cutting threads on lathe
 

I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.

cutting threads on lathe
 

On Mar 19, 6:33*pm, Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.

Carbide is a matrix of grains glued together, like concrete, and it
doesn't take as sharp an edge as HSS. I doubt you'll ever need carbide
on a lathe with so little power anyway. It's likely that if the
material was that difficult to cut the lathe would twist away when you
tried to force a carbide bit into the work.

High Speed Steel will cut stainless steel and Grade 8 hardened bolts,
it just dulls quickly.

jsw

cutting threads on lathe
 

Cydrome Leader wrote:

I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.

The 60 degree cheapo brazed carbide lathe bits I got were similarly
awful stock and the point wasn't fine enough for smaller threads. I
honed one of the bits with a diamond hone for a few minutes and the
results were much better.

cutting threads on lathe
 

Jim Wilkins wrote:
On Mar 19, 6:33?pm, Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.

Carbide is a matrix of grains glued together, like concrete, and it
doesn't take as sharp an edge as HSS. I doubt you'll ever need carbide

I though they were giant crystal or something like that. The "like
concrete" part makes sense.

on a lathe with so little power anyway. It's likely that if the
material was that difficult to cut the lathe would twist away when you
tried to force a carbide bit into the work.

High Speed Steel will cut stainless steel and Grade 8 hardened bolts,
it just dulls quickly.

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.

cutting threads on lathe
 

On Mar 19, 7:01*pm, Cydrome Leader wrote:
Jim Wilkins wrote:
...
Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.-

Carbide is fine under the right conditions. My old 10" South Bend
lathe is on the border where sometimes it works and sometimes it
doesn't. It's been better since I ground the uneven wear off the
compound slide and tightened the gibs. I get nearly a mirror finish
with carbide on stainless steel.

jsw

cutting threads on lathe
 

On Sat, 19 Mar 2011 22:33:39 +0000 (UTC), Cydrome Leader
wrote:

I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.


Wrong carbide, wrong rake, wrong lubricant, too high or too low, or
crappy chinese carbide without a good edge. Lots of possible reasons
for a crappy cut.

cutting threads on lathe
 

On Sat, 19 Mar 2011 22:33:39 +0000, Cydrome Leader wrote:

I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by
the spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too.
It looked like there was more tearing or smearing than cutting going on.

Make sure any cutting edge is sharp sharp. Not just "marketing sharp".
You want it scary sharp. Even touching it up with a bench grinder is
probably going to get it sharper than it was when you got it. If I
really care about a cut I rough the tool out on a grinder, but then I
hone it by hand on a stone.

If you were trying for something like a #5-40 thread, then be aware that
the thread is really deep compared to the material diameter, and that's
going to steal lot of strength from the piece. Consequently, your piece
will start bending away from the tool, and Really Bad things will
happen. I wouldn't try that deep a thread without using a center in the
tailstock. (actually for that sort of thing I use a die!) The finer the
thread is in proportion to the OD of the piece the less trouble you're
going to have doing the cut.

Make sure the tool height is correct -- you want to be bang on the center
of the work; get it off and your tool won't work right.

--
http://www.wescottdesign.com

cutting threads on lathe
 

Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.




The carbide was not ground for cutting the brass. You need a honed edge
and high rake angle brass. You are better off using HSS because you
can grind the proper angle on the tool. You could order inserts
designed for cutting brass too.

John

cutting threads on lathe
 

"Cydrome Leader" wrote in message
...
Jim Wilkins wrote:
On Mar 19, 6:33?pm, Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.

Carbide is a matrix of grains glued together, like concrete, and it
doesn't take as sharp an edge as HSS. I doubt you'll ever need carbide

I though they were giant crystal or something like that. The "like
concrete" part makes sense.

on a lathe with so little power anyway. It's likely that if the
material was that difficult to cut the lathe would twist away when you
tried to force a carbide bit into the work.

High Speed Steel will cut stainless steel and Grade 8 hardened bolts,
it just dulls quickly.

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.

I much prefer HSS to carbide for a lot of jobs and especially threading. You have to
have rigidity squared to use carbide well and horsepower too. Great for removing a
lot of material quickly or production jobs. I've got a 7.5 HP Reed Prentice with the
rigidity and HP and only use carbide 25% of the time.

cutting threads on lathe
 

"John" wrote in message
...
Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by
the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.




The carbide was not ground for cutting the brass. You need a honed edge
and high rake angle brass. You are better off using HSS because you can
grind the proper angle on the tool. You could order inserts designed for
cutting brass too.

John

Positive rake for brass is trouble, due to hogging. That's especially true
on a small, light duty machine.

Beyond that, threading tools should not have rake unless the rake angle is
compensated in the included angle, and then you are limited to the
questionable performance you'll achieve. The best policy is to keep rake
at 0 degrees when chasing threads, and to feed by the compound, which would
be set at 29 -1/2 degrees. I prefer 29 degrees, to insure the back side of
the thread cleans up.

Using a carbide tool for brass after it has seen steel is a huge mistake.
The keen edge that is necessary for the tool to cut well will have long
since been dulled, yielding poor performance. Brass tends to act like a
bearing, and will readily float a tool that is slightly dull, yielding
inconsistent results.

A person with little to no experience in chasing threads is never wise to
experiment with carbide. It takes almost nothing to chip the fine tip of a
carbide threading tool, which, once chipped, will perform poorly, if at all.
Stick with HSS unless you have more than a good reason to go to carbide,
then insure that you use the proper grade. That often spells the
difference between success and total failure.

Harold

cutting threads on lathe
 

On Sat, 19 Mar 2011 23:37:11 -0400, "Tom Gardner" w@w wrote:


"Cydrome Leader" wrote in message
...
Jim Wilkins wrote:
On Mar 19, 6:33?pm, Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by the
spare I had.

the cuts looked like **** too. They weren't really shiny and the "feel"
from the handcrank on the headstock/gear train didn't seem right. I was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too. It
looked like there was more tearing or smearing than cutting going on.

Carbide is a matrix of grains glued together, like concrete, and it
doesn't take as sharp an edge as HSS. I doubt you'll ever need carbide

I though they were giant crystal or something like that. The "like
concrete" part makes sense.

on a lathe with so little power anyway. It's likely that if the
material was that difficult to cut the lathe would twist away when you
tried to force a carbide bit into the work.

High Speed Steel will cut stainless steel and Grade 8 hardened bolts,
it just dulls quickly.

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.

I much prefer HSS to carbide for a lot of jobs and especially threading. You have to
have rigidity squared to use carbide well and horsepower too. Great for removing a
lot of material quickly or production jobs. I've got a 7.5 HP Reed Prentice with the
rigidity and HP and only use carbide 25% of the time.

NOT, repeat NOT for the original poster. I recently bought carbide
threading inserts for my CHNC lathe. WHAT AN IMPROVEMENT! On a machine
built for it, these are great. Of course, I never thread at less than
500 RPM on larger diameters and into the 1000s if going under one
inch. Don't know if the reflexes could ever be fast enough on a manual
machine.

Karl

cutting threads on lathe
 

"Karl Townsend" wrote in message
...
On Sat, 19 Mar 2011 23:37:11 -0400, "Tom Gardner" w@w wrote:


"Cydrome Leader" wrote in message
...
Jim Wilkins wrote:
On Mar 19, 6:33?pm, Cydrome Leader wrote:
I finally attached the thread cutting kit to a sherline lathe. The kit
came with a 60 degree carbide cutter.

Even with 1/4" brass rods, that broke in probably minutes, followed by
the
spare I had.

the cuts looked like **** too. They weren't really shiny and the
"feel"
from the handcrank on the headstock/gear train didn't seem right. I
was
only cutting 2 to 3 mils per pass.

I decided to gring my own with 1/4" HSS steel blanks on a Tormek knife
sharpener.

That worked much much better. The cuts look nice and shiny.

So what's the deal with the ugly finish I was getting with carbide? I
think I know why the tips snapped off, but the finish part I don't
understand. A mild steel rod looked awful with the carbide cutter too.
It
looked like there was more tearing or smearing than cutting going on.

Carbide is a matrix of grains glued together, like concrete, and it
doesn't take as sharp an edge as HSS. I doubt you'll ever need carbide

I though they were giant crystal or something like that. The "like
concrete" part makes sense.

on a lathe with so little power anyway. It's likely that if the
material was that difficult to cut the lathe would twist away when you
tried to force a carbide bit into the work.

High Speed Steel will cut stainless steel and Grade 8 hardened bolts,
it just dulls quickly.

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I
have,
I can't really test this anymore.

I much prefer HSS to carbide for a lot of jobs and especially threading.
You have to
have rigidity squared to use carbide well and horsepower too. Great for
removing a
lot of material quickly or production jobs. I've got a 7.5 HP Reed
Prentice with the
rigidity and HP and only use carbide 25% of the time.

NOT, repeat NOT for the original poster. I recently bought carbide
threading inserts for my CHNC lathe. WHAT AN IMPROVEMENT! On a machine
built for it, these are great. Of course, I never thread at less than
500 RPM on larger diameters and into the 1000s if going under one
inch. Don't know if the reflexes could ever be fast enough on a manual
machine.

They couldn't. g

For the OP, what Harold said. And don't forget to radius the tip of your HSS
threading tool. The correct amount for each thread pitch is published in the
manuals, and you can make a close approximation with a good loupe and a
caliper set to the right width.

First, though, just get the darned thing cutting right with a HSS tool, even
if you leave the tip sharp to start with. It's tricky on a very small lathe.
Follow Harold's recommendations.

--
Ed Huntress

cutting threads on lathe
 

Cydrome Leader wrote:

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.

FWIW, in the shop where I sit, they have a diamond wheel where they can
grind new points on carbide inserts; carbide is the only thing anybody's
allowed to use it on.

My first thought was rake, chip relief, and whatever you call the
height of the cutter, but then again, brass is kinda mushy in those
circumstances. I was once trying to turn down a piece of copper, and
the bit bit into the copper and the part bent like toothpaste.

Good Luck!
Rich

cutting threads on lathe
 

"Rich Grise" wrote in message
...
Cydrome Leader wrote:

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.

FWIW, in the shop where I sit, they have a diamond wheel where they can
grind new points on carbide inserts; carbide is the only thing anybody's
allowed to use it on.

Good reason -- high speed steel, or any ferrous metal, will eat your diamond
wheel alive. Steel really likes carbon, when you get it hot, and it doesn't
care how much the carbon costs. d8-)


My first thought was rake, chip relief, and whatever you call the
height of the cutter, but then again, brass is kinda mushy in those
circumstances. I was once trying to turn down a piece of copper, and
the bit bit into the copper and the part bent like toothpaste.

Good Luck!
Rich

Copper or any soft-to-medium copper alloy, especially yellow brass, will
grab a tool if the work or the tool aren't rigidly supported (MUCH shorter
overhangs are allowed than with steel), and if there is enough positive rake
to make the tool want to grab. Small lathes, including my SB 10L, are among
the machine tools that are vulnerable.

Standard lathe-bit side- (usually) or front (sometimes, as in plunge
cutting) rake for turning brass, as a safe starting point, has been negative
5 degrees, for over 100 years. However, most applications are done closer to
zero rake. Negative rake is tricky, too, sometimes causing the tool to
skate.

Harold's recommendations were spot-on.

--
Ed Huntress

cutting threads on lathe
 

Rich Grise wrote:
Cydrome Leader wrote:

Does HSS leave nicer finish when sharp than carbide on these materials?
Considering tiny pieces of the tips broke off the carbide cutters I have,
I can't really test this anymore.

FWIW, in the shop where I sit, they have a diamond wheel where they can
grind new points on carbide inserts; carbide is the only thing anybody's
allowed to use it on.

My first thought was rake, chip relief, and whatever you call the
height of the cutter, but then again, brass is kinda mushy in those
circumstances. I was once trying to turn down a piece of copper, and
the bit bit into the copper and the part bent like toothpaste.

Good Luck!
Rich

I noticed this too- copper seems really sticky, and the bronze bolts used
by utility companies are hard to even drill.