Parting cast iron

All good responses; it depends on what machine is being used, but generally super slow speeds are not the best idea, and power feed parting is not a really good idea, except with turret lathes with high ridigidity. Hand feeding give valuable feedback as to what the machine/tooling likes. Cast iron should be one of the easiest metals to part off.
 
As I learned it "Parting " on a manual lathe is a 1/4 speed operation.. Quarter speed meaning whatever the nominal speed is for turning the material it should be parted at 1/4 of that speed. Also the old school lubricant for cast iron is either lard or soluble mineral oil. I don't do a lot of cast iron, but I have used heavy (dark) thread cutting oil without problems. The keys to parting (on a manual machine) are slow speed, plenty of lubricant, a sharp tool, and a steady feed rate that produces a continuous flow of chips without flexing the tool.
 
NortonDommi said:
I run my parting blade upside down and the lathe in reverse and part at normal turning speeds without problem. I find you need to be a bit aggressive when parting on most materials.
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Unless the lathe has a screw on chuck.
 
NortonDommi said:
But NOT on Cast Iron.
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When cutting threads or turning cast iron, lubrication is generally not used. However, when parting, the lubes main purpose is to lube the SIDES of the groove with respect to the tool. Since there isn't much clearance (if any) between the sides and the tool, providing a lube will help to keep the cut going.
 
SLK001 said:
When cutting threads or turning cast iron, lubrication is generally not used. However, when parting, the lubes main purpose is to lube the SIDES of the groove with respect to the tool. Since there isn't much clearance (if any) between the sides and the tool, providing a lube will help to keep the cut going.
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For most things I use an insert blade and clearance is built in. In Cast Iron there is a lot of Graphite freed up when machining . This along with the Iron dust makes an incredibly good abrasive ESPECIALLY when mixed with a liquid which is why I swaddle a machine when using it on Cast Iron and clean it thoroughly afterwards.
I find hooking up a vacuum cleaner helps a lot with the dust and the air flow provides good cooling.
When cutting other materials such as steel I drop a bit of lube on the blade behind the insert for the reasons you have stated.
Some very knowledgeable people have told me that with Carbide use a flood coolant or none. Since I am a hobbyist I choose none in most cases, less mess. I do use lube with HSS though.
 
Thanks for all the replies, I appreciate them. The posts about turning the parting blade upside and running the chuck counterclockwise caught my attention. I was going to give it a shot, but after flipping the parting blade over I was unable to lower the tool holder enough to get the tip of the blade on the centerline of the work... I'm not sure if I'm missing something. I'd like try it so if anyone can tell me what I may be doing wrong I would be most appreciative . Thanks
 
projectnut said:
As I learned it "Parting " on a manual lathe is a 1/4 speed operation.. Quarter speed meaning whatever the nominal speed is for turning the material it should be parted at 1/4 of that speed. Also the old school lubricant for cast iron is either lard or soluble mineral oil. I don't do a lot of cast iron, but I have used heavy (dark) thread cutting oil without problems. The keys to parting (on a manual machine) are slow speed, plenty of lubricant, a sharp tool, and a steady feed rate that produces a continuous flow of chips without flexing the tool.
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I beg to differ; cast iron is always recommended to be cut dry, the use of any lubricant just makes a God awful mess and is unnecessary. With tapping, the use of a tapping fluid may be helpful to reduce torque and the possibility of breaking a tap, but I would avoid oily fluids.
 
For cast iron, a parting tool with a slight negative rake worked for me when I used to have to cut cast iron.
 
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