Peter Fairbrother wrote:

rlincolnh wrote:

I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can do
with it.
[...]

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

A possibility - the drive gear is pressing against the spindle-mounted gear
while under power at 2000 rpm, and moving the spindle's axis position. At
low speed a different gear is engaged, and turning by hand there is no real
force.

As I said, only a possibility.

btw I find your actual measurements slightly unrealistic. Are you sure you
did them right?

--
Peter Fairbrother

A lot of chinese stuff is not set up or aligned properly. An alignment
and leveling might make a good machine out of it. If you bolt the thing
down it will make it run even better. You've just added about two tons
of concrete to the base and got more mass and rigidity.

John

I hope some old hands can offer me some advice he

I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can do
with it.

Question 1.

I have chucked a 500mm length of 25mm 4140 with about 80mm extended from
the jaws. I can turn 50mm of that down to 17mm in a single pass at 2000
rpm and get a good finish (see second question) with a carbide insert.
It's like a knife through butter, the machine is totally smooth and
feels and sounds like it could do it all day. After letting it cool down
a little I use my Mitutoyo 0.001mm vernier micrometer to measure the
work - ok, the absolute value is a little out, no surprise, but the
diameter is constant to within a small fraction of 1 micron i.e. approx
0.0002/0.0003mm along the length of the 50mm cut. It's a bit hard to
visually interpolate between the vernier divisions on the micrometer,
but it's *way* less than 0.001mm variation. Then, just for the hell of
it, I mounted a DTI (0.01mm per division) on the carriage and rotated
the chuck by hand. Shock and horror - I see just under 1 division (~
0.008/0.009mm) fluctuation per rev. It's totally consistent, and if I
move the carriage along the length of the 50mm the DTI behaviour remains
identical. I ran the lathe at the lowest speed (70rpm), and the DTI
response is exactly the same, right along the 50mm length. I removed the
DTI and set about measuring diameter again, rotating the chuck 30
degrees, measure, rotate another 30 degrees, measure, etc. Dead
circular. Did that at several places along the 50mm length and every
measurement is within that fraction of a micron.

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

For the record, I took another pass again at 2000rpm but with a 0.5mm
DOC. The result is exactly the same.


Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter whether
the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at least) is
that the finish that I did get with a nominally 'finishing' insert
(larger radius tip) was worse than with a smaller radius tip that is
listed for 'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get a
single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it
curls down onto the cross-slide. Inevitably it falls forward towards the
chuck and if I don't stop the carriage feed (thereby breaking the chip)
the tangle of swarf gets caught up around the workpiece and mars the finish.

I almost don't even know what question to ask here. I would have
expected that I could get a good finish at a lower speed, and I would
have expected the chipbreaker to work. I would have expected the larger
radius insert to give a better finish, not a worse one.

I will be getting some HSS to gain experience with grinding my own
tools, but that won't happen for a month or more because my 'real' work
is consuming me night and day at the moment.

All observations/suggestions will be gratefully received.

Roger

rlincolnh wrote:

I hope some old hands can offer me some advice he

I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can
do with it.

Question 1.

I have chucked a 500mm length of 25mm 4140 with about 80mm extended
from the jaws. I can turn 50mm of that down to 17mm in a single pass
at 2000 rpm and get a good finish (see second question) with a carbide
insert. It's like a knife through butter, the machine is totally
smooth and feels and sounds like it could do it all day. After letting
it cool down a little I use my Mitutoyo 0.001mm vernier micrometer to
measure the work - ok, the absolute value is a little out, no
surprise, but the diameter is constant to within a small fraction of 1
micron i.e. approx 0.0002/0.0003mm along the length of the 50mm cut.
It's a bit hard to visually interpolate between the vernier divisions
on the micrometer, but it's *way* less than 0.001mm variation. Then,
just for the hell of it, I mounted a DTI (0.01mm per division) on the
carriage and rotated the chuck by hand. Shock and horror - I see just
under 1 division (~ 0.008/0.009mm) fluctuation per rev. It's totally
consistent, and if I move the carriage along the length of the 50mm
the DTI behaviour remains identical. I ran the lathe at the lowest
speed (70rpm), and the DTI response is exactly the same, right along
the 50mm length. I removed the DTI and set about measuring diameter
again, rotating the chuck 30 degrees, measure, rotate another 30
degrees, measure, etc. Dead circular. Did that at several places along
the 50mm length and every measurement is within that fraction of a
micron.

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

For the record, I took another pass again at 2000rpm but with a 0.5mm
DOC. The result is exactly the same.


Ok, that 500mm long length of stock inside the headstock; when it's
spinning at 2000rpm, it is resting against one side of the tube due to
centrifugal force which cocks the 50mm long part you are turning
slightly the other direction. Your tool turns it straight under those
conditions. When you stop the lathe, the whole bar straightens back out
and when you turn it slowly with the dial indicator on it, you see the
runout that was there at 2000rpm before you cut it straight.

Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter
whether the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at
least) is that the finish that I did get with a nominally 'finishing'
insert (larger radius tip) was worse than with a smaller radius tip
that is listed for 'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get
a single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it
curls down onto the cross-slide. Inevitably it falls forward towards
the chuck and if I don't stop the carriage feed (thereby breaking the
chip) the tangle of swarf gets caught up around the workpiece and mars
the finish.

I almost don't even know what question to ask here. I would have
expected that I could get a good finish at a lower speed, and I would
have expected the chipbreaker to work. I would have expected the
larger radius insert to give a better finish, not a worse one.

I will be getting some HSS to gain experience with grinding my own
tools, but that won't happen for a month or more because my 'real'
work is consuming me night and day at the moment.

All observations/suggestions will be gratefully received.

Roger

Steel cuts cleaner at higher rpm. At lower rpm it's tearing more than
cutting. If the chipbreaker is not working, the feedrate is not enough
or it could be too much depth of cut for the feedrate. Without flood
coolant it's going to be hard to get good cutting conditions without
cooking your part.

Fred

I can't help answer your questions but want to mention that just because
your micrometer says it measures the same at many points around the
diameter doesn't mean the part is round. See the following link

http://news.bbc.co.uk/onthisday/hi/d...00/3151539.stm

Coins of this sort would meet your critieria as round but are obviously
not. I have had steel bar which was like this but with 3 sides. Your DTI
would indicate if it was round or off centre depending on how many
high/low points existed around the circumference.

rlincolnh wrote:

I hope some old hands can offer me some advice he

I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can
do with it.

Question 1.

I have chucked a 500mm length of 25mm 4140 with about 80mm extended
from the jaws. I can turn 50mm of that down to 17mm in a single pass
at 2000 rpm and get a good finish (see second question) with a carbide
insert. It's like a knife through butter, the machine is totally
smooth and feels and sounds like it could do it all day. After letting
it cool down a little I use my Mitutoyo 0.001mm vernier micrometer to
measure the work - ok, the absolute value is a little out, no
surprise, but the diameter is constant to within a small fraction of 1
micron i.e. approx 0.0002/0.0003mm along the length of the 50mm cut.
It's a bit hard to visually interpolate between the vernier divisions
on the micrometer, but it's *way* less than 0.001mm variation. Then,
just for the hell of it, I mounted a DTI (0.01mm per division) on the
carriage and rotated the chuck by hand. Shock and horror - I see just
under 1 division (~ 0.008/0.009mm) fluctuation per rev. It's totally
consistent, and if I move the carriage along the length of the 50mm
the DTI behaviour remains identical. I ran the lathe at the lowest
speed (70rpm), and the DTI response is exactly the same, right along
the 50mm length. I removed the DTI and set about measuring diameter
again, rotating the chuck 30 degrees, measure, rotate another 30
degrees, measure, etc. Dead circular. Did that at several places along
the 50mm length and every measurement is within that fraction of a
micron.

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

For the record, I took another pass again at 2000rpm but with a 0.5mm
DOC. The result is exactly the same.


Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter
whether the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at
least) is that the finish that I did get with a nominally 'finishing'
insert (larger radius tip) was worse than with a smaller radius tip
that is listed for 'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get
a single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it
curls down onto the cross-slide. Inevitably it falls forward towards
the chuck and if I don't stop the carriage feed (thereby breaking the
chip) the tangle of swarf gets caught up around the workpiece and mars
the finish.

I almost don't even know what question to ask here. I would have
expected that I could get a good finish at a lower speed, and I would
have expected the chipbreaker to work. I would have expected the
larger radius insert to give a better finish, not a worse one.

I will be getting some HSS to gain experience with grinding my own
tools, but that won't happen for a month or more because my 'real'
work is consuming me night and day at the moment.

All observations/suggestions will be gratefully received.

Roger

No help with your question, but what brand of Lathe is this? I have
been thinking about a 14 X 40 geared head lathe for some time. But I
have heard that, even though many of them come from the same place, the
quality "control", finish and details of some brands is a lot better.
Any comments?
Pete Stanaitis,
western Wisconsin, USA
---------------------------

rlincolnh wrote:

I hope some old hands can offer me some advice he

I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can do
with it.

Question 1.

I have chucked a 500mm length of 25mm 4140 with about 80mm extended from
the jaws. I can turn 50mm of that down to 17mm in a single pass at 2000
rpm and get a good finish (see second question) with a carbide insert.
It's like a knife through butter, the machine is totally smooth and
feels and sounds like it could do it all day. After letting it cool down
a little I use my Mitutoyo 0.001mm vernier micrometer to measure the
work - ok, the absolute value is a little out, no surprise, but the
diameter is constant to within a small fraction of 1 micron i.e. approx
0.0002/0.0003mm along the length of the 50mm cut. It's a bit hard to
visually interpolate between the vernier divisions on the micrometer,
but it's *way* less than 0.001mm variation. Then, just for the hell of
it, I mounted a DTI (0.01mm per division) on the carriage and rotated
the chuck by hand. Shock and horror - I see just under 1 division (~
0.008/0.009mm) fluctuation per rev. It's totally consistent, and if I
move the carriage along the length of the 50mm the DTI behaviour remains
identical. I ran the lathe at the lowest speed (70rpm), and the DTI
response is exactly the same, right along the 50mm length. I removed the
DTI and set about measuring diameter again, rotating the chuck 30
degrees, measure, rotate another 30 degrees, measure, etc. Dead
circular. Did that at several places along the 50mm length and every
measurement is within that fraction of a micron.

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

For the record, I took another pass again at 2000rpm but with a 0.5mm
DOC. The result is exactly the same.


Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter whether
the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at least) is
that the finish that I did get with a nominally 'finishing' insert
(larger radius tip) was worse than with a smaller radius tip that is
listed for 'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get a
single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it
curls down onto the cross-slide. Inevitably it falls forward towards the
chuck and if I don't stop the carriage feed (thereby breaking the chip)
the tangle of swarf gets caught up around the workpiece and mars the
finish.

I almost don't even know what question to ask here. I would have
expected that I could get a good finish at a lower speed, and I would
have expected the chipbreaker to work. I would have expected the larger
radius insert to give a better finish, not a worse one.

I will be getting some HSS to gain experience with grinding my own
tools, but that won't happen for a month or more because my 'real' work
is consuming me night and day at the moment.

All observations/suggestions will be gratefully received.

Roger

....
Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter whether
the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at least) is that
the finish that I did get with a nominally 'finishing' insert (larger
radius tip) was worse than with a smaller radius tip that is listed for
'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get a
single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it curls
down onto the cross-slide. Inevitably it falls forward towards the chuck
and if I don't stop the carriage feed (thereby breaking the chip) the
tangle of swarf gets caught up around the workpiece and mars the finish.

....
I bet your feed is too low for chipbreaking. My rule of thumb for carbide;
increase your speed, increase your feed. When I got trouble seems its always
one or the other. Find the vendors table for each individual insert, they
will show a box of feeds, DOC, and speeds for good results. For your
machine, these numbers are at the extreme top end of what the lathe can do.

On my 10EE, I use only CNMG inserts with the LF (light-fine) chipbreaker for
finish cuts. I often have trouble with the long stringys though. For
ruffing, I use a standard CNMG insert (any auction special), minimum 0.100"
DOC, .007" or more IPR feed, and then run the machine fast enough for the
chips to turn blue. 20 years ago, my instructor taught me: If your chips
aren't blue, you're going too slow. Your machine may not have the power and
rigidity to do this.

Personally, I'd strongly recommend that you use HSS almost exclusively on
this lathe. HSS excels at great finish and accurate cuts at the speeds and
feeds this lathe is made for. Brazed carbide bits might work well for you
also.

Karl

Hi Pete,

I'm in Australia, so my comments won't be directly useful to you. The
lathe I have now is whatever Hare and Forbes (one of the bigger
machinery importers here) bring in and sell under their own name. I say
'the lathe I have now', because the first one that was delivered made
some very subtle noises in the headstock, so I went looking and found a
couple of problems. They looked fixable, and H&F got a professional
machine rebuilding company in to repair it. I stayed and got my hands
dirty while they pulled it down, and the further we went into it the
more horrible it became. The rebuilders told H&F that it would cost more
to 'try' and put right than it was worth, and, all credit due, H&F
replace it with the next model up. This machine runs well, but the
finish is poor by comparison with any of the older 'name' brands. What
you will find is fairly crudely finished castings, paintwork that is
crudely applied and obviously has no base preparation (chips/flakes as
soon as you look at it), and other ugly things that make you feel less
than happy. But if you can ignore that for a while and look at the
mechanical side of things I think you can see some differences. Make
sure you run the actual machine that you are going to buy, and look and
listen to the operation at different speeds. Listen and observe the
power feeds and leadscrew operation. Gradually tighten up the gibs and
see how the 'feel' changes. Extend the topslide and see how rigid (or
otherwise) it is. You have to realize that you're not buying a Hardinge,
but it is your hard-earned dollar that you're parting with, so check
everything you can think of - don't just stand back and think of how
good it will look in your garage! If you can find a machinist friend who
will have a look at a couple of models with you, so much the better. I'm
new to actually useing a lathe, but I have been around some well equiped
workshops for a long time, so I had a bit of an idea of what I should
see. Nevertheless, that first one blinded me in the showrooms.

Good luck, and don't be in a rush to get something. You're going to have
to live with it for a long time.

Roger



Pete & sheri wrote:
No help with your question, but what brand of Lathe is this? I have
been thinking about a 14 X 40 geared head lathe for some time. But I
have heard that, even though many of them come from the same place, the
quality "control", finish and details of some brands is a lot better.
Any comments?
Pete Stanaitis,
western Wisconsin, USA
---------------------------

rlincolnh wrote:

I hope some old hands can offer me some advice he

I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can
do with it.

Question 1.

I have chucked a 500mm length of 25mm 4140 with about 80mm extended
from the jaws. I can turn 50mm of that down to 17mm in a single pass
at 2000 rpm and get a good finish (see second question) with a carbide
insert. It's like a knife through butter, the machine is totally
smooth and feels and sounds like it could do it all day. After letting
it cool down a little I use my Mitutoyo 0.001mm vernier micrometer to
measure the work - ok, the absolute value is a little out, no
surprise, but the diameter is constant to within a small fraction of 1
micron i.e. approx 0.0002/0.0003mm along the length of the 50mm cut.
It's a bit hard to visually interpolate between the vernier divisions
on the micrometer, but it's *way* less than 0.001mm variation. Then,
just for the hell of it, I mounted a DTI (0.01mm per division) on the
carriage and rotated the chuck by hand. Shock and horror - I see just
under 1 division (~ 0.008/0.009mm) fluctuation per rev. It's totally
consistent, and if I move the carriage along the length of the 50mm
the DTI behaviour remains identical. I ran the lathe at the lowest
speed (70rpm), and the DTI response is exactly the same, right along
the 50mm length. I removed the DTI and set about measuring diameter
again, rotating the chuck 30 degrees, measure, rotate another 30
degrees, measure, etc. Dead circular. Did that at several places along
the 50mm length and every measurement is within that fraction of a
micron.

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

For the record, I took another pass again at 2000rpm but with a 0.5mm
DOC. The result is exactly the same.


Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter
whether the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at
least) is that the finish that I did get with a nominally 'finishing'
insert (larger radius tip) was worse than with a smaller radius tip
that is listed for 'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get
a single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it
curls down onto the cross-slide. Inevitably it falls forward towards
the chuck and if I don't stop the carriage feed (thereby breaking the
chip) the tangle of swarf gets caught up around the workpiece and mars
the finish.

I almost don't even know what question to ask here. I would have
expected that I could get a good finish at a lower speed, and I would
have expected the chipbreaker to work. I would have expected the
larger radius insert to give a better finish, not a worse one.

I will be getting some HSS to gain experience with grinding my own
tools, but that won't happen for a month or more because my 'real'
work is consuming me night and day at the moment.

All observations/suggestions will be gratefully received.

Roger

rlincolnh wrote:


I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can do
with it.
[...]

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

A possibility - the drive gear is pressing against the spindle-mounted gear
while under power at 2000 rpm, and moving the spindle's axis position. At
low speed a different gear is engaged, and turning by hand there is no real
force.


As I said, only a possibility.


btw I find your actual measurements slightly unrealistic. Are you sure you
did them right?

--
Peter Fairbrother

rlincolnh wrote:

Hi John,

Apart from the weight of the lathe itself, the base is pretty damn heavy
cast iron, and I tied both ends of the base together at floor level,
just so there couldn't be any tendency to spread or otherwise move.

I borrowed a *really* nice precision level from the university when I
was setting it up, and lengthways, front/back, etc is all within 1 minor
division on the scale.

Roger




The most important part of leveling is that the carriage remains level
as it travels down the ways. if the tool tips in or out a half
thousandth you lose or gain a thou. in diameter.

John

Thanks Fred,

I had wondered if the length inside the spindle could be a problem,
which was why I made a point of mentioning the length. But I hadn't
heard any signs of distress as I spun it up through different speeds on
the way to 2000, so I didn't worry too much about it. I'll try all this
again with a shorter piece.

Is coolant per-se going to affect the chip/chipbreaker interaction
(maybe by cooling the chip?), or are you saying that using coolant may
help in achieving the appropriate DOC and feed rate to make the
chipbreaker work?

Roger


ff wrote:
rlincolnh wrote:

I hope some old hands can offer me some advice he

I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can
do with it.

Question 1.

I have chucked a 500mm length of 25mm 4140 with about 80mm extended
from the jaws. I can turn 50mm of that down to 17mm in a single pass
at 2000 rpm and get a good finish (see second question) with a carbide
insert. It's like a knife through butter, the machine is totally
smooth and feels and sounds like it could do it all day. After letting
it cool down a little I use my Mitutoyo 0.001mm vernier micrometer to
measure the work - ok, the absolute value is a little out, no
surprise, but the diameter is constant to within a small fraction of 1
micron i.e. approx 0.0002/0.0003mm along the length of the 50mm cut.
It's a bit hard to visually interpolate between the vernier divisions
on the micrometer, but it's *way* less than 0.001mm variation. Then,
just for the hell of it, I mounted a DTI (0.01mm per division) on the
carriage and rotated the chuck by hand. Shock and horror - I see just
under 1 division (~ 0.008/0.009mm) fluctuation per rev. It's totally
consistent, and if I move the carriage along the length of the 50mm
the DTI behaviour remains identical. I ran the lathe at the lowest
speed (70rpm), and the DTI response is exactly the same, right along
the 50mm length. I removed the DTI and set about measuring diameter
again, rotating the chuck 30 degrees, measure, rotate another 30
degrees, measure, etc. Dead circular. Did that at several places along
the 50mm length and every measurement is within that fraction of a
micron.

So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

For the record, I took another pass again at 2000rpm but with a 0.5mm
DOC. The result is exactly the same.


Ok, that 500mm long length of stock inside the headstock; when it's
spinning at 2000rpm, it is resting against one side of the tube due to
centrifugal force which cocks the 50mm long part you are turning
slightly the other direction. Your tool turns it straight under those
conditions. When you stop the lathe, the whole bar straightens back out
and when you turn it slowly with the dial indicator on it, you see the
runout that was there at 2000rpm before you cut it straight.

Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter
whether the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at
least) is that the finish that I did get with a nominally 'finishing'
insert (larger radius tip) was worse than with a smaller radius tip
that is listed for 'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get
a single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it
curls down onto the cross-slide. Inevitably it falls forward towards
the chuck and if I don't stop the carriage feed (thereby breaking the
chip) the tangle of swarf gets caught up around the workpiece and mars
the finish.

I almost don't even know what question to ask here. I would have
expected that I could get a good finish at a lower speed, and I would
have expected the chipbreaker to work. I would have expected the
larger radius insert to give a better finish, not a worse one.

I will be getting some HSS to gain experience with grinding my own
tools, but that won't happen for a month or more because my 'real'
work is consuming me night and day at the moment.

All observations/suggestions will be gratefully received.

Roger

Steel cuts cleaner at higher rpm. At lower rpm it's tearing more than
cutting. If the chipbreaker is not working, the feedrate is not enough
or it could be too much depth of cut for the feedrate. Without flood
coolant it's going to be hard to get good cutting conditions without
cooking your part.

Fred

Thanks Karl,

For medium work with the MT chipbreaker and this steel TaeguTec are
showing 1 - 3.5mm DOC and about 200m/s at 0.2mm/rev feed. I guess I was
only making about 75% on the speed, and I estimate about the same or a
little less on the feed. I was feeding by hand so that I could feel what
the machine thought about what I was doing. It was very smooth and
seemed to be completely untroubled by the cut that I was putting on, but
the chip was glowing red for about 1/4" or more from the cutting edge,
and I was feeling sorry (and a little nervous) for the insert, so I
didn't push it any harder. I'll get some coolant going and see just how
hard I can push it, just so that I know. And then I'll get some HSS.

Roger


Karl Townsend wrote:
...

Question 2.

As I said above, the cut was taken at 2000rpm. I couldn't get an
acceptable finish at any speed below that, and it didn't matter whether
the DOC was 0.5mm or 3 - 4 mm. Even more strange (to me, at least) is that
the finish that I did get with a nominally 'finishing' insert (larger
radius tip) was worse than with a smaller radius tip that is listed for
'medium' turning.

The inserts are TaeguTec CCMT 09T304, MT chipbreaker, TT5100 carbide,
and CCMT 09T308, FG chipbreaker, TT5100 carbide, both in an SCLCR type
holder.

The chip breakers don't work, possibly because of the speed(?). I get a
single continuous streamer of swarf flowing up and back towards the
tailstock before gravity takes over after a couple of inches and it curls
down onto the cross-slide. Inevitably it falls forward towards the chuck
and if I don't stop the carriage feed (thereby breaking the chip) the
tangle of swarf gets caught up around the workpiece and mars the finish.


...
I bet your feed is too low for chipbreaking. My rule of thumb for carbide;
increase your speed, increase your feed. When I got trouble seems its always
one or the other. Find the vendors table for each individual insert, they
will show a box of feeds, DOC, and speeds for good results. For your
machine, these numbers are at the extreme top end of what the lathe can do.

On my 10EE, I use only CNMG inserts with the LF (light-fine) chipbreaker for
finish cuts. I often have trouble with the long stringys though. For
ruffing, I use a standard CNMG insert (any auction special), minimum 0.100"
DOC, .007" or more IPR feed, and then run the machine fast enough for the
chips to turn blue. 20 years ago, my instructor taught me: If your chips
aren't blue, you're going too slow. Your machine may not have the power and
rigidity to do this.

Personally, I'd strongly recommend that you use HSS almost exclusively on
this lathe. HSS excels at great finish and accurate cuts at the speeds and
feeds this lathe is made for. Brazed carbide bits might work well for you
also.

Karl

Hi Jim,

Yes, I know I shouldn't have done it, but the surface was very smooth...
(hangs head in shame).

I agree, it seems a bit strange to be able to measure (and visually
interpolate below) 1 micron with a workshop tool (after all, the
wavelength of light is abour 0.6 microns), but there you go. The body
divisions are 1 and 0.5 mm, the 50 thimble divisions are a decent size,
and the physical movement to get from one vernier division to the next
is enough that I can interpolate to 0.2/0.3 (under a mag-lamp). I don't
know what Mitutoyo claim for absolute accuracy, but it's very repeatable
and certainly makes for close comparisons.

No, I most certainly didn't even touch the chuck key.

Roger

jim rozen wrote:
In article , rlincolnh says...


a little I use my Mitutoyo 0.001mm vernier micrometer to measure the
work - ok, the absolute value is a little out, no surprise, but the
diameter is constant to within a small fraction of 1 micron i.e. approx
0.0002/0.0003mm along the length of the 50mm cut.


Not really what you were getting at, but I'm a bit suprised you can
read a vernier caliper to within one micron. Are you postive
you are interpreting the readings correctly?



Then, just for the hell of
it, I mounted a DTI (0.01mm per division) on the carriage and rotated
the chuck by hand. Shock and horror - I see just under 1 division (~
0.008/0.009mm) fluctuation per rev. It's totally consistent, and if I
move the carriage along the length of the 50mm the DTI behaviour remains
identical. I ran the lathe at the lowest speed (70rpm), and the DTI
response is exactly the same, right along the 50mm length.


Hmm. First off don't run the dial indicator on the workpiece
under power. That's bad for it.

Did you remove the workpiece from the chuck, and then replace it
there before performing this test?

Jim

Hi John,

Apart from the weight of the lathe itself, the base is pretty damn heavy
cast iron, and I tied both ends of the base together at floor level,
just so there couldn't be any tendency to spread or otherwise move.

I borrowed a *really* nice precision level from the university when I
was setting it up, and lengthways, front/back, etc is all within 1 minor
division on the scale.

Roger


john wrote:
Peter Fairbrother wrote:

rlincolnh wrote:


I have a new Chinese 14x40 gearhead lathe, and it seems to be a
reasonably solid unit although I'm still just finding out what I can do
with it.

[...]


So here's the question; How is it that I can produce a perfectly
circular result, yet which appears to be off-centre from the spindle
axis? For the life of me I can't visualize the conditions that would
lead to this.

A possibility - the drive gear is pressing against the spindle-mounted gear
while under power at 2000 rpm, and moving the spindle's axis position. At
low speed a different gear is engaged, and turning by hand there is no real
force.

As I said, only a possibility.

btw I find your actual measurements slightly unrealistic. Are you sure you
did them right?

--
Peter Fairbrother


A lot of chinese stuff is not set up or aligned properly. An alignment
and leveling might make a good machine out of it. If you bolt the thing
down it will make it run even better. You've just added about two tons
of concrete to the base and got more mass and rigidity.

John

In article , rlincolnh says...

No, I most certainly didn't even touch the chuck key.

Then it sounds as if the machine may be cutting slightly
tri-lobed.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

On Sun, 13 Mar 2005 03:18:32 -0500, john
wrote:

A lot of chinese stuff is not set up or aligned properly. An alignment
and leveling might make a good machine out of it. If you bolt the thing
down it will make it run even better. You've just added about two tons
of concrete to the base and got more mass and rigidity.

I have a new 12 x 36 chinese lathe that's still in the crate. I have
the cabinets also, which are about 1 1/2 - 2" shorter than what I'd
like them to be. I also didn't want the metal cabinets sitting
directly on the concrete due to potential rust stains. I was thinking
of laying down the correct level of plywood under the cabinets. This
thing weighs about 1,200 lbs and I'm concerned about the level
gradually changing and/or twisting the bed as the plywood compresses
over time.

Is it a bad idea to lay some plywood down under the cabinets? Figure
if I'm going to learn how to run this machine, I'd best start off with
it set up correctly. Sorry for the newbie questions.

rlincolnh wrote:

Thanks Fred,

I had wondered if the length inside the spindle could be a problem,
which was why I made a point of mentioning the length. But I hadn't
heard any signs of distress as I spun it up through different speeds
on the way to 2000, so I didn't worry too much about it. I'll try all
this again with a shorter piece.

Is coolant per-se going to affect the chip/chipbreaker interaction
(maybe by cooling the chip?), or are you saying that using coolant may
help in achieving the appropriate DOC and feed rate to make the
chipbreaker work?

Roger



Here is a good article on chipbreaking from the Modern Machine Shop
trade magazine:

http://www.mmsonline.com/articles/049804.html

Here's an exerpt:

"The chip formation process implies that a fresh metal interface is
continually produced between the tool material and the workpiece at
varying cutting forces, angles and temperatures. When a cutting edge
performs its metal cutting function properly, it deforms some of the
workpiece material plastically and then pushes it off. Chips separate in
either of three ways: they break by themselves, they break against the
tool, or they break against the workpiece (see Figure 1, below)."


Fred

Thanks fred, I've taken a copy of that.

Roger


ff wrote:
rlincolnh wrote:

Thanks Fred,

I had wondered if the length inside the spindle could be a problem,
which was why I made a point of mentioning the length. But I hadn't
heard any signs of distress as I spun it up through different speeds
on the way to 2000, so I didn't worry too much about it. I'll try all
this again with a shorter piece.

Is coolant per-se going to affect the chip/chipbreaker interaction
(maybe by cooling the chip?), or are you saying that using coolant may
help in achieving the appropriate DOC and feed rate to make the
chipbreaker work?

Roger



Here is a good article on chipbreaking from the Modern Machine Shop
trade magazine:

http://www.mmsonline.com/articles/049804.html

Here's an exerpt:

"The chip formation process implies that a fresh metal interface is
continually produced between the tool material and the workpiece at
varying cutting forces, angles and temperatures. When a cutting edge
performs its metal cutting function properly, it deforms some of the
workpiece material plastically and then pushes it off. Chips separate in
either of three ways: they break by themselves, they break against the
tool, or they break against the workpiece (see Figure 1, below)."


Fred