Howard
Posts: 24
Joined: 2007-01-15
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I did a dry run on a pressing in a vacuum bag and the bottom platen curled upwards sufficiently to crack it.
Here is the setup: The bottom platen is a 4 by 8 sheet of melamine coated ¾” MDF. The part that I was pressing is about 2 by 6 feet with a ¼” thick Masonite top platen. The top platen overhangs about 3/8 inch. The pressure was about ½ an atmosphere as I was pressing honeycomb. The honeycomb was in rectangular frame. The material was not centered in the bag but about 12 inches off center.
After I started the pump I heard a cracking sound and on examining the setup I found that the bottom caul was bowed upwards with the bow greatest at one end of the bag and gradually decreasing to flat about 3 feet from the end. There was a 2 foot crack going down the center of the bottom caul.
A few days ago I made a smaller pressing, 2 by3 feet, using the same setup with no problem The work came out dead flat.
Lucky I had decided to do a dry run.
Any ideas as to the problem?
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