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What goes in the Bag?

9/10/13       
Scott

I just got a vacuum bag and pump, I have been searching the web on how to use it properly and I am confused. I am just using it right now for making some 8 ft long trim pieces. Some things I read are, you need a board first with some saw cuts in it and then you need another one on top, and you need some wax paper and maybe some shrink wrap and then some say the saw cuts go up and some say they go down, Sheesh!
Maybe all this is fine, I am a newbie so please forgive me.

9/10/13       #2: What goes in the Bag? ...
Wyatt

Who did you buy the vacuum bag from? Vac-u-clamp provides an instructional DVD if you purchase from them.

9/11/13       #3: What goes in the Bag? ...
Scott

I bought a used, like new vacu clamp, bag and mark 6 pump I believe. It never came with the disk.
I glued up some oak veneer on sanded light weight mdf last night, I used titebond cold press veneer glue and left it in the bag for 1 1/2 hours. When I took it out the bond didn't seem great, I could peel the veneer off so not sure what I did wrong!
Thanks

9/11/13       #4: What goes in the Bag? ...
David R Sochar Member

Website: http://www.acornwoodworks.com

D Keil has made several videos that explain all the basics very well. Worth watching.

Darryl Keil Videos

9/11/13       #5: What goes in the Bag? ...
Wyatt

Why did you sand the mdf? Did you clean off any dust from sanding? Did you use enough glue? Most likely the glue hadn't dried. Titebond needs air to dry and there is no air in a vacuum. You can use it but it has to stay in the bag a lot longer. Try using a reactive glue like urea formaldehyde or epoxy. We use Titebond all the time but leave it in the bag a couple hours and then pull it out and put a platen and some weight on it so that it can cure further. It will get a decent cure in the bag but dries faster in the air.

9/11/13       #6: What goes in the Bag? ...
JeffD

A couple things.....first off as the others mentioned get one or 2 of the DVD's and watch them to get a feel for things first.

Now as to your glue-up....there's so many places a glue up can go wrong. Did you blow all the sanding dust off the mdf after sanding it? How did you apply the glue? 1-1/2 hours may not be enough time in a vac bag. I usually leave glue-ups with TB in the bag for 2-1/2 hours and then stack them when they come out.....I certainly don't try to separate the joint when I pull it out! PVA's will stick together after a short amount of clamping time, however leaving it for 24 hours before straining the joint still applies!

There are also many ways of pressing in the bag. Most often for veneers I use a platen on the bottom with the saw cuts to make it easier to evacuate the air. I don't bother with anything on the top as I want full contact on the veneer. If it's solid parts or thicker veneers like door skins I don't bother with the platen. I have a base about 9" x 12" x 8' long that I lay the bag on which keeps the parts flat. The pieces go in the bag and I usually pop in a screen at the top to make sure the air can evacuate easily.

There's a lot more to it than I can cover here, and a lot more I don't even know about, so get yourself the DVD's and try it again;>)

good luck,
JeffD

9/11/13       #7: What goes in the Bag? ...
rich

All the items you mentioned that go in the bag are there to allow full contact pressure on the veneer. You need some way to get air flow down the entire length of the bag to the hose. So plattens with grooves. Another platten on top to provide even, flat pressure across the veneer. Other items to keep hard, sharp edged glue from being stuck to the inside of the bag and the puncturing it when you load the next time. It's like any other woodworking tools and skills. You shouldn't expect to plug it in and get perfect work out. A lot of hobbyists go to Joe Woodworker site for beginner vacuum veneering skills. See if that site helps you.

9/12/13       #8: What goes in the Bag? ...
Scott

Thanks for all the help, I sanded the mdf because I glued up an old spoil board from the cnc. I was wondering what glue people recommend on the sanded mdf. I used titebond cold press veneer glue the first time and for whatever reason the veneer peeled right off, so back to the drawing board.

9/13/13       #9: What goes in the Bag? ...
Charles Member

Scott,

I use Pro-Glue dry resin glue with MDF.

I sand the MDF, but not to get it smooth and slick. I actually want to rough up the surface somewhat. Maybe 150 grit? This removes some of the glaze on the MDF that I buy from my supplier. Now the glue can adhere to the surface better.

For timing in the bag, there are guidelines depending on the temperature of the workpiece while it is in the bag. (Never let it get below 70F. It will never cure if you do.) When the time is up (I often leave it in longer, sometimes overnight) I remove the workpiece then prop it up on its edge so both sides get equal amounts of air for about a day. Only then do I try an adhesion test.

I also highly recommend the Darryl videos mentioned by others. He does a great job of covering the basics as well as some more advanced topics. I was able to complete a more advanced veneering project after watching one of them.

I do not use waxed paper. It may work, but I buy rolls of clear plastic (10'x100') available in the paint department of the big box stores. This keeps the glue off of my "bag" (I have a flip-top press) and is a lot more tear-resistant than waxed paper.

Welcome to the world of veneering and vacuum presses. You can do things with veneer and your new press that you cannot do otherwise. Enjoy!

9/13/13       #10: What goes in the Bag? ...
David Member

Scott,

I also recommend the videos by Keil. Look up "vacuum pressing systems", which is the name of his company. The basics are:

You need a platen best made from melamine. It should be a little smaller than the size of your bag. Run 1/8" by 1/8" grooves in an 8"x8" grid across the surface. This will face up in the bag and allow the air to evacuate. You will need to install a sleeve in an intersection of grooves closest to the opening of the bag which the vacuum hose will attach to and draw air through the grooves.

Set the piece to be veneered on the grooved platen inside the bag.

I always use a cover sheet that is about an 1/8" bigger all the way around. This helps to distribute the pressure onto the veneer as well as protect the edges from breaking under pressure. Put a round over on the cover sheet to prolong the life of the bag.

As for gluing, Titebond is ok for flat work. Leave it in the press for 3 -4 hours and then set it somewhere where it can get air on both sides overnight. You need to get the right amount of glue on there and to do that you can use a 1/16"x 1/16" notch glue trowel filed down to 1/32" high to spread the perfect amount of glue. I would check into urea formaldehyde glues that have a longer open time and cure to a rigid glue line unlike TB.

It really does broaden your woodworking horizons. Be patient and watch Keils videos. Happy Veneering.

9/15/13       #11: What goes in the Bag? ...
Dave

"Titebond needs air to dry"

Air is not required if there are enough moisture absorbing materials close enough to the glue line. Using a 1/4" MDF cover sheet is all that's needed to use clamp time specs for press time, e.g. 30min for Titebond II.

An interesting aspect of MDF is that it is porous. I once made a 1/4" MDF box using internal vacuum to clamp it (no bag/press) and paper held to the outside would kind of stick to it, i.e. it works a bit like a mesh/screen cover sheet.

Another useful aspect of MDF is that its grain is very laminar parallel to the face. You can use too much glue (easy w/ quarter sawn) and, while seemingly stuck solid, the MDF will peel off the veneer. The image is my worse experience w/ bleed through (wasn't thinking quarter grain).

While the cold press requires a longer clamp/press time, I've done glue coverage tests w/ TBII and couldn't peel the veneer off if I left it in the press for more than a few minutes.

...Scott, you said the veneer peeled off, was it at the glue line or did it peel off with MDF on the back of the veneer. The later wouldn't surprise me if you glued the veneer to the softer/weaker MDF core (surfaced spoil board).


View higher quality, full size image (1280 X 960)

9/15/13       #12: What goes in the Bag? ...
Scott

Thanks for the replies, I used a brand new jug of titebond cold press glue and it was the glue line that came apart , there was a tiny bit of mdf that came up, but very little! I also had a solid oak edge and it did not adhere to that either!

9/16/13       #13: What goes in the Bag? ...
Gerry

I've pressed hundreds of ft of veneer with Titebond Cold Press glue and have never had a glue failure. 1 hour is all you need for a good bond.
My guess is you didn't use enough glue. If you can see the MDF through the glue, you don't have enough glue.

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