Those Cheap Diamond Inserts

[Bob La Londe]

I was struggling trying to face some big 304 stainless mold inserts to
length. 1.5" diameter & 1.375" length. Saw cut of course. Parting
these off is an exercise in frustration.

For most stainless work I hand sharpen HSS Cobalt bits, but I was
struggling with my facing tool and to get decent finish would have to
touch it up after ever pass. I guess I could move the grinder over by
the lathe (cringe) and set a diamond bench stone on the tool cart, but
it was rough.

Now as some of you know a lot of mini lathe users swear by those little
21.51 or 21.52 DCMT diamond inserts. I had one tool with one in a tool
holder and I tried it because nothing else was working for me. I
finished both ends with a single pass on each end of the last six parts
with one insert that looks the same when I finished as when I started.
After I finished I started going through my box looking to see how many
spares I had. Ummm. Zero. There were two broken ones on the head
stock, but no spares.

The finish is decent. I just bought some more that are listed as
alloy/stainless. Also another turning tool, and a boring bar that uses
them as well. I almost bought a through coolant solid carbide boring
bar too, but that will have to wait until the next job comes in the shop.

I don't even think I was using it right. It was a right hand turning
tool and I was just face/plunging it into the saw cut end pushing a cone
off the middle as it finish. I was amazed at how well it worked with
such an aggressive cut and no chatter. I even considered turning up the
speed.

[Bob La Londe]

Post by Bob La Londe
I was struggling trying to face some big 304 stainless mold inserts to
length.  1.5" diameter & 1.375" length.  Saw cut of course.  Parting
these off is an exercise in frustration.
For most stainless work I hand sharpen HSS Cobalt bits, but I was
struggling with my facing tool and to get decent finish would have to
touch it up after ever pass.  I guess I could move the grinder over by
the lathe (cringe) and set a diamond bench stone on the tool cart, but
it was rough.
Now as some of you know a lot of mini lathe users swear by those little
21.51 or 21.52 DCMT diamond inserts.  I had one tool with one in a tool
holder and I tried it because nothing else was working for me.  I
finished both ends with a single pass on each end of the last six parts
with one insert that looks the same when I finished as when I started.
After I finished I started going through my box looking to see how many
spares I had.  Ummm. Zero.  There were two broken ones on the head
stock, but no spares.
The finish is decent.  I just bought some more that are listed as
alloy/stainless.  Also another turning tool, and a boring bar that uses
them as well.  I almost bought a through coolant solid carbide boring
bar too, but that will have to wait until the next job comes in the shop.
I don't even think I was using it right.  It was a right hand turning
tool and I was just face/plunging it into the saw cut end pushing a cone
off the middle as it finish.  I was amazed at how well it worked with
such an aggressive cut and no chatter.  I even considered turning up the
speed.

Its one of those things. You never see the big boys using those tiny
inserts. They always have these expensive inserts on giant tools that
make chips that hit the floor with a clank. I don't have a giant lathe,
but it does weigh a ton (2000lbs). Its only 3HP, but being a gear head
its putting out its full real power (whatever that is) at any speed. I
should be able to take a decent chip and not blow up inserts. To be
fair the lathe does have a coolant system, but I never use it due to the
mess. I tend towards cutting oil.

I know those little bitty inserts work on mini lathes, but I never
really used them much on the PM14x40 except where needed to cut a back
clearance or something like that. I should know better. They made a
bigger depth of cut and bigger feed per rev than other things and there
was less heat build up in the part. No coolant. Just a few drops of
cutting oil.

I'm going to quit pretending I have a big boy lathe and just go back to
everything I learned on the mini lathe that worked.

P.S. While I do not recommend them I made a lot of parts on the mini
lathe including paid parts. Not just brass or aluminum either.

[Richard Smith]

I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
solution into the iron
?

[Bob La Londe]

Post by Richard Smith
I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
solution into the iron
?

My apologies. I didn't at all mean something like a PVD diamond
coating. DCMT is a diamond shaped insert. Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings. My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by 10-16
mini lathe also work on a heavier machine. If the big boy inserts don't
work these still do. In this case I was cutting 304 stainless steel. It
improved the finish, didn't require sharpening, had less heat input, and
did the job much faster net elapsed time.

FYI: I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish. Diamond was popular when I
first started cutting aluminum on machine tools, and more recently ZrN
has become the popular coating. I've tried them and the simple fact is
a coated tool isn't as sharp. They might work better for larger tools
on larger machines, but on middle weight machines with limited
horsepower (5 or less) a bright sharp uncoated tool works best for me.
For high speed flood coolant makes the tool last without chip welding,
but coatings do not. On smaller tools horsepower isn't even a factor as
the tool can't take it anyway.

[Richard Smith]

Post by Bob La Londe

Post by Richard Smith
I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
solution into the iron
?

My apologies. I didn't at all mean something like a PVD diamond
coating. DCMT is a diamond shaped insert. Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings. My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by
10-16 mini lathe also work on a heavier machine. If the big boy
inserts don't work these still do. In this case I was cutting 304
stainless steel. It improved the finish, didn't require sharpening,
had less heat input, and did the job much faster net elapsed time.
FYI: I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish. Diamond was popular when
I first started cutting aluminum on machine tools, and more recently
ZrN has become the popular coating. I've tried them and the simple
fact is a coated tool isn't as sharp. They might work better for
larger tools on larger machines, but on middle weight machines with
limited horsepower (5 or less) a bright sharp uncoated tool works best
for me. For high speed flood coolant makes the tool last without chip
welding, but coatings do not. On smaller tools horsepower isn't even
a factor as the tool can't take it anyway.
--
Bob La Londe
CNC Molds N Stuff

Thx for this detail.
Interesting yes certainly.
Sorry "got the wrong end of the stick".

I used cutting insert tooling - aagh - 30 years ago.
Vertical milling shell-cutter on steel.
Did well - they'd never seen steel chip ejection like a chain-saw
cutting timber. Took a visit from the rep. who explained this is how
the tooling is supposed to be used :-)
Coated carbide inserts - coating the gold coloured one - a Ti nitride(?)
coating - for this steel.

[Bob La Londe]

Post by Richard Smith

Post by Bob La Londe

Post by Richard Smith
I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
solution into the iron
?

My apologies. I didn't at all mean something like a PVD diamond
coating. DCMT is a diamond shaped insert. Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings. My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by
10-16 mini lathe also work on a heavier machine. If the big boy
inserts don't work these still do. In this case I was cutting 304
stainless steel. It improved the finish, didn't require sharpening,
had less heat input, and did the job much faster net elapsed time.
FYI: I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish. Diamond was popular when
I first started cutting aluminum on machine tools, and more recently
ZrN has become the popular coating. I've tried them and the simple
fact is a coated tool isn't as sharp. They might work better for
larger tools on larger machines, but on middle weight machines with
limited horsepower (5 or less) a bright sharp uncoated tool works best
for me. For high speed flood coolant makes the tool last without chip
welding, but coatings do not. On smaller tools horsepower isn't even
a factor as the tool can't take it anyway.
--
Bob La Londe
CNC Molds N Stuff

Thx for this detail.
Interesting yes certainly.
Sorry "got the wrong end of the stick".
I used cutting insert tooling - aagh - 30 years ago.
Vertical milling shell-cutter on steel.
Did well - they'd never seen steel chip ejection like a chain-saw
cutting timber. Took a visit from the rep. who explained this is how
the tooling is supposed to be used :-)
Coated carbide inserts - coating the gold coloured one - a Ti nitride(?)
coating - for this steel.

Pushing it harder and harder. As I once offended Jim a little (sorry
Jim) over... time is money. Even if you are doing something for fun,
favor, self... time is still your most valuable nonrenewable resource.

I needed to make another batch of stainless mold cores today. (Stock
design that uses upto nine (9) 1.5in diameter cores to varY the size of
the casting. That's 18 cuts to true them up after they come off the saw.

My new inserts arrived a few days ago ago, but I wantedif I could bump
up the speed a bit with that little hobby lathe size insert. I had been
using at at 300 RPM in low gear. That's a starting SFM of 117 if I have
done the math right. I am sure there are folks pushing big turning
centers orders of magnitude faster, but this is after all only a bigger
import lathe. Its still an import lathe, and while its relatively
heavy, its light for its size.

Of course the SFM drops as the diameter is reduced. Maybe I could go
faster if I cranked up the speed as I reduced the diameter, but this is
a single phase gear head lathe. The motor just turns one speed. The
time to stop it and change gears would eat up any time savings.

Just for the heck of it I decided to see how much faster I could start.
At 460 RPM the insert was still doing fine. Still using the same insert
I used when I started this thread. I don't mean the same type. I mean
the same insert. That means the insert was hitting the outside of the
stock at 180 SFM. The number doesn't sound much bigger, but the part
time was definitely faster.

A couple ends with an intact insert at that speed and I decided to try
the last couple parts at 755 RPM. 296 SFM. That was significantly
faster. Part time was a lot shorter, and the insert still looks like
when I started. (I'll look at under magnification later) It wasn't so
fast that I had any issue keeping up, but it was fast enough I couldn't
do anything else, like move the stock in the saw to cut the next rough
blank.

Now that I have spares I think next time I cut a batch of these cores I
am going to push it until I chip an insert to see just what they will do.

Please bare in mind that these are relatively light cuts. The blanks
come off the saw at about 1.4" to 1.41" and get trued to 1.375".
--
Bob La Londe
CNC Molds N Stuff

[Jim Wilkins]

"Bob La Londe" wrote in message news:v9u22n$2ihff$***@dont-email.me...

You didn't offend me, I describe what I know best, which is low volume
custom work, perhaps relevant to a hobbyist. I haven't done enough
production machining to comment on it.

What is the insert? Maybe there's hope for using it on my leather belt
antique South Bend. So far except for the GTN-2 cutoff insert of unknown
make they have all quickly chipped. I get away with HSS only because it
doesn't need to hold size very long.
jsw

[Snag]

Post by Jim Wilkins
You didn't offend me, I describe what I know best, which is low volume
custom work, perhaps relevant to a hobbyist. I haven't done enough
production machining to comment on it.
What is the insert? Maybe there's hope for using it on my leather belt
antique South Bend. So far except for the GTN-2 cutoff insert of unknown
make they have all quickly chipped. I get away with HSS only because it
doesn't need to hold size very long.
jsw

I've been using a lot of carbide tooling on my 10" Logan since I
built the QCTP ... but I'm not getting rid of the lantern toolpost and
HSS stuff because thewe are just some things it works better on .

[Peter Fairbrother]

  I've been using a lot of carbide tooling on my 10" Logan since I
built the QCTP ... but I'm not getting rid of the lantern toolpost and
HSS stuff because thewe are just some things it works better on .

Yep. Any interrupted cuts, anything where you need a really sharp edge
(copper,anyone?), anywhere you do not have overwhelming power - inserts
are designed for use in powerful machines and don't usually have sharp
edges, so need more power than HSS.

Horses for courses. Though I mostly use inserts myself even on a minilathe.

Peter Fairbrother

[Snag]

   I've been using a lot of carbide tooling on my 10" Logan since I
built the QCTP ... but I'm not getting rid of the lantern toolpost and
HSS stuff because thewe are just some things it works better on .

Yep. Any interrupted  cuts, anything where you need a really sharp edge
(copper,anyone?), anywhere you do not have overwhelming power - inserts
are designed for use in powerful machines and don't usually have sharp
edges, so need more power than HSS.
Horses for courses. Though I mostly use inserts myself even on a minilathe.
Peter Fairbrother

And I just found out how fragile threading inserts can be ... I'm
sure glad I bought extras ! I hope I hit the knee of the learning curve
before I run out .

[Jim Wilkins]

"Snag" wrote in message news:v9vbbu$2rogo$***@dont-email.me...

On 8/19/2024 5:54 AM, Jim Wilkins wrote:

I've been using a lot of carbide tooling on my 10" Logan since I
built the QCTP ... but I'm not getting rid of the lantern toolpost and
HSS stuff because thewe are just some things it works better on .
--
Snag
Illegitimi non carborundum

-------------------------------

I happened upon a Multifix set while searching for a used dovetail type, and
like it very much for HSS because of the rotation in small steps. It's easy
to set a hand ground bit to both turn and face. Extra Chinese tool holders
fit the Swiss post perfectly. Size A is right for my 10" SB. I haven't
needed the more compact lantern post in years, a bolt and shim setup is more
versatile for turning a ball or socket with the compound.
https://www.ebay.ca/itm/403108379491

[Bob La Londe]

Post by Jim Wilkins
You didn't offend me, I describe what I know best, which is low volume
custom work, perhaps relevant to a hobbyist. I haven't done enough
production machining to comment on it.
What is the insert? Maybe there's hope for using it on my leather belt
antique South Bend. So far except for the GTN-2 cutoff insert of
unknown make they have all quickly chipped. I get away with HSS only
because it doesn't need to hold size very long.
jsw

  I've been using a lot of carbide tooling on my 10" Logan since I
built the QCTP ... but I'm not getting rid of the lantern toolpost and
HSS stuff because thewe are just some things it works better on .

There is certainly something to be said for being able to freehand grind
a specialty HSS tool, but for the most part I just put them in tool
holders for my QCTP.

[Bob La Londe]

Post by Bob La Londe

Post by Jim Wilkins
You didn't offend me, I describe what I know best, which is low
volume custom work, perhaps relevant to a hobbyist. I haven't done
enough production machining to comment on it.
What is the insert? Maybe there's hope for using it on my leather
belt antique South Bend. So far except for the GTN-2 cutoff insert of
unknown make they have all quickly chipped. I get away with HSS only
because it doesn't need to hold size very long.
jsw

   I've been using a lot of carbide tooling on my 10" Logan since I
built the QCTP ... but I'm not getting rid of the lantern toolpost and
HSS stuff because thewe are just some things it works better on .

There is certainly something to be said for being able to freehand grind
a specialty HSS tool, but for the most part I just put them in tool
holders for my QCTP.

I suppose a lantern tool post "might" be able to hold a smaller scrap of
HSS, but to really get the most out of your HSS a tangential holder
might be the way to go.

[Jim Wilkins]

"Bob La Londe" wrote in message news:va02fs$2veo1$***@dont-email.me...

I suppose a lantern tool post "might" be able to hold a smaller scrap of
HSS, but to really get the most out of your HSS a tangential holder
might be the way to go.

Bob La Londe
-------------------------------
I have a good selection of Armstrong and similar bit holders, obsolete
1960s-style tooling that matches my 1965 lathe. It's fine for carbon steel
up through Grade 8 bolt hardness and puttering geezer productivity.

I've seen only a few tangential holders for sale, for formed threading bits
and priced high. I made one to hold the shank of a broken carbide drill bit
nearly upright to turn the race grooves in a stainless thrust bearing sized
to fit pipe, for a solar array. My hands are still steady enough to grind a
threading bit to closely fit the arrow gauge.

Today's rainy day project is turning closer fitting spacers and bushings for
the ball bearings in the sawmill blade guide rollers.
jsw

[Bob La Londe]

Post by Bob La Londe
I suppose a lantern tool post "might" be able to hold a smaller scrap of
HSS, but to really get the most out of your HSS a tangential holder
might be the way to go.
Bob La Londe
-------------------------------
I have a good selection of Armstrong and similar bit holders, obsolete
1960s-style tooling that matches my 1965 lathe. It's fine for carbon
steel up through Grade 8 bolt hardness and puttering geezer productivity.
I've seen only a few tangential holders for sale, for formed threading
bits and priced high. I made one to hold the shank of a broken carbide
drill bit nearly upright to turn the race grooves in a stainless thrust
bearing sized to fit pipe, for a solar array. My hands are still steady
enough to grind a threading bit to closely fit the arrow gauge.
Today's rainy day project is turning closer fitting spacers and bushings
for the ball bearings in the sawmill blade guide rollers.
jsw

I have freehand ground a lot of things, and I can probably make an
adequate threading cutter, but a simple miter gage and slot in a tool
rest makes it achievable for nearly anybody. Even a puttering geezer.

[Jim Wilkins]

"Bob La Londe" wrote in message news:va0hrc$321n0$***@dont-email.me...

I have freehand ground a lot of things, and I can probably make an
adequate threading cutter, but a simple miter gage and slot in a tool
rest makes it achievable for nearly anybody. Even a puttering geezer.
Bob La Londe
--------------------------------------
So does a Univise on a surface grinder, when I want to be fussy. I haven't
seen a Baldor carbide grinder for less than $600.

[Bob La Londe]

Post by Bob La Londe
I have freehand ground a lot of things, and I can probably make an
adequate threading cutter, but a simple miter gage and slot in a tool
rest makes it achievable for nearly anybody.  Even a puttering geezer.
Bob La Londe
--------------------------------------
So does a Univise on a surface grinder, when I want to be fussy. I
haven't seen a Baldor carbide grinder for less than $600.

Diamond wheels are available for a lot of things. Yes, you can freehand
grind on a diamond wheel. A buddy of mine sells tungsten grinding kits
for various grinders that include adapters, and a cheap diamond coated
wheel he buys in bulk from China. He sells them to welders for shaping
tungsten electrodes. I have one of his cheap wheels and I sometimes use
it to rough finish the edge on a tool before honing on a bench stone or
lapping stick.

I have a whole bucket (smallish) of broken and worn out carbide mills I
save for making specialty tools. When I needed a special 7 degree
dovetail cutter to make a tool holder I ground one of an old carbide end
mill. Okay. I cheated. I cut the 7 degree cutting edge on a tool and
cutter grinder with a diamond wheel, but other edges and clearances I
just ground freehand.

[Peter Fairbrother]

Post by Bob La Londe

Post by Bob La Londe

   I've been using a lot of carbide tooling on my 10" Logan since I
built the QCTP ... but I'm not getting rid of the lantern toolpost
and HSS stuff because thewe are just some things it works better on .

There is certainly something to be said for being able to freehand
grind a specialty HSS tool, but for the most part I just put them in
tool holders for my QCTP.

I suppose a lantern tool post "might" be able to hold a smaller scrap of
HSS, but to really get the most out of your HSS a tangential holder
might be the way to go.

I bought a couple dozen HSS blanks, 10x10x100mm, maybe 20 years ago, and
still have a few unused ones, and several with cutting ends which I
don't use which could be reground if needed. No need to fiddle about
with scraps of HSS, though I do have a few home-made toolholders, mostly
of the weird and wonderful kind, for them when needed.

For smaller machines I make my toolholders/toolposts, one for each tool,
from a 50x50x30mm [18] block of mild steel. I mill a ~14mm slot on one
edge, then drill and tap a couple of M5 or so holes into it to hold the
tool in place. Then I drill a hole for the toolpost stud.

Add a couple screws, put in place on the rest with the tool, then shim
to center and tighten. Then you can change tool-plus-toolpost just using
the toolpost handle, and it is a much firmer hold than any other
toolpost I have come across.



Ketan (of Arceurotrade) once quite unwarrantedly called me a Hell's
Angel for the way I "brutalise" that minilathe (which is still running
well 20 years on, though it has had a bearing change. And a main spindle
change too, bent it somehow. Motor electronics replaced [47]. Hmm maybe
that comment wasn't so far off...

I don't do a lot of bigger stuff, but I do use harder-to-machine
materials like inconel, monel, stainless, copper, titanium, hastelloy
(ouch) etc.



Also alumina and other ceramics - for which I use the nearly-cheapest
diamond tooling, like drills, hole saws, cutting disks, to get back a
little towards the title of this thread. Keep them wet, underwater if
possible, take your time, be firm but not hard, and they cut like a
knife through butter, albeit a lot slower. Accurate on the second cut,
and the finish is lovely.

I have also used these on hastelloy, which I couldn't get to cut nicely
even with CBN inserts. A dremel in the toolpost is handy. Cheap diamond
tools are exactly that, cheap. They don't last that long, perhaps less
on steel [99], but if the alternative is waaay expensive or unavailable ..

I never use so-called machinable ceramics, far too expensive for zero
gain. If machining ceramics, or using diamond tooling, don't forget to
cover all slides and clean the machine immediately, as the dust will
kill accuracy.


Peter Fairbrother

Chester minilathe
2x Myford ML10
Myford ML3 extra looong bed
Boxford AUD
home-made CNC lathe
7 BCAs, one CNC'd
Seig X3 mill




[19] 25mm sometimes, but 30mm is better, sometimes 25mm isn't enough.

[49] to repair the electronics on a single=phase brushed DC minilathe or
minimill motor, don't bother with the kblc board if fitted, it is a POS.
Chuck it. A cheap chinese 180V DC controller from Ebay will do the job,
and if it breaks throw it away and buy another. I was doubtful and
bought a spare, still have it about 15 years later.


[99] the diamonds come off before they dissolve in the steel. If you are
using the expensive brazed ones it might be a problem

[Bob La Londe]

Post by Jim Wilkins
You didn't offend me, I describe what I know best, which is low volume
custom work, perhaps relevant to a hobbyist. I haven't done enough
production machining to comment on it.
What is the insert? Maybe there's hope for using it on my leather belt
antique South Bend. So far except for the GTN-2 cutoff insert of unknown
make they have all quickly chipped. I get away with HSS only because it
doesn't need to hold size very long.
jsw

I'm actually not 100% sure about this particular insert. It might be a
unicorn. I think it came on a tool. I'll let you know how the
alloy/stainless inserts I bought work out when I finally destroy this
one and have to swap it out.

I think the big deal is that the small insert has to have smaller
geometry so it works better when making smaller cuts.

[Charlie+]

Post by Bob La Londe

Post by Richard Smith

Post by Bob La Londe

Post by Richard Smith
I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
solution into the iron
?

My apologies. I didn't at all mean something like a PVD diamond
coating. DCMT is a diamond shaped insert. Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings. My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by
10-16 mini lathe also work on a heavier machine. If the big boy
inserts don't work these still do. In this case I was cutting 304
stainless steel. It improved the finish, didn't require sharpening,
had less heat input, and did the job much faster net elapsed time.
FYI: I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish. Diamond was popular when
I first started cutting aluminum on machine tools, and more recently
ZrN has become the popular coating. I've tried them and the simple
fact is a coated tool isn't as sharp. They might work better for
larger tools on larger machines, but on middle weight machines with
limited horsepower (5 or less) a bright sharp uncoated tool works best
for me. For high speed flood coolant makes the tool last without chip
welding, but coatings do not. On smaller tools horsepower isn't even
a factor as the tool can't take it anyway.
--
Bob La Londe
CNC Molds N Stuff

Thx for this detail.
Interesting yes certainly.
Sorry "got the wrong end of the stick".
I used cutting insert tooling - aagh - 30 years ago.
Vertical milling shell-cutter on steel.
Did well - they'd never seen steel chip ejection like a chain-saw
cutting timber. Took a visit from the rep. who explained this is how
the tooling is supposed to be used :-)
Coated carbide inserts - coating the gold coloured one - a Ti nitride(?)
coating - for this steel.

Pushing it harder and harder. As I once offended Jim a little (sorry
Jim) over... time is money. Even if you are doing something for fun,
favor, self... time is still your most valuable nonrenewable resource.
I needed to make another batch of stainless mold cores today. (Stock
design that uses upto nine (9) 1.5in diameter cores to varY the size of
the casting. That's 18 cuts to true them up after they come off the saw.
My new inserts arrived a few days ago ago, but I wantedif I could bump
up the speed a bit with that little hobby lathe size insert. I had been
using at at 300 RPM in low gear. That's a starting SFM of 117 if I have
done the math right. I am sure there are folks pushing big turning
centers orders of magnitude faster, but this is after all only a bigger
import lathe. Its still an import lathe, and while its relatively
heavy, its light for its size.
Of course the SFM drops as the diameter is reduced. Maybe I could go
faster if I cranked up the speed as I reduced the diameter, but this is
a single phase gear head lathe. The motor just turns one speed. The
time to stop it and change gears would eat up any time savings.
Just for the heck of it I decided to see how much faster I could start.
At 460 RPM the insert was still doing fine. Still using the same insert
I used when I started this thread. I don't mean the same type. I mean
the same insert. That means the insert was hitting the outside of the
stock at 180 SFM. The number doesn't sound much bigger, but the part
time was definitely faster.
A couple ends with an intact insert at that speed and I decided to try
the last couple parts at 755 RPM. 296 SFM. That was significantly
faster. Part time was a lot shorter, and the insert still looks like
when I started. (I'll look at under magnification later) It wasn't so
fast that I had any issue keeping up, but it was fast enough I couldn't
do anything else, like move the stock in the saw to cut the next rough
blank.
Now that I have spares I think next time I cut a batch of these cores I
am going to push it until I chip an insert to see just what they will do.
Please bare in mind that these are relatively light cuts. The blanks
come off the saw at about 1.4" to 1.41" and get trued to 1.375".

Interesting thread Bob, thanks, is this example the type of tool you are
talking about? Never come across the diamond tipped versions of inserts
but my original machining in industry experience was in the 1960's! Only
hobby level now..
https://www.ebay.co.uk/itm/115334715488?_nkw=diamond+inserts+carbide+lathe&itmmeta=01J5Q723XNA0GREWTN8RFZEQK2&hash=item1ada7c1860:g:YyUAAOSwUtJiUKWN&itmprp=enc%3AAQAJAAAA4HoV3kP08IDx%2BKZ9MfhVJKnC8gu8jBQODZUzjY6nfSpuZas%2FJzGcWIYLgG5EPfxVgG0wH1c4QdrYrUHqD4z98NSE8atbz28SHAAsTTB%2FvXsdw1KSXcN7%2Bx6cwyg%2FcKXwvDq3eEqXZbpx%2Bzxtc0f0%2Fp0BsyoIUtnlZlJQI86p6TyhETkaZsGuuwYw1Ayo2CHAORe6WE1WiaDElO8xogeQY1mItmsxVxjRLhavW15vEW5hMGkyR8srWzmxrGq4dX%2B9yZ23zhsDDiiDdifsQ%2Bk8r7IRPefZ9T%2FppdLbpKF%2FwpjM%7Ctkp%3ABk9SR_S-iOetZA
It says for non ferrous but you are using on stainless without any red
spark? Can they be touched up if/when the edge goes? I know its only a
single but looks uncheap to me! C+

[David Billington]

Post by Charlie+

Post by Bob La Londe

Post by Richard Smith

Post by Bob La Londe

Post by Richard Smith
I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
solution into the iron
?

My apologies. I didn't at all mean something like a PVD diamond
coating. DCMT is a diamond shaped insert. Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings. My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by
10-16 mini lathe also work on a heavier machine. If the big boy
inserts don't work these still do. In this case I was cutting 304
stainless steel. It improved the finish, didn't require sharpening,
had less heat input, and did the job much faster net elapsed time.
FYI: I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish. Diamond was popular when
I first started cutting aluminum on machine tools, and more recently
ZrN has become the popular coating. I've tried them and the simple
fact is a coated tool isn't as sharp. They might work better for
larger tools on larger machines, but on middle weight machines with
limited horsepower (5 or less) a bright sharp uncoated tool works best
for me. For high speed flood coolant makes the tool last without chip
welding, but coatings do not. On smaller tools horsepower isn't even
a factor as the tool can't take it anyway.
--
Bob La Londe
CNC Molds N Stuff

Thx for this detail.
Interesting yes certainly.
Sorry "got the wrong end of the stick".
I used cutting insert tooling - aagh - 30 years ago.
Vertical milling shell-cutter on steel.
Did well - they'd never seen steel chip ejection like a chain-saw
cutting timber. Took a visit from the rep. who explained this is how
the tooling is supposed to be used :-)
Coated carbide inserts - coating the gold coloured one - a Ti nitride(?)
coating - for this steel.

Pushing it harder and harder. As I once offended Jim a little (sorry
Jim) over... time is money. Even if you are doing something for fun,
favor, self... time is still your most valuable nonrenewable resource.
I needed to make another batch of stainless mold cores today. (Stock
design that uses upto nine (9) 1.5in diameter cores to varY the size of
the casting. That's 18 cuts to true them up after they come off the saw.
My new inserts arrived a few days ago ago, but I wantedif I could bump
up the speed a bit with that little hobby lathe size insert. I had been
using at at 300 RPM in low gear. That's a starting SFM of 117 if I have
done the math right. I am sure there are folks pushing big turning
centers orders of magnitude faster, but this is after all only a bigger
import lathe. Its still an import lathe, and while its relatively
heavy, its light for its size.
Of course the SFM drops as the diameter is reduced. Maybe I could go
faster if I cranked up the speed as I reduced the diameter, but this is
a single phase gear head lathe. The motor just turns one speed. The
time to stop it and change gears would eat up any time savings.
Just for the heck of it I decided to see how much faster I could start.
At 460 RPM the insert was still doing fine. Still using the same insert
I used when I started this thread. I don't mean the same type. I mean
the same insert. That means the insert was hitting the outside of the
stock at 180 SFM. The number doesn't sound much bigger, but the part
time was definitely faster.
A couple ends with an intact insert at that speed and I decided to try
the last couple parts at 755 RPM. 296 SFM. That was significantly
faster. Part time was a lot shorter, and the insert still looks like
when I started. (I'll look at under magnification later) It wasn't so
fast that I had any issue keeping up, but it was fast enough I couldn't
do anything else, like move the stock in the saw to cut the next rough
blank.
Now that I have spares I think next time I cut a batch of these cores I
am going to push it until I chip an insert to see just what they will do.
Please bare in mind that these are relatively light cuts. The blanks
come off the saw at about 1.4" to 1.41" and get trued to 1.375".

Interesting thread Bob, thanks, is this example the type of tool you are
talking about? Never come across the diamond tipped versions of inserts
but my original machining in industry experience was in the 1960's! Only
hobby level now..
https://www.ebay.co.uk/itm/115334715488?_nkw=diamond+inserts+carbide+lathe&itmmeta=01J5Q723XNA0GREWTN8RFZEQK2&hash=item1ada7c1860:g:YyUAAOSwUtJiUKWN&itmprp=enc%3AAQAJAAAA4HoV3kP08IDx%2BKZ9MfhVJKnC8gu8jBQODZUzjY6nfSpuZas%2FJzGcWIYLgG5EPfxVgG0wH1c4QdrYrUHqD4z98NSE8atbz28SHAAsTTB%2FvXsdw1KSXcN7%2Bx6cwyg%2FcKXwvDq3eEqXZbpx%2Bzxtc0f0%2Fp0BsyoIUtnlZlJQI86p6TyhETkaZsGuuwYw1Ayo2CHAORe6WE1WiaDElO8xogeQY1mItmsxVxjRLhavW15vEW5hMGkyR8srWzmxrGq4dX%2B9yZ23zhsDDiiDdifsQ%2Bk8r7IRPefZ9T%2FppdLbpKF%2FwpjM%7Ctkp%3ABk9SR_S-iOetZA
It says for non ferrous but you are using on stainless without any red
spark? Can they be touched up if/when the edge goes? I know its only a
single but looks uncheap to me! C+

If you read Bob's post 30/7/2024 he clarifies he's not talking about
diamond tipped inserts but diamond shaped rhombic inserts.

[Bob La Londe]

Post by David Billington

Post by Charlie+

Post by Richard Smith

Post by Richard Smith
I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool
"disappears" by
     solution into the iron
?

My apologies.  I didn't at all mean something like a PVD diamond
coating.  DCMT is a diamond shaped insert.  Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings.  My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by
10-16 mini lathe also work on a heavier machine.  If the big boy
inserts don't work these still do.  In this case I was cutting 304
stainless steel. It improved the finish, didn't require sharpening,
had less heat input, and did the job much faster net elapsed time.
FYI:  I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish.  Diamond was popular when
I first started cutting aluminum on machine tools, and more recently
ZrN has become the popular coating.  I've tried them and the simple
fact is a coated tool isn't as sharp.  They might work better for
larger tools on larger machines, but on middle weight machines with
limited horsepower (5 or less) a bright sharp uncoated tool works best
for me. For high speed flood coolant makes the tool last without chip
welding, but coatings do not.  On smaller tools horsepower isn't even
a factor as the tool can't take it anyway.
--
Bob La Londe
CNC Molds N Stuff

Thx for this detail.
Interesting yes certainly.
Sorry "got the wrong end of the stick".
I used cutting insert tooling - aagh - 30 years ago.
Vertical milling shell-cutter on steel.
Did well - they'd never seen steel chip ejection like a chain-saw
cutting timber.  Took a visit from the rep. who explained this is how
the tooling is supposed to be used :-)
Coated carbide inserts - coating the gold coloured one - a Ti nitride(?)
coating - for this steel.

Pushing it harder and harder.  As I once offended Jim a little (sorry
Jim) over... time is money.  Even if you are doing something for fun,
favor, self... time is still your most valuable nonrenewable resource.
I needed to make another batch of stainless mold cores today.  (Stock
design that uses upto nine (9) 1.5in diameter cores to varY the size of
the casting.  That's 18 cuts to true them up after they come off the
saw.
My new inserts arrived a few days ago ago, but I wantedif I could bump
up the speed a bit with that little hobby lathe size insert.  I had been
using at at 300 RPM in low gear.  That's a starting SFM of 117 if I have
done the math right.  I am sure there are folks pushing big turning
centers orders of magnitude faster, but this is after all only a bigger
import lathe.  Its still an import lathe, and while its relatively
heavy, its light for its size.
Of course the SFM drops as the diameter is reduced.  Maybe I could go
faster if I cranked up the speed as I reduced the diameter, but this is
a single phase gear head lathe.  The motor just turns one speed.  The
time to stop it and change gears would eat up any time savings.
Just for the heck of it I decided to see how much faster I could start.
At 460 RPM the insert was still doing fine.  Still using the same insert
I used when I started this thread.  I don't mean the same type.  I mean
the same insert.  That means the insert was hitting the outside of the
stock at 180 SFM.  The number doesn't sound much bigger, but the part
time was definitely faster.
A couple ends with an intact insert at that speed and I decided to try
the last couple parts at 755 RPM.  296 SFM.  That was significantly
faster.  Part time was a lot shorter, and the insert still looks like
when I started.  (I'll look at under magnification later)  It wasn't so
fast that I had any issue keeping up, but it was fast enough I couldn't
do anything else, like move the stock in the saw to cut the next rough
blank.
Now that I have spares I think next time I cut a batch of these cores I
am going to push it until I chip an insert to see just what they will do.
Please bare in mind that these are relatively light cuts.  The blanks
come off the saw at about 1.4" to 1.41" and get trued to 1.375".

Interesting thread Bob, thanks, is this example the type of tool you are
talking about? Never come across the diamond tipped versions of inserts
but my original machining in industry experience was in the 1960's! Only
hobby level now..
https://www.ebay.co.uk/itm/115334715488?_nkw=diamond+inserts+carbide+lathe&itmmeta=01J5Q723XNA0GREWTN8RFZEQK2&hash=item1ada7c1860:g:YyUAAOSwUtJiUKWN&itmprp=enc%3AAQAJAAAA4HoV3kP08IDx%2BKZ9MfhVJKnC8gu8jBQODZUzjY6nfSpuZas%2FJzGcWIYLgG5EPfxVgG0wH1c4QdrYrUHqD4z98NSE8atbz28SHAAsTTB%2FvXsdw1KSXcN7%2Bx6cwyg%2FcKXwvDq3eEqXZbpx%2Bzxtc0f0%2Fp0BsyoIUtnlZlJQI86p6TyhETkaZsGuuwYw1Ayo2CHAORe6WE1WiaDElO8xogeQY1mItmsxVxjRLhavW15vEW5hMGkyR8srWzmxrGq4dX%2B9yZ23zhsDDiiDdifsQ%2Bk8r7IRPefZ9T%2FppdLbpKF%2FwpjM%7Ctkp%3ABk9SR_S-iOetZA
It says for non ferrous but you are using on stainless without any red
spark? Can they be touched up if/when the edge goes?  I know its only a
single but looks uncheap to me!  C+

If you read Bob's post 30/7/2024 he clarifies he's not talking about
diamond tipped inserts but diamond shaped rhombic inserts.

That's true, but I did run across a reference (Stefan Gotteswinter video
maybe) to an actual diamond attached to a tool. There are also coatings
that are called diamond, although most are actually DLC "diamond like
coatings."

[Peter Fairbrother]

Post by Bob La Londe
That's true, but I did run across a reference (Stefan Gotteswinter video
maybe) to an actual diamond attached to a tool.

PCD diamond turning inserts are actually quite common. They are mostly
made from natural diamonds, sometimes synthetic. There is another kind
whose name I have forgotten which is even more diamond-y, though still
not a single diamond.


PCD inserts (or better CBN ones if machining steels) made for aluminium
can be of use to hobby people if careful; being sharper then ones made
for harder stuff they will cut with less force, useful on smaller less
powerful machines.

Recommended only once you have learned how to use inserts without
chipping them!



SPD single point diamond turning tools (which are single diamonds) are
often used in CNC machines for optical moulds and lenses. The finish is
used as-is, no polishing!!!

Sometimes used for high-accuracy machining of copper and copper alloys too.

When air bearings aren't smooth enough ..

I have a 1/2 carat single diamond tool for truing grinding wheels. Cost
about £!5 iirc, but that was a while ago. Hmm, still £14.99 on ebay.

Post by Bob La Londe
There are also coatings that are called diamond, although most are
actually DLC "diamond like coatings."

CVD chemical vapour deposition diamonds are frequently grown on tooling
surfaces; they are real diamonds, though not single diamonds when grown
on surfaces.

They are sometimes made into blocks in a nickel or cobalt matrix, as
found on circular saw blades and polishing disks, though often natural
diamonds are cheaper.



Peter Fairbrother

[Jim Wilkins]

"Bob La Londe" wrote in message news:va2mum$3fqc7$***@dont-email.me...

That's true, but I did run across a reference (Stefan Gotteswinter video
maybe) to an actual diamond attached to a tool. There are also coatings
that are called diamond, although most are actually DLC "diamond like
coatings."
Bob La Londe

-----------------------------------

I've watched an optical lathe turn a Germanium lens for a military vehicle
thermal imager with a clear single crystal diamond bit with the geometry of
brazed carbide. It may have been synthetic, the laser diodes I had for the
inter-satellite communications project were mounted on thin sheets of
artificial diamond on a gold-plated copper heatsink. Diamond is an excellent
conductor of heat but an electrical insulator.

[Charlie+]

Post by David Billington

Post by Charlie+

Post by Bob La Londe

Post by Richard Smith

Post by Bob La Londe

Post by Richard Smith
I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
solution into the iron
?

My apologies. I didn't at all mean something like a PVD diamond
coating. DCMT is a diamond shaped insert. Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings. My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by
10-16 mini lathe also work on a heavier machine. If the big boy
inserts don't work these still do. In this case I was cutting 304
stainless steel. It improved the finish, didn't require sharpening,
had less heat input, and did the job much faster net elapsed time.
FYI: I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish. Diamond was popular when
I first started cutting aluminum on machine tools, and more recently
ZrN has become the popular coating. I've tried them and the simple
fact is a coated tool isn't as sharp. They might work better for
larger tools on larger machines, but on middle weight machines with
limited horsepower (5 or less) a bright sharp uncoated tool works best
for me. For high speed flood coolant makes the tool last without chip
welding, but coatings do not. On smaller tools horsepower isn't even
a factor as the tool can't take it anyway.
--
Bob La Londe
CNC Molds N Stuff

Thx for this detail.
Interesting yes certainly.
Sorry "got the wrong end of the stick".
I used cutting insert tooling - aagh - 30 years ago.
Vertical milling shell-cutter on steel.
Did well - they'd never seen steel chip ejection like a chain-saw
cutting timber. Took a visit from the rep. who explained this is how
the tooling is supposed to be used :-)
Coated carbide inserts - coating the gold coloured one - a Ti nitride(?)
coating - for this steel.

Pushing it harder and harder. As I once offended Jim a little (sorry
Jim) over... time is money. Even if you are doing something for fun,
favor, self... time is still your most valuable nonrenewable resource.
I needed to make another batch of stainless mold cores today. (Stock
design that uses upto nine (9) 1.5in diameter cores to varY the size of
the casting. That's 18 cuts to true them up after they come off the saw.
My new inserts arrived a few days ago ago, but I wantedif I could bump
up the speed a bit with that little hobby lathe size insert. I had been
using at at 300 RPM in low gear. That's a starting SFM of 117 if I have
done the math right. I am sure there are folks pushing big turning
centers orders of magnitude faster, but this is after all only a bigger
import lathe. Its still an import lathe, and while its relatively
heavy, its light for its size.
Of course the SFM drops as the diameter is reduced. Maybe I could go
faster if I cranked up the speed as I reduced the diameter, but this is
a single phase gear head lathe. The motor just turns one speed. The
time to stop it and change gears would eat up any time savings.
Just for the heck of it I decided to see how much faster I could start.
At 460 RPM the insert was still doing fine. Still using the same insert
I used when I started this thread. I don't mean the same type. I mean
the same insert. That means the insert was hitting the outside of the
stock at 180 SFM. The number doesn't sound much bigger, but the part
time was definitely faster.
A couple ends with an intact insert at that speed and I decided to try
the last couple parts at 755 RPM. 296 SFM. That was significantly
faster. Part time was a lot shorter, and the insert still looks like
when I started. (I'll look at under magnification later) It wasn't so
fast that I had any issue keeping up, but it was fast enough I couldn't
do anything else, like move the stock in the saw to cut the next rough
blank.
Now that I have spares I think next time I cut a batch of these cores I
am going to push it until I chip an insert to see just what they will do.
Please bare in mind that these are relatively light cuts. The blanks
come off the saw at about 1.4" to 1.41" and get trued to 1.375".

Interesting thread Bob, thanks, is this example the type of tool you are
talking about? Never come across the diamond tipped versions of inserts
but my original machining in industry experience was in the 1960's! Only
hobby level now..
https://www.ebay.co.uk/itm/115334715488?_nkw=diamond+inserts+carbide+lathe&itmmeta=01J5Q723XNA0GREWTN8RFZEQK2&hash=item1ada7c1860:g:YyUAAOSwUtJiUKWN&itmprp=enc%3AAQAJAAAA4HoV3kP08IDx%2BKZ9MfhVJKnC8gu8jBQODZUzjY6nfSpuZas%2FJzGcWIYLgG5EPfxVgG0wH1c4QdrYrUHqD4z98NSE8atbz28SHAAsTTB%2FvXsdw1KSXcN7%2Bx6cwyg%2FcKXwvDq3eEqXZbpx%2Bzxtc0f0%2Fp0BsyoIUtnlZlJQI86p6TyhETkaZsGuuwYw1Ayo2CHAORe6WE1WiaDElO8xogeQY1mItmsxVxjRLhavW15vEW5hMGkyR8srWzmxrGq4dX%2B9yZ23zhsDDiiDdifsQ%2Bk8r7IRPefZ9T%2FppdLbpKF%2FwpjM%7Ctkp%3ABk9SR_S-iOetZA
It says for non ferrous but you are using on stainless without any red
spark? Can they be touched up if/when the edge goes? I know its only a
single but looks uncheap to me! C+

If you read Bob's post 30/7/2024 he clarifies he's not talking about
diamond tipped inserts but diamond shaped rhombic inserts.

Thanks David, I re-read that post but have never come across the inserts
he is talking about so I was looking for a link to clarify myself! C+

[Peter Fairbrother]

On 20/08/2024 07:50, Charlie+ wrote:

[...]

Only hobby level now..
https://www.ebay.co.uk/itm/115334715488?_nkw=diamond+inserts+carbide+lathe&itmmeta=01J5Q723XNA0GREWTN8RFZEQK2&hash=item1ada7c1860:g:YyUAAOSwUtJiUKWN&itmprp=enc%3AAQAJAAAA4HoV3kP08IDx%2BKZ9MfhVJKnC8gu8jBQODZUzjY6nfSpuZas%2FJzGcWIYLgG5EPfxVgG0wH1c4QdrYrUHqD4z98NSE8atbz28SHAAsTTB%2FvXsdw1KSXcN7%2Bx6cwyg%2FcKXwvDq3eEqXZbpx%2Bzxtc0f0%2Fp0BsyoIUtnlZlJQI86p6TyhETkaZsGuuwYw1Ayo2CHAORe6WE1WiaDElO8xogeQY1mItmsxVxjRLhavW15vEW5hMGkyR8srWzmxrGq4dX%2B9yZ23zhsDDiiDdifsQ%2Bk8r7IRPefZ9T%2FppdLbpKF%2FwpjM%7Ctkp%3ABk9SR_S-iOetZA

Those are PCD polycrystalline diamond tipped inserts. Diamond crystals
in a cobalt alloy matrix. For very hard materials sometimes, but far
more often for extreme wear resistance.

It says for non ferrous [..]

The carbon in the diamond dissolves in iron and steel (and nickel
alloys), so they don't last long on steel. You can use CBN cubic boron
nitride on steel etc for longer life, about the same price.

Hobby level chaps (and most small-batch pros, indeed most pros) should
generally stick to HSS or carbide, unless they are doing something unusual.

Can they be touched up if/when the edge goes?

No. Carbide inserts can sometimes be touched up with diamond (though
it's usually not worth doing unless you want something special), but not
PCD or CBN.

I know its only a single but looks uncheap to me! C+

Last time I bought any they were £20-odd each, and that was years ago.


Peter Fairbrother

[Charlie+]

Post by Peter Fairbrother
[...]

Only hobby level now..
https://www.ebay.co.uk/itm/115334715488?_nkw=diamond+inserts+carbide+lathe&itmmeta=01J5Q723XNA0GREWTN8RFZEQK2&hash=item1ada7c1860:g:YyUAAOSwUtJiUKWN&itmprp=enc%3AAQAJAAAA4HoV3kP08IDx%2BKZ9MfhVJKnC8gu8jBQODZUzjY6nfSpuZas%2FJzGcWIYLgG5EPfxVgG0wH1c4QdrYrUHqD4z98NSE8atbz28SHAAsTTB%2FvXsdw1KSXcN7%2Bx6cwyg%2FcKXwvDq3eEqXZbpx%2Bzxtc0f0%2Fp0BsyoIUtnlZlJQI86p6TyhETkaZsGuuwYw1Ayo2CHAORe6WE1WiaDElO8xogeQY1mItmsxVxjRLhavW15vEW5hMGkyR8srWzmxrGq4dX%2B9yZ23zhsDDiiDdifsQ%2Bk8r7IRPefZ9T%2FppdLbpKF%2FwpjM%7Ctkp%3ABk9SR_S-iOetZA

Those are PCD polycrystalline diamond tipped inserts. Diamond crystals
in a cobalt alloy matrix. For very hard materials sometimes, but far
more often for extreme wear resistance.

It says for non ferrous [..]

The carbon in the diamond dissolves in iron and steel (and nickel
alloys), so they don't last long on steel. You can use CBN cubic boron
nitride on steel etc for longer life, about the same price.
Hobby level chaps (and most small-batch pros, indeed most pros) should
generally stick to HSS or carbide, unless they are doing something unusual.

Can they be touched up if/when the edge goes?

No. Carbide inserts can sometimes be touched up with diamond (though
it's usually not worth doing unless you want something special), but not
PCD or CBN.

I know its only a single but looks uncheap to me! C+

Last time I bought any they were £20-odd each, and that was years ago.
Peter Fairbrother

Thanks Peter for all the detail, I'm better informed now, aprecciated.
C+