Question: Reccomendations for an independent 4 jaw chuck? - Page 3
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  1. #41
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    Quote Originally Posted by Limy Sami View Post
    Tight, now we've got that established, ........who's up for explaining about chuck gripping pressure decreasing as RPM increases?
    I remember the first time this happened to me with a 10" scroll 6-jaw. I was finishing a 1/2" diameter at somewhere north of 1000 rpm and when I tried to take the finish cut the workpiece pushed back into the chuck rather than take the feed pressure. Happily I was chucked on a good enough amount that the workpiece didn't transform into a projectile! It took me a second try before I realized what was going on. A bit more tightening of the chuck solved the problem in that case. Centrifugal force pulling those jaws out and loosening the grip on the work was new to me at that point.

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    Quote Originally Posted by eKretz View Post
    I remember the first time this happened to me with a 10" scroll 6-jaw. I was finishing a 1/2" diameter at somewhere north of 1000 rpm and when I tried to take the finish cut the workpiece pushed back into the chuck rather than take the feed pressure. Happily I was chucked on a good enough amount that the workpiece didn't transform into a projectile! It took me a second try before I realized what was going on. A bit more tightening of the chuck solved the problem in that case. Centrifugal force pulling those jaws out and loosening the grip on the work was new to me at that point.
    Scroll-operated chuck it's usually a combination of centrifugal pull with vibration in the cut you may not even notice. Even so, it is enough to motivate the scroll plate to move a tiny bit, the jaws providing the choice as to direction of pull - looser rather than tighter.

    Schunk not only make power chucks that compensate off the back of weighted actuator mechanisms - they also sell add-on "pendulum" top-jaws for balancing the forces on certain types of work.

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    Thanks for the help, one might think i am finally understanding your point. Dont really know what i was thinking earlier

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    Well i tend to disagree with you on that, in our first classes we were shown multiple photos and videos (non censored) of people who did not learn that lesson. All of us shit our pants the first time We spun our mighty celtic 12 at 500rpm and rightly so, the most important lesson i learned is that you can never be too careful (although now i realize that my question was kind of stupid)

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    Believe it of not, the young dumbass is actually aware of this. Once at work we were turning very small soft steel parts on our CNC lathe so we were at quite some rpms (it is equiped with a 125mm pneumatic schunk so that was not the problem) and even at max gripping force allowed the part was still being pushed in quite a bit. I guess this confirms the point Everyone is telling me, just cause you have the rpms, dont mean you can use em

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    Quote Originally Posted by GregSY View Post
    700RPM on a lathe is a lot like midnight.

    Nothing good happens after either one.
    Quote Originally Posted by GregSY View Post
    My point is....if you need to spin something more than 700RPM, or so, it's seldom big enough to need to be held in a big chuck. Spin your 4" chuck at 2000 if you must. But even then, most things cut well enough at 700.

    Ok OK... manual lathes, with no / minimal guarding, maybe .... But in cnc lathe territory, 700 rpm is in the tapping speed range, nowhere near turning (at proper sfm)..

    Where did you get 700rpm anyways? Dartboard? WAG?

    Sorry nothing to add to OP question that hasn't been said (don't run big chucks/workpieces at high rpm....)

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    700RPM because most lathes have a speed around that area, and from experience. I've been assuming this discussion is a manual lathe, no coolant, job shop type of situation. But even with a 'guard' - who cares? Guard or not, I don't want stuff flying out. As for CNC, I have little experience there, admittedly. But....other than a boss leaning on you to get those 4,000 widgets done by Monday for the Armbruster account...why do anything at 2000RPM? Until you get under, say, 3/4" dia I just don't see the need.

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    When using carbide inserts on the softer steel range even with larger diameters i am often in the range of 1000 or slightly above if you want the chips to break properly and to have a decent surface finish, most of the time 700 isnt enough

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    Quote Originally Posted by fratskop View Post
    Thanks for the help, one might think i am finally understanding your point. Dont really know what i was thinking earlier
    Oh, most of us started-off with far LESS of the knowledge. First few weeks of life, I'm told I didn't even have the ability to find me own Mum's nipples and get a lip-lock without help.

    Impatient, y'see. Being born premature at 5 1/2 months, eyes not open yet, and going into an incubator ... etc.



    Mind.. weren't for a "DNR" already on-file, I mought have risked ENDING in much the same condition, so...


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    Quote Originally Posted by fratskop View Post
    When using carbide inserts on the softer steel range even with larger diameters i am often in the range of 1000 or slightly above if you want the chips to break properly and to have a decent surface finish, most of the time 700 isnt enough
    Usta bee.. Got a wider choice of inserts for that long-since. They even work on lowly old cone-head SB hobby lathes and such.

    Even so, older lathes don't make the best of substitutes for modern CNC spindles nor OD grinders, either one.

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    Quote Originally Posted by GregSY View Post
    700RPM because most lathes have a speed around that area, and from experience. I've been assuming this discussion is a manual lathe, no coolant, job shop type of situation. But even with a 'guard' - who cares? Guard or not, I don't want stuff flying out. As for CNC, I have little experience there, admittedly. But....other than a boss leaning on you to get those 4,000 widgets done by Monday for the Armbruster account...why do anything at 2000RPM? Until you get under, say, 3/4" dia I just don't see the need.
    Prezactly. We now and then see a print of a 10EE with a silly-LOOKING 4" or 5" 4-jaw on it. Not so silly. I have both now. And collet systems as go well above an inch.

    4,000 RPM has only been on tap for a bit over 60 years...

    ..., but inertia and kinetic energy? FAR older yet!


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    I haven't read the entire thread so this may have been suggested already and I do know it is a PITA to change a 12" chuck, but it sounds to me like you need two chucks, perhaps 12" and a 6" for smaller work. And some kind of hoist to assist in changing them.

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    Worrying about a lathe capable of 1600 rpm
    and having a chuck only rated for half that
    seems like a problem with managing expectations.
    Somehow you have the idea that the chuck should
    be able to handle the full rpm potential of the
    lathe. Not sure why you think that.
    You can just as easily put 2 tons of load on a
    half ton rated truck. Nothing is stopping someone
    from doing this, except their good intelligent
    decision making skills. The same decision making
    comes into play when selecting what rpm to spin a
    chuck at. If you subject a large chuck to excessive
    speed, it will blow apart. No different than a
    grinding wheel subjected to excessive speed.
    One has to use their brain to be safe.
    Maybe you have been programmed to believe some lies
    about safety being the responsibility of the company
    that you work for. As in like, make a machine so
    fool proof that no operator can get hurt with it,
    no matter how many stupid things they may try.
    Well that is not how life is. Life is dangerous if
    you are not paying attention. Bottom line is this...
    It has been the normal thing for 100 years for the
    machinist to be the one responsible for selecting
    a safe and prudent speed to run lathe chucks and
    faceplates; and grinding wheels for that matter.
    Same goes for appropriately loading trucks for
    transport. If you don't trust yourself with your
    lathe, maybe buy only a 6" chuck. Else you just
    learn what speeds are appropriate and use your
    larger chuck with care.

    --Doozer

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    Yeah the point of chuck size had been Made clear to me and i think i Will start with a 6 or 8 inch one. And it Will definitely not be a walk in the park to take that 12” sucker off thats on there now (as stated its Some sort of pneumatic one and its really wide) i do have an engine hoist but ill have to see if it can be of any use

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    The other consideration of note when spinning up a lathe chuck to higher RPM is whether the chuck jaws are gripping on a rough diameter or a round and on center dimeter. If the diameter is rough and not on center, the chuck jaws aren't centered which means it's out of balance. In my experience even most bigger chucks that are rated for high speed are scary to run there - the vibration from being out of balance at high speed can usually be felt in the whole machine, and maybe even the floor.

    If you have a workpiece with unavoidable gross diameter differences - such as an 8" shaft with a ½" stub on the end, better to just grind the small diameter or turn and polish rather than try to spin it to the moon.

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    ...And no one said to always run the max speed and feeds.
    You can get a good surface finish going slow.
    This production-mindset of speeds and feeds often times
    violates common sense. Each situation is unique.
    Realize the difference between what the book says
    and real world. Those machinists will go the furthest
    in their career.

    -D

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    Youre right, i will add that i am not fixated on always running max speeds, i rarely ‘max it out’ i just figured it would be handy if i could use them if i ever needed to. I do nothing by the book since i started my first job, learned more in a Month than i ever did at school

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    If you need to spin 30000RPM and are afraid of the 12" chuck being too much, and know you should use the 4" chuck, but don't want to change it out, you can always use the 12" to chuck up the 4" chuck. lol.

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    Quote Originally Posted by GregSY View Post
    700RPM on a lathe is a lot like midnight.

    Nothing good happens after either one.
    Quote Originally Posted by GregSY View Post
    My point is....if you need to spin something more than 700RPM, or so, it's seldom big enough to need to be held in a big chuck. Spin your 4" chuck at 2000 if you must. But even then, most things cut well enough at 700.
    Quote Originally Posted by Doozer View Post
    ...And no one said to always run the max speed and feeds.
    You can get a good surface finish going slow.
    This production-mindset of speeds and feeds often times
    violates common sense.
    Each situation is unique. < of course!!
    Realize the difference between what the book says
    and real world. Those machinists will go the furthest
    in their career.

    -D
    Well no... not if you know what you are doing... I've ran parts where the (cnc lathe) spindle was at or near the max 4k rpm ALOT. It didn;t scare me because I knew the process and workholding... Now, ya I'm not running a manual lathe up to that (even if they had it) with a 12" chuck < that is common sense. NOW a nice little 5c, sure crank 'er up to 1500-2000 rpm, no problem.

    Here is an example of NOT COMMON SENSE. (sfw not gory)

    YouTube

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    Quote Originally Posted by GregSY View Post
    If you need to spin 30000RPM and are afraid of the 12" chuck being too much, and know you should use the 4" chuck, but don't want to change it out, you can always use the 12" to chuck up the 4" chuck. lol.
    ROFL!

    Riggggght..... Put the space shuttle on the back of a modified 747, "Fat Albert" can now do a fiery re-enty from orbit...???

    Oh, surely, it CAN!

    Shiney-wood f***ker would melt right TF out from UNDER the space shuttle and scatter its molten remains across half the planet.

    "No problemmmm." None of the pieces large enough for evidence in a Court 'o Flaw, after all.

    "Thus spake Tharwasachuckstra"



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