .125 deep at
2000 rpm and 5 IPM. I then peck drilled eight .234 dia. holes 1" deep
at 5000 rpm and 40 IPM. As a side test I peck drilled 4 more holes
with a #1 (.228) cobalt 135 degree split point stub drill without
spotting or center drilling at 6000 rpm and 60 IPM. I then took a
tenth indicator and checked each hole for location going the exact same
amount into each hole. The holes checked as follows:
First row of center drilled holes.
X Y
#1 +.0003 0
#2 +.001 -.0001
#3 -.0007 -.0002
#4 +.0003 +.0005
Largest amount out = .001 Average amount out = .00039
Second row of spot drilled holes.
X Y
#1 -.0012 0
#2 -.0002 -.0002
#3 -.0005 -.0006
#4 +.0002 -.0002
Largest amount out = .0012 Average amount out = .00039
Third row of hole made with NO spotting or centerdrilling.
X Y
#1 -.0011 +.0002
#2 -.001 -.0006
#3 -.0005 +.0004
#4 -.0007 -.0007
Largest amount out = .0011 Average amount out = .00065
Now 4 holes each may not be statistically significant but to
me this little test leads me to believe that the difference between using
centerdrills and spot drills is so minimal as to be non existent. So
much for my "centerdrills are better than spot drills theory" but
conversely, anyone claiming that spot drills are clearly superior to
centerdrills for hole location would have to show me some hard evidence
and not just rhetoric. I WILL say that as a result of this little test
I'll be using spot drills much more often if only because of the
chamfering now that I know they don't significantly throw off the
location. I'll also be plowing into material without centerdrilling OR
spot drilling more often as well.
==================================================================
--
BottleBob
http://home.earthlink.net/~bottlbob
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Posted by F. George McDuffee on August 28, 2008, 4:14 pm
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On Thu, 28 Aug 2008 12:19:58 -0700, BottleBob
>To All:
>
> This is from a post I made some years ago it amc. I thought the
>readers in here might enjoy a break from all the political trash
>talking. <g>
>
> Now let me just add that before my test I was of the opinion that
>centerdrilling was more accurate than spotdrilling.
>
>==================================================================
> I did a little test today on my day off. In a piece of 6061 I
>center drilled 4 holes with a .125 piloted center drill .1 deep at 2000
>rpm and 5 IPM. Then I spot drilled another row of 4 holes .125 deep at
>2000 rpm and 5 IPM. I then peck drilled eight .234 dia. holes 1" deep
>at 5000 rpm and 40 IPM. As a side test I peck drilled 4 more holes
>with a #1 (.228) cobalt 135 degree split point stub drill without
>spotting or center drilling at 6000 rpm and 60 IPM. I then took a
>tenth indicator and checked each hole for location going the exact same
>amount into each hole. The holes checked as follows:
>
>
>First row of center drilled holes.
>
> X Y
>#1 +.0003 0
>#2 +.001 -.0001
>#3 -.0007 -.0002
>#4 +.0003 +.0005
>
>
> Largest amount out = .001 Average amount out = .00039
>
>
>Second row of spot drilled holes.
>
> X Y
>#1 -.0012 0
>#2 -.0002 -.0002
>#3 -.0005 -.0006
>#4 +.0002 -.0002
>
>
> Largest amount out = .0012 Average amount out = .00039
>
>
>Third row of hole made with NO spotting or centerdrilling.
>
> X Y
>#1 -.0011 +.0002
>#2 -.001 -.0006
>#3 -.0005 +.0004
>#4 -.0007 -.0007
>
>
> Largest amount out = .0011 Average amount out = .00065
>
>
> Now 4 holes each may not be statistically significant but to
>me this little test leads me to believe that the difference between using
>centerdrills and spot drills is so minimal as to be non existent. So
>much for my "centerdrills are better than spot drills theory" but
>conversely, anyone claiming that spot drills are clearly superior to
>centerdrills for hole location would have to show me some hard evidence
>and not just rhetoric. I WILL say that as a result of this little test
>I'll be using spot drills much more often if only because of the
>chamfering now that I know they don't significantly throw off the
>location. I'll also be plowing into material without centerdrilling OR
>spot drilling more often as well.
>==================================================================
Thanks for sharing some hard data.
Another myth from the dawn of machining bites the dust. Was the
drill a "standard" split point or one of the self-centering
grinds such as a Bickford or Peugeot? What machine tool did you
use?
Do you intend to eliminate the spot/center drill and tool change
from any of your cnc programs? If so, what is your guesstimate
of cycle time saved?
Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).
|
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Posted by BottleBob on August 28, 2008, 5:33 pm
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F. George McDuffee wrote:
> On Thu, 28 Aug 2008 12:19:58 -0700, BottleBob
>> ==================================================================
>> I did a little test today on my day off. In a piece of 6061 I
>> center drilled 4 holes with a .125 piloted center drill .1 deep at 2000
>> rpm and 5 IPM. Then I spot drilled another row of 4 holes .125 deep at
>> 2000 rpm and 5 IPM. I then peck drilled eight .234 dia. holes 1" deep
>> at 5000 rpm and 40 IPM. As a side test I peck drilled 4 more holes
>> with a #1 (.228) cobalt 135 degree split point stub drill without
>> spotting or center drilling at 6000 rpm and 60 IPM. I then took a
>> tenth indicator and checked each hole for location going the exact same
>> amount into each hole. The holes checked as follows:
>>
>>
>> First row of center drilled holes.
>>
>> X Y
>> #1 +.0003 0
>> #2 +.001 -.0001
>> #3 -.0007 -.0002
>> #4 +.0003 +.0005
>>
>>
>> Largest amount out = .001 Average amount out = .00039
>>
>>
>> Second row of spot drilled holes.
>>
>> X Y
>> #1 -.0012 0
>> #2 -.0002 -.0002
>> #3 -.0005 -.0006
>> #4 +.0002 -.0002
>>
>>
>> Largest amount out = .0012 Average amount out = .00039
>>
>>
>> Third row of hole made with NO spotting or centerdrilling.
>>
>> X Y
>> #1 -.0011 +.0002
>> #2 -.001 -.0006
>> #3 -.0005 +.0004
>> #4 -.0007 -.0007
>>
>>
>> Largest amount out = .0011 Average amount out = .00065
>>
>>
>> Now 4 holes each may not be statistically significant but to
>> me this little test leads me to believe that the difference between using
>> centerdrills and spot drills is so minimal as to be non existent. So
>> much for my "centerdrills are better than spot drills theory" but
>> conversely, anyone claiming that spot drills are clearly superior to
>> centerdrills for hole location would have to show me some hard evidence
>> and not just rhetoric. I WILL say that as a result of this little test
>> I'll be using spot drills much more often if only because of the
>> chamfering now that I know they don't significantly throw off the
>> location. I'll also be plowing into material without centerdrilling OR
>> spot drilling more often as well.
>> ==================================================================
> Thanks for sharing some hard data.
>
> Another myth from the dawn of machining bites the dust. Was the
> drill a "standard" split point or one of the self-centering
> grinds such as a Bickford or Peugeot?
Unka George:
For those who may not be aware of the different drill points. Example
of Bickford point below, see figure 8. BTW, that's essentially the
type of point our Darex drill sharpener puts on drills.
http://www.mmsonline.com/articles/widening-interest-in-twist-drills.aspx
Example of Peugeot point below:
http://www.newmantools.com/machines/drillpoint.html
Example of the type of split point on our 135 degree stub length
cobalt drills, see Figure 4.8 below:
http://tinyurl.com/5pdcl2
> What machine tool did you
> use?
Fadal 40X20.
> Do you intend to eliminate the spot/center drill and tool change
> from any of your cnc programs?
If the drilled hole is simply a short clearance hole that doesn't need
to be chamfered (because it will later be counterbored or countersunk,
etc.) then I tend to eliminate a spot dilling operation.
If the hole is going to be reamed for a dowel pin, then I spot drill
as a matter of course, since a straight a hole is necessary. BUT, if
I'll be end mill boring the hole I don't bother with the spot drill.
If I need a chamfered hole, then of course I'll include a spot dilling
operation.
> If so, what is your guesstimate
> of cycle time saved?
The chip to chip tool change time can vary greatly from machine to
machine. Of course the cycle time saving can be significant for
multiple parts or multiple holes.
--
BottleBob
http://home.earthlink.net/~bottlbob
|
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Posted by F. George McDuffee on August 28, 2008, 5:51 pm
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On Thu, 28 Aug 2008 14:33:07 -0700, BottleBob
>Unka George:
>
> For those who may not be aware of the different drill points. Example
>of Bickford point below, see figure 8. BTW, that's essentially the
>type of point our Darex drill sharpener puts on drills.
<snip>
>
> > If so, what is your guesstimate
> > of cycle time saved?
>
> The chip to chip tool change time can vary greatly from machine to
>machine. Of course the cycle time saving can be significant for
>multiple parts or multiple holes.
========
Again, thanks for the references and hard data.
Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).
|
|
Posted by F. George McDuffee on August 28, 2008, 5:57 pm
Please log in for more thread options
On Thu, 28 Aug 2008 14:33:07 -0700, BottleBob
>Unka George:
>
> For those who may not be aware of the different drill points. Example
>of Bickford point below, see figure 8. BTW, that's essentially the
>type of point our Darex drill sharpener puts on drills.
<snip>
>
> > If so, what is your guesstimate
> > of cycle time saved?
>
> The chip to chip tool change time can vary greatly from machine to
>machine. Of course the cycle time saving can be significant for
>multiple parts or multiple holes.
========
Again, thanks for the references and hard data.
Time for a survey. How many of the group's money players
routinely skip the spot/center drill step with today's rigid CNC
machines?
What else are we doing that is a carryover from the overhead
shaft babbitt bearing machines in the blacksmith's shop?
Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).
|
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>
> This is from a post I made some years ago it amc. I thought the
>readers in here might enjoy a break from all the political trash
>talking. <g>
>
> Now let me just add that before my test I was of the opinion that
>centerdrilling was more accurate than spotdrilling.
>
>==================================================================
> I did a little test today on my day off. In a piece of 6061 I
>center drilled 4 holes with a .125 piloted center drill .1 deep at 2000
>rpm and 5 IPM. Then I spot drilled another row of 4 holes .125 deep at
>2000 rpm and 5 IPM. I then peck drilled eight .234 dia. holes 1" deep
>at 5000 rpm and 40 IPM. As a side test I peck drilled 4 more holes
>with a #1 (.228) cobalt 135 degree split point stub drill without
>spotting or center drilling at 6000 rpm and 60 IPM. I then took a
>tenth indicator and checked each hole for location going the exact same
>amount into each hole. The holes checked as follows:
>
>
>First row of center drilled holes.
>
> X Y
>#1 +.0003 0
>#2 +.001 -.0001
>#3 -.0007 -.0002
>#4 +.0003 +.0005
>
>
> Largest amount out = .001 Average amount out = .00039
>
>
>Second row of spot drilled holes.
>
> X Y
>#1 -.0012 0
>#2 -.0002 -.0002
>#3 -.0005 -.0006
>#4 +.0002 -.0002
>
>
> Largest amount out = .0012 Average amount out = .00039
>
>
>Third row of hole made with NO spotting or centerdrilling.
>
> X Y
>#1 -.0011 +.0002
>#2 -.001 -.0006
>#3 -.0005 +.0004
>#4 -.0007 -.0007
>
>
> Largest amount out = .0011 Average amount out = .00065
>
>
> Now 4 holes each may not be statistically significant but to
>me this little test leads me to believe that the difference between using
>centerdrills and spot drills is so minimal as to be non existent. So
>much for my "centerdrills are better than spot drills theory" but
>conversely, anyone claiming that spot drills are clearly superior to
>centerdrills for hole location would have to show me some hard evidence
>and not just rhetoric. I WILL say that as a result of this little test
>I'll be using spot drills much more often if only because of the
>chamfering now that I know they don't significantly throw off the
>location. I'll also be plowing into material without centerdrilling OR
>spot drilling more often as well.
>==================================================================