Intaglio: bur size and drill comp

[user name]

My intaglios are being milled with a 2 and 1mm bur. The crowns will be hitting slight high spots and not seating fully where there is a sharp edge on the prep; could be where the axial walls meet the occlusal or around some sharp edged anti-rotatioal groves in the prep.

I thought I understood drill compensation, but I need a lesson. What should it be set at to get the sharp areas fully rounded out? I didnt make notes of parameters before giving up my 3shape; the designs I got out of that always had generous removal in these areas.

 

[pjd cdt]

Open up a case and look under crown bottoms and see what your default is set at. Mine is 1.4mm sometimes I will change this to 1mm for lower anteriors.


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[user name]

Open up a case and look under crown bottoms and see what your default is set at. Mine is 1.4mm sometimes I will change this to 1mm for lower anteriors.


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What bur size does that correlate with? Mine is set as default at .8.

I guess Im not visualizing things correctly. Should the comp be the bur radius + a bit or the diamater +?

 

[Affinity]

Try cleaning them out with a brush before you sinter.

 

[JohnWilson]

Are you running a simulation to check for standard deviation before you mill?

Your cad design/parameters are only one part of the equation. Most fit issues I have seen are not because you designed a crown with a drill comp that doesn't match the "radius+" of your internal fine milling bur. Unless you are ****ing with the parameters in 3shape or now EXO these figures need not be altered.

Its on the CAM side most times anyhow

 

[pjd cdt]

What bur size does that correlate with? Mine is set as default at .8.

I guess Im not visualizing things correctly. Should the comp be the bur radius + a bit or the diamater +?

You have the Jensen vhf with 2mm,1mm,.6mm ?
Try changing default to 1mm to 1.4mm.
Do they use ds cam? I wouldn't be surprised if the .6 was only used on the occlusal.


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[CoolHandLuke]

your instinct might be to make the bur size in the compensation to be smaller, but you should actually make it slightly larger. if you are finishing the inside with 1mm, set it to 1.1mm or even 1.15mm. .8 means you'll be unable to have the bur reach some areas so it will be undermilled (as in some material will be left over).

in planmeca software there is the capacity to Overmill so you always have good fit but that is dangerous as it renders the planned material thickness to go out the window.

but in most CAM the overmilling features are locked off. for the same reason. it is dangerous to allow the mill free reign over how it wants to cut a unit, and it is very lazy workmanship on the part of a cnc operator to utilize it.

but so few of us want to sit there and keep calcing projects until the stock removal is precisely correct.

do you have the capacity to add a toolpath to do internal finishing with a .6mm or restmill with .6? finishing would cause a lot of tool wear and would likely break it but restmilling can be OK.

 

[user name]

your instinct might be to make the bur size in the compensation to be smaller, but you should actually make it slightly larger. if you are finishing the inside with 1mm, set it to 1.1mm or even 1.15mm. .8 means you'll be unable to have the bur reach some areas so it will be undermilled (as in some material will be left over).

My presumption was that if youre milling intaglio with a 1mm tool, drill comp should be at least 1mm; however my default is set to .8. I just cut one that would typically have been a problem with it set to1, and things look good, so I think my next batch Ill set it at 1.1 and let er rip.

 

[ceram1]

The reason you are seeing .8 is preciso default is accounting for the 20 plus percent zr shrinkage factor. It is to reduce the mentioned overmill. If you look at your 1 to 1 ratio materials (wax pmma ect) you will notice the default drill comp is set at 1.1. If the sharp areas are near the margins you can improve your results by selecting the margin in preciso cam, change type to inlay, rename the part inlay. This will utilize your. 6 mm near the margins. Helps a lot in wax especially. Adds time to milling is the drawback.

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[user name]

The reason you are seeing .8 is preciso default is accounting for the 20 plus percent zr shrinkage factor. It is to reduce the mentioned overmill. If you look at your 1 to 1 ratio materials (wax pmma ect) you will notice the default drill comp is set at 1.1. If the sharp areas are near the margins you can improve your results by selecting the margin in preciso cam, change type to inlay, rename the part inlay. This will utilize your. 6 mm near the margins. Helps a lot in wax especially. Adds time to milling is the drawback.

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One small correction...Ive discussed this in detail with the techs in charge at said retailer...The .8 is a mistake. It doesnt account for shrinkage. The default should be set at a minimum of 1.0. 1.1 is better, 1.2 is recommended. Ive done a bunch of testing on different types of angles on preps and have helped them to see the light. Check your Wiki when youre on the crown bottoms wizard. The .8 default is a mistake.

The shrinkage factor isnt happening in the CAD; the scaling happens in the CAM portion, hence...the mistake. .8 will work fine on any ideal prep, but if there are sharp edges with a radius of less than 1mm, .8 wont fully cut out the intaglio.

 

[ceram1]

One small correction...Ive discussed this in detail with the techs in charge at said retailer...The .8 is a mistake. It doesnt account for shrinkage. The default should be set at a minimum of 1.0. 1.1 is better, 1.2 is recommended. Ive done a bunch of testing on different types of angles on preps and have helped them to see the light. Check your Wiki when youre on the crown bottoms wizard. The .8 default is a mistake.

The shrinkage factor isnt happening in the CAD; the scaling happens in the CAM portion, hence...the mistake. .8 will work fine on any ideal prep, but if there are sharp edges with a radius of less than 1mm, .8 wont fully cut out the intaglio.

They may have made changes to this in you cad, my cad is now exo and not preciso. My build version of preciso is set at .8 on all of the Zirconia materials. .8 should be enough when milling zr with a ball end of 1mm. Any more might have less potential for interference at seating however blowing out tool comp/drill comp ect. wastes precious space especially in the anterior region. My wax default is set at 1.1 as I mentioned before.

 

[user name]

They may have made changes to this in you cad, my cad is now exo and not preciso. My build version of preciso is set at .8 on all of the Zirconia materials. .8 should be enough when milling zr with a ball end of 1mm. Any more might have less potential for interference at seating however blowing out tool comp/drill comp ect. wastes precious space especially in the anterior region. My wax default is set at 1.1 as I mentioned before.

Where to start...Preciso is exo.

Setting comp at the max of 1.5 wont blow out any valuable space. The bur still cuts out exactly what its supposed to leaving your cement gap exactly as you have it set. The only time it will cut out more is in areas where it would prevent seating. If you are stuck with a prep that has a sharp 90 degree edge for instance, the axial wall and occlusal table will both be cut accurately to within 1mm of the sharp edge, but to make the crown seat, the 1mm bur needs to get the center of the bur to the full depth of the cut. To do that, it needs to over penetrate; in a worst case scenario like a 90 degree angle, it will need to over penetrate up to 50% the diameter of the bur...hence 1.5.

As I said earlier, the .8 default is a mistake.

http://wiki.exocad.com/wiki/index.php?title=Designing_the_inside_of_the_crown

"In the third tab of the "Crown bottoms" dialog, you can also change the parameter for tool diameter compensation. If you have selected a material that is to be milled, the checkbox Anticipate milling [4] is checked by default. Under Diameter [5], you can chose the diameter of the tool to be used for milling. It is beneficial to chose a value slightly higher than the diameter of the actual tool you're using, e.g. chose 1.2mm when milling with a 1mm tool."

 

[sonlab]

User.. Call up support at Jensen tomorrow, they will clear things up

 

[ceram1]

Where to start...Preciso is exo.

Setting comp at the max of 1.5 wont blow out any valuable space. The bur still cuts out exactly what its supposed to leaving your cement gap exactly as you have it set. The only time it will cut out more is in areas where it would prevent seating. If you are stuck with a prep that has a sharp 90 degree edge for instance, the axial wall and occlusal table will both be cut accurately to within 1mm of the sharp edge, but to make the crown seat, the 1mm bur needs to get the center of the bur to the full depth of the cut. To do that, it needs to over penetrate; in a worst case scenario like a 90 degree angle, it will need to over penetrate up to 50% the diameter of the bur...hence 1.5.

As I said earlier, the .8 default is a mistake.

http://wiki.exocad.com/wiki/index.php?title=Designing_the_inside_of_the_crown

"In the third tab of the "Crown bottoms" dialog, you can also change the parameter for tool diameter compensation. If you have selected a material that is to be milled, the checkbox Anticipate milling [4] is checked by default. Under Diameter [5], you can chose the diameter of the tool to be used for milling. It is beneficial to chose a value slightly higher than the diameter of the actual tool you're using, e.g. chose 1.2mm when milling with a 1mm tool."

Preciso is Exo, NO $H1+!!! With a quite a few limitations set up wise, not really that different design tools ect... Next time you are designing a tooth#25 set your comp at 1.5 and let me know if you feel the space is valuable. But hey they're your crowns do them how you want.
I promise you, I am not leading you off your path of trying to understand these parameters, .8 will work 99% of the time for zr restorations. It is due to the shrinkage factor the parts are processed OVERSIZED. IE .8 becomes about 1.0125 mm. If you are milling WAX or PMMA you must use > 1mm(the actual part size). The setting of 1.1 should give you slack for you 3axis mill strategies. Many of these nuisance high spots you are experiencing are due to the set up you have. The way the cad creates extra space compared to the way your cam excavates it with the limitations of the machine you are using. I have milled about 18000-20000 units with your same set up. Its been a great evolution with Jensen, they do arguably more with this machine than anyone, other than maybe Ivoclar if you opt for the advanced cam.

 

[user name]

User.. Call up support at Jensen tomorrow, they will clear things up

I did speak to pretty much everyone at Jensen. They agreed with me. The .8 default is a mistake.

Preciso is Exo, NO $H1+!!! With a quite a few limitations set up wise, not really that different design tools ect... Next time you are designing a tooth#25 set your comp at 1.5 and let me know if you feel the space is valuable. But hey they're your crowns do them how you want.
I promise you, I am not leading you off your path of trying to understand these parameters, .8 will work 99% of the time for zr restorations. It is due to the shrinkage factor the parts are processed OVERSIZED. IE .8 becomes about 1.0125 mm. If you are milling WAX or PMMA you must use > 1mm(the actual part size). The setting of 1.1 should give you slack for you 3axis mill strategies. Many of these nuisance high spots you are experiencing are due to the set up you have. The way the cad creates extra space compared to the way your cam excavates it with the limitations of the machine you are using. I have milled about 18000-20000 units with your same set up. Its been a great evolution with Jensen, they do arguably more with this machine than anyone, other than maybe Ivoclar if you opt for the advanced cam.

As I said above... if there are no sharp edges, it doesnt matter if the comp is set to .8 or 1.5. The fit will be EXACTLY the same. The only time comp comes into play is where there is a sharp that results in a tight spot in the intaglio that cant be cut out by a 1mm bur; then having the comp set greater than the bur diameter will allow it to cut out enough to allow the crown to seat.