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    Default Lathe Parting Tool

    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

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    Depends on the lathe and the material.
    Try the southbend book "how to run a lathe"

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    Step one- get it as square as effin possible to the spindle axis.

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    If you are parting leaded brass , anything dead sharp and square will work.
    Parting plastic with a utility knife blade is not an poor method.

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    In regards to Digger Doug’s suggestion, is this the publication you were referring to?
    http://vintagemachinery.org/pubs/1617/3789.pdf
    If so, the Table of Contents doesn’t have an entry for parting tools. Be that as it may, I appreciate your suggestion none the less.

    It seems no matter what I do, eventually the part climbs up on tool and pulls the part out of the chuck and locks up the spindle. From there, I hacksaw the rest of the way, turn it around and face it off.

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    Study the "How to run lathe," then watch utube video.

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    There are nearly infinite ways that work ..ready-made Carbides can be so good even an otherwise HSS guy can love them.

    And a caveat:

    Most anything works for tiny diameters or tube shapes where walls are not thick. Tool-stick-out is short. Traverse depth is modest. Chip-jam not a major factor. One can focus on a tool shape that leaves near-as-dammit zero burr, even.

    Lovely stuff, a key player in the "money machine", and WELL worth that extra effort, high volume production.

    Very LITTLE works well if you have eight inches or better of solid alloy steel to part-off. Or even two inches, solid.

    The only thing I have seen, (but not yet tried) for that is a tool that resembles a big rectangle of die steel, cutter in the top corner.

    It drops straight DOWN to ride atop the cross. Fully supported. Zero "hang out" from any conventional tool post or tool holder. Not sure I want to be in the same machine-hall ever it jams, though.

    Seldom as I even have that sort of need, I just go and use the Kasto PHS, then do a facing op, same as I always have. Neither my lathe's general health, nor my pucker-factor budget is meant to be risked for sumthin' as simple to Just Deal With the quick and dirty way. I don' run no Hardinge cranking out a zillion tiny screws off "wire" stock no more.

    If you are doing "onsies" or "fewsies" and can AVOID the need to part-off in the lathe?

    Do so.

    It is more often a PITA than any other THREE ops, and ONLY worth it for at least a modest count of repeat ops, identical part and material.

    You are GOOD at this s**t and I am just a lazy old fraidy-pussy?

    I'm actually good with that, too.

    You have my respect. I have my Kasto!

    I was never one to drink bad wine, use slow computers, nor sleep with bitchy wimmin', either..

    Life is too short already.


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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.

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    Quote Originally Posted by crossthread View Post
    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.
    True as far as it goes, but one almost needs a cross-slide that would be good enough to "climb mill" if it were ON a mill, though. Or has had a lot of drag dialed-in by abusing a clamping bolt's proper nature.

    Eg: Zero backlash or it believes it has. CNC critters usually DO have that very quality, and THEIR ease of use of it at parting-off can fool we all-manual chickn's into looking for a free lunch off the back of adapting THEIR well-proven tooling.

    The tooling is not enough, all by itself. The positioning control is important as well

    If there is one, single, most-common, and CHRONIC issue with any "heavy" parting-off at any depth much beyond "trivial", it is that the stress can deflect any tool with serious reach DOWNWARD.

    Now it is "undershot" and wants to pull IN. If/as/when the cross can allow that movement? "Trouble happens". I did say "manual" is not interchangeable with CNC?

    Lovely for light, Hardinge "collet-runner" and similar repetitive high-volume use, most especially on plastics and non-ferrous.

    Not so good for heavier work, parting-off, "real steel".

    If I had to do that for a business, I'd like to see a cold-saw or equivalent live-tooled into the mix. Clears chips better than a single-pointer. OTOH "business" I'd BE running CNC. No other option makes much money. And I lIKE money.

    In "real life" some of us who might never admit to it start the cut, back way, finish with spindle under power, HAND hacksaw being cadenced to the steel. Works a treat. Only a LITTLE bit ugly. Or so the grownups tell me. I didn't do that. I must have been repeating Kindergarten recess class that day.

    Richard King is my witness, he'll tell you I'm a fake, and for several hours at ago, each episode! That does have an upside. Let's me get away to the brothels unremarked whilst y'all are distracted. That IS a dead microphone isn't it, Donald?


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    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

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    Quote Originally Posted by 4thTool View Post
    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
    Before you knock yourself out trying to part steel successfully, it's not about you, it's about the tool. Basically, the faster you can turn the part, the smoother the chip and the better it comes out of the groove. This is a practical impossibility with HSS: the edge will burn off immediately. The solution is a carbide tool, and the insert type is best because of the chip forming ability which narrows the chip allowing it to flow out of the groove. But it requires high surface speed and consistent, moderate feed to get decent insert life.

    HSS will work fine (but slower) on short chipping material like brass, bronze and cast iron, where a chip former on an insert does nothing.

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    Quote Originally Posted by Dumpster_diving View Post
    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
    Figure 5, heavy hollow-ground top-rib, waaay oversized tool compared to all-else the material has required, fishtail grind at the nose, serious rigid lathe, 4-Way right on the cross, no compound, low and slow with flood coolant to keep it cool, and ....one can get HSS to "survive".

    HuFlung is right about SFM, but wudd'n yah know it? We used to do this s**t in back gear.. WHEN.. the lathe was "strong" enough.

    One didn't get away with just 1 X blade-width, though. Had to keep widening the kerf, and working at the bottom of a canyon. Add 25% if not double the blade width to git 'er done.

    Saws still get the job done more predictably and well.

    Pissing up a rope is another way to waste time, but at least you don't crash the damned lathe doing that, the coolant is "just THERE, somehow", and the tooling dasn't cost a dime, either.


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    Quote Originally Posted by thermite View Post

    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

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    Gizmo Sir, ( OP )
    Lot's of good info posted here already.. this may be just a summation really.
    Part at the speed your turned the part. ( hss turn at hss sfm, carbide turn at carbide sfm ) The miller pamphlet is a really good source ( thanks to who ever posted that ) as is the "how to run a lathe" tome. Different materials need different speeds and feeds ( this should be self evident but somehow that seems to be lost now days in a 'one size fits all' society but I digress ).
    If the cutter starts to chatter apply more feed. Plan on facing the part so leave some meat. A part off tool is not a substitute for a cut off saw. The more rigid the machine the easier it is to part things off. A parting tool properly set up will not leave a 'tit' so make sure things are on center. (Same thing applies to a facing tool ) Look at your parting tool and blade and take note of the shape and set up accordingly. Wear safety glasses.
    Most of all keep at it.. it's a learned skill.
    As for size to be cut off.. I limit my 10 inch lathe to about and inch or so but on my W&S #3 I routinely cut off 2 inch parts.
    Hope you find this helpful.
    Stay safe
    Calvin B

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    4thTool,

    Whatever you do, be sure to where safety goggles and proceed with caution. I heard somewhere that back in the day, many of the guys in machine shops wearing patches over one eye received those injuries doing parting operations. When the blade snaps it must have a tendency to that particular region of the face.

    That said I find that on smaller lathes, I get the best results when the compound is facing parallel to the bedways / spindle axis. That reduces the slop of the compound from the equation. On bigger - stout / sturdy lathes the slop issues are less prevalent. Hope this helps.

    Best regards,

    Bob

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    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

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    Quote Originally Posted by MattiJ View Post
    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
    I didn't "worry" about either one. Smallest lathe under roof was ruled-out. Cinncy 20-something inch. Only had 8-foot of bed, and no balls at all. The 30 to 50 inchers could haul the mail. Or drag it, slowly! Old Niles are sort of kin to dinosaurs and crocodilians.

    Best part, of course, was that we were all paid by the hour!


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    If you use the standard HSS flat top blades that come with most holders, grind a groove in the top so that it folds the chip in. You can get an idea of what you need to grind by looking at a carbide insert.

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    Quote Originally Posted by mf205i View Post
    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 You can't solve all chatter problems by increasing the feed, as you might destroy your tool and the setup.

    Chatter may also indicate a need to increase both feed and rpm: the speed that works on the OD will be too slow as you get towards the center, so stop and shift up a gear. For this effect, I'm talking about parting off greater than 2" with carbide. Since it takes only about 10 seconds to part off a 2" bar, it's not that practical to stop and shift gears.

    Parting stainless steel is very sensitive to speed. Stainless parts very easily when the speed is high and as soon as the speed is too slow, the chatter/grumble begins. Stop and shift up immediately and voila, it works beautifully for another short distance. You might have to go through 2 or 3 gear shifts, but you'll do it so as to not chip the insert.

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    Quote Originally Posted by HuFlungDung View Post
    [LEFT][COLOR=#222222][FONT=Open Sans]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
    LOL! Not.. sort of the REVERSE, rather!

    Some of the new Carbides work so well it might be more accurate to expect a hard-on than a heart attack!!!

    Problem, of course, it that if we are still running manual lathes, we also need to have serious RPM on-tap. Which I do, between 10EE and the HBX, but.. I have not yet fitted new cross and nut, so am ever-aware that CNC with its low/no backlash positioners can do a lot of things that are riskier for my Old Iron. I'm not fussed, the saws work for me.

    Otherwise, even a person who didn't want to invest in Carbides for any OTHER purpose really should consider a good "system" for parting-off.


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