[OP]
Contributor
I am going to be making a vacuum frame press for my veneering work. Roughly 4'X5'. The platten top will be 1/2" mdf with a 2.5" thick Baltic Birch plywood frame underneath. Due to the size of my shop the press will be on horses while in use and hung on the wall for storage. My question is do you guys think that the 2.5" frame is thick enough to prevent the frame from flexing while in use. or should I make the frame thicker? I look forwar to hearing your thoughts. Thanks in advance.
Contributor
Platens go in the bag, so I'm guessing you are talking about a flat surface upon which the vacuum bag will rest. If so, a torsion box would be an ideal solution. 1/4" MDF would be plenty thick enough for the skins with a grid spacing of maybe 4". For a 4 x 5 ft box 2" should be plenty thick.
John
Contributor
I would make it a bit deeper or make it up as a torsion box. One thing I ran into with my 4' x 8' frame press was the 2" x 2" birch top frame bowing inward when under vacuum. I solved that by sizing the separate grooved platen that I use to be just under the inner dimensions of the top frame.
[OP]
Contributor
Yes, you could say I am talking about a torsion box. So the 1/2" platen top will have a grid of 1/8" wide by 3/16 deep groves to evacuate the air. and the torsion frame that the MDF is succured to is 2.5" thick. Thoughts?
Contributor
Instead of saw horses - get yourself a Bora Centipede.
They store great and have enough support to hold up a couple of mating pachyderms getting frisky with each other.
"Life is what happens to you while you're busy making other plans." - John Lennon
Contributor
Originally Posted by Adam Augustine
The vacuum frame presses I'm familiar with look like this. The lid is nothing more than a frame around the outside that holds the gasket seal and plastic membrane that does the pressing. The bottom is where the torsion box would go.
I've found that grid systems are unnecessary if you use breather mess under/over the work and one end extends to the vacuum port. I use heavy duty window screen for my breather mesh. It's so cheap that I can cut it to whatever size is needed.
John
Contributor
I wouldn't do it that way. A true torsion box will have a top and bottom skin to develop full strength and as John said at that scale the skins can be on the order of 1/4" thick. Nominal 1/4" lauan makes a nice light stiff box.
You can use breather fabric but I favor a separate grooved platen on top of the torsion box that both provides air evacuation channels and prevents my wood membrane frame from bending inward. The commercial aluminum extrusion frames are stiff enough to avoid that problem. You will need a good sealing surface on the top of your torsion box such as smooth plastic laminate or a good build of finish. You will be pulling a lot of air through unfinished mdf and your frame gasket needs a smooth surface to compress to.
Last edited by Kevin Jenness; 04-21-2024 at 1:46 PM.
Contributor
Kevin, do I interpret it correctly that the lid of your unit fits over the grooved platen snugly enough that the vacuum doesn't pull it towards the center? That was a huge problem with mine. Adding a mid-span crossbar didn't completely stop it. I went back to using a bag because of that, but I still have it.
John
Contributor
Yes, that's right. I suspect part of the reason (maybe the whole reason) commercial units don't have that problem is because the membranes are typically formed in a box shape and the vertical pleats take up the slack, whereas my simple flat polyurethane sheet pulls the frame in as it is sucked down to the platen. I too tried a crossbar initially without much success.
Contributor
As he warns, it's not a good design if you want a large unit, which I proved correct. Not complaining; I knew I was in unchartered waters, and found out the earth, indeed, is flat.
John
There is the commercial/industrial route. Has support, at least.
https://www.felder-group.com/en-us/p...-flex-p2186651
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