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Cut off tools and Inserts tip on breaking inserts.

metron9

Aluminum
Joined
Oct 29, 2009
Location
Minnesota U.S.A.
I was looking for a new cut off tool because the inserts on the one I am using are breaking.

On another forum I found this little hint that may help others with the same problem, I am pretty sure it is the reason for my problem.

"Important.
When using carbide DO NOT use intermittent cooling (dabbing on with a brush or a squeezy bottle ) as the heat/cool stress shatters the tip surface, run dry or flood.
"

I am cutting 1.125 1045 TGP bar that has a 3/8 hole through it.

I am using the Hertel MGTN-2-HT25 inserts.

Looking on ebay I see quite a few different ones. GTL 3 HT25, GTR 4 HT25, MGTR-2-8D HT10 etc...

Which ones will fit the tool holder I have that uses the MGTN-2-HT25 ?
Ebal search returns 23 listings search for "hertel insert cut off"

What width cutoff tool should I be using given the stock and size i am cutting.

SB-9 lathe - Belt drive - looking at getting a gator rubber belt drive as i still have slipping on heavy cuts.
 
Might ought to try a HSS cut of "T" type cut off tool--and .125 cut if waist is not a problelm. Not sure the SB can handle speed needed for carbide insert.
 
You make no mention of how the cutoff blade is mounted, so you may want to check that the blade is perpendicular with the Z axis, and that the cutting edge is on center.
Also, how rigid is your tool post/compound/cross slide? Insert type cutoff tools, or HSS, for that matter, don't function well with a limber set up.


Rex
 
I think you should stop the frustration of trying to get a carbide tool to work , and just get familiar to using a HS "T" blade .
I just had this discussion with a friend who bought a mill/drill and can't understand why he keeps breaking tips .
There are so many variables that have to be correct for a carbide tip cut off tool to work right .
perfectly square to the wok , proper tip height , uniform feed and SFPM.
Keep in mind that these tools are designed for production in a very controlled manner .
A belt drive SB is not the ideal machine for this .
The best analogy I can offer is to observe the action of a soil plow or in MN a snow plow :
under ideal conditions at the correct speed , the material flows smoothly and rolls off the cutting edge in an un interrupted manner . Now consider the conditions in metal : there is a verry narrow band of parameters that this condition occurs . The feed needs to be uniform so the chip load is constant . Problem is , that as the diameter decreases , the chip load decreases due to the diminishing circumference . Therefore it loses the momentum it needs to maintain a smothe flow . CNC lathes allow for this by automatically increasing the RPM too maintain a uniform SFPM ( surface feed per minute ) .
Even a seasoned machinist who has a " feel " for a machine will hand feed a cut off tool and sometimes experience a sudden crunch .
So unless you have a way to increase your lathes' RPM as the cut gets deeper , you will continue to have unpredictable results .
FBBob
 
The snowplow analogy is perfect I think. There is 300 acres of farmland in front of my house, I have a 10 acre hobby farm and heavy clay soil.
When I bought this place i bought a tractor and a 2 bottom plow, pigs, cows, chickens. I grew an acre of corn to feed the animals.
That 2 bottom plow with an under powered tractor in heavy clay had soil sticking all over it especially when it stopped and bogged down.
It was really fun to get the right speed there as that soil rolled like butter off the plow. 12 and more bottom plows across the street
turn that heavy clay like it was soft butter.

I have had very nice feeding and cutting but no crunches, the problem is the very edge of the insert cracks off perhaps a tiny crunch sound.
Anyway it stops cutting at that point. I think it is due to all of the problems you outlined as well as the heating of the tip and sudden coolant
shattering it.

I will take your advice and learn to use the HS "T" blade. First I will have to order one. I will do some research on the best holders.

I have a quick change Aloris type holder.
 
I have 3 lathes. 10L SB, a 13x40 SB and a 18x54 L&S. I wouldn't even consider using a carbide cutoff tool on either of the SBs. On the L&S they work great....for awhile, then fail. I set them up straight and centered, feed correctly and use continuous cooling. Those inserts are frail and very expensive. I now only use HSS everywhere and experience no problems. Perhaps in a production environment I might consider resolving the problem, but as a hobbiest doing one off pieces, it makes no sense. I am curious how others deal with this issue, but as far as I'm concerned, they are junk.
Steve
 
"SB-9 lathe - Belt drive - "

That's your problem right there. You don't have the power to pull a proper cut with carbide and it is a very light machine. What it likely happening is that the tool is rubbing as it is cranked in, then digs in and takes a big bite, snapping the insert. As others say, a HSS blade or even a blade ground from HSS should solve your troubles. Run at about half the speed you would when turning with HSS (100ft/min for turning, so 50ft/sec or less for cutoff).
 
Steve, that L&S should have no trouble at all running a carbide cutoff tool. I drip plain old tapping oil in the slot when cutting off in the crappy Takang at work and have no problems at all with carbide insert cutoff tooling, even on interrupted cuts. I can get dozens of hours of cutoff and grooving out of an insert and have broken maybe three since March. That machine is not nearly as solid as an L&S. Maybe you are feeding too heavy, especially as the diameter reduces and surface speed decreases?
 
I would check you have looked at the centre height and perpendicular first. These are usually the first solution to check. Also check to see if you could lower your gear if these don't work. Check tool to see if the seat is still good. Make sure your are as short as you can on overhang. After that I would look at different tooling, maybe a little thicker insert, your depth isn't that bad but if other things are causing issues also they can add up.

Hope this helps.
 
"After that I would look at different tooling, maybe a little thicker insert,..."

On a SB9, anything over .062 is hopeless due to chatter and power requirements. As for slowing down, it's probably going to be running at speeds suitable for HSS by the time the you can keep it from chattering and provide enough torque to pull the cut. You can probably buy a dozen sticks of HSS cutoff blade and get 100 sharpenings out of each of them for the cost of a box of 10 inserts.
 
"After that I would look at different tooling, maybe a little thicker insert,..."

On a SB9, anything over .062 is hopeless due to chatter and power requirements. As for slowing down, it's probably going to be running at speeds suitable for HSS by the time the you can keep it from chattering and provide enough torque to pull the cut. You can probably buy a dozen sticks of HSS cutoff blade and get 100 sharpenings out of each of them for the cost of a box of 10 inserts.

The inserts I was using are .086
When the last two go I will have a new HSS set up. I will keep tabs on how many cuts I get before the next one cracks.
 
I am amazed. This is weird...

Running 1/8" P20 (Thats typical grade of Carbide for cutting steel) Iscar, 20-30 years old.
Its an old 10" Colchester gearhead. I thought that lathe was flimsy....
I got the insert dull without chipping and retouched it on a carborundum wheel and its like new and not chipping either. At current rate the 20 inserts I have are gonna last several decades.
No Problem with lubrication, I always brush on a mixture of mineral and canola oil because it significantly reduces chatter and binding in gummy alloys.
Always feeding hard to supress chatter, usually not running typical carbide speeds, its just not worth it, 350 rpm on 2" mild steel.

I have had alumnium curls stir weld to a solid package in the chip breaker, accompanied by horrible tearing and rumbling noises.
No effect, remove the junk, back in the cut she goes.

Short version: I can see that an SB9 may have some serious problems , but a big honking 18" L&S ? No way......

Tighten down that compound slide! Loose gibts turn any serious parting into a nightmare
Feed hard! Retract the tool if it starts to sound weird or looks clogged.

Fun fact : I usually use it for chamfering because the Multifix allows to index it for 45° faster than any other generic tool.

Metron: Try this :
I was trying to part some tough steel, i think it was 1045 , prolly 1 1/2 ". At that time the compound was not tight and parting was a pain. I ran slow RPM and literally flooded the cut with canola oil. Suddenly the rumbling typical for carbide running way too slow with a horrible built up edge was replaced by a clean hissing sound of a chip curling from the goove.
 
That rumble from running too slow you mention, I feel pretty sure that's what's killing his inserts... material sticking to the insert and then breaking off, taking the edge with it. Very common when running carbide very slow on an underpowered lathe. You just can't get the surface speed and feed rate high enough to get the insert cutting cleanly. You have to either run a very slow speed or feed so lightly it is as I said above, rubbing, then grabbing. A flimsy machine will only accentuate the grabbing tendency.
 
I really do get good fast cutting though, nice curls as well. Don't know the speed, I am using the sb9 with the leather belt, motor to the big pulley is on the fast setting
and the belt in the center position. So it's not slow or in back gears. I could try the fastest speed.
I just know I am going through to many inserts for the number of cuts.
Perhaps I get 8 cut pieces

I am looking at the EMPIRE blades but they also have Carbide tips.

Might be better to get a better band saw (I have a cheap china 64 inch x 1/2 inch blade) as I have to face both sides anyway.
 
Hmm, this one goes against instinctive knowledge:

I had trouble with brazed carbide stuff. It went away after i backed down the depth of cut and doubled the feed rate.
Now obviously you cant back down the engagement of the cutter with parting tools but .086 doesnt sound so bad.
 
...Might be better to get a better band saw (I have a cheap china 64 inch x 1/2 inch blade) as I have to face both sides anyway.

Parting off in a lathe is one operation which everyone approaches with some trepidation when they are starting out. When I first got into machining I did that many times--chickened out and used a bandsaw--and, of course, it worked and got me through the job. But the bottom line is that if you're serious about machining sooner or later something is going to come along where you have no choice and have to part off a piece. So the sooner you figure it out the better off you'll be. Even a little South Bend will part off most materials if you have the right tooling and setup so grab some HSS and start practicing. Ultimately you'll be glad you did...
 
Exactly what I plan to do. Just ordered a variety of HSS blades. Thank's everyone for the input.

Parting off in a lathe is one operation which everyone approaches with some trepidation when they are starting out. When I first got into machining I did that many times--chickened out and used a bandsaw--and, of course, it worked and got me through the job. But the bottom line is that if you're serious about machining sooner or later something is going to come along where you have no choice and have to part off a piece. So the sooner you figure it out the better off you'll be. Even a little South Bend will part off most materials if you have the right tooling and setup so grab some HSS and start practicing. Ultimately you'll be glad you did...
 








 
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