Vacuum bag platen questions

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 1 May 2007 09:58:34 -0700, damian penney wrote:

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:
http://www.vacupress.com/accessories.htm#evacunet
That mesh must be a little larger than the top platen, so there is no air trapped on top of the work.
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.
--
Art Greenberg
artg at eclipse dot net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 1 May 2007 11:39:37 -0700, damian penney wrote:

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.
--
Art Greenberg
artg at eclipse dot net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Fair enough, that makes sense. Okay well wish me luck going to give it a whirl as soon as I get home :)
Damian
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.