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  1. #21
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    Quote Originally Posted by SmlG54 View Post
    Hey Rob, I didn't follow what you meant. I get saw long but not holding onto a post.
    And jaws are soft pie jaws matching part radius (dont know if that comes into play)


    AND edit: The more I look at it, the more it looks like trolling to me. Is that whats going on or is this just some way over my head stuff I dont know the lingo for?
    And if it is trolling, well done, and go f-yourself (but I say it like a new yorker so we all know how they say it )
    What I mean is, saw the blank long enough to hold only enough to Machine the part complete (except the part you're holding on to) a post, is in reference to the extra material that is only in existence for clamping on. After that you can figure out the best way to remove the post without having the Chuck on the part itself. I hope that makes sense.

    If I were Trolling, it would be funny at least. I don't care enough to not get some laughs out of it.

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  3. #22
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    Quote Originally Posted by litlerob1 View Post
    What I mean is, saw the blank long enough to hold only enough to Machine the part complete (except the part you're holding on to) a post, is in reference to the extra material that is only in existence for clamping on. After that you can figure out the best way to remove the post without having the Chuck on the part itself. I hope that makes sense.

    If I were Trolling, it would be funny at least. I don't care enough to not get some laughs out of it.
    I'll toss you another technique.. Double 'em up.. Cut to double the length for a single part.. Machine one part,
    and then use the first part to hold the second part.. Machine the second part, and part it off. And then you can
    finish the backside of the first part if need be. You can cut down on the waste that way sometimes.

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    lilrob is the real deal, he doesn’t fool around. His advice was either to part off “out & away” or turn, rechuck and "part the chucked end off". You’re on the edge with this part...

    Wedding rings (like mine after 40yrs, get wimpy thin and act funny)…

    Even with Pi jaws given your (part section) thickness, a saw blade width gap (and too heavy a grip) can be found by a good inspector. It’s bad enough → that a (high dollar ground & hardened collet) grip on a .125” wall 1 inch Dia. 4130 tube that is .002” under collet nominal Dia. will project a deformity several inches down the tube with the end point actually going high, image attached. Then it gets back to normal with a more half circle shape shortly after… It’s pretty small, but they were detecting these things WAY-WAY back before my time with “last word” indicators.

    It will have as many lobes as the collet has parts. They will look like the feathers (construction joining decorations) on a 2 or 4 piece English snooker cue under close examination (very long half oval – strange shape depressions). It’s just hard, make the Pi jaws right & find the pressure that doesn’t deform & live with it (AND YOU RULE).

    Good luck,
    Matt
    Attached Thumbnails Attached Thumbnails snooker.jpg  

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    Quote Originally Posted by SmlG54 View Post
    I am using bored soft pie jaws at around 125 psi.

    These parts are for our company. So far I was told that if it measures in the chuck correctly then it's fine. (many would stop there)
    .
    Full stop right there!!!

    You were TOLD that, but does the PRINT say that?

    Actually, that method of in-process inspection might just be correct but there should be clear notes on the print indicating what to measure.

    For example, your thin walled part might be a sleeve that is pressed into something with a matching bore.
    It likely don't matter a hill of beans that it's out of round, but it's size must be within a strict tolerance.

    For example I am dealing with a miserable group of parts not unlike yours. Thankfully however the engineer had the brains to make the tolerance notes as such:

    Dia 6.830 +/-.002 AVG,
    Max envelope 6.841

    OD or part is given as .156 +0/-.003 wall thickness.

    In this case I can be out of round by as much as .022 Total and the part will still function as intended.

    So in your case it just might be an accepted practice to measure it while still in the chuck as you don't need to figure the averages and you know that
    if they are within the tolerance ( both ID and OD ), they are also concentric.
    The only thing they need to do is add the notes to the blueprint.

    Obviously final inspection will need to do the correct measurements and evaluate per-print.

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    Quote Originally Posted by litlerob1 View Post
    What I mean is, saw the blank long enough to hold only enough to Machine the part complete (except the part you're holding on to) a post, is in reference to the extra material that is only in existence for clamping on. After that you can figure out the best way to remove the post without having the Chuck on the part itself. I hope that makes sense.

    If I were Trolling, it would be funny at least. I don't care enough to not get some laughs out of it.
    That actually did make sense. The "Post" is the extra material that will not be apart of the finished piece. The "Post: is the extra the extra to hang on to, ie clamp in chuck. Gotcha.

    But btw. Go f-yourself anyway, just cuz.

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    So there are 2 possiblitlies when we need Round parts that aren't Round.

    1. The Chuck is causing out of Roundness, in one way or another.
    2. The Material is springing or whatever the technical term is.
    3. I guess someone could drop it on the floor, or hit it with a Hammer. But I didn't think I needed to add that one.

    There are ways to deal with those things, in different ways.

    So the Operator needs to figure out which one it is. Once we establish the problem then it's much easier to find the solution. Instead of just yelling; "Hey, Mom it's not Round-fix it". We used to have a stick-poke Emoji, I can't remember the BB for it.

    R

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    Quote Originally Posted by SeymourDumore View Post
    Full stop right there!!!

    You were TOLD that, but does the PRINT say that?

    Actually, that method of in-process inspection might just be correct but there should be clear notes on the print indicating what to measure.

    For example, your thin walled part might be a sleeve that is pressed into something with a matching bore.
    It likely don't matter a hill of beans that it's out of round, but it's size must be within a strict tolerance.

    For example I am dealing with a miserable group of parts not unlike yours. Thankfully however the engineer had the brains to make the tolerance notes as such:

    Dia 6.830 +/-.002 AVG,
    Max envelope 6.841

    OD or part is given as .156 +0/-.003 wall thickness.

    In this case I can be out of round by as much as .022 Total and the part will still function as intended.

    So in your case it just might be an accepted practice to measure it while still in the chuck as you don't need to figure the averages and you know that
    if they are within the tolerance ( both ID and OD ), they are also concentric.
    The only thing they need to do is add the notes to the blueprint.

    Obviously final inspection will need to do the correct measurements and evaluate per-print.
    Yeah... it's tricky, print calls for concentricity +- .001.
    I am given a print and then told don't worry about the print (more or less). The guy knows what he is talking about, he has helped re-engineer the parts and assign tolerances for the company.

    Just a non-normal to see specs and deviate and then say "hey, this is what I am finding" and then "....do it anyway"

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    Quote Originally Posted by SmlG54 View Post
    Yeah... it's tricky, print calls for concentricity +- .001.
    Concentricity is a locational tolerance between features not a roundness callout.

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    Quote Originally Posted by SmlG54 View Post
    Yeah... it's tricky, print calls for concentricity +- .001.
    I am given a print and then told don't worry about the print (more or less). The guy knows what he is talking about, he has helped re-engineer the parts and assign tolerances for the company.

    Just a non-normal to see specs and deviate and then say "hey, this is what I am finding" and then "....do it anyway"
    Just as a brain fart...


    We have to integrate a lot of the time with Rennishaw high precision encoder rings. Basically thin sectioned partially tapered rings of all sorts of diameters (seem to be of some kind of stainless with the encoder "groves" on the external cylindrical surface).

    Even though these rings are stress relaxed (thermally) and precision manufactured they go on a LOT about TRI-Lobarity… or trilobarity*.. (Something that may crop up when dealing with higher tolerances and "springy " shapes" / locked in stresses.

    An "Oval" is one possible "springy" distortion, but it could be that a three lobed distortion is more natural and stable to the piece you are working with ? Think Three leaf clover shape ( in exaggerated form from distortion on tenths).

    Kinda "Riffing off" Matt and LittleRob1's comments and others @SmlG54 do you have the means map out the actual shape of the part ? $5 says it may be more complex like Trilobed. I just have this hunch that these locked stresses will "Default" to a tri-lobed pattern.

    The twisted 1/2 arsed logic I'm going on here is that an "Oval" shape may indicate unwanted locked in stresses (in this case) and a tri-lobed shape would indicate that the material and process is sufficiently "Stress" relived / relaxed / evened out (or at least getting there). Just helps to narrow things down / trouble shoot and then easier to derive a set of "Test" procedures (especially if you have to partially machine the part and then stress relive it and then leave on a shelf for a couple of weeks (or something) and then finish ? <The guys here would know better than I on that >.


    Also curious what machine are you running this on and also curious where you got your pie-jaw/soft jaws from ? [I'm learning sh*t myself]. (Maybe you mentioned that / will re-read the thread.).


    __________________________________________________ _________________________________________________

    * Not a foppish manner affected by Trilobites.


    ** In the Renishaw case there are six bolts + a tapered fitting so the trilobarity is ironed out by how the component is tightened onto its tapered base / fitting. (As opposed to interference fit).



    __________________________________________________ __________________________

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    Anyone know how to convert KGF (I think it means kilogram force) into PSI? On thin walled parts on a 6" hydraulic chuck with pie jaws I have turned it down to 6 the minimum it takes for it to close making light cuts. The max setting is 35 which is full line pressure. What does 6 KGF convert to in PSI?

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    Quote Originally Posted by Dualkit View Post
    Anyone know how to convert KGF (I think it means kilogram force) into PSI? On thin walled parts on a 6" hydraulic chuck with pie jaws I have turned it down to 6 the minimum it takes for it to close making light cuts. The max setting is 35 which is full line pressure. What does 6 KGF convert to in PSI?
    Let me get an espresso and wake up... I can do that. I'm sure there's a web page for that. I used to have old American Astronautical Engineering textbooks that had crazy math in foot pounds per second and the like... I'm originally European / UK so metric... so much easier than these "Imperial" based equations with wackadoodle conversion constants.


    Give me a mo.


    I'm kinda hoping this thread does not turn Into a Hardinge commercial lol ;-)

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    Quote Originally Posted by Dualkit View Post
    Anyone know how to convert KGF (I think it means kilogram force) into PSI? On thin walled parts on a 6" hydraulic chuck with pie jaws I have turned it down to 6 the minimum it takes for it to close making light cuts. The max setting is 35 which is full line pressure. What does 6 KGF convert to in PSI?
    just linear grip force.

    Technically Metric for force is the Newton that's why they use "F" as force. [Physicists tend to get their knickers in a twist about Mass versus weight... ].


    1 kg is approximately 2.2 lbs.


    So maximum grip force or "thrust" could be of the order of 40,000 lbs which is 18144 Kg (of force) "F". which is actually 181440 Newtons (or thereabouts) [You guys don't use Newtons.].


    Maximum clamping forces ish (depending on machine and rpm etc.).


    40,000 lbs (f) ---> 18144 Kg(F)

    30,000 lbs (f) ---> 11608 Kg (F)

    20,000 lbs (f) ---> 9070 Kg (F)

    10,000 lbs (f) ---> 4535 Kg (F)

    5000 lbs (f) ---> 2268 Kg (f)

    ^^^ All at direct ratio of 2.204 lbs (or nearly) to 1 Kg "Force"... 10 newtons. [1 Kg = 10 newtons ]. Pressure is force per unit area Pounds / square inch … and in Metric land it's Newtons / Meter ^2(Squared) [Big numbers].


    ___________________________________________


    So taking literally what you are saying @Dualkit 6KGF "converts to " 13.22 pounds of thrust... So lets say your gripping surface area is on your pie jaws... Rough guess for a 2 1/2" diameter part and not so deep pie jaws gripping maybe 2.5"^2 surface area gripping would give a pressure on the part of approximately 5 lbs / square inch ? [<< Need to check my janky math on that as I don't know geometry of part or pie jaws and rpm + cutting conditions etc. ].

    I'll look through the Hardinge catalogues for special work holding / low pressure fixtures / custom workholding.


    ____________________________________

    @Dualkit Depending what machine you have Hardinge are well into their step chucks and so called 'Emergency" step chucks that can be custom bored as opposed to being ordered. However on page 15 here http://hardingeus.com/usr/pdf/2327.pdf they have their "Force-Limiting Step Chuck"


    "Solutions for thin-wall or delicate parts • Adjusts grip in a fail-safe process eliminating the nuisance of manually adjusting your drawbar force • Operate at normal pressure with the properly selected spring in accordance with the wall thickness of your workpiece • Maintains ID and OD concentricity • Grip up to a 6" workpiece • Increases cycle time • No more out-of-round or crushed parts "


    ^^^
    No affiliation but wondered how well the springs that you have to select adequately and accurately scale the force applied in a non-fiddly way (through the draw bar) ? Haven't used them don't know how effective they are ?


    Not sure if the expanding mandrel / expanding ID collet has any use or merit to OP either ? [Need to re-read thread].
    Last edited by cameraman; 07-11-2018 at 03:23 PM.

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    Quote Originally Posted by SmlG54 View Post
    Yeah... it's tricky, print calls for concentricity +- .001.

    Just a non-normal to see specs and deviate and then say "hey, this is what I am finding" and then "....do it anyway"
    OK, that’s usually what they really need with things that look like this (beside size). So for bores to be concentric it follows that the thickness of the ring will be uniform.

    The quickest way “I know of” around the machine is to use a ball attachment on a mic like I mentioned in post #16. Just motor around the ring 6 or so times is good enough, pic attached.

    Good luck,
    Matt
    Attached Thumbnails Attached Thumbnails ballattach_for_mic.jpg  

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    Quote Originally Posted by Matt_Maguire View Post
    OK, that’s usually what they really need with things that look like this (beside size). So for bores to be concentric it follows that the thickness of the ring will be uniform.

    The quickest way “I know of” around the machine is to use a ball attachment on a mic like I mentioned in post #16. Just motor around the ring 6 or so times is good enough, pic attached.

    Good luck,
    Matt
    Aye...

    However concentricity refers to a notional center... So I think OP said external surface is the reference surface...

    So just saying (not to contradict your application) that one could gauge just like the nice photo you have provided and still have tri-lobarity of the order of tenths and still gauge the relative thickness as having almost zero deviation (less than 40 millionths (ish-ish)).


    I agree having better knowledge of the application would be super helpful but "Up-stream" management is not so common in the USA at the moment (as compared to Japan) but OP seemed to indicate that the engineers work more closely with the machinists than is perhaps typical.


    @Matt M that's a cool point that you raise... As when part springs back to its natural state it could still be tri-lobed and yet have the inner shape / surface be kinda "concentric" i.e. inner shape follows outer shape and reference surface very precisely.

    If it's bored in a non concentric fashion (inner to outer surface) then you would get Off center artifact like what your technique hunts down... That's when you get the boasters chimming in like "Hey what your problem I hold 1/2 tenths all day long " Yeah right... 4140? Grinding probably not needed and the part is not hardened afterwards ? I don't think and kinda interested what effect that "Stock" would have on all this and OP's troubles as well as stress relief and putting stuff on a shelf for a few weeks and then finish? ]. .

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    Quote Originally Posted by SmlG54 View Post
    I am using bored soft pie jaws at around 125 psi.

    These parts are for our company. So far I was told that if it measures in the chuck correctly then it's fine. (many would stop there)
    Trying to pick some brains and see how others approach it.
    The part measures true and concentric after #1 but changes by +- .002 after id work.
    and then changes a little more after unclamping.
    Apologies for being really dumb here … Do you literally mean 125 psi ?


    So a 6" ring that eventually only has a wall thickness of 0.1"... Length of ring is 2.75 "OAL"...


    So I really don't know the depth and exact set up of your pie jaws you are using to grip the part/work.


    So if you grip that part by 1/4" at 125 psi that's about 625 lbs of thrust. So a 300 Lb guy would easily deform that part if standing on that ring... no ? By two thou ? ((I understand radially symmetrically applied forces? but still ).


    Maybe I'm smoking crack but would seem to me that would be plenty of force to deform the part if things are not set up really well ? Also on such a large diameter part with so much material removal that it would seem to me that part would need quite a lot of time to "Settle down" dimensionally (like folks are saying here). . [Also apologies for being stupid as I assumed you were going for tenths and now I realize you are trying to stay within one thou.. (Stupid metric guy that needs to wear glasses that I am )]. .

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    In addition to the material and/or the chuck causing ovality, the tooling might also be involved. Especially if you're using negative rake inserts, with a large nose, and the material is part-hard or has a seam. If that's the case, you might want to try positive rake tooling and perhaps lighter roughing cuts to reduce part or tool deflection. Finish cut is obviously the most important, but out of roundness can telegraph to the last operation.

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