e.max sprue cracks

[normanmilquetoast]

I've been doing e.max for several months and really love it, but I've had a problem the last few cases. After I cut off the sprue and as I'm grinding the nub, a crack develops. I'm not sure what I'm doing differently. Maybe it's my cut off disk or grinding stone.
Any suggestions?

 

[TheLabGuy]

Sounds like your creating too much heat, which causes a fracture.....You will see this occur on E.max appear in thin areas if it's heated too quickly.

 

[Toast]

Sounds like your creating too much heat, which causes a fracture.....You will see this occur on E.max appear in thin areas if it's heated too quickly.

I agree with Rob, too much heat. I've had this happen before back in the day with E2. Also happens when I apply too much pressure with a diamond around the neck of an emax crown where it goes from thick to thin. I use a super hard green stone from brassler (sorry don't know what the # is) that cuts emax like butter with little heat. You can heal the crack by putting some wonder peg inside the crown and running it up in your proc. oven to about 900*C with a 15 second hold time, if it doesn't heal, gradually increase your final temp until it does.

 

[sixonice]

I've been doing e.max for several months and really love it, but I've had a problem the last few cases. After I cut off the sprue and as I'm grinding the nub, a crack develops. I'm not sure what I'm doing differently. Maybe it's my cut off disk or grinding stone.
Any suggestions?

no question your developing too much/excess heat. try going slower, less pressure and i like to either dip it quick in water while i am taking the sprues off or you can have a little piece of dampened sponge to give it a quick cool down while your working.

 

[finnster68]

High speed with water works well

 

[normanmilquetoast]

Thanks guys.
What type of stones do you use to grind the sprues?