CAD and CAM combination output differences?

[NicelyMKV]

I would like to discuss the major differences I see between my CAD design and different CAM/ machine combinations. I would see differences from time to time and just assumed it was my design. I recently started toying around with milling in house. Still experimenting with different materials and all that good stuff. I sent the same file to a milling center and also milled it myself. I immediately noticed a big difference in my occlusal and interproximal contacts compared to theirs? I then sent another case to another center and had the same fits i had internally. Sent that same file to another with high occlusions and very tight interproximals? I have been doing this on and off for a few weeks now. Bridges are another major difference. Fits of the same file vary greatly.

The differences are always the same with the same milling centers. Just wondering what others have experienced? I keep hearing these greatly varying occlusal settings etc. wondering if it has to do with the CAM? I do know that with Sum3D and my Roland, I get a finished result identical to whats on the screen of my design. I have heard others leaving occlusions wide open in their design software just to get light occlusal after the fact.

Jason

Sent from my iPad using Tapatalk HD

 

[DMC]

You have too much spare time obviously. LOL

 

[NicelyMKV]

You have too much spare time obviously. LOL

Its why I can't afford a Haas very unproductive individual

 

[YMS96]

I would like to discuss the major differences I see between my CAD design and different CAM/ machine combinations. I would see differences from time to time and just assumed it was my design. I recently started toying around with milling in house. Still experimenting with different materials and all that good stuff. I sent the same file to a milling center and also milled it myself. I immediately noticed a big difference in my occlusal and interproximal contacts compared to theirs? I then sent another case to another center and had the same fits i had internally. Sent that same file to another with high occlusions and very tight interproximals? I have been doing this on and off for a few weeks now. Bridges are another major difference. Fits of the same file vary greatly.

The differences are always the same with the same milling centers. Just wondering what others have experienced? I keep hearing these greatly varying occlusal settings etc. wondering if it has to do with the CAM? I do know that with Sum3D and my Roland, I get a finished result identical to whats on the screen of my design. I have heard others leaving occlusions wide open in their design software just to get light occlusal after the fact.

Jason

Sent from my iPad using Tapatalk HD

You need to design the file with the specific output in mind. You can't just create an STL and send it to 10 different machines and expect them to all come back the same. I've heard the same thing about files coming back too high or intruding too much on the contacts and I'm guessing they do this as a safety net, it's easier to remove then it is to add type of thing.

 

[NicelyMKV]

So if I have an object in STL format, different cams should or should not mill it differently? I figured a file with its dimensions we're pretty much static? The end result should be a direct representation of the file sent? Right?

 

[charles007]

Occlusion set at .26 then .29, now .30 and still high occlusion.........Out of occlusion in places and grabs Almore Shimstock in other spots.. 8 micron
Contacts.....want even go there........

 

[k2 Ceramic Studio]

Really interesting thread, I would have said the same as Nicely that once an.stl is produced then you should get back what you have sent from every system you send it to. But and I think its a big but, When you have your own milling system you change little things, like how much out of occlusion you want it and what your minimum thickness needs to be. I don't think anything you set up is scientific I think its down to your systems calibration, you know what your system gives you, so you know how to design too your milling units output. But when you send it to another lab it only needs to be out by +/- .3 in one axis and have a tight bite or a very thin area or a missing contact and so on, unless people are trained to calibrate there systems every month then you will always get different dimensional changes from mill unit to mill unit, it is almost impossible to do an automated calibration. we need to mill a specific shape then measure about 6 different points on it to 0.015 and put the information through a special program that then makes very small changes and then we have to do it again and again until it tells us we are within acceptable boundaries(0.015)

 

[Slipstream]

Remember the drill compensation settings will be mill specific - you won't get the same fit from a single file on 3 different machines - their bur dimesions will be different as will be the milling strategy from each cam - the Roland is 5 axis or 3+2 depending on your settings - a lot of the milling centers are running volume machines with just 3 axis milling, all will fit well if designed for the machine they are going to be manufactured on.

 

[DMC]

Mills have various systems for offsetting the Z-lenght of tool.

Some better than others. Non-contact Laser tool probe, or simple contact to complete an electrical circuit, or a button that needs to be depressed. Is there crap on your tool sensor? So, thickness will vary a wee-bit in the Z-axis.

Internal fits should be very very similar, but other surfaces may vary more.

Then, there is the obvious difference in tools being used. Some stop at 1mm diameter, some go much smaller.

Some spindles have more runout than others....so tool as defined in CAM may not be 100% the same as actual spinning tool diameter.

Then, there is the software resolution of the CNC Controler, then the actual mechanical resolution of mill.

Also some CAM can be adjusted to minimum step of .01, or .005mm etc etc....

Some tools are more accurate than others. (diameter)

Then, there is the actual mill calibration.

Can't thnk of any more stuff at the moment.

I;m eating lunch and need to concentrate on my sandwich at the moment...hard to think. LOL

 

[CoolHandLuke]

probably a lot more factors to consider than that, scott. some 1mm tools have a degree of flexibility to their shaft. sometimes people sinter their crowns with the margin up, some sinter with the occlusal up. some zirconia might be kept in a warm environment, or the tool might be heating while milling. sometimes the milling path can error out (recently we had it where the mill just would not mill using the 1mm bur, only the 2mm. same file nested in a different position cleaved in half on the second attempt. the third managed to punch a big hole in the puck as soon as the bur hit the puck. very strange)

then again, some zirconia manufacturers give expansion rates to 4 digits, and some milling machines are only capable of reading to the 3rd digit. this i think might be the biggest issue currently faced. metoxit blocks and bruxzir blocks have expansion rates 4 digits long, and my mill only accepts the first 3 digits. so i have to round off, and it can be tricky to compensate for in die spacer and contact areas.

 

[YMS96]

then again, some zirconia manufacturers give expansion rates to 4 digits, and some milling machines are only capable of reading to the 3rd digit. this i think might be the biggest issue currently faced. metoxit blocks and bruxzir blocks have expansion rates 4 digits long, and my mill only accepts the first 3 digits. so i have to round off, and it can be tricky to compensate for in die spacer and contact areas.

Do you really think 4 decimal places matters that much?

 

[DMC]

No, it does not. Total B.S.

What is .1% of 1cm (width of a crown) How about .01% of 1cm? 1000um x .0001 = nothing! Did you graduate High School math? Lets step back and think about it a little....

Show me your math.

Nobody sinters crowns occusal side up. That's stupid if you do.

 

[DMC]

For example....1.252 (Three digits after decimal) or 20.13% are the same exact thing....one is V ratio (Magnification) the other is Shrinkage expressed in a percentage....

Now...if a crown is 1cm wide (to keep math simple) then show me your math to figure what your talking about with the 4th place after decimal.

This distance is beyond your CAM and resolution of CNC mill...therefor total BS un-neccessary info.

If you have a bridge for a Sperm Whale that is Eight feet long...then maybe. MAYBE!

 

[CoolHandLuke]

1cm wide post sintering or pre sintering?

post sintering at an arbitrary shrinkage of 1.2375 (average shrinkage of Metoxit brand) the crown must be exactly 1.2375 cm before sintering yes? but compensation for die spacer has been made on this crown, such that the walls of the crown are .6mm on each side (so subtract 1.2mm and the internal diameter must be no bigger than 1.2255 cm)

say my CAM can only resolve to the 3rd digit. now i have to go which way when entering the shrinkage in my CAM? up or down? if i go up to shrinkage of 1.238, my crown must now be maximum 1.238 cm, internally my fit will be what? it can't resolve the 4rth digit, so i will be 1.226 cm

if i go down, exterior is max 1.237, internal is max 1.225

so it makes a difference of almost a tenth of a milimeter IN BOTH DIRECTIONS! need i tell you thats the measure of an open contact vs closed, or open bite vs too tight?

now, should we talk 1cm pre-sintering? if so, shrink those values to under 1cm for post-sintering results, and you should find they need to be accurate to the 5th decimal point to be good.

its the whole discussion of the accuracy of your milling machine, people say all they like, the machine is 10um accurate... really? nah bro. the cam only accepts the 3 digits.

 

[DMC]

1st digit after decimal is mm
2nd digit is 1/10th of a mm or 100um
3rd digit is 1/100th of a mm or 10um
4th digit is 1/1000th of a mm or exactly 1um

Most mills and CAM do not work in single microns.
It doesn't work that way Mr. Luke. Show me a mill with single micron resolution in the software and hardware. Maybe a $800k DMG....that's about it. Lava and KaVo are 10um step encoders.



I don't know why you are complicating the matter by talking about each opposing side of the crown and talking about die spacer and such, but OK here we go....you would need to take 1/2 of the difference (half on each side). So...what is 1/2 of a single micron? That's the slop on each side for using the 4th digit....which again I say is total B.S. info to be using.

Go back to using the 3rd digit and we take 1/2 of 10um....which is 5um on each side. Pretty far from your stated 100um slop. (1/10th of a mm)




Um-k?

How you go from 1um to 100um is beyond me.

 

[NicelyMKV]

The only decimal place I worried about was at the end of my GPA. Let me know if I was gonna walk with everybody else or not.....


Sent from my iPad using Tapatalk HD

 

[NicelyMKV]

I did think about shrinkage factors as well. The only thing was most fit pretty much the same on the die. The occlusions and interproximals are what we're so different. There were a few milling centers where I actually had to do some internal adjusting though.


Sent from my iPad using Tapatalk HD

 

[CoolHandLuke]

i "complicate" the matter by speaking about both sides of the crown because remember, the resolution is both + and -. +10um and -10um

thats a big swing. if its big on one side and the other, i've got a tall, bulbous crown. thats a garbage FCZ. all the time spent designing it to the correct bite just went poof.

now, what should happen if the crown happens to only sinter to 75% instead of 85% of density? again, large crown. easily broken, and will come back. thats money out of somebody's pocket. thats a sintering time that wasnt long enough, too hot, or on a bed of bad beads.

 

[PDC]

After reading about all the issues involved with milling your own crowns in this thread, do those of you who are lab owners with milling machines feel you are more productive (more crowns/day) and have fewer issues (occlusion, contacts,etc.) than if you outsourced the scan? In other words, are you producing more crowns in the same amount of time as you were when you outsourced the scans or is dealing with the milling machine increased your overtime?

 

[JohnWilson]

While I am a real noob to milling one of my main worries prior to purchasing was what the real world numbers were as it relates to actual cases that needed to be remilled for one reason or another. We have had a few cases that were just a bitch but mostly one and done.

Where the most advantage is the speed, same day crowns are amazing, being able to bang a coping fast has saved my ass a few times now.

Playing with milling wax on Friday , I scanned and designed 10 full contour singles in 1.5 hours. I could never hand wax those that fast