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

On Thu, 28 Aug 2008 12:19:58 -0700, BottleBob
wrote:

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).

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/wi...st-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

On Thu, 28 Aug 2008 14:33:07 -0700, BottleBob
wrote:

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).

On Thu, 28 Aug 2008 14:33:07 -0700, BottleBob
wrote:

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).

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?

When "the kid" was laid off we took lathe jobs for money. 1000s of parts and
less than $2 a part. We went to stub length drill no spot or center drill
and went right to size. The Hardinge CHNC held less than .001 diameter
tolerance as long as we re-sharpened the drill every 500 or so parts. Had to
use a Darex M5 grinder for resharpening.

Karl

"BottleBob" wrote in message
m...
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.
================================================== ================


Bravo! Excellent post. I guess it truly is time to recycle posts!

A sample of 4 IS statistically significant. A sample of 3 is still
significant. Samples beyond 8 in tests like these offer little statistical
advantage over samples of 5.

But your speriment would suggest to *never* center or spot drill, if using
stub drills #1 or bigger!
60 ipm?? goodgawd.... That's like hammering in a nail!

The big problem with center drills is that goddamm pilot breaks off readily
in alloy steels like 4140. Very readily.

The advantage with c-drills is that if you need a 60 deg chamfer, it's right
there.
It would probably be perty useful to have sets of spotting drills of
numerous chamfer angles, from 60 deg, to 120 deg, as my set kluged c-sinks.

Another speriment would be to vary the speed of entry of stub drills, to see
how that affects hole accuracy.
There was a thread on that in amc (by yours truly), but with no real
consensus, iirc. I do remember Gary Lucas essentially saying eff slow and
careful, just bury dat em effer right in--which is what you did at 60 ipm.

Bottle, you shoulda been a puhfessuh.... perhaps in chemistry.
--
DT










--
BottleBob
http://home.earthlink.net/~bottlbob

DrollTroll wrote:
"BottleBob" wrote in message

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.
================================================== ================


Bravo! Excellent post.

DT:

Why thank you.

I guess it truly is time to recycle posts!

I don't really consider this recycling, since this is a different
newsgroup and I didn't add in amc.


A sample of 4 IS statistically significant. A sample of 3 is still
significant. Samples beyond 8 in tests like these offer little statistical
advantage over samples of 5.

But your speriment would suggest to *never* center or spot drill, if using
stub drills #1 or bigger!

Sometimes you need a chamfer on the hole edge.

60 ipm?? goodgawd.... That's like hammering in a nail!

Truthfully, I don't normally use such a high feed for drilling, but I
intentionally used that feed to simulate the worst possible condition
to see the results. That way when I used a lower feed the drill would
tend to deflect less and be more centered. Or so went my hypothesis at
the time.


The big problem with center drills is that goddamm pilot breaks off readily
in alloy steels like 4140. Very readily.

One way to get around that is to center drill ONLY with the pilot, and
use a pilot over half the drill dia.


The advantage with c-drills is that if you need a 60 deg chamfer, it's right
there.
It would probably be perty useful to have sets of spotting drills of
numerous chamfer angles, from 60 deg, to 120 deg, as my set kluged c-sinks.

Another speriment would be to vary the speed of entry of stub drills, to see
how that affects hole accuracy.
There was a thread on that in amc (by yours truly), but with no real
consensus, iirc. I do remember Gary Lucas essentially saying eff slow and
careful, just bury dat em effer right in--which is what you did at 60 ipm.

Bottle, you shoulda been a puhfessuh.... perhaps in chemistry.

An inside joke that only a handful would get, eh? LOL

--
BottleBob
http://home.earthlink.net/~bottlbob

DrollTroll wrote:
"BottleBob" wrote in message
m...

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.
================================================== ================



Bravo! Excellent post. I guess it truly is time to recycle posts!

A sample of 4 IS statistically significant. A sample of 3 is still
significant. Samples beyond 8 in tests like these offer little statistical
advantage over samples of 5.

But your speriment would suggest to *never* center or spot drill, if using
stub drills #1 or bigger!
60 ipm?? goodgawd.... That's like hammering in a nail!

The big problem with center drills is that goddamm pilot breaks off readily
in alloy steels like 4140. Very readily.

I'm not a professional machinist but do machine various stainless alloys
and En24 (4340) regularly and have only had problems with centre drills
breaking easily when I bought a few cheap ones. Now I know it's not
worth it and buy good quality ones and don't have a problem. I do use
spotting drills also in place of centre drills, mostly on the mill, or
stub drills where appropriate and cost effective.

The advantage with c-drills is that if you need a 60 deg chamfer, it's right
there.
It would probably be perty useful to have sets of spotting drills of
numerous chamfer angles, from 60 deg, to 120 deg, as my set kluged c-sinks.

Another speriment would be to vary the speed of entry of stub drills, to see
how that affects hole accuracy.
There was a thread on that in amc (by yours truly), but with no real
consensus, iirc. I do remember Gary Lucas essentially saying eff slow and
careful, just bury dat em effer right in--which is what you did at 60 ipm.

Bottle, you shoulda been a puhfessuh.... perhaps in chemistry.

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?


I almost always do NOT spot or center for a hole IF I can use a short enough
drill and there is not reason to be concerned about a couple thou run-out.
Clearance hole, holes that will be bored or milled out, etc.

By short enough, I mean about 5-6x diameter of flute length.

I do tend to not use center drills on a mill, but use spotters...much more
robust and able to take more of a beating. I hate trying to dig out the tip
of a drill from a piece of customer owned stock.

Mike

On Thu, 28 Aug 2008 16:57:25 -0500, F. George McDuffee
wrote:

On Thu, 28 Aug 2008 14:33:07 -0700, BottleBob
wrote:

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).
I almost never use center drills, but instead use split point drills
if I don't want or need a small edge break. Hole location is very
good. I do center drill when cross drilling round stock. Often when
the hole is to be form tapped I will use a center drill in order to
have a broken edge after the hole is tapped.
Eric

Please do tell us how exactly you compensated for the indexing error
in your X/Y spindle position to claim base accuracy to a couple 10's
in your hole positions.....
JR
Dweller in the cellar

On Thu, 28 Aug 2008 12:19:58 -0700, BottleBob
wrote:

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.
================================================= =================

On Thu, 28 Aug 2008 19:02:29 -0400, "DrollTroll"
wrote:
snip
The advantage with c-drills is that if you need a 60 deg chamfer, it's right
there.
It would probably be perty useful to have sets of spotting drills of
numerous chamfer angles, from 60 deg, to 120 deg, as my set kluged c-sinks.
snip
FWIW
see http://www.use-enco.com/CGI/INPDFF?P...PARTPG=INLMK32


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).

JR North wrote:
Please do tell us how exactly you compensated for the indexing error
in your X/Y spindle position to claim base accuracy to a couple 10's
in your hole positions.....

JR North:

That's an honest question. First, this was done on Fadal 40X20 CNC.
The table positioning accuracy is listed as being .0002, and the
positioning repeatability is listed as being .0001, see below for
specifications:

http://tinyurl.com/6qyog5

Now Fadals have an M46 code that is called "Positive Approach".

================================================== ======================
M46 Positive Approach:

This code causes the machine to move the X and Y axes in a negative,
then positive, direction before the execution of a fixed cycle
(G73-G89). The X and Y axis move .015 in the negative direction at 25
inches per minute, then move .015 in the positive direction at 3 inches
per minute. This returns the machine back to the original location and
then the fixed cycle will execute.
================================================== ======================

What this feature is designed to do, is essentially remove the
influence of any backlash in the ballscrew axis drives. Although,
there is usually very little backlash in a ballscrew system, and any
that there may be is compensated for in the control. The backlash
correction amount is input in the control after doing a backlash
adjustment (which should be done every year or so depending on how
heavily the machine is used). Any backlash on an axis can be easily
checked by positioning your tenth indicator against an object and
moving the axis back and forth with the handwheel, the machine
compensates for backlash almost immediately.

Anyway, I virtually always use positive approach in all my
drilling/boring cycles.

The hole drilling and checking in my little test should fall within
the positioning repeatability range. Could I have been off by a tenth
or so? Perhaps.


--
BottleBob
http://home.earthlink.net/~bottlbob