Pressed Copings Rock

[Autumn]

Our copings don't rock prior to pressing but some of our copings develop a slight rock after pressing. Any ideas as to why this is happening?

 

[sixonice]

Our copings don't rock prior to pressing but some of our copings develop a slight rock after pressing. Any ideas as to why this is happening?

Make sure your using the proper investment ratio for copings - and following the manufacturers instructions. That is where I would start first. If your good on that, then it HAS to be between when the wax up's are sprued & removed off the die. Do you invest immediately after you sprue them? Are you spruing them ON the die? I would. Are you being careful when removing the wax-up off the die?

 

[Autumn]

I'm sorry if I didn't explain my issue more clearly. The copings fit fine after the castings are done. Our problem arises once they are waxed over and pressed in the pressing oven. It is then that some of the copings develop a slight rock.

We have wondered if the metal could be too thin and warping during pressing from the pressure. Any ideas? Is there an ideal thickness for the metal? We try to keep it no thinner than 3/10.

 

[wwcanoer]

are you using Pulse-press-to-metal?

when i experience something similar, it's because an area is too thin and has "bulged" I simply relieve the metal and 99% that takes care of it. I'm using JP-1, and try to keep metal .2-.3mm.

hope that helps

carol

 

[Autumn]

We are using Pulse and we also use JP1 and PN3. Thank you for the idea. We will try it.

 

[sixonice]

I follow you now - your doing press-to-metal. Something you may want to be absolutely certain that you are doing is when your waxing, to wax a short "tang" or "fish hook" or "T-bar" on the lingual side of the coping to prevent the copings from shifting in the investment while being pressed. There is alot of pressure coming down during the pressing process. These little stabilizers lock the coping in the investment and prevent any movement during processing.
As stated in an earlier post is making sure you are keeping true to the manufacturers recommendations on minimal metal thicknesses to prevent bulging or deformation. Generally, higher gold content alloys have to be a little thicker than semi-precious ones.