CNC grinding method of manufacture
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    Default CNC grinding method of manufacture

    I am applying for a grinding position in which training will be provided, I currently have skills in manual milling and turning and setting and operating of CNC mill grinders. I have been given a pre interview question about the method of manufacture of a part which will determine whether I get an interview or not but I don't have much knowledge of CNC cylindrical grinding.

    I have attached the drawing

    The exact wording of what they asked me is as follows

    "Further to your recent email for the grinding position, please can you complete the attached test piece before we progress any further. If you can please just jot a few notes down on how you would work/programme this piece. The material is tungsten carbide."

    Can anyone tell me step by step how this would be produced on a CNC grinder.screenshot_20200210_153757_com.google.android.apps.docs.jpg

    Sent from my FIG-LX1 using Tapatalk

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    The question is vague. Is the ID to be ground? If so, just 1 ID, or both... Can't see tolerances. Personally, I'd vote for expanding mandrel on the smaller ID, a little less in length than that ID, proceed to grind OD and 1 ID in 1 setup, then flip, collet on OD, and grind remaining ID if both ID's need grinding.

    Option B, grind OD between centers (if edge breaks/chamfers allow), then collet on OD and grind both ID's in 2nd setup.

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    Quote Originally Posted by pianoman8t8 View Post
    The question is vague. Is the ID to be ground? If so, just 1 ID, or both... Can't see tolerances. Personally, I'd vote for expanding mandrel on the smaller ID, a little less in length than that ID, proceed to grind OD and 1 ID in 1 setup, then flip, collet on OD, and grind remaining ID if both ID's need grinding.

    Option B, grind OD between centers (if edge breaks/chamfers allow), then collet on OD and grind both ID's in 2nd setup.
    Thanks mate. I'm assuming it's all to be ground, how else would you machine tungsten carbide? How would the holes be machined around the outside. I know how it could be produced on a lathe so thinking in terms of a turret with driven tooling in my head but as I say not really sure if it would be done the same way on a grinder. I've seen OD grinding but not familiar with internal grinding. Is there any sort of roughing process or do you just plunge into a solid bar? I intend to make them fully aware that I'm no expert but just trying to show some initiative in that I've done some research. So I really appreciate the help.

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    Quote Originally Posted by pianoman8t8 View Post
    The question is vague. Is the ID to be ground? If so, just 1 ID, or both... Can't see tolerances. Personally, I'd vote for expanding mandrel on the smaller ID, a little less in length than that ID, proceed to grind OD and 1 ID in 1 setup, then flip, collet on OD, and grind remaining ID if both ID's need grinding.

    Option B, grind OD between centers (if edge breaks/chamfers allow), then collet on OD and grind both ID's in 2nd setup.
    Don't bother, the Wanker cross posted up in CnC section, getting MUCH help there.

    Moderator need to lock this here thread.

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    Quote Originally Posted by digger doug View Post
    Don't bother, the Wanker cross posted up in CnC section, getting MUCH help there.

    Moderator need to lock this here thread.
    What's you're problem?

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    Quote Originally Posted by digger doug View Post
    Don't bother, the Wanker cross posted up in CnC section, getting MUCH help there.

    Moderator need to lock this here thread.
    I suggested that he post in the Abrasive section given that he'd probably get more help here than the regular cnc section, also the Abrasive "Peeps" seem a little more laid back and dare is say it more mature + seems the application is more about pure grinding methods and techniques and "Cnc" second.

    He's first time poster.

    On other forums they have linking tools between threads so it's not such a disaster, I thought this would be a rare exception where double posting would make some sense given how the forum naturally "behaves" .

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    Quote Originally Posted by luke1985 View Post
    I am applying for a grinding position in which training will be provided, I currently have skills in manual milling and turning and setting and operating of CNC mill grinders. I have been given a pre interview question about the method of manufacture of a part which will determine whether I get an interview or not but I don't have much knowledge of CNC cylindrical grinding.

    I have attached the drawing

    The exact wording of what they asked me is as follows

    "Further to your recent email for the grinding position, please can you complete the attached test piece before we progress any further. If you can please just jot a few notes down on how you would work/programme this piece. The material is tungsten carbide."

    Can anyone tell me step by step how this would be produced on a CNC grinder.screenshot_20200210_153757_com.google.android.apps.docs.jpg

    Sent from my FIG-LX1 using Tapatalk
    Those form tolerances and call outs are pretty mission critical, they're not very clear on your posted photo.

    Any chance you have a better higher res/ cleaner versions ?

    HAAS multi grind ? Nice, serious gear.

    Any other machines / processes they have in house you are aware of ?

    Don't worry we won't do all your homework for you ;-)

    a few nudges and kicks in the right direction (I'm not an expert but work in related application areas. ~ Somewhat curious as to the different skinning of "Cats" + the interview pre filter technique they are using here ).

    I.e. what are they looking for ?

    @Doug go easy man , Luke just Brexited :-)

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    Your part requires electric discharge machining to remove the core of the cylinder and to rough bore the side hole pattern. The OD and ID are finished ground to remove the EDM surface damage and to meet the size, surface finish and roundness specification.. The radial cylindrical and conical holes are finished to size by orbital grinding. . The Diagrind company website has the ID grinding tools.

    The radial holes might also be roughed out with custom made diamond hole saws. That would require a backup mandrel to prevent chipping of the ID surface.

    Most of the grinding work could be done on a Moore jig grinder or it's modern equivalent.

    The print dimensions are too small to read. The strategy for machining might change depending on the overall size of the part.

    I suspect the test question is the equivalent of sending a new hire to the tool crib for a left handed monkey wrench. A knowledgeable new hire might object to being set up to play the fool.
    Last edited by Robert R; 02-11-2020 at 09:47 AM.

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    Quote Originally Posted by Robert R View Post
    The OD and ID are finished ground to remove the EDM surface damage and to meet the size, surface finish and roundness specification..
    What do you think about honing the bore instead of grinding ?

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    @Luke 1985 your drawing is almost illegible...

    But having blown it up and squinting at it appears that the gross dimensions are in inches ?

    What little surface finish call outs I could read they seem to be "Imperial" / American. 32 finish ?

    The basic surfaces and form tolerances if they are imperial seem very loose/ broad (almost low tolerance ?) +/- 0.005 is that mms or " (inches) - Seems they are using mixed units maybe ?

    Other thing that occurs to me is that in your interview they may ask you about how different types of forms are sintered using tungsten carbide powders and the processes related to that... I.e. what your blanks will be to work with. + corresponding form tolerances of your initial blanks that you have to work with ?

    I'm not sure what the limits on hollow forms are for Tungsten carbide ? ~ And related processes outside of 3d printing etc.

    In general cylindrical grinding and plunge grinding and form grinding are not beyond the wit of man (i.e. they can train you) but I suspect that they are testing your ability to relate all the sections and features to each other and also notice odd or unusual or asymmetric features in the drawing as well.

    I.e. Basic spatial reasoning - in three dimensions and can you un-wrap and project surfaces in your head etc. visualize what's going on properly. [not every applicant will be able to do that.] ~ might be they need to filter out folks that are "spatially challenged" or have serious and pervasive deficits in common sense ? Seems they will train you and clue you in on their in-house processes.

    @Luke 1985
    do see if you can zoom in on the drawing and take four shots with your smart phone etc. 'cuz the diagram is as close to being illegible as you can get really.

    Ta.

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    Quote Originally Posted by EmanuelGoldstein View Post
    What do you think about honing the bore instead of grinding ?
    A one inch diameter diamond ID grinding wheel costs roughly 50 dollars. The cost of a 120 grit roughing and 300 grit finishing wheel would be less than 100 dollars.

    ID honing would require the purchase of the adjustable mandrel, the guide shoe, and a rough and finish set of diamond honing stones. The cost would be greater than a 1000 dollars. It would also require some time to get the process working. Honing follows the existing hole alignment. The process would not be able to align the ID bore with the reference OD surface. The cost and time cannot be justified for a single part.

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    Quote Originally Posted by Robert R View Post
    ID honing would require the purchase of the adjustable mandrel, the guide shoe, and a rough and finish set of diamond honing stones. The cost would be greater than a 1000 dollars. It would also require some time to get the process working. Honing follows the existing hole alignment. The process would not be able to align the ID bore with the reference OD surface. The cost and time cannot be justified for a single part.
    Ah, but he was not told how many parts ! If we assume 500 pcs, then ....

    I like ID grinding but would not want to do this job. And I'd get around the concentricity problem by honing the bore first, then putting the part on a mandrel to grind the o.d. He could add a nice expanding arbor to the tooling order

    Since he's spending imaginary money, I still think I'd go for the hone ....

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    If we told you how do it and gave you a detailed routing when in the interview could you explain why and your thinking? Those would be my next coming face to face questions.
    I'd drill and rough bore the center hole while the carbide still soft.(no sense buying that extra gram weight)
    Cross holes a pain but since inline maybe wire or just ground. Perhaps starter holes done when still green but the best you could do here is +/- .015 on spacing.

    Then you have to think about what datums or loading surfaces from there.
    The ends need to get qualified somewhere and there are chamfers on the part end and how to do section C.

    Don't try to bullshit them or say things you do not understand. You will get caught and maybe that is part of the test.
    Be honest with what you know. You do not want to get in "You found this on the internet".
    It may be best to say here are some ideas from my past experience and that you do not understand some with a whole lot of "I don't know and that's why I want to come work for you".
    Not an easy part to fab. The question looks like a baited trap.
    I do not know is better than I know it all. If I had to answer this for a job interview there would be so many caveats and maybes.

    I'm thinking that no one here can really help you.
    Look at it and say what your experience tells you and perhaps things you are not so sure of or have no idea how to handle.
    Be honest and up front as to who you are and what makes sense in your experiences.
    I'll take the unsure rookie who knows when to say I'm not sure over the I have it all guy anyday. One of these I can train, the other will become a problem child.
    Bob

    PS to EG: even at 500 to 5000 I'd grind it but all shops are different.

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    Quote Originally Posted by CarbideBob View Post
    PS to EG: even at 500 to 5000 I'd grind it but all shops are different.
    Really ? I love a good id grinder but diamond wheels, carbide workpiece, ugh

    I'd still put it on a mandrel tho ... get concentricity plus you can kiss both ends to get squareness.

    Now you're going to tell me that's stupid, too

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    I never said stupid but for me carbide and diamonds wheels is fun and faster than grinding steel.
    Don't forget that the ID is stepped with two inside diameters and an angle between them.
    I like the mandrel and likely where I'd go but hows this for different: OD on a Dedtru, clamp off that to square the ends on a Harig 612 and then again for the ID work, grind the "C" slot in a vmc with an air spindle.
    Somewhere along the line is the groove (easy) and the inside and outside corner breaks.

    I could make up different routings for this part all day long. Much dependent on what machines on the floor.
    Of all I can see with a not very good print the cross holes worry me the most and seem the most expensive and time consuming.

    This is simply a very strange question asked to get an interview for a grinder hand job.
    Why would you expect a floor person to even be slightly able to route a part like this?
    It's like me asking a guy from a round tool shop how to make a VDB-125 or a CBN tipped top-notch groover but even worse.
    Something smells funny.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    Don't forget that the ID is stepped with two inside diameters and an angle between them.
    I didn't see that at all so my first reply to this test would be, "Can you give me a decent print, fer chrissakes ? How the hell do you expect anyone to work from this piece of shit !"

    Then they'd know you were a Real Machinist right off

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    Quote Originally Posted by EmanuelGoldstein View Post
    I didn't see that at all ....
    See, .......you missed the obvious details on even a bad print.... not giving you an interview Mr. Rookie.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    See, .......you missed the obvious details on even a bad print.... not giving you an interview Mr. Rookie.
    Too lazy ... shitty, blurry smartphone photo displayed sideways. Ick

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    Quote Originally Posted by EmanuelGoldstein View Post
    Too lazy ... shitty, blurry smartphone photo displayed sideways. Ick
    Too lazy, hard to read print... we will put that down on your pre-interview application and call you when needed...
    Bob

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    Quote Originally Posted by CarbideBob View Post
    Too lazy, hard to read print... we will put that down on your pre-interview application and call you when needed...
    Good thing I am not looking for a job


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