Horizontal hairline cracks

tehnik

tehnik

Active Member
Full Member
Messages
505
Reaction score
12
Hello!

I have a question about hairline cracks that I have on some cases. I am mostly using katana zirconia (UTML and STML) that have this problem. After sintering I have discovered very thin horizontal cracks near the place I had connectors. Usually under the connector but this time a bit farther away (see the picture). What is causing this?
 

Attachments

  • Capture.JPG
    Capture.JPG
    19.4 KB · Views: 94
B

bigbrush

Active Member
Full Member
Messages
153
Reaction score
34
How many connectors?
Maybe you have some vibrations
 
tehnik

tehnik

Active Member
Full Member
Messages
505
Reaction score
12
I use always 3 connectors. I mill with Roland 52DC and the table is fixed to the stone wall.

PS. The cracks have been also on very thick screw retained crowns.
 
B

bigbrush

Active Member
Full Member
Messages
153
Reaction score
34
Check your collet and clean it, maybe you have zirkon dust in it.
 
tehnik

tehnik

Active Member
Full Member
Messages
505
Reaction score
12
I cleaned it just a few days ago.
 
B

bigbrush

Active Member
Full Member
Messages
153
Reaction score
34
So you have zo check your stepmotors. But is it possible there is a mistake in your millingpath? Please check the touch in begainning to cut sprues. That could be a mistake while the cracks are only near it.
good luck
 
sidesh0wb0b

sidesh0wb0b

Well-Known Member
Donator
Full Member
Messages
5,648
Reaction score
649
could it be a "seam" in the layered portion of the puck? bjust guessing here. no idea otherwise
 
user name

user name

Well-Known Member
Full Member
Messages
6,960
Reaction score
1,633
Post a couple good photos
 
OpalEssence

OpalEssence

Member
Full Member
Messages
59
Reaction score
4
could be the connector positioning.
 
JMN

JMN

Christian Member
Full Member
Messages
12,205
Reaction score
1,884
I don't know, but I'm wondering if you smoothed out the interface point between the connector and coping. If it is left as a sharp 90ish degree bend it won'd mill out like that, and will overmill (to get out all the stuff you indicated in design should not be ther but it'll take more too to get it gone.)

This could possibly lead to a weakness propgating through the coping as the changes in thickness are always going to be stress points and it my do the windshield crack trick as it continues milling.

Just a guess.
 
user name

user name

Well-Known Member
Full Member
Messages
6,960
Reaction score
1,633
No. Howd that ever get past the call screener. Get off the phone you big dope. Whats happening to our Country. Is this the failed experiment of public education gone arye?
 
JMN

JMN

Christian Member
Full Member
Messages
12,205
Reaction score
1,884
No. Howd that ever get past the call screener. Get off the phone you big dope. Whats happening to our Country. Is this the failed experiment of public education gone arye?
I guess I could be a lightening rod for the failure of public education being worthless and boring.
 
Kam Yu

Kam Yu

Active Member
Full Member
Messages
136
Reaction score
32
Hello!

I have a question about hairline cracks that I have on some cases. I am mostly using katana zirconia (UTML and STML) that have this problem. After sintering I have discovered very thin horizontal cracks near the place I had connectors. Usually under the connector but this time a bit farther away (see the picture). What is causing this?
What are you using to smooth down the sprue?
 
tehnik

tehnik

Active Member
Full Member
Messages
505
Reaction score
12
I am using burs meant for metal to smooth them on green state.
 
user name

user name

Well-Known Member
Full Member
Messages
6,960
Reaction score
1,633
In green state?! I use white rubber wheels.
 
Kam Yu

Kam Yu

Active Member
Full Member
Messages
136
Reaction score
32
My tech used white wheels. She would get those white half moon cracks where the sprue was. I changed her fine diamond burs and those pear shaped green state burs for final smoothing (from vacalon). No more cracks. I think you can use almost anything but you will have to be more careful about generating heat.
 
Jack_the_dentureman

Jack_the_dentureman

Active Member
Full Member
Messages
247
Reaction score
17
just buy a milling machine and look at materials and accessories.
I found a movie from the Komet.
they use burs for elastic materials, and acrylic rubber for smoothing. it looks like you can save money.
will it be good? someone tried something?
 
Car 54

Car 54

Well-Known Member
Donator
Full Member
Messages
7,953
Reaction score
1,122
In green state?! I use white rubber wheels.

Same here. The white oxide wheels from Pacific Abrasives, or the ones Larry sells (Wagner) that he just turned me on to.

I suppose if you use them to quickly or aggressively could generate some undue heat?
 
sidesh0wb0b

sidesh0wb0b

Well-Known Member
Donator
Full Member
Messages
5,648
Reaction score
649
Same here. The white oxide wheels from Pacific Abrasives, or the ones Larry sells (Wagner) that he just turned me on to.

I suppose if you use them to quickly or aggressively could generate some undue heat?
whatever turns you on i suppose!
 
Top Bottom