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    Milled Bridges Rocking Again

    Discussion in 'Metal' started by NickB, Jul 18, 2016.

    1. NickB

      NickB Member Full Member

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      We solved the bridge issue we were having a while back, but its now happening again. Ive been using the stabilizer bar feature in Sum3D, and it seems to help somewhat, but these little bastards have begun to rock again. I suspect its the same issue as before (waxers carelessly spruing).....so I decided to leave the connectors kind of long when cutting the bridge off of the wax ring......this allows the waxers to sprue the bridges without getting their hot wax too close to the bridge itself.

      It seemed to work for a while. But now they rock like crazy again. Also having issues with the cement gap, as one setting doesnt mill out enough, it the dies wont seat and I have to use a high speed to dig it out. Then the next setting they fit a little loose after we make an adjustment. Its getting frustrating and the guy who came here to teach us this stuff from Zahn was kind of a goof ball and simply could not help us with any tips.

      Starting to winder if this stuff was even worth it. Any help from your experience would be appreciated.
       
    2. CoolHandLuke
      Fiendish

      CoolHandLuke Well-Known Member Full Member

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      refresh my memory, what design system and what milling system and what cam calculations are you using.

      it is possible that the design parameters do not match the capabilities of the cam calculation software, which in turn produces poor units.
       
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    3. NickB

      NickB Member Full Member

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      We are using a Roland DWX-50 along with 3Shape scanning software and Sum3D milling software. By design parameters, are you speaking of our settings regarding
      cement gaps etc? When the wax is placed on the model, usually the wax bridge fits well. But once in metal, its terrible many times. Plus, the margins are open and sometimes
      a bit extended in metal, while in wax, they fit like a glove. We've changed our run up settings in our burnout furnace and triple checked our ratios with investment. Handwaxed
      units fit well. So I doubt its the investment ratio.

      Can you give me an example of how the parameters not matching could cause a problem?
       
    4. CoolHandLuke
      Fiendish

      CoolHandLuke Well-Known Member Full Member

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      handwaxed units fit well post-cast, but computer designed ones seem to have problems once cast...

      then you may need to consider the wax itself as problematic. try a new supplier. wax pucks are dirt cheap.
       
    5. user name
      Question

      user name Well-Known Member Donator Full Member

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      Or...youre casting with too much metal. You should have minimumal/no button left; just some of the runner bar. With too much metal youre shifting the heat center of the casting so the button draws metal from the runner bar/reservoir instead of your pattern. Distortion every time.
       
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    6. NickB

      NickB Member Full Member

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      We used proper amounts of metal. We also ensure that the waxups are not at the center of the ring for cooling purposes. We used to have investment breakdown with flash all over our metal units, but we fixed that by slowing down
      our run up times in the furnace.
       
    7. NickB

      NickB Member Full Member

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      And we did try new wax pucks. Multiple ones actually. All rocked still.
       
    8. CoolHandLuke
      Fiendish

      CoolHandLuke Well-Known Member Full Member

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      then you are indeed processing incorrectly.

      whoever is providing your alloy should also have recommended an investment and provided full instruction on using that investment. otherwise they are doing you a disservice.
       
    9. user name
      Question

      user name Well-Known Member Donator Full Member

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      Photo of a casting before you cut it off...?
       
    10. JMN
      No Mood

      JMN Christian Member Donator Full Member

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      Don't know how your waxers are spruing, but what I saw caused a lot of bridge issues is how much/how far the wax had to be built to reach the copings.

      If you have a high variance on height, even it out and let it cool before adding onto the bar. You should only and barely "glue" the bridge to the bar, if you are adding 2mm of wax to reach one and the other is already attached the cooling wax will contract and warp your bridge that used to fit perfectly before casting.
       
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    11. kimba

      kimba Active Member Full Member

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      In my experience , all , or the vast majority of problems with rocking bridges is in the pattern before it is invested. Maybe the waxers are heating the pattern up too much when spruing? not taking as much care with milled patterns as they perceive they are more robust than handwaxed patterns? The cynic in me sometimes thinks that some metal workers will try to find problems in milled patterns because "there is no way a machine will do it better than them by hand" I do lower my expansion ratio for bridges , but I don't think this is your problem if hand wax is fitting and milled are not. Have you personally milled , sprued and cast to see the results? I had this problem with a metalworker who swore blind it was the investment, so I got a different investment for him. same problem . This went on until we did a challenge . Me wax 2 bridges , him wax 2 bridges mill 2 bridges. We each sprued and cast 3 . Guess what .. mine all fitted , his a mix. sorry for the long winded response , but I think its in the spruing for what its worth. Hope this helps
       
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    12. JMN
      No Mood

      JMN Christian Member Donator Full Member

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      I really like the method you used to test. That was an excellent non confrontational proof positive way to find the facts.
       
    13. kimba

      kimba Active Member Full Member

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      I thought so , but to this day he still thinks I am a pri-k!!! go figure
       
    14. JMN
      No Mood

      JMN Christian Member Donator Full Member

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      Sheesh.
       
    15. CoolHandLuke
      Fiendish

      CoolHandLuke Well-Known Member Full Member

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      it happens. to some, i appear condescending and confrontational. to others, i'm the lone member of the DLN Hall fo Fame for being non confrontational.

      *shrug*
       
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    16. Sevan P
      Twisted

      Sevan P Well-Known Member Full Member

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      Seems to me this tech just wants to get done with the work load, and doesn't care. We had a ceramist that broke a full round house Zr bridge in 2 spots while doing a first bake cause she that all bridges are fired the same from 3 unit to 14 unit. WTF!!! I asked here would she fire a full arch metal lingual bridge in the same program as a 3 unit frame pfm bridge? She said no, then I said why would you not do the same on a Zr bridge? I don't know she said...................... unfortunately old techs are stuck on old ways and don't get it sometimes. But the investing parts has never changed, talk to the high up on the food chain and let them know this is what is causing the issues and if the techs can't get in gear then maybe it is time for some replacements.

      Water to liquid and sprueing of round house pfms are so crucial for fit not everyone should to it. maybe train and hone a single tech to be responsible for them narrowing the chances down a bit and if it happens again you know exactly who to go to.
       
    17. NickB

      NickB Member Full Member

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      That is what I personally suspect. The waxers, for the most part, dont speak much English (although they do understand it fairly well) and they take personal offense when you try to correct them.
      But yeah, I think Ill try to sprue it myself and see what happens. Typically, when investing, they always pour the investment to the top of the ring former.....yesterday I had them stop pouring the
      ring completely full, only ensuring that they covered the wax patterns with at least enough to dry grind the tops. This means the wax patterns will be further away from the center of the ring.

      Ill post photos later of the milled bridges while in wax form....and post photos tomorrow once they've been cast.

      Nick
       
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    18. NickB

      NickB Member Full Member

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      What investment do you guys use for your milled wax? We use microstar HS. I doubt its the investment.....I think microstar is very good. Just wondering if there is another investment
      meant for any milled wax in particular.
       
    19. JMN
      No Mood

      JMN Christian Member Donator Full Member

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      That happens when your service patches are installing and have noncritical functions offline.
       
    20. CoolHandLuke
      Fiendish

      CoolHandLuke Well-Known Member Full Member

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      no it happens BECAUSE YOU'RE A BUMBLING NINCOMPOOP

      [​IMG]
       
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