I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

Michael Koblic,
Campbell River, BC

On 10/31/2010 04:58 PM, wrote:
I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

It's more that there's really no way to cut the center of the circle --
the best any drill bit or center cut mill can do is sort of mash the
metal out to where it can be cut, and to minimize the amount of material
that has to be so "mashed".

I'm no machinist, so take these with a grain of salt. But here are some
solutions that I can think of:

1: get a more rigid machine to work with. I can do what you're talking
about just fine in aluminum on a Smithy "3 in 1" (lathe, drill, lousy
excuse for mill), but I doubt it'd like me trying in steel.

2: Check your alloy -- are you using one of the absurdly easy-to-cut
alloys like 11L14? Can you?

3: Pre "drill" with a smaller mill, let it walk around, then finish with
a larger mill.

4: Put the part in a rotary table, and come down in the 'z' direction
while rotating the table -- this will keep your cut moving around, and
should make it easier on the machine.

5: I assume you'd be doing this already if you could, but consider
drilling a 1/16" pilot hole, and milling down over that. It'll leave a
hole or a dimple in the middle of your big hole, but even that small of
a pilot hole should span what your mill really can't easily get through.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Sun, 31 Oct 2010 16:58:48 -0700, wrote:

I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

Michael Koblic,
Campbell River, BC

not all center cutting EMs are created equal. I'd try a made in USA
quality two flute.

Tim's suggestion to leave a dimple if you can is a good one.

You need a more rigid machine. Assuming you aren't going right out and
buying one, tightening the gibs etc. helps. You might try a low rpm -
there will be a sweet spot where it won't chatter about so bad.

good luck

karl

In addition to Tim's suggestions, use a quality cutting lubricant, a quality
endmill, and recheck tightness of head-to-column and column-to-base screws.

Forces like those you're encountering can cause the material around the tips
of setscrews to be displaced, effectively allowing them to walk.

If the drill point/web is fed to the desired final depth, the endmill will
then be cutting everything but the center of the hole, until it stops
without using more downward Z force.
Retract the endmill immediately to prevent it from just rubbing, which will
dull a good endmill fairly rapidly.

--
WB
..........


wrote in message
...
I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

Michael Koblic,
Campbell River, BC

wrote in message
...
I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

Michael Koblic,
Campbell River, BC

The tendancy to go around in circles hints that there might be something
slightly asymmetric in the mill. In my minimill, the collets are well
centered on the rotation, but the rotation axis angle is slightly off from
the z-axis, but not enough to cause problems with the coarse stuff I have
done so far. The perpendicularity of the Z-axis to the stage was way off,
but at least that was adjustable.

On Sun, 31 Oct 2010 16:58:48 -0700, mkoblic wrote:

I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

Are you going full depth in one peck?

Thanks,
Rich

"anorton" wrote in message
news snip-
The tendancy to go around in circles hints that there might be something
slightly asymmetric in the mill. In my minimill, the collets are well
centered on the rotation, but the rotation axis angle is slightly off from
the z-axis, but not enough to cause problems with the coarse stuff I have
done so far. The perpendicularity of the Z-axis to the stage was way off,
but at least that was adjustable.

The harsh reality is that end mills do not make good drills.

A study of the geometry of an end mill quickly discloses the fact that there
is little chip relief between the flute and the centerline of the cutter.
All it takes is a slight chip load, one side greater than the other, for the
end mill to begin oscillating as has been described. The problem can be
addressed by relieving the end mill towards center, creating greater chip
space, but that comes at the cost of losing considerable strength in the end
mill, possibly resulting in a broken lip.

Do note that an end mill does not normally create a flat bottom, but leaves
a high spot in the center.. They are ground with a slight taper towards
center to insure that the periphery is the lowest point in contact, creating
a flat cut when the cutter is advanced on material.

Part of the problem with using an end mill for drilling is the fact that the
periphery is relieved with a primary and secondary land. They are intended
to cut on the periphery. Drills, by sharp contrast, are circular ground, so
they pilot. The circular portion is generally relieved to reduce the
contact area in an effort to lower friction.

If one desires to create spot faces or shallow counterbores, the option to
use a counterbore with a pilot is always open. That yields not only a flat
cut, but prevents the oscillation that is so troublesome. Negative
aspect is that it's easy to break the pilots.

Harold

On Sun, 31 Oct 2010 22:13:05 -0700, Rich Grise
wrote:

On Sun, 31 Oct 2010 16:58:48 -0700, mkoblic wrote:

I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

Are you going full depth in one peck?

All one eighth of an inch? If it were a deeper hole, I'd be wondering
if it wasn't material being caught up between the bit and the bore and
suggest a vacuum to suck it away or a stream of coolant to wash it
away.

--
Small opportunities are often the beginning of great enterprises.
-- Demosthenes

Tim, if you haven't had the mill head column off of your machine to improve
the metal-metal contact area to the headstock top surface, you might
consider doing this procedure to gain some rigidity when milling.

The one I worked on was a 12x20 made in 1999 maybe.

While you're milling something fairly aggressively, put your left hand
fingertips at the seam of the contact surfaces at te base of the column. If
you feel movement, this procedure may increase milling rigidity
considerably.

The mating surface of the column flange is likely fairly accurately flat, as
it was probably turned (faced) on a lathe.
The top surface of the headstock may be one of those areas where a factory
worker ran a power scraper on it, just to smooth it somewhat, followed by
filling the seam gap with filler putty.

I managed to get the headstock surface flat, by rough filing, and checking
for contact area with plain printer paper laying on the headstock surface,
and rubbing a (machined flat with a large shell mill on a large machine)
flat thick slab of aluminum on the paper to make a carbon copy (although
aluminum oxide) of the contact area.

I put cardboard and shop rags in the opening to catch the filing swarf.

When I started, there was probably only about 15% contact between the two
surfaces.. when I had finally had enough exercise, the contact area was
probably closer to about 75%, and the rigidity of the mill was increased
greatly as a result.

--
WB
..........


"Tim Wescott" wrote in message
...

It's more that there's really no way to cut the center of the circle --
the best any drill bit or center cut mill can do is sort of mash the metal
out to where it can be cut, and to minimize the amount of material that
has to be so "mashed".

I'm no machinist, so take these with a grain of salt. But here are some
solutions that I can think of:

1: get a more rigid machine to work with. I can do what you're talking
about just fine in aluminum on a Smithy "3 in 1" (lathe, drill, lousy
excuse for mill), but I doubt it'd like me trying in steel.

2: Check your alloy -- are you using one of the absurdly easy-to-cut
alloys like 11L14? Can you?

3: Pre "drill" with a smaller mill, let it walk around, then finish with a
larger mill.

4: Put the part in a rotary table, and come down in the 'z' direction
while rotating the table -- this will keep your cut moving around, and
should make it easier on the machine.

5: I assume you'd be doing this already if you could, but consider
drilling a 1/16" pilot hole, and milling down over that. It'll leave a
hole or a dimple in the middle of your big hole, but even that small of a
pilot hole should span what your mill really can't easily get through.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 11/01/2010 08:31 AM, Wild_Bill wrote:
Tim, if you haven't had the mill head column off of your machine to
improve the metal-metal contact area to the headstock top surface, you
might consider doing this procedure to gain some rigidity when milling.

The one I worked on was a 12x20 made in 1999 maybe.

While you're milling something fairly aggressively, put your left hand
fingertips at the seam of the contact surfaces at te base of the column.
If you feel movement, this procedure may increase milling rigidity
considerably.

The mating surface of the column flange is likely fairly accurately
flat, as it was probably turned (faced) on a lathe.
The top surface of the headstock may be one of those areas where a
factory worker ran a power scraper on it, just to smooth it somewhat,
followed by filling the seam gap with filler putty.

I managed to get the headstock surface flat, by rough filing, and
checking for contact area with plain printer paper laying on the
headstock surface, and rubbing a (machined flat with a large shell mill
on a large machine) flat thick slab of aluminum on the paper to make a
carbon copy (although aluminum oxide) of the contact area.

I put cardboard and shop rags in the opening to catch the filing swarf.

When I started, there was probably only about 15% contact between the
two surfaces.. when I had finally had enough exercise, the contact area
was probably closer to about 75%, and the rigidity of the mill was
increased greatly as a result.

My biggest complaint about rigidity on that thing is the quill, which I
can somewhat deal with by adjusting the quill lock.

My biggest complaint about the use of the thing as a mill at all is that
the quill drive (which is the only adjustment in the z plane) is much
coarser than the x and y feeds and an odd number in both english and
metric, being something like 0.43 inches. To top off the pain, it's got
an itty bitty knob. So even when I've got the rigidity issues dealt
with, it's very difficult to get the height difference between features
accurate.

So even if the thing were made out of tungsten and worked as smooth as
silk, I'd still be wishing for a mill that had a decent vertical feed
mechanism.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Mon, 01 Nov 2010 09:32:40 -0700, Tim Wescott
wrote:

On 11/01/2010 08:31 AM, Wild_Bill wrote:
Tim, if you haven't had the mill head column off of your machine to
improve the metal-metal contact area to the headstock top surface, you
might consider doing this procedure to gain some rigidity when milling.

The one I worked on was a 12x20 made in 1999 maybe.

While you're milling something fairly aggressively, put your left hand
fingertips at the seam of the contact surfaces at te base of the column.
If you feel movement, this procedure may increase milling rigidity
considerably.

The mating surface of the column flange is likely fairly accurately
flat, as it was probably turned (faced) on a lathe.
The top surface of the headstock may be one of those areas where a
factory worker ran a power scraper on it, just to smooth it somewhat,
followed by filling the seam gap with filler putty.

I managed to get the headstock surface flat, by rough filing, and
checking for contact area with plain printer paper laying on the
headstock surface, and rubbing a (machined flat with a large shell mill
on a large machine) flat thick slab of aluminum on the paper to make a
carbon copy (although aluminum oxide) of the contact area.

I put cardboard and shop rags in the opening to catch the filing swarf.

When I started, there was probably only about 15% contact between the
two surfaces.. when I had finally had enough exercise, the contact area
was probably closer to about 75%, and the rigidity of the mill was
increased greatly as a result.

My biggest complaint about rigidity on that thing is the quill, which I
can somewhat deal with by adjusting the quill lock.

My biggest complaint about the use of the thing as a mill at all is that
the quill drive (which is the only adjustment in the z plane) is much
coarser than the x and y feeds and an odd number in both english and
metric, being something like 0.43 inches. To top off the pain, it's got
an itty bitty knob. So even when I've got the rigidity issues dealt
with, it's very difficult to get the height difference between features
accurate.

So even if the thing were made out of tungsten and worked as smooth as
silk, I'd still be wishing for a mill that had a decent vertical feed
mechanism.

Can I interest you in a Gorton MasterMill?

http://picasaweb.google.com/gunnerasch/NewGorton#

Needs a bit of work, but nothing major and would be a fun winter project
for folks

Gunner


"Confiscating wealth from those who have earned it, inherited it,
or got lucky is never going to help 'the poor.' Poverty isn't
caused by some people having more money than others, just as obesity
isn't caused by McDonald's serving super-sized orders of French fries
Poverty, like obesity, is caused by the life choices that dictate
results." - John Tucci,

Yep, I knew the downfeed had to be changed as soon as I saw it. I ended up
making a different knob and added a dial indicator for Z adjustments.

There are several other methods of changing the downfeed.. one includes a
small gearbelt, two pulleys and a handweel/crank. I think I saw this
modification in the Chaski 3-in-1 Machines forum.

There are lots of refinements that most of the Chinese machines need. They
aren't particularly difficult modifications, but they can involve
significant amounts of time.

--
WB
..........


"Tim Wescott" wrote in message
...
My biggest complaint about rigidity on that thing is the quill, which I
can somewhat deal with by adjusting the quill lock.

My biggest complaint about the use of the thing as a mill at all is that
the quill drive (which is the only adjustment in the z plane) is much
coarser than the x and y feeds and an odd number in both english and
metric, being something like 0.43 inches. To top off the pain, it's got
an itty bitty knob. So even when I've got the rigidity issues dealt with,
it's very difficult to get the height difference between features
accurate.

So even if the thing were made out of tungsten and worked as smooth as
silk, I'd still be wishing for a mill that had a decent vertical feed
mechanism.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 11/01/2010 11:00 AM, Wild_Bill wrote:
Yep, I knew the downfeed had to be changed as soon as I saw it. I ended
up making a different knob and added a dial indicator for Z adjustments.

There are several other methods of changing the downfeed.. one includes
a small gearbelt, two pulleys and a handweel/crank. I think I saw this
modification in the Chaski 3-in-1 Machines forum.

There are lots of refinements that most of the Chinese machines need.
They aren't particularly difficult modifications, but they can involve
significant amounts of time.

A big knob and a dial indicator (or a clever mount for a digital
caliper) would go a long way to making it more usable.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 11/01/2010 09:45 AM, Gunner Asch wrote:
On Mon, 01 Nov 2010 09:32:40 -0700, Tim
wrote:

On 11/01/2010 08:31 AM, Wild_Bill wrote:
Tim, if you haven't had the mill head column off of your machine to
improve the metal-metal contact area to the headstock top surface, you
might consider doing this procedure to gain some rigidity when milling.

The one I worked on was a 12x20 made in 1999 maybe.

While you're milling something fairly aggressively, put your left hand
fingertips at the seam of the contact surfaces at te base of the column.
If you feel movement, this procedure may increase milling rigidity
considerably.

The mating surface of the column flange is likely fairly accurately
flat, as it was probably turned (faced) on a lathe.
The top surface of the headstock may be one of those areas where a
factory worker ran a power scraper on it, just to smooth it somewhat,
followed by filling the seam gap with filler putty.

I managed to get the headstock surface flat, by rough filing, and
checking for contact area with plain printer paper laying on the
headstock surface, and rubbing a (machined flat with a large shell mill
on a large machine) flat thick slab of aluminum on the paper to make a
carbon copy (although aluminum oxide) of the contact area.

I put cardboard and shop rags in the opening to catch the filing swarf.

When I started, there was probably only about 15% contact between the
two surfaces.. when I had finally had enough exercise, the contact area
was probably closer to about 75%, and the rigidity of the mill was
increased greatly as a result.

My biggest complaint about rigidity on that thing is the quill, which I
can somewhat deal with by adjusting the quill lock.

My biggest complaint about the use of the thing as a mill at all is that
the quill drive (which is the only adjustment in the z plane) is much
coarser than the x and y feeds and an odd number in both english and
metric, being something like 0.43 inches. To top off the pain, it's got
an itty bitty knob. So even when I've got the rigidity issues dealt
with, it's very difficult to get the height difference between features
accurate.

So even if the thing were made out of tungsten and worked as smooth as
silk, I'd still be wishing for a mill that had a decent vertical feed
mechanism.

Can I interest you in a Gorton MasterMill?

http://picasaweb.google.com/gunnerasch/NewGorton#

Needs a bit of work, but nothing major and would be a fun winter project
for folks

If you were closer, maybe -- if you factor in lost time I think I can
get a decent mill locally for as much as the trip down & back would
cost. But if I'm ever going to be in your area with a trailer I'll
probably contact you.

Ideally I'd get a smaller mill -- the biggest things that I seem to end
up making are model airplane parts, and those just don't get big.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:

On 10/31/2010 04:58 PM, wrote:
I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

It's more that there's really no way to cut the center of the circle --
the best any drill bit or center cut mill can do is sort of mash the
metal out to where it can be cut, and to minimize the amount of material
that has to be so "mashed".

I'm no machinist, so take these with a grain of salt. But here are some
solutions that I can think of:

1: get a more rigid machine to work with. I can do what you're talking
about just fine in aluminum on a Smithy "3 in 1" (lathe, drill, lousy
excuse for mill), but I doubt it'd like me trying in steel.

2: Check your alloy -- are you using one of the absurdly easy-to-cut
alloys like 11L14? Can you?

3: Pre "drill" with a smaller mill, let it walk around, then finish with
a larger mill.

4: Put the part in a rotary table, and come down in the 'z' direction
while rotating the table -- this will keep your cut moving around, and
should make it easier on the machine.

5: I assume you'd be doing this already if you could, but consider
drilling a 1/16" pilot hole, and milling down over that. It'll leave a
hole or a dimple in the middle of your big hole, but even that small of
a pilot hole should span what your mill really can't easily get through.

The problem is almost certainly one of machine rigidity. Yesterday I
milled several 1/2" holes through 1/4" HRS (3" sq tube) with a three
flute center cutting end mill with no pre-drilling and no issues at all
on my Bridgeport. The holes milled smooth as butter with a few drops of
cutting oil, and finished with the usual thin disk of metal hanging by a
thread that knocked off with no effort.

On 2010-11-01, Pete C. wrote:

Tim Wescott wrote:

On 10/31/2010 04:58 PM, wrote:
I am sorry to ask something very basic. My excuse is that I am testing
the Forte Agent :-)

I need to make round holes in steel, 1/8" deep, with flat bottoms. The
diameter is usually either 1/4" , 5/16", 3/8" or 1/2" and is not
critical.

I do these on my mini-mill. I pre-drill the hole to the required depth
undersize and then use a 4-flute mill to square up the profile.

All is well until I start getting near the bottom. The machine begins
to labour and there is a tendency for the table and/or the head to
want to move in a circular fashion, clamping x and y notwithstanding.
I assume that this is due to the mill beginning to remove more
material, particularly the center portion of the hole.

The end-mills are supposed to be centre-cutting. There are two flutes
that meet in the middle, the orthogonal two flutes do not. All the
pictures I could find suggest that these are indeed centre-cutting
end-mills.

So the question is: Is this a normal behaviour for end-mills in this
situation? If not, what is the likely cause? Is there a better
procedure to do this?

It's more that there's really no way to cut the center of the circle --
the best any drill bit or center cut mill can do is sort of mash the
metal out to where it can be cut, and to minimize the amount of material
that has to be so "mashed".

I'm no machinist, so take these with a grain of salt. But here are some
solutions that I can think of:

1: get a more rigid machine to work with. I can do what you're talking
about just fine in aluminum on a Smithy "3 in 1" (lathe, drill, lousy
excuse for mill), but I doubt it'd like me trying in steel.

2: Check your alloy -- are you using one of the absurdly easy-to-cut
alloys like 11L14? Can you?

3: Pre "drill" with a smaller mill, let it walk around, then finish with
a larger mill.

4: Put the part in a rotary table, and come down in the 'z' direction
while rotating the table -- this will keep your cut moving around, and
should make it easier on the machine.

5: I assume you'd be doing this already if you could, but consider
drilling a 1/16" pilot hole, and milling down over that. It'll leave a
hole or a dimple in the middle of your big hole, but even that small of
a pilot hole should span what your mill really can't easily get through.

The problem is almost certainly one of machine rigidity. Yesterday I
milled several 1/2" holes through 1/4" HRS (3" sq tube) with a three
flute center cutting end mill with no pre-drilling and no issues at all
on my Bridgeport. The holes milled smooth as butter with a few drops of
cutting oil, and finished with the usual thin disk of metal hanging by a
thread that knocked off with no effort.

That's how it worked with my manual Bridgeport too.

i

On Nov 1, 5:06*pm, Ignoramus31297 ignoramus31...@NOSPAM.
31297.invalid wrote:
...
The problem is almost certainly one of machine rigidity. Yesterday I
milled several 1/2" holes through 1/4" HRS (3" sq tube) with a three
flute center cutting end mill with no pre-drilling and no issues at all
on my Bridgeport. The holes milled smooth as butter with a few drops of
cutting oil, and finished with the usual thin disk of metal hanging by a
thread that knocked off with no effort.

That's how it worked with my manual Bridgeport too.
i-

My ~700 Lb Clausing is marginal for boring steel cleanly with an
endmill. It's OK at 1/2" diameter but not much larger. It has some
trouble fishmouthing 3/4" and 1" pipe with large taper-shank endmills,
not that chatter marks hurt a stick welded joint.

I think it's a little less rigid than a mill-drill. I didn't cut much
steel on the RF-31 and have bored only plastic and sheet aluminum on a
Bridgeport.

jsw

On 2010-11-01, Jim Wilkins wrote:
On Nov 1, 5:06?pm, Ignoramus31297 ignoramus31...@NOSPAM.
31297.invalid wrote:
...
The problem is almost certainly one of machine rigidity. Yesterday I
milled several 1/2" holes through 1/4" HRS (3" sq tube) with a three
flute center cutting end mill with no pre-drilling and no issues at all
on my Bridgeport. The holes milled smooth as butter with a few drops of
cutting oil, and finished with the usual thin disk of metal hanging by a
thread that knocked off with no effort.

That's how it worked with my manual Bridgeport too.
i-

My ~700 Lb Clausing is marginal for boring steel cleanly with an
endmill. It's OK at 1/2" diameter but not much larger. It has some
trouble fishmouthing 3/4" and 1" pipe with large taper-shank endmills,
not that chatter marks hurt a stick welded joint.

I think it's a little less rigid than a mill-drill. I didn't cut much
steel on the RF-31 and have bored only plastic and sheet aluminum on a
Bridgeport.

jsw

With my old Bridgeport, I once drilled/endmilled a 5/16" hole
in a 51200 hard chrome steel bearing ball. It was painful (lots of
heat), but it worked.

I still have it, I put that ball on a chuck key handle.
i

On Mon, 01 Nov 2010 11:46:02 -0700, Tim Wescott
wrote:

On 11/01/2010 09:45 AM, Gunner Asch wrote:
On Mon, 01 Nov 2010 09:32:40 -0700, Tim
wrote:

On 11/01/2010 08:31 AM, Wild_Bill wrote:
Tim, if you haven't had the mill head column off of your machine to
improve the metal-metal contact area to the headstock top surface, you
might consider doing this procedure to gain some rigidity when milling.

The one I worked on was a 12x20 made in 1999 maybe.

While you're milling something fairly aggressively, put your left hand
fingertips at the seam of the contact surfaces at te base of the column.
If you feel movement, this procedure may increase milling rigidity
considerably.

The mating surface of the column flange is likely fairly accurately
flat, as it was probably turned (faced) on a lathe.
The top surface of the headstock may be one of those areas where a
factory worker ran a power scraper on it, just to smooth it somewhat,
followed by filling the seam gap with filler putty.

I managed to get the headstock surface flat, by rough filing, and
checking for contact area with plain printer paper laying on the
headstock surface, and rubbing a (machined flat with a large shell mill
on a large machine) flat thick slab of aluminum on the paper to make a
carbon copy (although aluminum oxide) of the contact area.

I put cardboard and shop rags in the opening to catch the filing swarf.

When I started, there was probably only about 15% contact between the
two surfaces.. when I had finally had enough exercise, the contact area
was probably closer to about 75%, and the rigidity of the mill was
increased greatly as a result.

My biggest complaint about rigidity on that thing is the quill, which I
can somewhat deal with by adjusting the quill lock.

My biggest complaint about the use of the thing as a mill at all is that
the quill drive (which is the only adjustment in the z plane) is much
coarser than the x and y feeds and an odd number in both english and
metric, being something like 0.43 inches. To top off the pain, it's got
an itty bitty knob. So even when I've got the rigidity issues dealt
with, it's very difficult to get the height difference between features
accurate.

So even if the thing were made out of tungsten and worked as smooth as
silk, I'd still be wishing for a mill that had a decent vertical feed
mechanism.

Can I interest you in a Gorton MasterMill?

http://picasaweb.google.com/gunnerasch/NewGorton#

Needs a bit of work, but nothing major and would be a fun winter project
for folks

If you were closer, maybe -- if you factor in lost time I think I can
get a decent mill locally for as much as the trip down & back would
cost. But if I'm ever going to be in your area with a trailer I'll
probably contact you.

Ideally I'd get a smaller mill -- the biggest things that I seem to end
up making are model airplane parts, and those just don't get big.

I figure the Gorton Ive got is worth tops...$800 at most. It needs some
cleanup and painting and the quill is stuck in the head..but its not a
big deal to get it fixed up. B&S#9 ..which Wells Index will grind to R8
for $250

If a guy wants a mill to fix up and use..Id make someone a hell of a
deal on it. Trade for guns, cash, other Stuff...shrug

Im not in love with it and Ive got other things to do this winter than
fix it up. I took a year rebuilding my other Gorton, doing an hour here
and there at a buddies shop and it meets my needs very nicely.

Anyone interested...its up for grabs

Gunner

"Confiscating wealth from those who have earned it, inherited it,
or got lucky is never going to help 'the poor.' Poverty isn't
caused by some people having more money than others, just as obesity
isn't caused by McDonald's serving super-sized orders of French fries
Poverty, like obesity, is caused by the life choices that dictate
results." - John Tucci,