Trouble to parting off on a regular lathe

[toughmudder]

Everytime i try to parting off a 1" steel rod, the carbide parting off insert brake before reaching the midle of the rod. I tried to cut off as close as 1" from the chuck and adjust the insert holder to stick out only the lenght needed to reach the midle of the rod. Still no luck. Wondering if anybody has suggestion for my problem

 

[toughmudder]

Everytime i try to parting off a 1" steel rod, the carbide parting off insert brake before reaching the midle of the rod. I tried to cut off as close as 1" from the chuck and adjust the insert holder to stick out only the lenght needed to reach the midle of the rod. Still no luck. Wondering if anybody has suggestion for my problem

Forgot to add the rpm 129

 

[eKretz]

1. Get your RPM up where it belongs. I'd be closer to 1,000 RPM if you have coolant. 600 if you don't, but use cutting oil.

2. Check that your tool tip is on center.

3. Ensure that you are running a light and even feedrate. .001" - .0015" per rev if you've got it. Otherwise, light and consistent hand feed.

 

[L Vanice]

1. Get your RPM up where it belongs. I'd be closer to 1,000 RPM if you have coolant. 600 if you don't, but use cutting oil.

2. Check that your tool tip is on center.

3. Ensure that you are running a light and even feedrate. .001" - .0015" per rev if you've got it. Otherwise, light and consistent hand feed.

The type of steel is also important. Some steel is easily machinable and many types are not. And the machine needs to be rigid in every portion that holds the work and the tool. Some lathes are just not up to the job of cutting off a 1" bar of steel. There is much to be said in favor of cutoff bandsaws where the job is suitable.

Larry

 

[MrWhoopee]

Retired job shop owner here. I gave up on inserted parting tools over 20 years ago. It just got too expensive replacing the blade everytime there was an oops. If you're only losing the insert, you're winning. Now, as a home hobbyist, I use inserted carbide for everything, everything EXCEPT parting.

 

[john.k]

As mentioned ,your sfpm is too low when the diameter is small ........there is no way around this,as if you increase rpm to the 10,000 or so needed for efficient cutting,the loose part becomes a projectile.

 

[trevj]

1. Get your RPM up where it belongs. I'd be closer to 1,000 RPM if you have coolant. 600 if you don't, but use cutting oil.

2. Check that your tool tip is on center.

3. Ensure that you are running a light and even feedrate. .001" - .0015" per rev if you've got it. Otherwise, light and consistent hand feed.

Yep. get the revs up, way way up, and use power cross feed if you have it.

We used to buy the cheap import 'combo kits' from KBC Tools for the last shop I worked in. Like Mr. Whoopee above says, you blow an insert, usually it takes out the holder. If a holder made it through the whole box of inserts it came with, we always had a few spares inserts around, and the kits were pretty cheap to boot.

We made a LOT of shims in Al-Bronze and 17-4PH, for F-18 landing gear rigging, and assorted flight surfaces. from about .006" on up, but rarely as thick as the kerf of the parting tool. Parting was something we all got very good at! Spend a morning prepping stock, spend the afternoon parting of slice after slice, and spend the next couple days Facing off the shims on both sides, to specific thicknesses to make up a whole set so the guys could have them for their repair kits when they deployed, or so that when they came in looking to have "this" size made, we could send them out carrying it, rather than waiting.

There is a real sweet spot, in the rate of feed, when you are hand feeding, and you will know it when you hit it, it is fairly obvious, it just works, rather than chattering or loading up.

 

[Bill D]

No expert here but I often notice the toolpost has been rotated so it is no longer at 90 after the tool breaks. Which is cause and which the effect I am not sure. I do watch the outboard end of the HSS cutoff blade and see it wiggle side to side as the cut gets deeper. If the wiggle looks like too much I back out and shift over a fraction to give side clearance.
Bill D

 

[john.k]

What generally happens with HSS is a built up edge forms on the blade ,and the cut gets wider ,with swarf jamming in the cut..........if you partoff is strong enough ,its just noisy ,but if the blade can deflect ,something breaks.

 

[true temper]

You didn’t say what you are using for a lathe. Heavy lathes part much better than light duty wet noodle lathes.

 

[Mechanola]

Speed needs to go up with decreasing diameter of stock, feed should be slowed down increasingly, tool must be tough, sharp, and on axis, coolant is necessary. As L Vanice says, use saw for small series to be chucked individually. In most cases sawing spoils less stock than parting off, too. Finally, steel bars can be loaded with core tensions. Beware of green bars

 

[APD]

Everytime i try to parting off a 1" steel rod, the carbide parting off insert brake before reaching the midle of the rod. I tried to cut off as close as 1" from the chuck and adjust the insert holder to stick out only the lenght needed to reach the midle of the rod. Still no luck. Wondering if anybody has suggestion for my problem

Proper tool height is essential for parting tools, check that.
Setup must be rigid. Sometimes the cutting forces will pull or push the tool toward or away from chuck, and the cut is no longer perpendicular to spindle axis. Puts lots of stress on tool.
What happens if you try to part 1/2" rod of the same material?
Need to look at what the chips are doing before the tool breaks.
Are they getting packed into the groove or breaking off? Sometimes its necessary to stop the feed and let the chip break off.

 

[Scottl]

I don't know what lathe you are using but if it is a lightweight model or worn enough to be a bit loose you might consider buying or making an upside down cutoff tool holder that mounts behind the workpiece. These aren't as likely to dig in and break if you hit a loose spot on your machine.

 

[Bill D]

Everyone says to make sure tool is on center. Do any say better to be below center if in doubt.
Bill D

 

[wheels17]

Make sure the tool is perfectly square to the work. I square the holder off the face of the chuck with a 123 block.
Lock the carriage before you start.

 

[Joe Gwinn]

I use an Iscar parting blade with a carbide nugget doing the cutting. Although I do ensure that the blade is exactly perpendicular to the spindle rotation axis, the nugget is half the width of the blade, making imprecise perpendicularity far less likely to cause trouble. I also use the upside down blade and reverse rotation, to prevent self feeding of blade into work. Not to mention a continuous coolant stream directed into the ever-deepening groove. Speed (rpm) is maybe half of turning speed. Sometimes use power feed, sometimes by hand, but both are quite reliable.

But to achieve that reliability, I first had to tighten up just about every relevant part of the lathe, and I used chattering while parting off as the acid test directing that tightening-up process.

 

[DDoug]

Forgot to add the rpm 129

Post a few pix of the set up and the whole lathe.

 

[basalt]

Everytime i try to parting off a 1" steel rod, the carbide parting off insert brake before reaching the midle of the rod. I tried to cut off as close as 1" from the chuck and adjust the insert holder to stick out only the lenght needed to reach the midle of the rod. Still no luck. Wondering if anybody has suggestion for my problem

 

[basalt]

Up the speed, use oil, tool upside down run it in reverse.

 

[Ben]

I use a carbide parting tool on my Leblond Regal 15". I usually run about 90 to 120 RPM and use power feed at the slowest rate. I use plenty of cutting oil. I have parted many parts with not problem. I the same cutter on my 16" American with no problems. I always insure the tool is at 90 degrees and on dead center. On the American I usually use HHS at slow RPM and lowest feed with plenty of cutting oils. A sharp tool bit helps a lot.
Ben