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    Milled Bridges Rocking Again

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

    1. vurban210
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      vurban210 Active Member Full Member

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      I'm not quite sure i understand what you are saying. In fact, none of this makes any sense to me. I mean, I understand how you are milling but I am not sure what happens after that. Are you leaving the milled support bar in place just reducing its mass? Is that what you are saying?

      IMO - once milled the bridge should be completely removed of support bars and the like, then fit to the model, adjustments made and then properly sprued. Sure, you can mills sprues on a single unit and leave them attached but when it comes to a multi element bridge it would be insane to think that there are not forces in that wax that need to be released.

      On another topic, casting with bars is absolutely pointless. Casting without a button is also pointless. Both are also quick ways to have issues. When metal cools it creates a vacuum and it has to pull metal from somewhere otherwise it is going to create tensions as well as porosity.

      Runner bars, reservoir sprues, indirect sprues, direct sprues, hollow sprues, square sprues, plastic bars, and on and on and on. It is all a complete and total waste of time. (Also a way to get more $$ out of your pocket) The only thing you need to properly sprue everything from a single anterior unit to a foll roundhouse is some rolls of spool/sprue wax and some utility wax. That is it.

      This is just my $0.02 worth.
       
    2. dmonwaxa

      dmonwaxa Moderator Staff Member Full Member

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      Sevan, Pics please if available.
       
    3. dmonwaxa

      dmonwaxa Moderator Staff Member Full Member

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      PTC ...Carving/Contouring chart and guide. Placed on the wall or on the bench as a mat.

      But this is for you...
      20160721_073757.jpg 20160721_073817.jpg 20160721_074000-1.jpg
       
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    4. CatamountRob
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      CatamountRob Banned Member Full Member

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    5. Sevan P
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      Sevan P Well-Known Member Full Member

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      Let me see if we still have it. This was a while ago.

      Sent from my SM-G920V using Tapatalk
       
    6. NickB

      NickB Member Full Member

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      The waxers have been spruing a certain way....and on occasion I will mill and bridge with sprues/bar in order to keep them from incorrectly spruing it the way they have been.
      Yet it appears what Im doing is also wrong?
      So you're saying I shouldn't have a bar at all? Sounds odd to me since virtually every lab I know of does it. Im certainly open to not using bars though. Perhaps Ill experiment
      with that soon if we have a slow day.
       
    7. vurban210
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      vurban210 Active Member Full Member

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      When it comes to the bars I am referring to only the spruing part, not the milling process. And I should correct myself, I do not use preformed bars but when a feeder bar is required I will make my own from wire wax. (hard to explain in writing and I will take some photos.) The reason is that when casting it is important to always cast thick to thin. (in mass) Most of these bars that are preformed have small feeders, then a large runner bar and then again small feeders. So it is thin-thick-thin and this makes for troubles.

      More importantly is the placement of everything in the ring and controlling where the cooling happens. That is the key, you can't stop the forces but you can control them.
       
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    8. Sevan P
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      Sevan P Well-Known Member Full Member

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      I find that a 6ga or 8ga clear plastic sprue works very well for the main bar when casting a full arch, just heat it up and bend it to fit. Then sprue the frame off that. Casting the milled bar is just ridiculous imho.

      Sent from my SM-G920V using Tapatalk
       
    9. vurban210
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      vurban210 Active Member Full Member

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      Yes, that was what I was trying to say but you said it much more concisely.

      Maybe I am just too set in my ways, but everything I understand about milling wax leads me to believe that casting the milled bar would be a huge issue. I've cut bridges out of pucks and seen them go one way or the other when the tension is released.

      One other thing that I have learned is to cast in nothing less than ~150 grams for everything, and larger rings if needed. It is crazy when I see people trying to use a 60 gram ring to cast a ton of waxups.
       
    10. Solid

      Solid Member Full Member

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      you're casting with the milled bar after reducing it? how do you reduce that bar ..using heated wax knife?
       
    11. CoolHandLuke
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      CoolHandLuke Well-Known Member Full Member

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      i know youve more or less reduced this to a problem you know how to solve already, i just wonder why you don't go straight to milling CoCr or Ti copings instead of wax and cast?
       
    12. NickB

      NickB Member Full Member

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      Ive seen those options when choosing the material when entering cases. What exactly are those?
       
    13. NickB

      NickB Member Full Member

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      No, I use no heat when doing this...only taking a bur and cutting away at it from the rear (away from bridge.)
       
    14. CoolHandLuke
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      CoolHandLuke Well-Known Member Full Member

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      well, first you get a titanium disc to mill, such as:

      [​IMG]

      then you mill your coping in it.
       
    15. NickB

      NickB Member Full Member

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      Ah, okay. I've never used Titanium. Works well? It can be used the same as if it were a non-precious or SP alloy as far as applying porcelain goes?
       
    16. CatamountRob
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      CatamountRob Banned Member Full Member

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      How well it works seems to be debatable, some love it, others don't. I believe it requires a different porcelain system than run of the mill PFM's.
       
    17. CoolHandLuke
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      CoolHandLuke Well-Known Member Full Member

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      that it does.

      but it effectively eliminates the whole wax and cast stage for NP anyway. you can always outsource gold.
       
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