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Spoken like a true Virginian Thermite as usual. To the OP, I found out years ago that the thing that helps me the most is using power crossfeed. Even if everything is set up properly I get much better results if I use power feed to apply steady controlled pressure to the tool. On some material it is fine to just crank it in but on a tough cut power feed works best for me.
Would someone please direct me to a definitive source on how to grind a lathe parting tool, set it up, and use it. Hopefully a discussion of limitations will be included.
Thank you,
gizmo
http://www.millerbroach.com/assets/missuse2.pdf
I have found this 4-page pdf by Miller Broach to be an invaluable resource on the use of cut-off tools
Very LITTLE works well if you have eight inches or better of solid alloy steel to part-off. Or even two inches, solid.
I wouldn't worry about parting 2 inches on a properly sized lathe. (something in ballpark of at least 8" chuck with >2" chuck bore)
Parting 8 inches diameter on the other hand I'm not sure if I want to try
First off, if you’re using HSS, use the “P” blades as they only require that you kiss the very front of the bit to give 6-8ish degrees of clearance as it presents to the work, I use my belt grinder. The “P” blades are the ones that are T shaped with the trough down the top. For most steels use a tool holder that adds several degrees of back rake and for brass don’t use any back rake at all. FYI, the Aloris tool holder adds 4 degrees of back rake on their holders and this has proved to be a good compromise for general use. The thin and tall bits are the easiest to use.
In case you are wondering, the T type blades will work but the P types work much better and are so much easier to use and take less time and skill to sharpen. The “T” blades have tapered sides and must be ground all over to use.
To be clear, the back rake angle on the “P”-parallel bits is best controlled by the choice of tool holder. Do not grind on the top or sides, just the front-end.
Put the tool on center, if you put the tip below center you run the real risk of having the part roll over the bit, this breaks things.
With M2, 2/3 or less of normal turning speed would be a good place to start.
With HSS, a good dark cutting oil is a must. Just for fun I have tried ATF, hydraulic oil, motor oil, gear oil and a semi synthetic water based coolant and by far the best results and finish were obtained with the sulfurized, chlorinated, cutting oil.
Decades ago I routinely parted off 1.250 Diameter 4140 pre hard without incident. I was using a 618 Atlas with HSS in Armstrong tooling, set on large washers-shims in place of the rocker.
I will confess that whether it’s my Monarch or that puny 618, I don’t find it necessary to lock anything on the lathe. It’s just not that picky or technical.
I almost forgot, this lesson you must not ignore. When it starts to chatter, you MUST INCREASE THE INFEED.
Stick with it; I learned to part 45+ years ago. Once you get it you will wonder how it was ever a problem.
Take care, Mike
I wonder if you ancient HSS users (I've been machining for only 40 years) would have a heart attack if you saw how well carbide parting tools work
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