I think I have a parting problem........

[Fabrickator]

I am not sure I agree. My small south bend lathe does very well at parting. Admittedly it was learning how to properly part. My problem was being a fraction too low, thinking it would cut better. I learned after a few mistakes that being low was bad , being low often caused a disaster since the piece would lift and all hell would break loose. Being high by a small amount was acceptable until it stopped cutting, it would not lift.

Being dead on, would be best. But there might still be a lift danger .. So being high by about .0005 might not be a bad thing. Being dead on, I still worry .. Being low.. never.

I agree that you never want the cutting tip to be anywhere near "low" of center. I run mine a bit just above. Also, I disagree that smaller, hobby lathes are not capable of parting??? I suggest that you look at my 4" Hollow Vessel project and see how the tool post is set up on the carriage/cross slide, and how I cut an 1/8" pass through a 4" ball of 6061 aluminum. Granted, it had to be finished afterward, but it does cut it and I just allow a bit extra material to clean it up.

I use an Aloris (kind of expensive) with replaceable tool bits, like yours. Align the tool, post, compound and cross-slide directly over the carriage and under the tool for maximum support. Use a live center to prevent flexing. Always try to keep the part being cut as short to the chuck as possible. Some say no more than 1" extension for every 1" of diameter (or something like that) to minimize deflection. When I cut the 4" ball, I only chucked a 1 1/2" L X 5/8" Diameter tenon on the drive end. I took my time with a couple of thou at a time, ran the spindle as slow as the machine allowed and used cutting oil to keep the tool happy. It took about 30-40 minutes and was still pistol hot when I got done.

 

[pstemari]

The one thing that made the biggest difference for my parting success was using a square to align the tool every time. One other thing is that you can't be shy about it—hit the power feed and drizzle on oil until you're through.

I have a Dorian insert blade w block, an insert tool for smaller diameters from latheinserts.com, and a bunch of hss cobalt blades. They all work just fine.

One other thing to note is that the side rake on the cutting edge determines which side gets the little pip. You can save yourself some finishing work by choosing the insert or blade orientation to match your work setup.

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[Grumpy Gator]

I agree with all of the above. But if you only make a one pass part off then you run the risk of chips loading up in the cut.Never a good thing. If your cut off tool is 1/8 thick back off 3/16 and make a relief channel halfway down to the center. Then advance the tool and cut off on your mark.
Old school is still cool
**G**

 

[Fabrickator]

I agree with all of the above. But if you only make a one pass part off then you run the risk of chips loading up in the cut.Never a good thing. If your cut off tool is 1/8 thick back off 3/16 and make a relief channel halfway down to the center. Then advance the tool and cut off on your mark.
Old school is still cool
**G**

I'm with you on that and forgot to mention it regarding my Sphere project. That was a very deep cut, having to actually stop and avdvance the blade to complete it. A lot of the time it took was to back up, clear the chips, oil and continue. I did, and always open up the cut for chip clearance.

 

[pstemari]

My little Taig has a rear tool post for parting that holds an inverted blade, which really helps with chips. The big lathe doesn't have any issues with chip clearance: the Dorian inserts and parting blade pop out nice tight little coils that look like watch springs.

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