Centering work in a 4-jaw chuck
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  1. #1
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    Default Centering work in a 4-jaw chuck

    Years ago back around 2006 IIRC Forrest Addy posted an excellent tutorial on centering work in a 4 Jaw chuck and I printed it off and saved it in my laptop, well several years ago my old laptop crashed and I have since lost the printed copy.
    I searched PM for about an hour and cant it find anyone know or care to point me to it?

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    Quote Originally Posted by J.Ramsey View Post
    Years ago back around 2006 IIRC Forrest Addy posted an excellent tutorial on centering work in a 4 Jaw chuck and I printed it off and saved it in my laptop, well several years ago my old laptop crashed and I have since lost the printed copy.
    I searched PM for about an hour and cant it find anyone know or care to point me to it?
    I have never seen the tutorial but it is about as easy as falling off a log so I have never needed one.

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    Dial indicator on a mag base, stuck on the cross slide at the back. More or less at center height. If not on a mag base, on a tool holder, on the quick change tool post.
    Eyeball the part to sorta center.
    Adjust the cross slide so the needle is moving in the same direction as the back side of the part. As in, as the part centerline moves aft, the needle moves that way. If the needle goes around on the indicator, you did crap job of eyeballing the centering to start with.
    Hand turn the chuck until the needle is as far back as it will get, gently loosen off the frontmost chuck jaw. Rotate 180 degrees. Tighten the frontmost jaw. Watch the needle move while you do this. You will see the needle center up.
    Rinse. Repeat as required.
    Only dick with the jaws when they are opposite the indicator. One pair at a time.

    Takes less time to do than to type it out
    The dial indicator at the back puts it out of the way. If the high part is between jaws, work one pair then the other.
    The direction of the needle travel will tell you which way to move the jaw at the front (where it is really easy to access). You can see intuitively which way to move the part, and the needle will move with it, so you see how much to move.

    If it causes you stress, practice more. It should essentially be reflex to center up a part in a 4 jaw. Hold a scriber or pointed bit of rod in a tailstock chuck, press the point in to a center punch mark and you can center up on marked out locations on plate and the like.

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    Is it the following thread link?

    Setting up 4-jaw chuck

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    Quote Originally Posted by trevj View Post
    Dial indicator on a mag base, stuck on the cross slide at the back. More or less at center height. If not on a mag base, on a tool holder, on the quick change tool post.
    Eyeball the part to sorta center.
    Adjust the cross slide so the needle is moving in the same direction as the back side of the part. As in, as the part centerline moves aft, the needle moves that way. If the needle goes around on the indicator, you did crap job of eyeballing the centering to start with.
    Hand turn the chuck until the needle is as far back as it will get, gently loosen off the frontmost chuck jaw. Rotate 180 degrees. Tighten the frontmost jaw. Watch the needle move while you do this. You will see the needle center up.
    Rinse. Repeat as required.
    Only dick with the jaws when they are opposite the indicator. One pair at a time.

    Takes less time to do than to type it out
    The dial indicator at the back puts it out of the way. If the high part is between jaws, work one pair then the other.
    The direction of the needle travel will tell you which way to move the jaw at the front (where it is really easy to access). You can see intuitively which way to move the part, and the needle will move with it, so you see how much to move.

    If it causes you stress, practice more. It should essentially be reflex to center up a part in a 4 jaw. Hold a scriber or pointed bit of rod in a tailstock chuck, press the point in to a center punch mark and you can center up on marked out locations on plate and the like.
    I do it the same way but with the indicator to the front. When the dial rotates clockwise to the highest point
    the high side of the part is toward you Turning the chuck key in the jaw nearest you clockwise will reduce the
    amount of runout. After that you just have to chase it down, reducing the error till you get it perfect.

    The lines on the face of the chuck are a big help. You can usually save time if you put a little extra effort into
    eyeballing the part to get it close--leaves you with less runout to deal with when using the indicator. If your
    first pass with the indicator is less than 30 thou it's much easier to dial that out.

    I agree about practicing. After a while it becomes almost instinctive--you'll find you're not really thinking about
    what you're doing when dialing something in. I don't use a 4-jaw as much as I used to so sometimes when I've
    got one mounted on the spindle for a specific job I'll take a little time after that job is finished to practice on
    something else...

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    Raw pieces you can impress on the bench, the classic scriber and punch. A point opposite the four-jaw and centered is the piece. The tailstock must be adjusted beforehand. You can also spot drill any desired place of a face. A ball tip center is advantageous.

    In the same manner I set tool holders square to axis by pushing them loosened against the face of the chuck (not revolving, of course). Or I center a chuck on the miller table with a cylinder clamped in collet holder in the spindle.

    Work that’s already given its outer shape and or dimensions needs to be aligned with the aid of a dial test indicator.

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    Quote Originally Posted by moonlight machine View Post
    I have never seen the tutorial but it is about as easy as falling off a log so I have never needed one.
    Falling off a log is waaay harder. Especially if there's any altitude to the sumbich and/or rough landing zone, and you are not really into PAIN!




    I can see the value if you are having to learn it from a book whilst in hospital with both arms in casts. Once you escape and actually lay-hands on a physical manifestation of an actual 4-j independent chuck, it should come natural in a few minutes.

    - First comes "Aha!", that's how the f****r works!", as you realize the obvious: that advancing one screw naturally has to have its opposite mate retract to allow room. But ONLY that much or just a smidge LESS! Backlash thing.

    No joke. People FIGHT this, and for years, when they should know better. Metals don't squeeze easily, and plastics should not be asked to do.

    - then comes accurate. Mark One Eyeball, sharpish stylus, reliable source of light to gage first the gap, then the drag.

    - Speed does take a while longer, largely because to become "fast" you simply have to hit it by "calibrated eyeball" really close, first go, otherwise chase-tail, check, chase tail again, repeat.

    Only ever needed a DI when I had to pick-up on an existing feature to less than a thou.

    Read: "Near-as-dammit NEVER."

    DI is otherwise a time-wasting nuisance, plus risk of damage to the DI, most any "normal" work.


    It ain't hard.

    But one has to go grab the chuck and practice.

    Any gadget-assisted shortcut always takes longer.

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    Quote Originally Posted by LKeithR View Post
    I do it the same way but with the indicator to the front. When the dial rotates clockwise to the highest point
    the high side of the part is toward you Turning the chuck key in the jaw nearest you clockwise will reduce the
    amount of runout. After that you just have to chase it down, reducing the error till you get it perfect.

    The lines on the face of the chuck are a big help. You can usually save time if you put a little extra effort into
    eyeballing the part to get it close--leaves you with less runout to deal with when using the indicator. If your
    first pass with the indicator is less than 30 thou it's much easier to dial that out.

    I agree about practicing. After a while it becomes almost instinctive--you'll find you're not really thinking about
    what you're doing when dialing something in. I don't use a 4-jaw as much as I used to so sometimes when I've
    got one mounted on the spindle for a specific job I'll take a little time after that job is finished to practice on
    something else...
    I taught guys to adjust the position of the slide so that the needle moved the same way as the part, while the needle was pointed at the headstock. No trying to remember which way was which, the adjustments moved the part and the needle the same way.

    As for those that think risking a $15 cheapass dial indicator is too much risk to take... Y'all need a better paying job! LOL!
    Life is too short to spend it squinting at stuff that is way easier to see when you put an indicator on it.
    If you need actual precision, tenths or less, then the good indicator, as fits the needs, gets used.

    Indicators are simple, relative movement indicators, and for 4 jaw work, it don't take a bank loan to buy what is adequate.

    Cosine errors? We don't care about no steenkin' cosine errors!

    Only thing about methods that matters in the end, is if it works well enough to meet spec, in a time short enough to keep the boss off yer ass! Lots of ways to skin a cat, eh?

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    Quote Originally Posted by trevj View Post
    As for those that think risking a $15 cheapass dial indicator is too much risk to take... Y'all need a better paying job! LOL!
    That's the very point, Pilgrim.

    I spent much of my life WITH a better-paying job.

    I begrudge the TIME I still think of as worth several hundred dollars an hour to FIDDLE with a DI I didn't need even in 1959 when I could NOT afford one and had to learn how to do well without it.

    Which, of course, is part of how I GOT those "better paying jobs".


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    Quote Originally Posted by thermite View Post
    ...Only ever needed a DI when I had to pick-up on an existing feature to less than a thou...

    ...Any gadget-assisted shortcut always takes longer...
    Well, I'd have to say that while this may work for you you're definitely in the minority on this one. For the vast majority
    of us a simple, inexpensive dial indicator and some solid experience is the fastest, simplest way to dial in most stuff
    in a 4-jaw chuck. I have futzed around with odd-shaped objects and when dialing in hole centres but for something
    that's already round I can't see how a dial indicator isn't your go to tool...

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    Quote Originally Posted by LKeithR View Post
    for something that's already round...
    Anything "already round" acts like a cam ... until centered so well it no longer does.

    One just lets the high spot bump a darning needle, adjust-out half the air gap, opposite side to the high-spot, repeats until no more detectable gap.

    Fine work, one may drag a sharp tool-tip until it shows no diff, full-circle, either.

    That sounds crude, just go and do it the best you can find it in you to do. i'm serious.

    THEN put a DI on it and take note it is pretty damned accurate.

    Do it no other way long enough, and on a chuck you are very familiar with, it is also pretty damned FAST, too.

    And of course.. there's TONS of tasking where so damned much metal is there to come off the stock you don't even HAVE TO BOTHER getting it any closer than 20 to 50 thou of runout. Unaided eyeball can easily do that - or better - no reference point or marking, either one.

    Which is REALLY faster than even reaching across the cart for a DI and mount, setting it up, taking it down and asiding back to storage.

    Not that i'm all that monotheistic over any of that. Got "many" collet-systems, too.

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    Perhaps the earliest Brown&Sharpe indicator. The rod is in a center punch impression. At the bottom of the last photo, the "hook" end, when attached to the indicating rod will ride "under" a piece of round stock for indicating in the same manner.

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    It's easiest to just clamp it in - make sure all 4 jaws are good and tight. Then, turn on the lathe and touch the cutting tool against the part and move it around. It'll make the metal shinier, and that shiny area will be centered.

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    Quote Originally Posted by GregSY View Post
    It's easiest to just clamp it in - make sure all 4 jaws are good and tight. Then, turn on the lathe and touch the cutting tool against the part and move it around. It'll make the metal shinier, and that shiny area will be centered.
    ummmh... and the manner in which one "turns on" such a lathe?

    Might it involve flowers, candy, waylube lovingly applied to private places, then sweet nothings whispered into the bore:

    "Oh, you beautiful thang, you! Want get naked and touch a really, really hard and very well-formed tool?"

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    Anybody who tries to center work in a 4 jaw without using two chuck keys and a dial indicator is wasting time. Quit iterating!

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    HA! This guy^.

    Half the battle is knowing the chuck. Rarely have I seen a tiny (<6”) diameter chuck worn to the point of being infuriating to use. But some other 20”/28”/36” 4-jaws seemed to move a jaw by only seating the key in the screw. Get to know the chuck and as above, it becomes innate.

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    Quote Originally Posted by Curt Brown View Post
    Anybody who tries to center work in a 4 jaw without using two chuck keys and a dial indicator is wasting time. Quit iterating!
    Meah.. see Post #16.

    When the handles on two chuck keys wudda been wot? Four feet apart and more, plus 25 and more foot stroll around the lathe to get AT one of them?

    No gain!

    It was easier to use the "Jog" button and just one...


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    I'm probably the odd man out here. But the only time I use an indicator to center work, is when there can be no Machining of the OD. Otherwise I eyeball it close (maybe get the Tool close to compare) then Turn the OD---yay centered.

    IMO it's a waste of time. If the part is going to upset the balance or is a hazard, that is not what I would call "close". But I can eyeball a part within .01" pretty quick. (Assuming it is regular, round Bar Stock and all other variables are normal)

    And I have no idea WTF Post #15 is. Like splaying your body across the bed of a small lathe to handle 2 keys at once? That doesn't sound like my kind of ride. It would have to be a tiny little baby lathe anyway, right? Am I picturing something different?

    R

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    Quote Originally Posted by litlerob1 View Post
    And I have no idea WTF Post #15 is. Like splaying your body across the bed of a small lathe to handle 2 keys at once? That doesn't sound like my kind of ride. It would have to be a tiny little baby lathe anyway, right? Am I picturing something different?

    R
    I don't believe you are. That being said, tightening one jaw enough to work safely usually moves the work a thou or two, even if the other is snug, so I don't think I'd WANT to be leaning over the carriage and/or ways, hauling on two keys at the same time, waiting for my leg to bump the lever... And before you say "don't have the carriage right there" it would take more time to move the damn thing a few feet than it does just to spin the chuck a half-turn! Utter nonsense.

    And just to throw my own opinion out there, 12 o'clock or bust! Maybe that comes from me being a taller guy, but I like looking from the top down, rather than from the side. Now that I'm thinking about it, I think it's really more like 11 o'clock. Makes no difference as long as the jaws you're working on are in line with the indicator's reading.

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    It's worthwhile to learn to adjust by "halving the air gap" as described earlier. It really speeds things up. I use the tip of the indicator for this and I'm usually within a few thou when I bring the indicator into play. If necessary, I can eliminate that just by snugging up the jaws. (Instead of checking that the part hasn't shifted when clamped tightly and having to correct it.)

    The only thing I would add is to focus on the for cardinal points of the jaws. Even if the high point is between two adjacent jaws, you can only fix it at the jaws. If there's still a high point after it's centered at the jaws there are other issues.

    Made extra chuck keys for the two key thing. Don't use them. It's awkward and doesn't seem to improve speed or control.

    I'm but a crude blacksmith so, if I can do it, anyone can do it. 😉


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