I'm trying to part off some 12mm (1/2") PVC rod and am hoping to not
have to face the resultant parts.

The sides of the cut are terrible, not smooth at all.


I'm using a HSS parting off tool similar to this:
http://www.assetplant.com/WebRoot/Store/Shops/shop/5512/2DE6/890C/F386/E667/C0A8/C83B/12E3/1-2.jpg


Any pointers on how I should sharpen the tool?

How important is finishing the tool with an oil stone after grinding?


Should I have a dip/notch on the top face behind the cutting edge to
deflect the "chip"?



How critical is the speed?



Thanks.

"Aussie" wrote in message
...
I'm trying to part off some 12mm (1/2") PVC rod and am hoping to not
have to face the resultant parts.
The sides of the cut are terrible, not smooth at all.
I'm using a HSS parting off tool similar to this:
http://www.assetplant.com/WebRoot/Store/Shops/shop/5512/2DE6/890C/F386/E667/C0A8/C83B/12E3/1-2.jpg
Any pointers on how I should sharpen the tool?
How important is finishing the tool with an oil stone after
grinding?
Should I have a dip/notch on the top face behind the cutting edge to
deflect the "chip"?
How critical is the speed?
Thanks.

Something is wrong but I can't tell what without examining all the
details of your setup, many things can cause problems.

When my 1/16" wide HSS cutoff blade stops behaving well, usually when
parting stainless, I hollow-grind the end to the curve of the wheel
and stone the cutting edge to feel sharp to my finger. My Multifix
tool holder gives the blade a 4 degree back rake angle. I stopped
grinding a chip breaker in the top surface because I can't make it as
smooth as the factory finish.

As for speed, if the blade chatters I reduce it until the cut quiets
down, typically at 300 RPM.

It cuts PVC water pipe very smoothly, enough to use it for turning to
final diameter.

-jsw

On 16-May-17 7:15 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
I'm trying to part off some 12mm (1/2") PVC rod and am hoping to not
have to face the resultant parts.
The sides of the cut are terrible, not smooth at all.
I'm using a HSS parting off tool similar to this:
http://www.assetplant.com/WebRoot/Store/Shops/shop/5512/2DE6/890C/F386/E667/C0A8/C83B/12E3/1-2.jpg
Any pointers on how I should sharpen the tool?
How important is finishing the tool with an oil stone after
grinding?
Should I have a dip/notch on the top face behind the cutting edge to
deflect the "chip"?
How critical is the speed?
Thanks.

Something is wrong but I can't tell what without examining all the
details of your setup, many things can cause problems.

When my 1/16" wide HSS cutoff blade stops behaving well, usually when
parting stainless, I hollow-grind the end to the curve of the wheel
and stone the cutting edge to feel sharp to my finger. My Multifix
tool holder gives the blade a 4 degree back rake angle. I stopped
grinding a chip breaker in the top surface because I can't make it as
smooth as the factory finish.

As for speed, if the blade chatters I reduce it until the cut quiets
down, typically at 300 RPM.

It cuts PVC water pipe very smoothly, enough to use it for turning to
final diameter.

-jsw


Thanks Jim.


As usual after posting asking for advice I tried again with more success.

I ground the front face square with a little bit of rake.

The top face is flat & square
I dressed it with a flat diamond knife sharpener.
I increased the speed to 850RPM.

I had to grind the top face down about 4mm as the tool holder isn't the
correct one for my lathe.


It's not perfect but its much better than the 'rubbed & melted" cut I
was getting before.

http://imgur.com/a/eYmJo

"Aussie" wrote in message
...
On 16-May-17 7:15 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
I'm trying to part off some 12mm (1/2") PVC rod and am hoping to
not
have to face the resultant parts.
The sides of the cut are terrible, not smooth at all.
I'm using a HSS parting off tool similar to this:
http://www.assetplant.com/WebRoot/Store/Shops/shop/5512/2DE6/890C/F386/E667/C0A8/C83B/12E3/1-2.jpg
Any pointers on how I should sharpen the tool?
How important is finishing the tool with an oil stone after
grinding?
Should I have a dip/notch on the top face behind the cutting edge
to
deflect the "chip"?
How critical is the speed?
Thanks.

Something is wrong but I can't tell what without examining all the
details of your setup, many things can cause problems.

When my 1/16" wide HSS cutoff blade stops behaving well, usually
when
parting stainless, I hollow-grind the end to the curve of the wheel
and stone the cutting edge to feel sharp to my finger. My Multifix
tool holder gives the blade a 4 degree back rake angle. I stopped
grinding a chip breaker in the top surface because I can't make it
as
smooth as the factory finish.

As for speed, if the blade chatters I reduce it until the cut
quiets
down, typically at 300 RPM.

It cuts PVC water pipe very smoothly, enough to use it for turning
to
final diameter.

-jsw


Thanks Jim.


As usual after posting asking for advice I tried again with more
success.

I ground the front face square with a little bit of rake.

The top face is flat & square
I dressed it with a flat diamond knife sharpener.
I increased the speed to 850RPM.

I had to grind the top face down about 4mm as the tool holder isn't
the correct one for my lathe.


It's not perfect but its much better than the 'rubbed & melted" cut
I was getting before.

http://imgur.com/a/eYmJo


I suspect that your cutoff bit may not be perfectly square to the
spindle axis.

When I reinstall the toolpost I turn the compound to 28 or 29 degrees
for threading, roughly align the toolpost and tighten its bolt, then
loosen the compound swivel screws and press the cutoff holder against
the spindle end to perfectly square it while retightening the swivel
screws.

If I tighten the toolpost bolt last instead I unavoidably shift things
a little from the wrench torque.
-jsw

On 18-May-17 12:08 AM, Jim Wilkins wrote:
"Aussie" wrote in message
...
On 16-May-17 7:15 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
I'm trying to part off some 12mm (1/2") PVC rod and am hoping to
not
have to face the resultant parts.
The sides of the cut are terrible, not smooth at all.
I'm using a HSS parting off tool similar to this:
http://www.assetplant.com/WebRoot/Store/Shops/shop/5512/2DE6/890C/F386/E667/C0A8/C83B/12E3/1-2.jpg
Any pointers on how I should sharpen the tool?
How important is finishing the tool with an oil stone after
grinding?
Should I have a dip/notch on the top face behind the cutting edge
to
deflect the "chip"?
How critical is the speed?
Thanks.

Something is wrong but I can't tell what without examining all the
details of your setup, many things can cause problems.

When my 1/16" wide HSS cutoff blade stops behaving well, usually
when
parting stainless, I hollow-grind the end to the curve of the wheel
and stone the cutting edge to feel sharp to my finger. My Multifix
tool holder gives the blade a 4 degree back rake angle. I stopped
grinding a chip breaker in the top surface because I can't make it
as
smooth as the factory finish.

As for speed, if the blade chatters I reduce it until the cut
quiets
down, typically at 300 RPM.

It cuts PVC water pipe very smoothly, enough to use it for turning
to
final diameter.

-jsw


Thanks Jim.


As usual after posting asking for advice I tried again with more
success.

I ground the front face square with a little bit of rake.

The top face is flat & square
I dressed it with a flat diamond knife sharpener.
I increased the speed to 850RPM.

I had to grind the top face down about 4mm as the tool holder isn't
the correct one for my lathe.


It's not perfect but its much better than the 'rubbed & melted" cut
I was getting before.

http://imgur.com/a/eYmJo


I suspect that your cutoff bit may not be perfectly square to the
spindle axis.

When I reinstall the toolpost I turn the compound to 28 or 29 degrees
for threading, roughly align the toolpost and tighten its bolt, then
loosen the compound swivel screws and press the cutoff holder against
the spindle end to perfectly square it while retightening the swivel
screws.

If I tighten the toolpost bolt last instead I unavoidably shift things
a little from the wrench torque.
-jsw




Thanks Jim, I've been squaring it by eye. On my machine it might be
easiest to try squaring the side of the parting off blade against the
face of the chuck body. I'll try it out.

On 5/16/2017 3:37 AM, Aussie wrote:
...
The sides of the cut are terrible, not smooth at all.
...

PVC and poor finish says "heat" to me. Try water as a coolant.

"Bob Engelhardt" wrote in message
news
On 5/16/2017 3:37 AM, Aussie wrote:
...
The sides of the cut are terrible, not smooth at all.
...

PVC and poor finish says "heat" to me. Try water as a coolant.

The photos appear to show that the bit deflected when the decreasing
rigidity of the parted-off end could no longer force it straight.

On 5/18/2017 11:24 AM, Jim Wilkins wrote:
"Bob Engelhardt" wrote in message
news
On 5/16/2017 3:37 AM, Aussie wrote:
...
The sides of the cut are terrible, not smooth at all.
...

PVC and poor finish says "heat" to me. Try water as a coolant.

The photos appear to show that the bit deflected when the decreasing
rigidity of the parted-off end could no longer force it straight.



Maybe, but in the 2nd picture, the tool appears to be aligned properly.
Too much "in", if anything.

And the twisted off nub looks gummy, as if over heated.

Of all the possible problems, heat is the easiest one to check for: do a
cut while spritzing it with water.

On 19-May-17 12:28 AM, Bob Engelhardt wrote:
On 5/18/2017 11:24 AM, Jim Wilkins wrote:
"Bob Engelhardt" wrote in message
news
On 5/16/2017 3:37 AM, Aussie wrote:
...
The sides of the cut are terrible, not smooth at all.
...

PVC and poor finish says "heat" to me. Try water as a coolant.

The photos appear to show that the bit deflected when the decreasing
rigidity of the parted-off end could no longer force it straight.



Maybe, but in the 2nd picture, the tool appears to be aligned properly.
Too much "in", if anything.

And the twisted off nub looks gummy, as if over heated.

Of all the possible problems, heat is the easiest one to check for: do a
cut while spritzing it with water.



I'll try some coolant.

Maybe methylated spirits / denatured alcohol ?
(Less clean up issues)

"Aussie" wrote in message
...
On 19-May-17 12:28 AM, Bob Engelhardt wrote:
On 5/18/2017 11:24 AM, Jim Wilkins wrote:
"Bob Engelhardt" wrote in message
news On 5/16/2017 3:37 AM, Aussie wrote:
...
The sides of the cut are terrible, not smooth at all.
...

PVC and poor finish says "heat" to me. Try water as a coolant.

The photos appear to show that the bit deflected when the
decreasing
rigidity of the parted-off end could no longer force it straight.



Maybe, but in the 2nd picture, the tool appears to be aligned
properly. Too much "in", if anything.

And the twisted off nub looks gummy, as if over heated.

Of all the possible problems, heat is the easiest one to check for:
do a cut while spritzing it with water.



I'll try some coolant.

Maybe methylated spirits / denatured alcohol ?
(Less clean up issues)

http://www.boedeker.com/fabtip.htm
"Aromatic" in chemistry refers to ring-structured hydrocarbons such as
toluene.

I'd be careful with anything flammable around powered machinery.
Usually I machine dry unless a bit of cutting oil quiets chatter or
improves the finish. Parting off is the exception, then I drip oil for
steel or kerosine for aluminum in the cut with a needle oiler, which
is tedious but effective. PVC machines very well if the machine is set
up right and adequately supports the work without deflecting it.
http://littlemachineshop.com/product...ProductID=2276
-jsw

On Thu, 18 May 2017 09:24:32 +0800, Aussie wrote:

On 18-May-17 12:08 AM, Jim Wilkins wrote:
"Aussie" wrote in message
...
On 16-May-17 7:15 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
I'm trying to part off some 12mm (1/2") PVC rod and am hoping to
not
have to face the resultant parts.
The sides of the cut are terrible, not smooth at all.
I'm using a HSS parting off tool similar to this:
http://www.assetplant.com/WebRoot/Store/Shops/shop/5512/2DE6/890C/F386/E667/C0A8/C83B/12E3/1-2.jpg
Any pointers on how I should sharpen the tool?
How important is finishing the tool with an oil stone after
grinding?
Should I have a dip/notch on the top face behind the cutting edge
to
deflect the "chip"?
How critical is the speed?
Thanks.

Something is wrong but I can't tell what without examining all the
details of your setup, many things can cause problems.

When my 1/16" wide HSS cutoff blade stops behaving well, usually
when
parting stainless, I hollow-grind the end to the curve of the wheel
and stone the cutting edge to feel sharp to my finger. My Multifix
tool holder gives the blade a 4 degree back rake angle. I stopped
grinding a chip breaker in the top surface because I can't make it
as
smooth as the factory finish.

As for speed, if the blade chatters I reduce it until the cut
quiets
down, typically at 300 RPM.

It cuts PVC water pipe very smoothly, enough to use it for turning
to
final diameter.

-jsw


Thanks Jim.


As usual after posting asking for advice I tried again with more
success.

I ground the front face square with a little bit of rake.

The top face is flat & square
I dressed it with a flat diamond knife sharpener.
I increased the speed to 850RPM.

I had to grind the top face down about 4mm as the tool holder isn't
the correct one for my lathe.


It's not perfect but its much better than the 'rubbed & melted" cut
I was getting before.

http://imgur.com/a/eYmJo


I suspect that your cutoff bit may not be perfectly square to the
spindle axis.

When I reinstall the toolpost I turn the compound to 28 or 29 degrees
for threading, roughly align the toolpost and tighten its bolt, then
loosen the compound swivel screws and press the cutoff holder against
the spindle end to perfectly square it while retightening the swivel
screws.

If I tighten the toolpost bolt last instead I unavoidably shift things
a little from the wrench torque.
-jsw




Thanks Jim, I've been squaring it by eye. On my machine it might be
easiest to try squaring the side of the parting off blade against the
face of the chuck body. I'll try it out.

Thats the proper way to do it.


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