concave, or 'domed' vinyl
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
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basquiattag
- Posts: 17
- Joined: Thu Jan 14, 2010 6:11 pm
concave, or 'domed' vinyl
Is this generally the result of too little cooling time?
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montalbano
- Posts: 139
- Joined: Tue Aug 11, 2009 3:03 pm
- Location: Settala (MI), Italy
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If you are referring to records which tend to dish, the problem is not in the cooling time but elsewhere. More cooling will help a little, but you will risk to be unable to trim the records when they will be out from the press.
Probably it is due to the fact that the upper and lower moulds have slightly different thicknesses. This means that the heat exchange is slightly different between eachother and therefore one side heats up and cools down earlier than the other side.
With the Alpha Toolexs, also the earliest ones, you can correct this problem by setting some extra time in step 7, that is the timer used to let the record sit "idle" into the press after the cooling water valve has closed and before the press opens. The record will cool down anyway, but more evenly on both sides, and this will help it to stabilize a little bit more.
Another reason can be that the records are too thick in their center, in this case when stacked they will dish for sure.
I would recommend to check the pipings, either upper and lower mould must heat and cool from inside to outside, in other words the thermic cycle must go in couple the hydraulic pressure, that is the standard.
Aluminium spacers can help a lot, but the crucial thing is the profile of the moulds.
You have to break a record and measure its thickness with a Vernier gauge. If the center is thicker than the outer part, then there is something wrong with the profile of the moulds or with the pipings.
Normally, all moulds need reprofiling after many thousands pressings as they wear out quicker in the center. The same thing affects the plates of the press.
With a couple hundreds dollars you can have your moulds reprofiled and have an even record's thickness from outside to inside.
If the problem is in the plates of the press, you might need an emergency procedure, and that is to use one or two useless stampers, trim them to say an outer diameter of 15 cm and an inner diameter according to the diameter of the centralising bosses of your press, then put the between the top of the press and the plate holding the upper mould. This will work for a while but it's not the proper solution.
Also, back to aluminium spacers, don't forget that they will make bad records look flat after one night. They will seem to be OK, but the tension will still be there ... Just let the records expose to heat for any reason, they will dish again. Guaranteed.
Ciao
Probably it is due to the fact that the upper and lower moulds have slightly different thicknesses. This means that the heat exchange is slightly different between eachother and therefore one side heats up and cools down earlier than the other side.
With the Alpha Toolexs, also the earliest ones, you can correct this problem by setting some extra time in step 7, that is the timer used to let the record sit "idle" into the press after the cooling water valve has closed and before the press opens. The record will cool down anyway, but more evenly on both sides, and this will help it to stabilize a little bit more.
Another reason can be that the records are too thick in their center, in this case when stacked they will dish for sure.
I would recommend to check the pipings, either upper and lower mould must heat and cool from inside to outside, in other words the thermic cycle must go in couple the hydraulic pressure, that is the standard.
Aluminium spacers can help a lot, but the crucial thing is the profile of the moulds.
You have to break a record and measure its thickness with a Vernier gauge. If the center is thicker than the outer part, then there is something wrong with the profile of the moulds or with the pipings.
Normally, all moulds need reprofiling after many thousands pressings as they wear out quicker in the center. The same thing affects the plates of the press.
With a couple hundreds dollars you can have your moulds reprofiled and have an even record's thickness from outside to inside.
If the problem is in the plates of the press, you might need an emergency procedure, and that is to use one or two useless stampers, trim them to say an outer diameter of 15 cm and an inner diameter according to the diameter of the centralising bosses of your press, then put the between the top of the press and the plate holding the upper mould. This will work for a while but it's not the proper solution.
Also, back to aluminium spacers, don't forget that they will make bad records look flat after one night. They will seem to be OK, but the tension will still be there ... Just let the records expose to heat for any reason, they will dish again. Guaranteed.
Ciao
Phil from Phono Press, Milan, Italy
http://www.phonopress.it
http://www.phonopress.it
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Aussie0zborn
- Posts: 1828
- Joined: Sat Mar 11, 2006 8:23 am
- Location: Australia
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