Stress Breakers, Direction Changer ETc

[Mike2]

Hello All,
I had a request to place one on a larger bdg. In my version of Exocad, it says use at own risk?? Not very easy to place as the ATT application has many versions of different attachments. I chose a simple key way design, and had issues sizing and placing into proper position. Anyhow, anyone have a source as to how to b successful with this as the one I made did not turn out correctly....did the male upside down and the keyway wasnt milled all the way out. SOOOO looking for tutorial, I will search you tube in meantime.
Thanks in advance.

 

[JMN]

Those will be tricky to mill since most designs (I've seen anyway) have squared or sharp angles. Mills don't have the nifty machinst tools to cut square holes and the like with a rotating tool. (yes, they really exist) If the design has corners, round tools heads cannot cut them without overcutting into the corners.
And what you end up with is exactly what you desribe, incomplete milling as the round head cannot reach the rest of the area. So you get something like this instead:

You'll need a female and male design that is rounded at every turn/direction change of the proposed output. Intentionally designed so that the radii of the angles of the inside of the turns are greater than the radius of your smallest burr that is applicable to the stock you are milling. Even with rounded corners, they can still be too small for a .6mm burr if that's all you have for that material.

And that's as much help as I can be here. Real curious as to the answer as well if you are not designing the component yourself.

 

[sidesh0wb0b]

I think a Tube-Lock deisng may work.... but that is if you have that option for designing. otherwise, @JMN is correct and the mill cannot mill those corners.
that being said, why is anyone doing these any more? i love they called them "stress breakers" when the stress is greatest at these cantilevered areas. if ever i saw one of these style bridges break, it was at this junction or on the abutment supporting it. IMO its the lazy way of cutting corners for the dentist. at the least, more prepping should be done to parallel things up some. or ortho. or implants. too many options nowadays to put this type of stuff in the mouth still.

 

[JMN]

I think a Tube-Lock deisng may work.... but that is if you have that option for designing. otherwise, @JMN is correct and the mill cannot mill those corners.
that being said, why is anyone doing these any more? i love they called them "stress breakers" when the stress is greatest at these cantilevered areas. if ever i saw one of these style bridges break, it was at this junction or on the abutment supporting it. IMO its the lazy way of cutting corners for the dentist. at the least, more prepping should be done to parallel things up some. or ortho. or implants. too many options nowadays to put this type of stuff in the mouth still.

I think stress breaker is the term for what they do to the tech, not for the prosthetic.

 

[CoolHandLuke]

in what world do our mills not have square end tools?

and in what world would the cam software behind it NOT allow you the ability to edit the tool geometry?

cutting a keyway is a simple matter. designing a keyway is not even close to a simple matter for a person who has little experience with that function within the cad software.

making a keyway work long term is even more of a feat.

you really should make it out of metal, and given the propensity to work with milled metal copings, this seldom happens as more doctors and labs go to zirconia.

you should have a radiused or flat end end mill to make flats that need to lap together. ball end tools work better for profiles so they are commonly used in milling non-straight edges.

now to the juicy question of 'how do i integrate that in my cam?' to which i must reply 'you should consult not merely your support, but your shuppourt should be fluent in the mechanics of machinistry and not simply be a rep'

remember: reps just want you to buy supplies (LIKE MILLING TOOLS AND PUCKS) so they will set your machine to cut all materials poorly.

 

[Mike2]

Sooo... after watching some you tube and some more work I was able to design a split bdg. I have a keyway design, but my K5 would not mill it out. The connector would not fit together in green or sintered state. Anyone have a CAM/CNC solution or B willing to mill it for me??

 

[CoolHandLuke]

couple questions (and before you think i'm volunteering, i'm not)

1. you are aware the sharp edges on the male end will be a chipping liability?

2. you are aware that the connectors between teeth will get glossed over?

3. you are aware that placing the connector in the middle of the bridge is not correct?

4. bridging from cuspid to 3rd molar is beyond too long of span for full contour.

5. connection between cuspid/premolar is way narrow. i hope its tall to compensate.

this is a nightmare waiting to happen.

ignoring all of that, what is the diameter of the FEmale end at the widest and narrowest parts?

 

[Mike2]

Glossed over?? Not sure what u mean by middle of the BDG as this is what Dr's around here do.(premolar is probably compromised and dr wants to crown before pulling, if it fails he can remove,separate and fill in abut.) The diameter is 2.4mm of female. The span is what it is? I wasn't told that we are limited to a certain span while being trained years ago on Zr. Thanks for all the input, wish I new a little more like yourself, Dr may be switching material option and accepting liability as I won't be redoing this one for free, already took up way too many brain cells I could've killed with BEER.

 

[CoolHandLuke]

in red: conector is narrow, potential fracture point. on female end ive highlighted areas too small for burs to cut. these areas will not get milled, they will get skipped. 80% of labs who use milling solutions that just come from argen or ag or cap or zahn (zirkon or uncle hank) employ very broad-stroke raster milling. small cutters are only employed on the cameo side, not intaglio side. wrongfully then, people who misunderstand how milling takes place, design with the smallest cutter diameter possible and chalk up the smeared edges and missed details to 'bad quality machine'

this is why roland was so well loved. its cam solution from big box vendors employed rest milling in the intaglio using small diameter tools.

 

[CoolHandLuke]

regarding the span of zirconia, you are limited. very much so.

the more Compressive mpa you have the more rigid your structure is. the more rigid it is, the less room you have to use in a 3point bending scenario.

i'll tell you i just finished a 4point bending analysis of a bunch of different materials for a thing i'm doing, and zirconia did not flex more than .4mm before catastrophic failure. boom. big badaboom. huge compressive force required between to narrow points or small compressive force between two points far apart.

the longer your span, the easier it breaks.

so most manufacturers only indicate 2 pontics.

you have 4 pontics.

AND you have a stressbreaker in one of them.

this case will be ridiculously easy to break and fail. glad to hear you accept no liability. but seriously rethink making a bridge this big in the future.