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  1. #1
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    Default lathe drilled hole not concentric

    Hi guy,

    This is probably a newbie question.

    I am drilling a 0.116" hole into the end face of a 304 stainless part. The hole is usually centered on one axis and not on the other. So if I measure from the outer diameter of the drill hole to the turned out diameter of the part, I will measure something like:
    Top:0.436
    Bottom: 0.435
    Left: 0.432
    Right: 0.438
    Hole diameter is on size and no observable difference in diameter in any orientation.

    Machine is a Mazak QT15 lathe. Tool is a Ultratool solid carbide jobber drill. Held in a Maritool ER32 collet tool holder with cheap Chinese collet. Material is 304 stainless. Chucked using aluminum soft jaws on previously turned surface. Soft jaws were machined in the past and have been on and off the machine multiple times.

    If I use a HSS drill bit, the hole location is substantially less concentric.

    It has been a long time since I indicated in the x-axis on this tool pocket.

    So basically my question boils down to what is causing the hole to be on center on one axis but not other?

    Thanks,

    -Jim

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    If you deliberately drill a hole off center, there is always some rotational angle that will put the hole on an axis ... think about it.

    When you drill your 0.116 I am guessing you follow general wisdom and do not spot face before drilling. If so, when your flimsy drill point hits the center bump left from facing with a slightly off center facing tool, it is deflected a bit. Affect will be more with the less rigid hss drill.

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    Chuck another part and put an indicator on it to check the runout. There are a number of issues that could be causing the lack of concetricity, but I think the most likely one is that your soft jaws need to be rebored. You can never assume that soft jaws will have the same runout if you take them off and put them back on.

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    Quote Originally Posted by kb0thn View Post
    Hi guy,

    This is probably a newbie question.

    I am drilling a 0.116" hole into the end face of a 304 stainless part. The hole is usually centered on one axis and not on the other. So if I measure from the outer diameter of the drill hole to the turned out diameter of the part, I will measure something like:
    Top:0.436
    Bottom: 0.435
    Left: 0.432
    Right: 0.438
    Hole diameter is on size and no observable difference in diameter in any orientation.

    Machine is a Mazak QT15 lathe. Tool is a Ultratool solid carbide jobber drill. Held in a Maritool ER32 collet tool holder with cheap Chinese collet. Material is 304 stainless. Chucked using aluminum soft jaws on previously turned surface. Soft jaws were machined in the past and have been on and off the machine multiple times.

    If I use a HSS drill bit, the hole location is substantially less concentric.

    It has been a long time since I indicated in the x-axis on this tool pocket.

    So basically my question boils down to what is causing the hole to be on center on one axis but not other?

    Thanks,

    -Jim
    .
    1) if more error when drilling (compared to boring) try a spot or center drill first before using drill bit. avoid a extra long spot/center drill.
    .
    2) if you got tram error or drill bit holder leaning to side or lower at a angle than the longer the tool the more the tool tip is off center.
    .
    3) grid shift error. when any tool tip whatever length is not at center of rotation. if mechanically everything is ok then usually a electronic parameter adjustment is used to fine adjust if the tool tip is moved to the center of chuck rotation. grid shift adjustment usually talking .0002" to .005" adjustment. grid shift can vary if machine temperature is changing. many check grid shift monthly, usually indicating a just bored hole. remember if you got tram error than a longer indicator setup will show a just bored hole is off position differently than a shorter indicator setup
    .
    4) servo oscillation. if tool tip held in position and servo moving back and forth .001 or .002 not stopping this can cause problems. normally servo stops moving within a second but when it doesnt stop moving it can be going back and forth either fast or slow. if you put a indicator on tool tip and can see it moving that confirms its oscillating.
    .
    5) backlash when tool tip moves to position from different direction and it varies than might have to always move from same side or direction. not only can slides be loose they can have a tilting action or direction change like a 4 legged chair with one leg short. when you lean in chair it sits on 3 chair feet not all 4 feet, if you lean differently it sits on a different foot and a different foot come up. hard to describe. and a tool tip can shift in 2 different directions when it tilts that is sideways and up/down

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    I don't even understand the question. IS this hole supposed to be on Centerline of the Part?

    If the answer is Yes. I agree with red (beard not james?? WTF) Rebore the jaws and indicate the OD, then indicate the Tool tip.

    R

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    Default Question & suggestion

    Prudent suggestions so far.

    I'd like to know how deep this hole is? I'm drilling holes in 304 stainless 1-5/8 to 2-1/4" deep and would consider that pretty good for my application(.391 dia.). Even if it has a little walk at first contact, it can throw this off. For my application, I use a 3/4 dia. spotting drill first-- no flex there. But as drill wears, it starts to drift by the time it reaches the other side.

    Mark the part as to its orientation to the chuck an see if the drift is always in the same direction. What configuration drill are you using?

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    What's the print call out for concentricity?

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    So... You don't know how much the part is running out in the chuck, you don't know if the drill is on center or even close, and, you don't mention any spotting tool you're using so I assume there is none, AND, you want us to tell you why the holes you drill are not concentric???

    I can't think of a reason. But if you measure it in four different spots from your original measurements you may find it is actually off less, or more.

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    Quote Originally Posted by danil View Post
    I'd like to know how deep this hole is? I'm drilling holes in 304 stainless 1-5/8 to 2-1/4" deep and would consider that pretty good for my application(.391 dia.). Even if it has a little walk at first contact, it can throw this off. For my application, I use a 3/4 dia. spotting drill first-- no flex there. But as drill wears, it starts to drift by the time it reaches the other side.
    1/2" deep. I'm only measuring the hole at the surface.

    Quote Originally Posted by chip_maker View Post
    What's the print call out for concentricity?
    It doesn't. It's our part for our product. There's a stack of slip rings that screw into this hole (once tapped) and if it is "too far" out of concentric, the slip ring brushes smack into their housing. 0.01" isn't going to do that, but on particularly bad parts or if I use HSS drill bit, it becomes too much.


    Thanks for the suggestions, guys. Time to do some measuring.

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    Quote Originally Posted by Derek Smalls View Post
    So... You don't know how much the part is running out in the chuck, you don't know if the drill is on center or even close, and, you don't mention any spotting tool you're using so I assume there is none, AND, you want us to tell you why the holes you drill are not concentric???

    I can't think of a reason. But if you measure it in four different spots from your original measurements you may find it is actually off less, or more.
    Thanks dude, that was helpful. I was looking for a little guidance on where to start looking. I wasn't born a machinist god and I've got a problem I haven't seen before and just wanted a little help to get me going in the right direction. Sorry I wasted your time by forcing you to reply to a stupid inquiry.

    right back

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    Don't be a pussy. If the hole is on Centerline, and the part is spinning in a Chuck, then you can measure until your calipers runnoft. It won't get you any closer, that's why I asked.

    So if you are using a Live Tool to Drill this hole. Then it's a different solution.

    Thick skin requirements here on PM. (Though less lately,now we're catering to Millennials)

    R

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    Seen a fella at Booger King last night that had a "Fighting Machinists" T-shirt on.
    I asked him about it.... ???

    Seems it'a all about inter termoil.

    (Grumpy old men?)

    Just guessing that he picked it up on Facebook?




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    Think Snow Eh!
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    Is your material actually round?

    Do you still lack concentricity if you turn the OD in the same op? If it doesn’t go away doing this, problem is on the drill side, not the work holding or out-of-round stock.

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    Quote Originally Posted by kb0thn View Post
    Thanks dude, that was helpful. I was looking for a little guidance on where to start looking. I wasn't born a machinist god and I've got a problem I haven't seen before and just wanted a little help to get me going in the right direction. Sorry I wasted your time by forcing you to reply to a stupid inquiry.

    right back

    Well, considering that it is a lathe app and not a mill, not only doo I not know what you mean by "out on one axis", but I'm pretty sure that you don't either....


    1) You have not addressed the previous question about a spot face or c-drill?

    2) If you issue is constant and repeatable, it could be the fixturing.
    In this regard, you want to mark the part to coincide with a feature on the chuck.
    Is the problem always the same spot?


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    Quote Originally Posted by G00 Proto View Post
    Is your material actually round?

    Do you still lack concentricity if you turn the OD in the same op? If it doesn’t go away doing this, problem is on the drill side, not the work holding or out-of-round stock.
    It is drilled in same op. I am facing the part (no nub), drilling with carbide drill, and then doing OD features. So when I measure wall thickness, it is measuring from OD of drilled hole to turned OD. That is (and that I'm a stupid millennial, apparently) is why I'm confused about it being non-concentric. Just trying to wrap my mind around how I'm getting an on-size hole that is non-concentric. I can understand getting an oversized hole from a drill bit that is angled or too high or off center on x-axis.

    I am not center drilling. My experience with center drilling the stainless has been (very) poor center drill life. And reduced tool life of the tool that uses the center's hole. And the cutting tool literature I have read generally recommends not center drilling.

    Thanks!

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    Quote Originally Posted by Ox View Post
    Well, considering that it is a lathe app and not a mill, not only doo I not know what you mean by "out on one axis", but I'm pretty sure that you don't either....
    Yeah, I'm lacking terminology. It's not concentric. But it's on size.


    Quote Originally Posted by Ox View Post
    1) You have not addressed the previous question about a spot face or c-drill?
    No spot face or c-drill. Tooling rep specifically recommended against.



    Quote Originally Posted by Ox View Post
    2) If you issue is constant and repeatable, it could be the fixturing.
    In this regard, you want to mark the part to coincide with a feature on the chuck.
    Is the problem always the same spot?
    That's a good question and one I am about to check. It is quite repeatable the dimensions. But I have been checking after pulling the part out of the chuck. I'll look at in relation to the chuck. Thank you and others for that suggestion.

    -Jim

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    Don't bother with 2) if you are turning in same opp.

    Just put a c-drill in it and make parts.
    All you need to doo is spot it - even just .030

    Save the tool rep recommendation for milled parts. (if at all)
    The tool may last longer w/o a spot, but at the cost of not going where you want it to.


    [full disclosure]
    I aint no tool rep, and may not have a clue what's what.
    [/full disclosure]



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    Quote Originally Posted by Ox View Post
    Don't bother with 2) if you are turning in same opp.

    Just put a c-drill in it and make parts.
    All you need to doo is spot it - even just .030

    Save the tool rep recommendation for milled parts. (if at all)
    The tool may last longer w/o a spot, but at the cost of not going where you want it to.


    [full disclosure]
    I aint no tool rep, and may not have a clue what's what.
    [/full disclosure]



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    Ox
    ^^^^
    This

    but i'd be more concerned on how he is checking it. I am guessing Calipers

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    Quote Originally Posted by kb0thn View Post
    Thanks dude, that was helpful. I was looking for a little guidance on where to start looking. I wasn't born a machinist god and I've got a problem I haven't seen before and just wanted a little help to get me going in the right direction. Sorry I wasted your time by forcing you to reply to a stupid inquiry.

    right back
    Ok, so my first post was condescending. You started out by saying "This is probably a newbie question", IF, you truly were a "noobie" and had no idea what the possible causes of your problem could be, or where to start looking, I'd be more than happy to help, breaking it down into baby steps if needed. Problem is, in your OP you list what you ALREADY know could be possible causes, but seemingly you've done nothing to investigate any of them. You seem to want someone here to magically solve your problem.

    You already know that runout can be a cause, you mention that the soft jaws have been on and off without being remachined. Is that the cause? I don't know, put a damn indicator on the part and see if it's running true! If it's not, and the runout matches the error you see in concentricity, then there's your problem.
    Same with the tool being off center. How the hell do you expect any of us to know if that's the problem when you haven't checked it, though again, you say you already know it may be off and could cause an issue.

    I'm not trying to insult you, but it only makes sense for you to FIRST check the things that you suspect may be the problem, confirm or dismiss each of them as the source of the error, then, if you're still stumped, ask for help here.

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    Quote Originally Posted by Delw View Post
    ^^^^
    This

    but i'd be more concerned on how he is checking it. I am guessing Calipers
    What is wrong with calipers to make sure he is within .010" of center, so that the part works.

    Are you one of those people that build a fixture for everything and refuse to use a vise?


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