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You can't polish MIM parts

Discussion in 'Handguns: Revolvers' started by Bubba613, Jun 18, 2013.

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  1. Bubba613

    Bubba613 member

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    Another myth dies. Here are pics of the Smith PC637 Gunsmoke.
     

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  2. Mauser lover

    Mauser lover Member

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    Oops, I didn't realize that you couldn't polish MIM parts. Glad to know you can though!

    Just as a side note, why can't you polish MIM parts? (in the myth)
     
  3. WC145

    WC145 Member

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    MIM parts polish up nice if done right -

    Bobbed and polished 360J hammer
    [​IMG]

    I don't have any good pics of the trigger but this one will give you an idea
    [​IMG]
     
  4. rswartsell

    rswartsell Member

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    At one time "sintered" parts were not good candidates for polishing because they had a hardened "crust" encasing steel of a less hardened character which formed the "core". Polishing could penetrate the "crust" and expose the softer "core" which would not perform to the standards of the hardened "crust". If you accept this as true, it once was not a good idea to fool with these parts. As I only dimly understand it, the current technologies used in producing modern "MIM" parts alleviate the vast majority of these concerns.

    I make no claim to being a metallurgist, or even a production engineer.
     
  5. Old Fuff

    Old Fuff Member

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    Yes you can polish MIM parts, but under high magnanification you will see tiny pits in the surface that don't go away. This is because the material is not truly homogeneous, but made up of metal particles fused together with the remains of a binder.

    You can get similar results by simply dry-firing the gun and let the parts burnish where they come into contact under pressure. Other then cosmetic affect, polishing elsewhere doesn't make any meaningful difference.

    Want to see the difference? Look at a hammer taken from a pre-war S&W revolver that was polished on the sides before it was case hardened, vs. what you see today. :barf:

    I won't bring up the fact that S&W cannot color-caseharden MIM hammers and triggers, and unlike Taurus doesn't even flash-chrome them for better appearence. All this of course comes under the heading of cosmetics, which is not critical for function but does relate to quality which is now lost. :banghead:
     
  6. PabloJ

    PabloJ Member

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    Don't let them BS you there is nothing wrong with the MIM parts.
     
  7. rswartsell

    rswartsell Member

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    Sounds like "don't think too hard and just trust me religiously", not a big subscriber to that. Current MIM production seems to work well, but telling the Old Fuff and I we are wrong "just 'cause" ain't feeding any bulldogs.

    Even without being a metallurgist, I understand that "natural" steel has a crystalline form that has the advantage of "chemical bonding" that takes advantage of the positive and negative charges of the outside shells of the sub-atomic orbits to "weld" molecular structures in a far more homogenous way than powder and binder under heat and pressure will ever achieve. There isn't anything that mysterious about that. I encourage resistance to "because I said so".
     
    Last edited: Jun 18, 2013
  8. Jaymo

    Jaymo Member

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    I still prefer forged.
     
  9. glocking26

    glocking26 Member

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    Smith + Wesson went to MIM parts for one reson to cut cost. They still use forged parts on some there P.C. Guns why.... Because they know there better. But you'll pay for them. MIM parts may hold up as good as forged parts but they look like parts off a toy gun. Oh yea I carry a 340pd and it shoots great but I still hate looking at the trigger...but that's just me.
     
  10. Jaymo

    Jaymo Member

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    I was going to say, "Lookit that. You CAN polish a turd. But, you still can't pick it up by the clean end."
    But, I decided to be nice.
    And, yes, I do have a few pieces that use MIM parts.
    Funny thing, my Judge hammer and trigger are either CCH or fake CCH.
    Go figure.

    That said, your hammer and trigger came out looking far better than I would have expected, being MIM parts.
    I would polish mine, but I'm just too darned lazy.
     
  11. DPris

    DPris Member

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    Fuff has it.
    Denis
     
  12. fletcher

    fletcher Member

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    Steel in MIM parts also has a crystalline structure and relies on the same bonding method ("sea of electrons" around a lattice of cations) to join the atoms. The big disadvantage of MIM is porosity. Because of the use of binders, it is more difficult to achieve theoretical density. Internal defects really weaken a structure's static and fatigue properties.

    To the original post, and as noted earlier, MIM parts can certainly be polished, but the appearance will be dependent on the amount of porosity present.
     
  13. PRM

    PRM Member

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    Really - must be why S&W are replacing MIM Hammer Blocks with the older style stamped ones. The block in my Model 60-9 has snapped into (twice) with less than 200 rounds fired.
     

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  14. evan price

    evan price Member

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    Polishing a MIM part is akin to polishing a slab of granite. Yes, the end product looks good, but even in highly polished granite countertops you still find pits and voids where there are gaps in the material.
     
  15. MrBorland

    MrBorland Moderator

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    As far as I can tell, this thread's about putting enough shine on an MIM part to be pleasing to the eye. Whether it's too porous to be a true "polish" is minutiae, IMO. Looks good to me.

    And how well MIM parts perform, why they're used, their strengths & weaknesses, personal preference/bias, etc. have all been discussed ad nauseum in plenty of other threads.
     
  16. mope540

    mope540 Member

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    looks great.



    everything, including a fine diamond, looks pitted under high magnification
     
  17. fletcher

    fletcher Member

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    Its an accurate comment.

    Under enough magnification any surface will likely show some defect, but it won't necessarily look pitted. A properly polished surface on wrought material will show no pitted look well up to 1000x - we do this routinely with metallography. Keep going to many thousands, such as in a SEM, and one may see something.
     
  18. 460Shooter

    460Shooter Member

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    Not high road material.

    No offense meant, and no, I realize I'm not a moderator, but I'd keep comments like that to yourself. You can disagree without being rude. The mods don't take well to people who yell inflamatory things like that.

    Also, it is an accurate statement Fuff made. Old Fuff has been sharing great tips, info, and wisdom on THR for a long time. I have yet to read something he has written that is incorrect regarding handguns, or "DUMB", and he is well respected here. Please treat him, and all forum members with respect.

    Looks great OP. I've polished MIM, and it certainly does improove the appearance.
     
  19. Walkalong

    Walkalong Moderator

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    Exactly. ;)
     
  20. CraigC
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    CraigC Member

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    Ha! :D


    Proof that there are no dumb questions, only dumb answers.
     
  21. Old Fuff

    Old Fuff Member

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    I may be a little bit misunderstood (or maybe more then that). If so, it's my fault.

    From a functional perspective they're doesn't seem to be anything wrong with most MIM parts - hammer and trigger in particular- used in current and recent Smith & Wesson revolvers. If one is satisfied with that go forth and buy these products.

    The Old Fuff however is spoiled, and wants much more then that. He has examined in great detail all kinds of Smith & Wesson revolvers which date from the Civil War to present, and in his view if one goes beyond functional they're are some that are better from the fit & finish perspective. How important this is or isn't depends on the individual, and given today's marketplace in both new and used (but like new) guns anyone can have what they like, and the Old Fuff has never been one to say, "My way or no way!"

    Now to be honest if S&W or any other of the principal handgun makers made what they used to in today's manufacturing economy, most of us - including me - couldn't afford to buy them. It is also why most manufacturers are turning to pistols with polymer or similar frames rather then revolvers because these can be made at a price-point where the industry makes a profit and the buyer doesn't have to max their credit card.

    So there is no reason to start a war here, and if some disagree with me that's fine because I won't lose any sleep. The Old Fuff has a thick skin that's bullet proof. ;)
     
  22. Bubba613

    Bubba613 member

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    Some people buy guns because of their function.
    Some people buy guns because of their appearance.

    For the former, present S&W models provide superior performance and function.

    For the latter they should stick with inferior performing guns from the 60s and 70s.
     
  23. CraigC
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    CraigC Member

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    Now THAT is funny! Now injection molded parts are actually better than hand-fitted forged parts. Wishful thinking at its finest (funniest).

    Here's a hint, if you examine the finest guns on earth, you won't find any injection molded parts that get installed as-is. What you will find are forged parts that are hand-fitted. What S&W has done is to cut manufacturing costs and MIM parts cut skilled labor costs. Now they can be thrown together by assemblers, rather than master gunsmiths. Has not a damn thing to do with making anything better but their bottom line. Which is sad considering that most of their revolver designs date back to the turn of the last century.
     
  24. 1911Tuner

    1911Tuner Moderator Emeritus

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    Apparently, Bubba has never handled a real Smith & Wesson, Colt, Winchester, etc.

    'Tis the world that we live in.

    Back up another 30 years and find a nice Smith & Wesson still in good shape that dates back to the 30s or 40s, and you can feel the difference just by pickin' it up. One of those things that can't be explained. It has to be experienced in order to be understood.
     
  25. CraigC
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    CraigC Member

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    I find that they have an aura that one can feel before even seeing it. ;):p
     
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