VHF S1 milling machine

[3DCAM]

Hello, I started to get broken zirconia abutment after I Mill them with my VHF S1 milling machine all the crowns are coming good but the abutment, called tech. support and they told me if there is a problem with the milling the crowns should be broken too. If anyone had the same problem let me know what should I do?

 

[CoolHandLuke]

obviously the parameters for milling crowns and milling abutments is different; your CAM provider should have shown you that when you pick abutment or crown you use different calculations.

that means whoever told you there would be a problem with crowns wasn't paying close enough attention.

tech support should not be dismissing you so quickly without walking through all the different scenarios.

is this a problem that has only occurred recently? by that i mean did you do the bridge a few days ago but these abutments more recently? have you milled any crowns in the same puck?

have you been able to isolate if all the breaks happen in the same *type* of zirconia? for example we used to mill all abutment from High Strength zirconia and all crowns in High Translucency zirconia; what i am suggesting is your batch of puck for abutment (if its different) might be a bad batch.

is there any problem with the air supply to your unit? is the air on an air dryer?

did someone bump the machine?

is it using a different tool for abutments? do you think the tool might be cutting too fast or deflecting too much during your operation (this is part of the calculation i spoke of earlier)

do you do anything different for abutments than you do for crowns?

 

[user name]

@CoolHandLuke
You know this isn't my area of expertise, but what I think Im seeing is his abutments are breaking from (possibly) when the access hole is being cut. Is it possible the wrong type of bur is being used and the shaft is bumpingthe Zr and breaking it off? Im just guessing there are different options for burs and the wrong choice is maybe being selected. (?)

 

[CoolHandLuke]

@CoolHandLuke
You know this isn't my area of expertise, but what I think Im seeing is his abutments are breaking from (possibly) when the access hole is being cut. Is it possible the wrong type of bur is being used and the shaft is bumpingthe Zr and breaking it off? Im just guessing there are different options for burs and the wrong choice is maybe being selected. (?)

it certainly is, and that was what one of my questions was inferring. the wrong tool or a good tool with the wrong speed is engaging at the wrong time. possible that 5 axis engagement had been employed and was unsuccessful but in breaks like this in my experience it is usually due to cutting parameters being wrong. zirconia is soft enough that even a tiny bit of vibration or deflection is enough to break the entire part.

 

[zero_zero]

It looks like the tool shank cone hit the abutment while it was finishing off the access hole. Check the strats to see if there's an error in the entered tool measurements.
Also try to cut it again while keeping an eye on the whole process...then you can pinpoint exactly, when and how the breakage happens.

 

[Joe]

so, we've got two S2's. They are set up exactly the same. One mills abutments better than the other. Shouldn't be any reason for it, but it's true. Anyway, I usually only have problems with really tall units (deep holes). With those I will not put the hole all the way through but just leave a thin solid zirconia part in the middle. That way it's easily removed pre or post sinter and the tools don't reach far enough in to have a collision.

 

[Joe]

also, check / clean your collet. Make sure you're identifying the holes correctly in the CAM. Turn them upside down? Cross your fingers and toes...

 

[CoolHandLuke]

so, we've got two S2's. They are set up exactly the same. One mills abutments better than the other. Shouldn't be any reason for it, but it's true. Anyway, I usually only have problems with really tall units (deep holes). With those I will not put the hole all the way through but just leave a thin solid zirconia part in the middle. That way it's easily removed pre or post sinter and the tools don't reach far enough in to have a collision.

could be a very easy to explain reason for it. one being slightly further from the air source might have an effect on finish, same as one might have a PSU that is outputting cleaner power. one could be on a sturdier table. doesnt take much to do bad zirconia.

 

[3DCAM]

so, we've got two S2's. They are set up exactly the same. One mills abutments better than the other. Shouldn't be any reason for it, but it's true. Anyway, I usually only have problems with really tall units (deep holes). With those I will not put the hole all the way through but just leave a thin solid zirconia part in the middle. That way it's easily removed pre or post sinter and the tools don't reach far enough in to have a collision.

How can I do it? (I will not put the hole all the way through but just leave a thin solid zirconia part in the middle)

 

[Sevan P]

What version Cam are you using? V6 or V7? Also when you set it up in the Cam how are you doing it ? Also what tools are you using?

Sent from my SM-N950U using Tapatalk

 

[RCKSTR]

It looks like incorrect tool parameters, causing the shank of the bur to collide with the abutment (likely the .6mm). Are you using burs supplied by your CAM provider or 3rd party? Take the time to watch one mill and see where it fails. Are you selecting abutment from the indication menu and clicking the "has holes" button? Try using 1 star instead of 3 star to eliminate the .6mm bur

 

[3DCAM]

So I milled 2 old abutments yesterday they were done 2 months ago and they became good but the other 2 abutments failed again

 

[3DCAM]

It looks like incorrect tool parameters, causing the shank of the bur to collide with the abutment (likely the .6mm). Are you using burs supplied by your CAM provider or 3rd party? Take the time to watch one mill and see where it fails. Are you selecting abutment from the indication menu and clicking the "has holes" button? Try using 1 star instead of 3 star to eliminate the .6mm bur

My burs from Henry Schein and I used 1 star and 3 star still failing

 

[CoolHandLuke]

So I milled 2 old abutments yesterday they were done 2 months ago and they became good but the other 2 abutments failed again

ok, theres your answer.

your sprues are way at the bottom of the puck.

the sprues need to counterbalance the forces of holding the unit in the puck as it vibrates. move the sprues further up to the middle of the UNIT (not necessarily middle of the puck, but center of mass of the unit)

the top of the abutment has no support, which is why it is breaking.

 

[RCKSTR]

What CAD software are you using? The insertion direction may be the culprit here

 

[RCKSTR]

ok, theres your answer.

your sprues are way at the bottom of the puck.

the sprues need to counterbalance the forces of holding the unit in the puck as it vibrates. move the sprues further up to the middle of the UNIT (not necessarily middle of the puck, but center of mass of the unit)

the top of the abutment has no support, which is why it is breaking.

You wont be able to do that if its a split file with the crown, the margin will be in the under cut area and will have to be redone by hand. Also the contours will never be right after green state. I have milled dozens of them with the sprue below the margin line, successfully.

 

[CoolHandLuke]

You wont be able to do that if its a split file with the crown, the margin will be in the under cut area and will have to be redone by hand. Also the contours will never be right after green state. I have milled dozens of them with the sprue below the margin line, successfully.

i know, its unfortunate but for some units sacrifices must be made. compromises, even. its why ive never been a fan of designing abutments, but rather screw retained crowns.

 

[RCKSTR]

My suggestion would be mill it again in wax, if it blows apart, its a machining strategy problem. If so, try milling as crowns with screw access instead of abutment.

 

[Joe]

How can I do it? (I will not put the hole all the way through but just leave a thin solid zirconia part in the middle)

if you're designing in 3shape, tell the software to not use the screw hole that the implant .dme wants to put in. Put your own hole in using the holes and attachments tools. Adjust the length and placement of the hole so that it doesn't penetrate through to the ti base. Leave 0.5mm and grind it out in the green state.

 

[RCKSTR]

This is one of the many reasons I love SUM3D, so much control over machining. I hate the "safe" bumpers up bowling version of milling.