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My toughest machining job yet.........

LinefinderLinefinder ModeratorPosts: 7,365 Senior Member
I'm probably the oldest toolmaker apprentice in the world. I don't have enough working life left to become really good at it, as I'm reminded almost every working day. But this project was bad.....oh my gosh......it was bad.

Engineering needed a pin (or dowel, if you prefer). 2.79" long with a diameter of .046" out of hardened stainless steel. For the half inch off each end, the tolerance was "if we can measure a difference, it's not close enough". The remainder of the pin had a tolerance of +.0000"/-.0003".

Knowing this was going to be a tough act to pull off, I stared off by prepping, heat treating and drawing 5 blanks. Then off to the grinding room where equipped with a surface-grinder, spin indexer, and counterbalance fixture, I ruined all of them in less than 45 minutes.

Back to the stockroom, and prepping and heat treating ten blanks. This took me into day two. (For a simple pin, mind you......simply a pin).

Long story short.....nearing the end of day two, I had two blanks left when I finally got one that I think meets spec. I say think, because Metrology took off early on Wednesday, and there was no one there to "officially" measure my part. What a way to start the T'giving holidays.

To add insult to injury, engineering estimated two hours to produce this pin. Best I can figure, I had almost 16 hours in it. But, OTOH, our most skilled toolmaker told me it would have taken him only two or three tries (he spent five years on a surface grinder at another company) to do this part, but also said it would have taken him just about as much time.

If this pin doesn't pass Metrology on Monday, I'm gonna open a vein.

Mike

Originally, my intent was to use a "close sized" mold ejector pin, but as per normal......everything we had on hand was either too small (no good at all), or slightly too big (not much better).
"Walking away seems to be a lost art form."
N454casull
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Replies

  • earlyearly Senior Member Posts: 4,950 Senior Member
    My Dad was a thread grinder when I was a boy. Made the ball screw for the launch platform's for NASA rockets.
    One of my firearms mentors was a tool & die maker.
    It'd be my guess that even incredibly smart people can't have a lifetime of experience without the lifetime part.
    My thoughts are generally clear. My typing, not so much.
  • TeachTeach Senior Member Posts: 18,428 Senior Member
    If you tell those engineers to "make it yourself" I'll be they rethink their tolerances!
    Jerry
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Teach wrote: »
    If you tell those engineers to "make it yourself" I'll be they rethink their tolerances!
    Jerry

    Maybe. I'm getting used to working within a thou, but man, this thing sure was long compared to diameter. The chatter was what ate my lunch. I've no idea how to hold something so long and thin that insures less than.0003" chatter. If I did indeed successfully pull off this part, it's pure dumb luck. It'd probably take me just as long (or longer) to do it again.
    "Walking away seems to be a lost art form."
    N454casull
  • BigDanSBigDanS Senior Member Posts: 6,992 Senior Member
    Did they specify the temperature of the pin when measured? Talk about spec'ing it with an RCH...

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • jaywaptijaywapti Senior Member Posts: 4,981 Senior Member
    Since most of my close tolerance machining is related to gunsmithing, I can appreciate what it takes to get sub .0001 tolerance.

    My worst job was not machining but lapping, we had to lap the oil seal end of gears with diamond dust and check them with a color optical comparator, if the color was not all the same shade of red, it was out of tolerance, the oil seal itself was a "carbon seal"

    JAY
    THE DEFINITION OF GUN CONTROL IS HITTING THE TARGET WITH YOUR FIRST SHOT
  • TeachTeach Senior Member Posts: 18,428 Senior Member
    I got pretty good at holding a .0002" diameter tolerance on bored holes, but that was only over a distance of an inch or two on Diesel engine wrist pin bushings. Long skinny stuff- - - - -that's the worst possible thing to hold a tight tolerance!
    Jerry
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    BigDanS wrote: »
    Did they specify the temperature of the pin when measured? Talk about spec'ing it with an RCH...

    D

    No, they didn't. Which makes it even sillier. The diff between room temp and after holding this pin in your hand for ten seconds is almost a couple thou. They don't ever think of things like that, so I always assume ambient temp.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Now that's the best idea yet.

    I said they were engineers. I never said they were good ones.
    "Walking away seems to be a lost art form."
    N454casull
  • bisleybisley Senior Member Posts: 10,798 Senior Member
    Linefinder wrote: »
    I said they were engineers. I never said they were good ones.

    Good engineers, from any field, are really smart, capable guys/gals. The problem is that mediocre engineers are more prevalent, and still have the same arrogance that nearly all of them seem to have. I've always said that a full year of their training concentrates on teaching them to belittle problem solvers who can make stuff work without 5-6 years of college training. As a land surveyor, my worst frustrations came from dealing with civil engineers, surpassing even lawyers and realtors. It is a pleasure to work with an engineer who loves simple solutions to complex problems, but there aren't enough of them to go around.

    Your problems most likely arise from a failure in engineering, for hanging too much emphasis on an unrealistic level of precision. If it's a prototype for some great new invention, that's one thing. But, if it is the final product and this is actually the mass production final solution, the engineering is bad.
  • knitepoetknitepoet Senior Member Posts: 21,644 Senior Member
    Better you than me my friend :yikes:
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • TeachTeach Senior Member Posts: 18,428 Senior Member
    bisley wrote: »
    As a land surveyor, my worst frustrations came from dealing with civil engineers, surpassing even lawyers and realtors.

    The female body had to be designed by a civil engineer- - - - - - -who else would put the toxic waste dump right next to the playground?
    :uhm:

    Jerry
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    It passed, although I suspect metrology had no better method of measuring it than I had of making it.

    I'd rather be lucky than good. But I'll never again do this without a fight that'll make the pencil-pushers pee themselves.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • TeachTeach Senior Member Posts: 18,428 Senior Member
    The next message from R&D- - - - -"Looks good, now figure out how to make a thousand of them, and keep it under budget!"

    Jerry
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    This actually was a fix for a $30K mold that we'd outsourced because our workload was such that we couldn't get it done in the required timeframe. As usual, anything you outsource requires a few tweaks. But, in hindsight, it would have been a lot easier to modify the mold itself, rather than fab such a finicky pin. It's easier to bore the female than create the male from scratch.

    Lesson learned.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Molten plastic under 66 tons of pressure can squeeze thru damn near zero. I'm whining about .0003 tolerance, but the guys that make the actual part inserts for the mold bases work with as close to a zero tolerance as you can get.

    While the .0003 tolerance is tough, the problem really was simply that the aspect ratio of thickness to length was ridiculous. As to the numerical tolerance itself, the real toolmakers just consider it another day at the office.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Most days I do. Some days, not so much. OJT in this field can be frustrating at times.
    "Walking away seems to be a lost art form."
    N454casull
  • JerryBobCoJerryBobCo Senior Member Posts: 8,194 Senior Member
    I just read through this thread, and don't have any idea about most of what's been posted. Probably a good thing I work on something simple like computers.
    Jerry

    Gun control laws make about as much sense as taking ex-lax to cure a cough.
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Simplified, I made a very thin 3" long needle without a point. It doesn't look like anything much. But it ate my lunch. I don't know anyone that is familiar with machining that would want to do it. I don't want to do it again.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • DoctorWhoDoctorWho Senior Member Posts: 9,496 Senior Member
    The guy I work for makes diverse types of parts for many different purposes, I tried to describe your problem, he was pretty interested in how you finally solved it.
    "There is some evil in all of us, Doctor, even you, the Valeyard is an amalgamation of the darker sides of your nature, somewhere between your twelfth and final incarnation, and I may say, you do not improve with age. Founding member of the G&A forum since 1996
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Truth of the matter is that I didn't really solve it. I just snuck up on the tolerance a tiny bit at a time. It took a really, really long time. And more attempts than I care to remember. I have no lessons to pass on. I got lucky this time. It'll probably never happen again. If your guy wants to replicate it via my advice... my advice is to be really patient, and have a lot more raw stock on hand than seems appropriate. I mean a lot more stock.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • Six-GunSix-Gun Senior Member Posts: 8,155 Senior Member
    .0003"? You couldn't just eyeball it? :jester:
    Accuracy: because white space between bullet holes drives me insane.
  • DoctorWhoDoctorWho Senior Member Posts: 9,496 Senior Member
    Well my hats off to you !
    I can barely understand the description !
    "There is some evil in all of us, Doctor, even you, the Valeyard is an amalgamation of the darker sides of your nature, somewhere between your twelfth and final incarnation, and I may say, you do not improve with age. Founding member of the G&A forum since 1996
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Six-Gun wrote: »
    .0003"? You couldn't just eyeball it? :jester:

    You have an engineering background it seems ��
    "Walking away seems to be a lost art form."
    N454casull
  • coolgunguycoolgunguy Senior Member Posts: 6,624 Senior Member
    cpj wrote: »
    Im surprised you haven't made 13 of them with a rock, file, and sandpaper in some third world hole county while defending yourself from marauding hordes of machete wielding attackers dressed in loin cloths and coconut shells.


    Shamelessly stolen!:worthy:
    "Bipartisan" usually means that a bigger than normal deception is happening.
    George Carlin
  • LinefinderLinefinder Moderator Posts: 7,365 Senior Member
    Today was good.......I hogged out sixteen tapered pins that had to be within .005" in length and diameter. Angular slope plus or minus a quarter degree.

    Child's play. I can do that with my eyes closed, almost. I'm ashamed to work for a company that allows such slop.

    But sometimes, it's a nice break. Today was a nice break.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • DoctorWhoDoctorWho Senior Member Posts: 9,496 Senior Member
    Good work !

    Sounds like fun in any case, the success part really.
    "There is some evil in all of us, Doctor, even you, the Valeyard is an amalgamation of the darker sides of your nature, somewhere between your twelfth and final incarnation, and I may say, you do not improve with age. Founding member of the G&A forum since 1996
  • BuffcoBuffco Senior Member Posts: 6,244 Senior Member
    Man. If you only knew how many times I utter the phrase, "That's close enough," while building crap....

    One of my favorite construction sayings: "I've cut this stud twice, and it's STILL too short!"
  • jbp-ohiojbp-ohio Senior Member Posts: 10,263 Senior Member
    Buffco wrote: »
    Man. If you only knew how many times I utter the phrase, "That's close enough," while building crap....

    One of my favorite construction sayings: "I've cut this stud twice, and it's STILL too short!"

    "Close enough for Government work!"
    "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not." Thomas Jefferson
  • coolgunguycoolgunguy Senior Member Posts: 6,624 Senior Member
    Buffco wrote: »
    Man. If you only knew how many times I utter the phrase, "That's close enough," while building crap....

    One of my favorite construction sayings: "I've cut this stud twice, and it's STILL too short!"
    jbp-ohio wrote: »
    "Close enough for Government work!"

    "Good enough for the girls I date"
    "Bipartisan" usually means that a bigger than normal deception is happening.
    George Carlin
  • DoctorWhoDoctorWho Senior Member Posts: 9,496 Senior Member
    coolgunguy wrote: »
    "Good enough for the girls I date"

    Until you find extra equipment !
    "There is some evil in all of us, Doctor, even you, the Valeyard is an amalgamation of the darker sides of your nature, somewhere between your twelfth and final incarnation, and I may say, you do not improve with age. Founding member of the G&A forum since 1996
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