Parting / cut off tool

[Susquatch]

Not intending to complicate things here, but it's also worth noting that too slow a cut can work harden the metal and make parting very difficult, while too fast a cut can overload the tool and break it. Best is a sharp tool fed at the right rate. A powered cross slide is a big help. For a large diameter part, the surface speed can change dramatically as the cutting diameter gets smaller. That dictates changes in rpm as the cut proceeds.

 

[mbond]

I would think that a powered cross feed is a disadvantage during parting because it can't change the rate at which the tool advances as the diameter decreases. I have never seen one that does anyways. I have little experience, but I have always done this manually to control the rate of tool advance in proportion to the deminishing diameter.

Some materials do require negative rake angles, but they need custom ground tools - not inverted ones. Typically they are materials that deform plastically instead of elastically and are generally difficult to machine. Not steel, aluminum, brass etc. but certain lead alloys, some types of plastic, and other exotic metals used in the nuclear industry.


Today I managed to break another carbide point on an aluminum blank. Building up practical knowledge will take time

 

[Upnorth]

I would think that a powered cross feed is a disadvantage during parting because it can't change the rate at which the tool advances as the diameter decreases. I have never seen one that does anyways. I have little experience, but I have always done this manually to control the rate of tool advance in proportion to the deminishing diameter.

Some materials do require negative rake angles, but they need custom ground tools - not inverted ones. Typically they are materials that deform plastically instead of elastically and are generally difficult to machine. Not steel, aluminum, brass etc. but certain lead alloys, some types of plastic, and other exotic metals used in the nuclear industry.


Today I managed to break another carbide point on an aluminum blank. Building up practical knowledge will take time

Power cross feed works great for me. 370 RPM for A-2 tool steel. I can't remember the feed per rev though.

 

[Upnorth]

I would think that a powered cross feed is a disadvantage during parting because it can't change the rate at which the tool advances as the diameter decreases. I have never seen one that does anyways. I have little experience, but I have always done this manually to control the rate of tool advance in proportion to the deminishing diameter.

Some materials do require negative rake angles, but they need custom ground tools - not inverted ones. Typically they are materials that deform plastically instead of elastically and are generally difficult to machine. Not steel, aluminum, brass etc. but certain lead alloys, some types of plastic, and other exotic metals used in the nuclear industry.


Today I managed to break another carbide point on an aluminum blank. Building up practical knowledge will take time

Are you using cutting fluid? I use lots of it when parting. LPS gold is what I use.

 

[mbond]

wd40 is all I have on hand

 

[Susquatch]

I would think that a powered cross feed is a disadvantage during parting because it can't change the rate at which the tool advances as the diameter decreases. I have never seen one that does anyways. I have little experience, but I have always done this manually to control the rate of tool advance in proportion to the deminishing diameter.

I'm no expert, my previous lathe had no power cross feed. 11 years ago, I got a new Gearhead Lathe that does. Do I'm still learning too. Prolly will till my bride throws the dirt in over me.

That said, that's not my understanding. Depth of cut and speed are related but not that strongly. You can do the same depth of cut from beginning to end, but you have to keep the surface speed within the acceptable range for the tool and the material. That means speeding up the lathe as you cut deeper. On the other hand, the feed depth of cut can stay constant.

Some materials do require negative rake angles, but they need custom ground tools - not inverted ones.

The tool inversion is just a way to stop the tool from digging in and twisting the tool holder in a dangerous inward path. Which will break something. It has nothing to do with exotic materials.

That said, exotic materials do require special methods. Typically a unique insert as well as feeds and speeds. Fortunately, most of us don't use these materials because..... we can't afford them!

Typically they are materials that deform plastically instead of elastically and are generally difficult to machine. Not steel, aluminum, brass etc. but certain lead alloys, some types of plastic, and other exotic metals used in the nuclear industry.

Yup!

Today I managed to break another carbide point on an aluminum blank. Building up practical knowledge will take time

WD40 will work on aluminium but it isn't even really necessary. Steels are another matter and cutting oil is much more important.

Big question. Are you using aluminium cutting inserts? This is important. Most insert tooling comes with inserts for steel. They will work on aluminium but not very well. Since you know materials better than most, it helps to visualize the cutting process from a granular perspective. Steel grains prefer to be torn out. So a duller harder tool is required. Aluminium prefers to be peeled by a much sharper tool. Try to find the aluminium version of the insert, follow its cutting recommendations, and I'll bet you have better success.

 

[Susquatch]

Today I managed to break another carbide point on an aluminum blank. Building up practical knowledge will take time

This will no doubt raise the ire of the industrial machinists on here for whom carbide inserts = speed = money.

But I like to recommend using HSS before carbide. You can do and learn things with HSS that you can't really do with carbide. When something bad happens, it's a simple trip to the grinder. Not a trip to the bank for the cash to buy good carbide. And to be clear cheap carbide is just junk. Which might also explain your problem.

HSS is a much better platform to learn on. That's my opinion not supported by all.

Best to duck now before the pros who earn a living machining start throwing their tools at us!

Or just get behind me. I'm used to taking the flack.

 

[DPittman]

I would think that a powered cross feed is a disadvantage during parting because it can't change the rate at which the tool advances as the diameter decreases. I have never seen one that does anyways. I have little experience, but I have always done this manually to control the rate of tool advance in proportion to the deminishing diameter.

It's true that as the work diameter changes the rate of infeed should technically change also however the power cross feed provides a constant rate that is sometimes hard to achieve by hand. This constant infeed seems to help with parting. On my lathe I find I part off better with power feed than by hand feed. I can also increase motor speed as I go as it has on the go variable speed adjustment (but of course the infeed rate stays relative with speed).

 

[mbond]

I learned a lot about 20 years ago - now I'm trying to remember it

 

[Susquatch]

I learned a lot about 20 years ago - now I'm trying to remember it

Relearning is way more fun than trying to remember......

 

[slow-poke]

Not intending to complicate things here, but it's also worth noting that too slow a cut can work harden the metal and make parting very difficult, while too fast a cut can overload the tool and break it. Best is a sharp tool fed at the right rate. A powered cross slide is a big help. For a large diameter part, the surface speed can change dramatically as the cutting diameter gets smaller. That dictates changes in rpm as the cut proceeds.

Noted.

One handy feature of an ELS is you can just tap the up button as the diameter decreases while power cross feeding.

 

[whydontu]

I would think that a powered cross feed is a disadvantage during parting because it can't change the rate at which the tool advances as the diameter decreases. I have never seen one that does anyways. I have little experience, but I have always done this manually to control the rate of tool advance in proportion to the deminishing diameter.

Some materials do require negative rake angles, but they need custom ground tools - not inverted ones. Typically they are materials that deform plastically instead of elastically and are generally difficult to machine. Not steel, aluminum, brass etc. but certain lead alloys, some types of plastic, and other exotic metals used in the nuclear industry.


Today I managed to break another carbide point on an aluminum blank. Building up practical knowledge will take time

Another reason why everyone should own a Monarch lathe. Power cross feed includes the ability to increase spindle rpm proportional to workpiece diameter. Set the dials to desired SFM and workpiece O.D. then hit GO.

 

[Tom O]

Sounds like someone should come up with something that takes the center readings off the DRO or possibly a proximity sensor and mate them with the VFD.
( just another brain fart put out )