How vital is the use of a platen when vacuum pressing?

[Glen Blanchard]

I am about to embark on the world of vacuum pressing and have seen mentioned the use of a platen (or platens) during the vacuuming process. Are these necessary for a good result? I had thought that one just places the glued up piece in the bag by itself and turned on the pump. What exactly is the purpose of a platen and when should one be used?

Thanks.

[Todd Bin]

If you notice, the platens have 1/8" groves cut in them in a grid pattern. This is to allow a path for the air to excape the bag. Otherwise if the front of the bag seals then the air can't get out of the back.

When you make your platen and cauls use an 1/8" round over bit on all the edges. That relieves some of the stress on the bag and will keep it from ripping.

[Glen Blanchard]

If you notice, the platens have 1/8" groves cut in them in a grid pattern. This is to allow a path for the air to excape the bag. Otherwise if the front of the bag seals then the air can't get out of the back.

When you make your platen and cauls use an 1/8" round over bit on all the edges. That relieves some of the stress on the bag and will keep it from ripping.

Thanks Todd. Is the size of the platen a function of the piece being pressed or the size of the bag? It sounds like it is determined by the size of the piece placed in the bag.

What is the recommended material? MDF seems like it would be ideal.

[David DeCristoforo]

"Is the size of the platen a function of the piece being pressed or the size of the bag?"

Both. The main thing is to have enough "loose bag" to "wrap" whatever you are pressing. You don't want the bag stretched over or around anything because it could tear. So if you are pressing something relatively flat, you can use a larger bed. For something that is more "3D", use a smaller bed to leave more of the bag free to conform to the shape.

Not Tod

[Al Navas]

Glen,

Just one small item:

Make sure that the nipple on the piece that accepts the hose tip is placed at the intersection of two of the grooves in the platen. If it isn't, you may never attain sufficient vacuum.

Which vacuum press system will you use?


.

[Glen Blanchard]

Thanks guys. I think I have a handle on it now. I will be using it for the first time this Friday to veneer a panel approx 12" x 12".

Al - It looks like I will get the Woodcraft system.

David - As per your comments, since this is indeed flatwork, I'll create platens (I guess I might as well make two of them as this is flat, and place one above and one below) in the neighborhood of 14" x 14". Sound about right?

MDF okay to use?

[John Lucas]

Glen,
MDF OK. I use white melamine particle core board because it is inexpensive and the glue can be chipped off easily. I have made and used several different platens. I use the smallest one that still allows the object to be covered.

[Kevin Johnson]

Hi Glen,

Although everyone is correct that you should have a platen. I recently did some fairly large panels for a bar, the largest was about 16" x 7' without them. I did not have any problems. I do plan to get around to making some platens, but I was able to successfully press them without.

[Bill Wyko]

Check out www.veneersupplies.com (http://www.veneersupplies.com) they have a bunch of info on vacuum pressing. Joe will answer your e-mails too if you can't find what info your looking for. He also makes some very high quality vacs and bags. Not to mention his veneers.

[David DeCristoforo]

"...one above and one below..."

Not necessary. You only need the one "platen" with the grid to allow air to be drawn out. You can place a "caul" on top if you wish but this does not need to be "heavy duty". A piece of 1/4" ply or mdf will suffice. Remember that vacuum pressure is completely even over the entire area, not like with clamps where you need a thick caul to spread the pressure.

[Chris Padilla]

I'll second the white melamine and it takes a ding or two better than MDF. Both are quite heavy in large pieces, however.

[Larry Fox]

Like others by bottom platen is melamine. I don't use a top platen, instead I use the breather-mesh product that Joe sells. It has worked out great so far but, to this point, I have only done flatwork in my press.

[Eric Gustafson]

My vac setup is pretty rinky-dink atm, but it works for the occasional need I have. I have a good vacuum pump I bought on craigslist and I am using space bags :eek:, which someone said are unusable, but they work just fine for me. Instead of a platen, I use a piece of burlap over the piece I am clamping. The burlap keeps the bag from sealing the valve opening just fine.

[Jim Becker]

The platen(s) is(are) pretty important in my experience. I tried it once without and had some significant issues. I've also found that the mesh that Joe Woodworker sells is very useful to get a really good even clamping as it helps the air evacuate properly.

[Jamie Buxton]

I use a vacuum press a lot, and I never use a platen for air escape. Air molecules are teeny-tiny little things. They'll find a way to get from areas of high pressure to areas of low pressure.

The only time I use a platen is when I want to laminate something which must be flat -- for instance slab-style doors for cabinets. For that, I have a torsion box which is very flat, and it goes inside the bag.

[Tim Johnson]

I might also suggest that if you use plain MDF as a platen that you place a piece of wax paper between your work and the platen, just in case you used a little too much glue and left it in the bag overnight to "make sure" everything was set up properly. After a few trials with my vacuum press, made from Joe Woodworker kit, I now know how much glue is just enough to get the job done and not make a piece of expensive firewood. I use a platen on the bottom that is slightly larger than the work piece, place the work piece on top of the platen, then cover both with the plastic netting. Works great.

[Jamie Buxton]

Maybe I should add one more bit of explanation. I make my own bags. There is an ordinary flexible vinyl 1/4" tube which goes from the pump to the bag. It goes through the glued seam at the end of the bag, and continues inside. Inside the bag, the tube has perforations every 6" or so. The perforations are holes punched through the tube with a 1/16" bit. The perforated tube flops around inside the bag. Often when I slide a workpiece into the bag, the tube kinda cuddles up to one edge of the workpiece. Or sometimes it justs lies on top of the workpiece. The tube is stiff enough that the atmospheric pressure never squishes it completely flat. Air in the bag needs only to get to any one of those holes in the tube, and it will get sucked out.

[Dave Tinley]

I, also use a melamine platen. It is roughly 2 inchs less then the bag size, on all four sides. I used to use 1/4 ply for my cauls. but always seemed to need different sizes for the work I was pressing. I found some nylon fabric used by gardners for weed control, it works great. I am guessing it is similar to what Joe sells.

BTW- Joe sells a glue (Better Bond) in a liquid form, has crushed pecan shells in it. Works super, no mixing and best of all, very, very little bleedthru.
Since I do alot of work with white oak, I used to get lots of bleed thru with other ureas, but not so with this stuff.


Dave

[Don Kondra]

A couple of points I would like to repeat/clarify.

One of the purposes of the platen is to provide a flat reference surface for the lamination.

If you do not place a caul on the platen/under the laminae the vacuum will actually pull the veneer into the grid of slots cut to aid in the evacuation of air. I actually plan to use this as an element in panels for a show piece :)

You also need a caul on top of the lamination, the plastic alone is not enough to ensure the veneer is pressed "flat". For instance, if you have an uneven coat of glue, the plastic alone is not enough to flatten the glue out.

Also, if you are pressing a curly wood, a caul will result in a flatter panel and less sanding to achieve a flat surface. The water in the glue will swell the curl in the wood and the plastic alone is not enough to "flatten it".

And the size of the caul is important, it should be the same size as the lamination. If it is larger the bag will tend to pull/bend it into the void around the lamination and result in less pressure in the center of the glue up.

Just to keep things clean, I wax the platen, I wax the cauls and relieve their edges and I wrap the lamination in plastic between the cauls to contain any squeeze out. Keep the inside of the bag clean, any debris will be "pressed" into the lamination.

I use either 1/4" baltic birch or MDF for cauls.

Oh, on the issue of using grooves in the platen to help evacuate the air or not. I have done laminations on the side with the grooves and the side without the grooves. Both will work but I find I get a better "press" on the side with the grooves. Obviously I tried the flat side of the platen to eliminate cutting two cauls :)

Cheers, Don