# Inserted Carbide Parting-off Tool



## Brian Rupnow (May 24, 2015)

So--I have to ask---I have read a lot of various reports about carbide inserted parting off tools.  I have only ever used HSS parting off tooling, and it scares me right to death every time I use it. I know the correct set up, speeds and feeds, exact center height, lock the saddle, use lots of cutting fluid to flush out chips, keep the tool at exactly 90 degrees to the central axis  blah, blah, blah. I know how to sharpen my tools and the correct relief angles required.--And even so, about one time out of five the blade digs in, the lathe gives a mighty groan, and either the belt slips, the tool breaks, it pulls the piece out of the chuck, or I manage to slap the e-stop button and then go and change my shorts!!!!--I do NOT want to mount an upside down -run my lathe in reverse-mount my parting off tool on the wrong side of the saddle cut off solution. I want to know from people who really have and use inserted carbide parting off tooling.--Is it really better? My 10" x 18" lathe has speeds ranging from a low of 115 RPM (which I generally use for parting off) to a high of 1620 RPM in about 6 available "stages", and it doesn't lack for power. I do not have flood coolant. I do not have power feed on the cross slide. If the inserted carbide parting off tooling is really that much better, I might just be able to afford the seemingly outrageous price they want for one. I find that for 95% of the parting off and grooving I do, that .093"  (3/32") seems to be about right. The largest stock I would ever part off is probably 2" diameter steel.--Opinions, please.---Brian


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## kuhncw (May 24, 2015)

Hi Brian,

I've used an Iscar Self Grip SGFH 19-2 inserted cutoff blade for quite a few years.  They are pricey, but the blade works well for me.  I've used the blade in an 11 inch Logan and now in my 13 inch Sheldon.  There are other brands and cheaper blades.  I can only comment on the Iscar.  This blade carries a narrow insert in the 0.093 or less range.  I sometimes drip some tapping fluid or cutting oil into the cut.

Chuck


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## modelman1838 (May 24, 2015)

I bought one of these carbide insert parting off tools about 16 years ago when they were first available for the smaller lathe such as the Myford super seven. It does work really well and you can part off quite large diameters of about 2 ins at much higher speed even without coolant. I think they score by having the best rake and clearance angles for the job built into them, achieved by many years of experimenting. They really do work.
 Hugh.


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## Swifty (May 24, 2015)

I have been using a 4mm wide carbide parting for years as well as a HSS one. I found that the carbide is too wide for most of the smaller diameters, too much chatter etc. so most of the time I have been using the HSS one. Recently I bought a QCTP and a set of 16mm shank tools to suit, one of the tools was a carbide parting tool, it is only 3 mm wide and it works great. Depending on your diameter and material, I feel that you speed is too slow when parting off. Generally I use a speed af about 550 RPM, mostly in brass and aluminium, but also when required, in steel as well.

Paul.


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## Brian Rupnow (May 24, 2015)

Okay Paul---You just made me google it.--And the answer is surprising to me. 17 foot per minute for cast iron, 57 fpm for brass, 83 fpm for aluminum, and 37 fpm for mild steel. That is recommended speed for parting off with an HSS parting off tool. Based on parting off a 3/4" (19 mm) shaft, that would be 87 rpm for cast iron, 290 rpm for brass, 422 rpm for aluminum, and 188 rpm for steel.


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## Brian Rupnow (May 24, 2015)

I'm impressed!!! I just parted off a piece of 3/4" cold rolled steel at 210 rpm, which is as close as my lathe can get to 188 rpm. It went very smoothly, and far better than the 115 rpm I have been using for the last 5 years!!! Big head-slap for me.---Damn--I should have figured that out 5 years ago. I still think I will pursue the inserted carbide blades though.


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## Brian Rupnow (May 24, 2015)

This is the .093" HSS cutting tool that I used to make that cut.


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## bazmak (May 24, 2015)

Hi Brian,the variable speed lathe is great for nudging the speed while cutting
The carbide blades are good but i prefer HSS.What i have found is that you need an increased top rake angle for steel something like for alum.Even so i still avoid parting off or hold my breath
Usual fault for digging in  if everything is set correctly is lack of ridgidity
or play in slides etc.The tool you are using looks good with large inbuilt top rake.For large Dias i also cut so far ,withdraw and move the compound/saddle sideways a couple of thou to the waste side for extra clearance


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## Swifty (May 24, 2015)

One of the biggest problems of parting off is, the surface speed decreases as you get near the centre, fine if you have constant surface speed, but not the usual thing. I seem to break tips on blades always as it gets towards the centre, and lose surface speed. I have to admit that I'm a bit of a speed demon when it comes to machining speeds, guess I'm just impatient.

Paul.


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## Niels Abildgaard (May 25, 2015)

A rather expensive but foolproff way:

http://www.homemodelenginemachinist.com/showthread.php?t=10176


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## goldstar31 (May 25, 2015)

I've used the rear parting tool as described in Vol 142 of Model Engineer and later in George Thomas's epic Model Engineers Workshop Manual for years now and I used  a lolloping along 200 or 350rpm in using a a simple Eclipse hss. I've used it on a far from perfect old Myford ml7 and then a 918 and now a Myford Super 7B which I restored. Within limits, the speeds are no issue but the maximum diameter of round is 2". I use lard oil which I have advocated for 'ever' which is what traditional turners used until it became too expensive for cost accountants( Grrrrh!)

The only trick or difficulty is grinding the 1" kerf along the top of the blade. I first used my tool and cutter grinders but most workers do not have one and one to do the 140 degree kerf.  So with care, the kerf can be 'ettled'( the auld Scots from the Alliance Francaise- atelier) using a drill press with a worn cutting off disk.

That kerf, I must assure you is the secret of parting off. The blade, be it angled or not gets a ribbon of steel( or whatever) and as the ribbon comes off- downwards it jams in the kerf. And the thing breaks unless it is narrowed- using the rounded or vee'd kerf.

AS I repeat, the GHT tool post gets a very neat thin ribbon of swarf and provided the work is supported, one can cut an absolutely smooth face almost to the centre.

GHT- for whom I have a high regard as a brilliant model and professional engineer overdid the need to do the front cutting edge at an angle of again 140( male) degrees. I did it- it worked fine- but the regrind which only requires a lick was left as flat cutting edge.

If people want, the kits for both the Myford size and laerger are from Hemingwaykits but mine is just from bits of scrap.

There is NO mystique, black art or the need to have ( and try to regrind carbide). I can regrind carbide but don't.

I hope this helps

Norman


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## gus (May 25, 2015)

I find the 1/16" HSS Parting Tool from LMS to be quite suitable for my Sakai Mini Lathe. With dobs of Tapmatic Cutting Fluid and not so greedy digging in,I get good results cutting steel, brass,C.I. etc etc. Very important to keep groove wide to prevent tool seizing. It is important to have tool sharpness maintained. If it doesn't cut well, its about time grind sharpen.
For aluminum,I use Tapmatic Tapping Fluid(for aluminium only).
My luck is bad with carbide insert parting tool. Or perhaps I should rewind and check what went wrong.I still have the Japanese parting tool.The inserts is expensive.:wall:


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## purpleknif (May 25, 2015)

Been doing this stuff full time for thirty years and the whole secret to this tool is clearance. Mostly on the back side.


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## goldstar31 (May 25, 2015)

It would be interesting to learn the views of those who have actually made and used a Thomas rear tool.

I've had mine about the same length of time as my Quorn- about 1974.

Regards

Norman


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## GLCarlson (May 25, 2015)

Brian Rupnow said:


> do NOT want to mount an upside down -run my lathe in reverse-mount my parting off tool on the wrong side of the saddle cut off solution.



Given that a lot of history -and experts, GHT for example- think that this is the OPTIMAL method, why not?  I understand some concern with a threaded spindle (vs Camlock), but the rear mount solves that. There is a hypothetical risk to the saddle dovetails, but while I've seen that discussed, I've never seen a report of the dovetails actually being damaged by the lifting forces.

I'm genuinely curious: why would one rule out a time-tested method, used by many with reported good success, which solves all of the problems one is having with the "classic" method?

FWIW, I've been using an upside down parting tool on my lathe for 30 years- it fails safe, isn't finicky, and works great.


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## Brian Rupnow (May 25, 2015)

Best reason ever--There is no room on my lathe to put one.


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## goldstar31 (May 26, 2015)

Brian
          Point taken about room but GHT in his pedantic and infinite wisdom catered for such eventualities and  did drawings for 'overhang' on both the shorter saddle on the ML7 and the Drummond( which I both owned!)

For others who are following the discussion, my 918 or 9x20 or actually a 920( Ugh!), I had a subtable of steel to use the Myford tee slotted designs. I had several very useful Myford and GHT bits and whilst Myford slots are awful, I re-iterate, I wasn't going to dispose of them when a bit of steel solved the problem.

Good luck- anyway.

Norman


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## GLCarlson (May 26, 2015)

Brian Rupnow said:


> Best reason ever--There is no room on my lathe to put one.



I confess that hadn't occurred to me!  Also reassuring- you haven't identified some non-obvious but horribly important reason to avoid this approach. I'm always worried I've missed something when an expert absolutely rejects a method.


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## bazmak (May 26, 2015)

I have used a rear tool post for parting off and it works well.May make another
as i have room and the T slots on the C4.My only dislike is that as an old school engineer i like to see and hear the chips,it tells a story.With high speed machining and CNC its fast and blind.You start with a blank and finish with a part the in between is a blur


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## Brian Rupnow (May 26, 2015)

GLCarlson---You're calling me an expert?--Good Lord man, I just fumble along with all the "want to be" machinists out there. I AM an expert design engineer. I am a novice at this machining business.---Brian


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## barnesrickw (May 26, 2015)

Rear post helps a lot.


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## kiwi2 (May 27, 2015)

Tubal Cain has done a series of videos on parting.
[ame]https://www.youtube.com/watch?v=82LtUTBmxwQ[/ame]
He tried a carbide tool and was surprised at how well it did.

Regards,
Alan C.


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## goldstar31 (May 27, 2015)

Funny but the earlier Tubal Cain( Tom D Walshaw) didn't but designed much of people today are copying. He produced a Gibraltar tool post which flies in the face of his successor.

The difficulty in carbide is that it is difficult( not impossible) to recondition. OK, I can do it on most straight edges but refuse to cock up a decent diamond wheel into a funny shape - and then get it back to flat.
On the other hand, I can alter abrasive disks quickly and more cheaply to do carbon and hss tooling.  Repeating myself, I used a worn disk to do my blade instead of the quoted 140 degree Thomas one.

Worth thinking about. My Tubal Cain was- gulp- a lecturer in machining where there was a lot of machining. He argued with Thomas- but that is normal!

Cheers

Norman


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## pjpickard (May 31, 2015)

Norman,

Could you post a pic of the angle that is ground in the cut off tool? I have never been able to wrap my head around what GHT was getting at.

Thanks,

Paul


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## goldstar31 (May 31, 2015)

pjpickard said:


> Norman,
> 
> Could you post a pic of the angle that is ground in the cut off tool? I have never been able to wrap my head around what GHT was getting at.
> 
> ...


 
I have a blockage about photos.

Quite simply, GHT ground 1" on the thickest edge of his parting ground in the shape of a ( female)vee of 140 degrees. I was simpler and created a ( female) round groove.

If you look at it, all that GHT and me have done is created a method of narrowing a ribbon. So the tendency( which has bugged lesser mortals- hic!) of breakage is minimum.


Enjoy

Norman


We are ecstatic, the family has another new piano. One to go with our  Grand and I'm more or less free of doctors so I'm going for a month's rest.

My 85th birthday!


Hurrah

Norman


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## gus (Jun 1, 2015)

Hi Kiwi2.

Thanks for posting Tubal Cain's video on parting.  Parting off in Trades School was a nightmare. Our C & G  aka City & Guilds qualified machining instructors were not really highly skilled turners and was not able to demonstrate parting off to impress Gus. They did parting a wee bit nervous.Years later I witnessed an old hand parting off 2 '' Mild Steel Bar stock skillfully with ease. Too bad I did not spend enough time watching and learning from him. I do parting with LMS ''T'' Parting Tool with success.It best to check tool sharpness and regrind if necessary.
Tubal Cain was a good teacher.


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## canadianhorsepower (Jun 1, 2015)

Finally a good video why to cut in reverse mode 
or to install a cutting tool at the back of your cross slide.
When using my Taig lathe I put the tooling always upside down
LOVE it Thm:Thm:Thm:
enjoy

[ame]https://www.youtube.com/watch?v=-RZRq0olsxM[/ame]


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## barnesrickw (Jun 1, 2015)

I have a rear tool post for my Taig, but so far I've used it mostly for parting.  I'll have to try some other tools.  One good thing about it is if you use a tool other than 1/4 inch square, the center of the tool and stock will still be in align because the tool references on the bottom of the post on the cutting side.


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## goldstar31 (Jun 2, 2015)

barnesrickw said:


> I have a rear tool post for my Taig, but so far I've used it mostly for parting. I'll have to try some other tools. One good thing about it is if you use a tool other than 1/4 inch square, the center of the tool and stock will still be in align because the tool references on the bottom of the post on the cutting side.


 
When Hemingwaykits did the little GHT kit, they included the design for a single blade and a lathe tool holder rather than the 2 thicknesses of parting blades. Why, I presume that this was then the alternative to the QCTP because GHT at the time made a rotating and highly accurate 4 way tool post which was better than the original one made by Myfords.
GHT had 2 Myford ones originally -one for steel and one for brass. Aluminium hadn't been much in use then. I suppose you pays your money and takes yer choice. 
Me, I made up another rear tool post but to Martin Cleeve's fabricated design( 3 bits of metal bolted up) which held Two lathe tools.  Still have it.
I rather like the Cleeve stuff of 'Turrets without milling ' article which utilises cob ends and no cost or need to mill or do anything mind bending.

People have forgotten now all these things because they spend time buying things instead of reading what has been tested and then written about.

Of course, we had no money then. I made scale model aircraft using old single edge razor blades and broken glass scrapers  from bombed out buildings! :hDe:


Cheers

Norman


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## gus (Jun 3, 2015)

Hi Big Bro Norman,

I share your  idea/practice making DIY Model Aircrafts with what's on hand and saving pennies and pounds. Coming from a poor child/boyhood has more advantages thandisadvantages. We make our own toys for pennies.Walk into any model aircraft shops,and you find enthusiats squandering money on ready makes. Its hard and expensive to buy balsa wood in Singapore as there are not too many who want and can DIY their model aircrafts and fly them.  Despite this scenario,I DIY 4 fighter model aircrafts-------Zeros     Spitfires    Mustangs   etc. 
Gus must be the only one in  5 million in Singapore who can DIY build his own model aircraft engines. 
Now building the Howell V-2. Had no warning the V-2 is a Pandora Box with many surprises.

Take care.

A M.I.C. QCTP from UK or USA will cost Gus a bomb landed in Singapore. So its DIY my own. Cutting the dovetails male and female was scary for first-timer Gus. I am into my second QCTP and enjoy using it every time I work on the lathe.


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## Brian Rupnow (Aug 4, 2015)

After many delays, and much confusion, I finally, today, received the Aloris parting off tool and the inserts to go with it. My total bill, including tax, was an outrageous $226.00 Canadian. I was unable to get .093" inserts, and had to settle for a  0.123" (3 mm) wide carbide insert. I rushed home to try it and see if it would fit in my 10" x 18" Craftex lathe with a quick change toolpost on it. It did fit into my standard cut-off blade tool holder, and I was able to center the tip of the cutting edge on the centerline of the chuck. I ran the lathe at 360 RPM and cut off a piece of 3/4" mild steel rod. It did chatter, same as my old 0.093" HSS blade, but it rapidly cut thru the 3/4" steel with no problem other than some chatter. I immediately picked up the cut off portion to look at, and burned Hell out of my thumb and finger---(won't do THAT again!!) So--Okay, it works. How much better does it work than the HSS blade?--Well, I don't really know at this point. I have found that I was running the lathe at much too low an rpm for even the HSS cutting blade, and that is what was causing so many of my parting off problems. Once I bumped up the speed of the lathe to give me the proper parting off speed in "inches per minute', the old HSS blade cut quite well. I may have wasted $226 but if so, then I consider it a "learning pain"---OUCH!!! Then again, it may be one of my wiser purchases. Only time and use will tell.----Brian.


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