I'm about to fire up my new vacuum press for the first time and was wondering what the consensus is concerning platens. I read on Woodweb that you only need a grooved platen on the bottom while other places (joewoodworker.com) indicate that you need grooved platens top and bottom. Also do the grooves on that bottom platten face toward or away from the bag?
Thanks, Damian
I use grooved plattens top and bottom for flat work. The grooves always face away from the bag.
For work that is not flat, I use a form that is flat on the bottom, and place a grooved platten under it. On top, I use a non-grooved platten of thin bending plywood (or ordinary 1/4-inch plywood if the curve is gentle enough to use that). Between the bag and that platen, I place plastic evacuation mesh sold for the purpose:
Remember to coat your platens with something that the glue you're using will not adhere to. I've had good luck with paste wax. Plastic packing tape should work well, too. Remember to keep the grooves clear.
Why do you place the grooves of the MDF platen away from the bag, but the breather mesh, which does the same job as the grooves against the bag?
I currently have a grooved mdf platen for the bottom, and then two solid melamine platens to go above and below the veneer sandwich. Will I need to coat the melamine with wax or will that be fine on its own?
The reason for the grooves is to allow air to flow from all points inside the bag to the vacuum pump. If the grooves are facing the bag, they could become blocked as the pressure inside the bag decreases. That might trap air in some portion(s) of the bag, which in turn could prevent you from having equal pressure across the work being glued.
The breather mesh is designed to prevent the bag from interfering with air flow, so its OK to have it against the bag.
Melamine probably doesn't need any additional treatment.
Fair enough, that makes sense. Okay well wish me luck going to give it a whirl as soon as I get home :)
Damian
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