# Selecting and Using Tungsten Carbide Partoff Tooling (Long)



## quinette7 (Sep 30, 2010)

My Thoughts on Selecting and Using Tungsten Carbide Partoff Tooling

I hope the following doesnt sound like an ad for Iscar, but it is their tooling that I know the best. I wrote it several years ago to answer a specific question, and thought it would be of benefit to this group. I want to preface my remarks by saying that I worked as a technical sales rep for Iscar from 1995 to 2001, but I no longer have ties with the company or any other. Following Iscar, I worked in the same capacities for Valenite and Mitsubishi, and I retired in 2006, so some of my knowledge about Iscar products is 10 years old now. Most of my job was spent doing technical troubleshooting on both CNC and manual machines. Partoff and grooving accounted for about 40% of my business. My personal machining has always been strictly a hobby.

Here's a little historical background of Iscar's partoff line, as best I know it, while ignoring their extensive Cut-Grip groove/turn line of tools. Iscar was just a small company until they developed and introduced the tungsten carbide partoff insert. Then the machining world changed. The first generation was the GTN style. Despite the fact that this tool design was a major improvement in partoff technology, there was room for improvement, and Iscar chose not to spend any effort defending their patent. A lot of these are still used today, and there are a number of imitators who make inserts that will fit the Iscar blades. The insert/blade interface of the GTN is a simple wedge shape. Unfortunately, the insert can move deeper into the blade's pocket under heavy cyclical loads. I have seen close-up movies graphically illustrating this. Personally, I avoid this design. The second generation was the GFN, the "F" designating a fixed stop that prevents insert movement. The third generation was the Do-Grip (pronounced dew-grip). The advantage here was that the insert was double ended, giving greater economy per cutting edge. The real innovation was their ability to mold these inserts so that the two cutting edges were twisted in relation to each other. While the edge that is in use is horizontal to the groove it is cutting, the second edge is tilted so that it does not rub along the walls of the groove. This allows the insert to cut a groove deeper than the insert's length, a limiting factor for double ended inserts that aren't twisted. (This was not possible in the thinner insert widths when the Do-Grip was introduced - check their catalog for current information.) The insert and its pocket in the steel blade both have a generally rectangular profile. The clamping finger of the blade is lifted by a wrench with a camming action. The next generation evolved into a partoff/grooving/turning tool, the Heli-Grip, which is a high productivity tool for CNC machines. It can be used on a manual machine, but not to optimum effectiveness. In the larger insert sizes, the Do-Grip and Heli-Grip inserts and blades are interchangeable, but not in the narrower sizes that can be used on our lathes. I believe that the home machinist should stick to the 2 or 3mm wide inserts. The key point about the Do-Grip/Heli-Grip insert retention system is that, even without screw-down clamping, the insert is held well enough to permit aggressive lateral turning and the resulting significant side loads. The necessary tool movements for successful grooving and turning with the same insert can be programmed into a CNC machine, but only roughly approximated on a manual machine. One disadvantage to the double-ended inserts is that if the insert cracks when using the first edge, the second edge is usually unusable. But, in that case that end of the blade is usually scrapped, too. I use both the GFN and Do-Grip/Heli-Grip styles. You can find similar tools from competitors.

While I love using tungsten carbide inserts for turning, boring, and facing on my lathe, and eagerly threw away all of my HSS partoff blades once I learned how to use partoff inserts, I have some hesitation making a broad recommendation for other hobbyists using manual lathes. The initial investment of blade, blade holder, and box of inserts is at least $300. Using a square shank tool, rather than blade style, offers initially lower entry price, but they are only single sided and don't offer the ability to shorten the amount of blade extension. And crashes WILL occur. I'm still nervous when I do it. I've crashed 2 blades within the past year. Partoff can make for an expensive hobby. Let me share some things I've learned with those who have chosen to use carbide. If HSS partoff blades work well for you, stick with it - it is a cheaper solution for the hobbyist. Pardon me for using Iscar's nomenclature - it's what I know the best. Other companies make good partoff tooling, also, but I think Iscar has taken it to a fine art, with some options that no one else offers. I also like Sandvik's tools. 

One of the biggest challenges in the partoff operation stems from the fact that the tool is nearly as wide as the groove it cuts, making chip removal and coolant entry major problems. The cutting geometry of the insert is the key to forming the chips into a shape which is narrower than the groove. When conditions are right, these chips wind up into a watch-spring shape (when cutting ductile metals) that rides upon the top of the blade, partially in the partoff groove. When they get to be approximately the size of a quarter, they break off, and the next one forms. Except for short-chipping metals like cast iron, any other chip shape is less than optimum. The formation of "pig's tails", "rat's nest's", "6's and 9's", etc, all increase the chance of catching in the groove and leading to a crash.

I have a Birmingham 12x36. When I first started working with Iscar, I spent hours at night and weekends testing their partoff tools at different feeds and speeds, comparing the types of chips that formed. Unfortunately, the original 1.5 HP motor on this lathe wasn't up to this task. I suspect that I was lugging the motor down to a speed where the starting windings were engaging, for the starting contacts burned out. The next thing I saw was smoke curling around my legs. I replaced this motor with an American made 1.5 HP motor, which seems to have significantly more torque and has performed flawlessly. If you hear clicking sounds from your motor when parting off, it may be your starting contacts engaging. This has led me to think that 3mm (.118") is the widest practical partoff insert for a 12x36. A 2 mm or 2.2mm wide insert would have advantages with this respect. Since 3mm is the most commonly used width in industry and therefore offers the widest range of grades/chipformers/lead angles, I began to use it primarily to help me troubleshoot my customers' more challenging partoff problems.

Even on an enclosed CNC machine with a good coolant pump, it is difficult to get proper and consistent coolant flow to a partoff insert because it is buried deep within the groove. If the flow is intermittent due to obstruction by the chips, the thermal shock caused by suddenly quenching a hot insert can cause the insert to crack. Iscar addressed this my supplying blades with coolant ports beneath the insert, shooting coolant directly where the insert contacts the material. This greatly improves insert life, but I would guess that less than 10% of partoff applications use it. I choose to run my partoff tool dry, for I find this the least objectionable compromise. If you successfully use coolant, keep doing so. Since I use tungsten carbide turning inserts, I seldom use coolant except for hand applied cutting fluids for drilling and threading, and sometimes grooving aluminum. Since the partoff operation happens so quickly, I don't have enough time nor enough hands to hand apply cutting fluid and control the lathe, too. And if my lathe slings any more fluids on my wife's car, my lathe and I will both be sleeping under the stars.

Partoff requires an extremely rigid setup. Always partoff as close to the chuck as physically possible. If I can't partoff within about an inch of the chuck or collet, I'll use the bandsaw. Iscar recommends that the cutting edge of the insert be .003" above the centerline of the lathe. This allows for a slight downward flex in the setup, for if the insert goes below centerline, the workpiece tends to want to ride up over the insert, which can cause a sudden, catastrophic crash. You can try to measure this with a dial indicator and jig, but due to the complex insert geometry at the cutting lip, I think I am safe to challenge anyone to prove that they can do this accurately. Theoretically, the top of the toolblock should be at centerline of the lathe, but I never got a satisfactory answer from Iscar as to whether the insert cutting lip is made to be at the same height as the top of the toolblock, or .003" above it. (Perhaps I am being overly precise about my uncertainty.) Be sure to lock the carriage clamp. I prefer to use a partoff blade with a clamping style block so I can keep the blades' overhang to the bare minimum. Using a big block of brass, I've mounted the partoff tools on the back side of my cross-slide, but in the upright position rather than inverted. So by just reversing the spindle direction, the tool is always readily available. I use an Iscar SGTBK 32-9 block to hold a 1.25" tall blade. I may someday modify this block with an additional groove on the other side to allow the partoff blade to be held upside down, allowing the chips to fall out easier. 

Using an insert with a right or left cutting angle, one can reduce, but seldom eliminate, the diameter of the nub that remains on the part, but these cutting angles also force the chip into a coil-spring shape rather than a watch-spring shape.

You want a tough carbide grade on a manual machine, and Iscars IC328 is probably the toughest available throughout the industry. I'd much rather have an insert wear than chip - once it chips, the insert, the blade, and maybe the workpiece, are history. Except for high temperature and aerospace alloys, Iscar recommends something near 300 SFM for many materials (I don't have their current reference material at hand). But this is assuming a CNC machine with plenty of well-directed coolant. What RPM should you use on a manual machine, without coolant? Everyone is going to have a different opinion. With a 1" diameter workpiece, 300 SFM equates to 1150 RPM. And theoretically, the RPM should increase as the tool approaches the centerline. Most modern CNC lathes are capable of increasing RPM to maintain a constant SFM while parting off, up to their RPM limit. My manual lathe will stay at the originally selected RPM, so the actual SFM drops very quickly to zero as the tool approaches centerline. Iscar product managers have explained to me that using slower SFM actually puts increasingly higher loads upon the tool. This is just one more reason that partoff tools tend to crash when they have almost completed the cut. I don't know about you, but I'm too chicken to engage the crossfeed lever at 900 RPM (my closest to 1150 RPM) when my face is just 18 inches away from it. I often use 600 RPM, which in itself took a great leap of faith when I first learned to do this, being about 10 times faster, if I remember correctly, than I used with HSS partoff blades. At 600 RPM and .003" feed rate, a 1" diameter bar parts off in 17 seconds. I am curious to see what RPM other people use with their carbide partoff inserts.

I use two different chipformers for partoff - the "C" and the "J". Generally, the "J" forms a watch-spring shaped chip at a feed rate of .0015" to .003" per revolution. It has a positive top face geometry for a freer cut and lower feed rates, but is not as strong as a "C" chipformer. The "C" has a narrow lip with negative geometry before the chip flows into a positive cavity on the top face. This makes for a tougher insert, and more commonly used in industry, but requires a higher cutting force. It will generally form a watch-spring chip between .003" and .006" per rev. In most cases the "J" is better suited for our machines, but I have had instances where the "J" chattered, but the "C" did not. Thus, I have both. These inserts can be hand fed, but I prefer to use the cross-feed. Then I can precisely control the feed rate and adjust it if the chip shape is incorrect. But if you are only parting off one piece, this benefit loses its value. When I was commonly troubleshooting partoff problems over the phone, it was hard to tell if someone was hand-feeding to fast or too slow, but a power cross-feed eliminated that unknown factor.

This is all I can think of at the moment. I hope it helps some of you to decide if tungsten carbide tooling is right for you.

Bob G


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## Niels Abildgaard (Nov 27, 2010)

Thank You Bob G. for a very informative write.

Hate parting intensely and am working on a system that can maybe reduce the number of crashes.

I used to much money to buy a 2 mm set with GTN type inserts and were using it until chrashing.
Not very long time.
I observed that the first 4-6 mm went very well,then noise changed and bang.Your explanation is absolutely rigth .

 I have EDMed  a parting blade 3.2mm wide that carry a 2 mm Tang-Grip insert and when noise became funny followed up with the other end having a 4 mm insert.This is not a production way but it did not self-destruct.
Someone want a copy?


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## quinette7 (Nov 27, 2010)

Niels -

The Tang-Grip was introduced after I left Iscar - I've never seen one, except on their website. Boy - if you can make a blade to hold their inserts and solve a problem, more power to you! :bow:

I like the way you think!

Bob G


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## Niels Abildgaard (Dec 17, 2010)

Here are some more pictures of parting tool for chickens.
The strategy of a narrow step and a broad step and a narrow worked very well on a real lathe and I am making the block that can put it on my Boxford. 
My EDM friend asks if it is worthwhile to make more for sale to partinghating amateurs?


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## Niels Abildgaard (Dec 23, 2010)

Am ready for test on Boxford but dare not before X-mas

Merry X-mas


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## Niels Abildgaard (Jan 22, 2011)

Bob G is absolutely right again
Have tried parting using a 2 mm wide C geometry Tangrip insert on a Boxford lathe with 500Watt.
Not disaster but did not work either.It chatters and if I give more feed lathe stalls.
Next step is to try J geometry and if this does not help I will eBay the whole damned lot and grow turtles.


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## Blogwitch (Jan 22, 2011)

For those with slightly larger lathes, I would recommend you read this post by one very satisfied home machinist.

I showed them on here a fair while back.

http://madmodder.net/index.php?topic=4255.0


Bogs


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## Niels Abildgaard (Jan 25, 2011)

Have been following Quinette(Bob G) and have tried J geometry and was very succesfull.
Lot of swarf.no panic sounds and smiles all over my face.Surface is also quite good.
Get Yourself a Tangrip blade for a 4 mm insert and modify one end for a 2 mm insert and You will never again be scared of parting.

Regards 

Niels


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## rake60 (Feb 4, 2011)

Bob

You don't need to apologize to me for sounding like an Iscar ad.

My pockets are not deep enough to allow me to have Iscar tooling in my home shop, 
but I remember my introduction to their parting/grooving tools.

I was handed a 10 MM wide insert tool to cut a 1" deep groove in a 112" diameter part.
Here to fore, we used the old school Manchester groove tools with HHS inserts. 
Surface speeds averaged 20 SFM, you had to keep it flooded with coolant and feed it 
somewhere around .008" per revolution.

The Iscar rep told me to run it at 300 SFM and crank it in as hard as I could by hand.

When I saw those deep blue 6's and 9's flying out of that groove, I was amazed!
The machine never labored a bit.

When I was moved up to the CNC department, I was again a little skeptical when the 
program was written to take a 5 MM Iscar tool into a 3" diameter pin at 750 SFM to a 
diameter of .125" where the machine would stop and you'd reach in and break the finished 
part off by hand. 

First few times the "Pucker Factor" was a REAL factor! LOL

You learn to trust it.

Rick


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## Niels Abildgaard (Mar 25, 2011)

A 5 inch piece of sea water resistant aluminium (not nice cutting) was parted using the step parting procedure.
Tool was reversed after 5 to 6 mm advance so it takes time but did not self destruct.

Regards Niels Abildgaard


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## Niels Abildgaard (Jan 24, 2012)

Parting two crankshaft discs of a piece of 100 mm scraptanium steel (,definitely not freecutting) ,takes around 20 minutes each using the step parting tools as shown.I have not mentioned before that 2 mm, 3 mm and 4 mm Tangrip inserts all have the same insert to blade geometry.
I go in 7-8 mm with the 2 mm thing,follow up with a 3 mm and a 4 mm .


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## aRM (Dec 18, 2012)

NIELS
Hello  there
Seen  a  demo  of  these  TANGRIP  Inserts.  They  are  awesome.
What  specific  insert  would U  recommend  for  Stainless,  BMS - Bright Mild  Steel etc.  ???
Any  Dual  blades  available  ???
Would  appreciate  a  couple  ???
Know  it's  been  a  long  time  since  this  posting.
However,  some  of  us  are  late in  the  game  !!!
Thanks in  anticipation.
aRM


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## Niels Abildgaard (Dec 8, 2013)

Cat and dog are my best fans.
View from bridge of my lathe ship.
The stepparting system is an overkill for many jobs and I am trying to make a simpler and cheaper system,but still based on ISCAR tang-grip inserts.
Next picture shows a double ended tool.One end has already got a TGAD blade and TAG n1.4j insert.The post brings me a TGAD 3 blade tomorrow from Ebay and that will sit on the other end.
Third picture is same thing from another angle.
Same for last picture.


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## kuhncw (Dec 8, 2013)

Niels,  your newest cutoff blade mount looks like a good idea.

Also, I very much enjoyed the photos of your cat and dog.  Especially like the cat as that is my favorite color and marking for a cat.  

Best Regards,

Chuck


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## Niels Abildgaard (Dec 22, 2013)

Wife died tuesday from cancer.
What kept me from going insane was a mental picture of  the ultimate part off tool
and beg your forgiveness for showing it.
It functions very well and was good to have in one hand and wife in the other.
I still need an easy way of putting it perpendicular to the workpiece.


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## kuhncw (Dec 22, 2013)

Niels,  I'm very sorry to hear of your loss.

Regards,

Chuck


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## Niels Abildgaard (Dec 22, 2013)

Chuck

Thank You


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## Swifty (Dec 22, 2013)

Niels, please accept my condolences, it must be a terrible time for you.

Paul.


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## Niels Abildgaard (Dec 27, 2013)

Thank You Swifty.
I have known nicer times indeed


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